guttation experiment

Guttation, how plants deal with too much water

Guttation is how plants expel excess water or nutrients through tiny openings on leaves and stems. and water content.

Key facts about guttation:

Name – guttation Common name – crying plant, weeping leaves, teary plant, dewdrop Type – plant physiological process

Occurrence – often Observation time – early morning Affects – houseplants & low-lying plants

• Read also: Is guttation bad for plants?
• Will your plants guttate?

This biological process enables plants to restore balance between their nutrient intake and needs.

→ Recently, science is realizing plants use guttation to communicate !

What is guttation?

It takes place when roots of a plant absorb more water than the plant actually needs.

Tiny, specialized cells on the surface of a leaf or stem are connected to veins and sap channels of the plant. This cluster of cells works as a nozzle. It releases water from the plant’s vascular system to the outside, forming drops that look like dewdrops.

This process where excess pressure is released from inside the plant is called guttation.

• These nozzle-like cells are called hydathodes . They’re a special class of stomata. Stomata are bean-shaped cells that open up to let the plant breathe and transpire.

• Less than 5 % of all water that goes in a plant is released through guttation. Nine tenths is from transpiration, a more powerful phenomenon.

About the term “Guttation”:

• The verb to say this “guttate”, but it isn’t very common. Simply, variations like “guttation is observed” or “hydathodes exude/secrete/release” are used. “Guttant” is the fluid expelled .
• It comes from latin “gutta” which means “drop”. An easy memory trick is to remember words in English like “gutter” and French “goutte” (also “drop”) and go from there.

To understand why plants developed guttation as they evolved, it helps to brush up the following:

• how water is used in a plant .
• techniques plants developed to move this water around, creating pressure.

Hydathode nozzles are one of the biological tools plants use to regulate pressure inside them.

How does a plant use water?

Water used to transport nutrients up and down the stems and leaves is called sap. But there are more uses of water in a plant than simply transportation! Here is a short list of how a plant uses water:

• Nutrient transport from roots to leaves and vice-versa
• Cells are full of water. On a microscopic level, this is where chemical reactions take place .
• In some plants, water shapes the plant , such as the shy but rugged Mimosa pudica which closes when touched.
• Some seed pods use water to eject seeds : when dry, they burst and project seeds far away. A typical example is the common Geranium .
• On the surprising Ginkgo biloba , water fertilizes the seed: it carries the male pollen to the female ovum inside the hull to fertilize it.

Plants are under pressure

If ever you’ve opened a fresh coconut , you must have noticed that when the hull is slit, drilled or broken, coconut water spurts out . The pressure inside the coconut is higher than the pressure of the air around it. You can also see happen when slitting open a watermelon : the last few inches simply split open on their own.

Thanks to a combination of chemical reactions , tissue structure and cell components , a plant is able to control water in and around it.

• Starchy stems help Dracaena resist drought . S tarch captures water molecules and releases them when the weather is dry.
• Capillarity helps many flowers pull water up from ground level. This is the basis for fun experiments with cut peonies or carnations absorbing dye up to their petals.

Guttation is one of the ways excess pressure is released . If not for this, the plant might burst at weak spots of veins and leaves!

When to find guttation on plants

Night-time and early morning

Plants breathe at night and still need sap to flow up and down the plant. Guttation takes over to force sap and water up when transpiration stops being effective.

• Daytime breathing is powered by transpiration or “sweating”. In warm, dry air, water evaporates from leaves and creates a “vacuum” inside the plant.  This vacuum pulls nutrient-rich sap up.
• At nighttime, evaporation and transpiration don’t work as well . The plant compensates by having the roots push water upwards. To do this, roots use chemicals to attract water from the surrounding soil.
• This builds up pressure in the plant and sap and minerals are pushed up. It’s such a strong phenomenon that excess water needs to be released at the tip of leaves through guttation!

Days of high moisture and humidity

When the air is near or above 100% relative humidity , it’s impossible for a plant to sweat.

• Even during daytime, guttation must take over to get sap circulating through the plant.

Excess moisture in the soil

It isn’t a common reaction, but guttation is one way of helping the plant evacuate excess water around roots . It’s a coping the plant uses to protect roots from rotting.

• Some plants use gutation to drain soggy soil around them like the weeping willow tree . It’s doubly weeping!
• Guttation isn’t necessarily a sign of over-watering.

Young plants

Seedlings and young plants tend to guttate more than older, more established plants.

Plant mechanisms similar to guttation

• Gummosis is mostly mentioned when a disease like canker triggers too much fluid release.
• But it is also a perfectly natural phenomenon that also occurs in healthy plants.
• When the environment changes too drastically, gummosis occurs to help the plant adjust. This happened to one reader’s Acacia dealbata trees .

Bleeding, resulting from a wound to the plant, is different.

Dew and dewdrops are something entirely different , but are also useful to plants. Plants can maximize dew without being responsible for creating it.

• Is guttation a disease that harms plants?

Smart tip about guttation

Guttation can even reach the point where sap drips to the ground. It can leave hard-to-remove stains on almost every surface, indoors and out!

So hose it away outside, and wipe it up indoors.

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Wowww I fell on a gold mine of information. Absolutely love the way things are explained with examples. I can feel the author’s own interest and excitement about guttation while reading this hahhaha

It is a fascinating topic, and once you’ve learned about it, a drop on a leaf becomes much more than poetry!

I want to use 2 pictures from your website for my book on guttation. Please allow me to reuse the same. Thanks.

Sanjay Singh MizanTepi University, Ethiopia

• Anemone coronaria – the Poppy anemone!
• Saintpaulia, clearly a must-have
• Common vervain health benefits and therapeutic value
• Plant patent – how can anyone claim to own nature?
• Hydrogel water crystals to beat drought
• Weeping willow, a majestic waterside tree
• Watering responsibly – we’re all involved
• Why does my dracaena have yellow leaves?
• Lower fever naturally with plants

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Come explore with us!  

Science News Explores

Scientists say: guttation.

This is a process that forces water out of a plant’s leaves and stem

The droplets on the edges of this strawberry leaf are the result of guttation.

NoahElhardt/Wikimedia Commons

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By Bethany Brookshire

April 10, 2017 at 5:50 am

Guttation (noun, “Guh-TAY-shun”)

This is a process in which water seeps out at the tips or edges of a plant’s leaves. The water is from xylem — the main water transport tissue in a plant. Usually, extra water escapes through tiny holes in the plant’s leaves and stem called stomata . But sometimes, those stomata are closed. When that happens, the pressure from water entering the roots continues to force water up through the plant. The water — and nutrients it picks up on the way — forces its way out as droplets at the tips and edges of leaves.

In a sentence

Bees like water from guttation because it picks up nutrients as it travels through the plant.

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Guttation: Path, principles and functions

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Guttation 1: chemistry, crop husbandry and molecular farming

• Published: 09 January 2013
• Volume 12 , pages 147–172, ( 2013 )

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Guttation is one of the most conspicuous visible phenomena in plants occurring in a wide range of plants. The guttation fluids, though look clear and translucent, carry a number of organic and inorganic constituents. The organic component may include sugars, amino acids, general proteins, antimicrobial phylloplane proteins, transport proteins for transporting sucrose, purine and cytokinins, toxic elements etc. and enzymes such as peroxidases, dehydrogenases, ATPases, in addition to mRNA, ATP, reductants and other important ingredients of plant life. Guttation fluids also contain a number of natural plant hormones such as auxins, gibberellins, cytokinins, abscisic acid etc., apart from several vitamins. Recent discoveries have revealed the presence of a number of salts, ions, nutrients and macromolecules in guttation fluid playing significant role in enhancing disease resistance, tolerance to toxic elements, photosynthetic efficiency, biomass production and economic yield of agricultural crops. In the light of aforementioned discoveries in guttation transgenic plants have been created to serve as bio-factories for producing various kinds of phytochemicals of immense agricultural, pharmaceutical, nutriceutical, therapeutic, cosmeceutic and commercial significance impacting food productivity and human health adding happiness to life.

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Acknowledgments

The authors extend their deep sense of gratitude to Dr. Amare Ayalew, Head of School of Plant Sciences, Dr. Kindie Tesfaye, Dean, College of Agriculture and Environmental Sciences and Dr. Nigussie Dechassa, Vice-President, Research Affairs & Extension Services of Haramaya University, Ethiopia for improving the text of the manuscript.

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Singh, S., Singh, T.N. Guttation 1: chemistry, crop husbandry and molecular farming. Phytochem Rev 12 , 147–172 (2013). https://doi.org/10.1007/s11101-012-9269-x

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DOI : https://doi.org/10.1007/s11101-012-9269-x

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Fungal Guttation, a Source of Bioactive Compounds, and Its Ecological Role—A Review

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Guttation is a common phenomenon in the fungal kingdom. Its occurrence and intensity depend largely on culture conditions, such as growth medium composition or incubation temperature. As filamentous fungi are a rich source of compounds, possessing various biological activities, guttation exudates could also contain bioactive substances. Among such molecules, researchers have already found numerous mycotoxins, antimicrobials, insecticides, bioherbicides, antiviral, and anticancer agents in exudate droplets. They belong to either secondary metabolites (SMs) or proteins and are secreted with different intensities. The background of guttation, in terms of its biological role, in vivo, and promoting factors, has been explored only partially. In this review, we describe the metabolites present in fungal exudates, their diversity, and bioactivities. Pointing to the significance of fungal ecology and natural products discovery, selected aspects of guttation in the fungi are discussed.

1. Introduction

Filamentous fungi produce a wealth of bioactive metabolites, many of which are considered important from the human point of view. Among them, toxic compounds are naturally produced, such as mycotoxins, cytotoxic agents, and carcinogens, as well as potentially useful molecules, including antibiotics, fungicides, insecticides, and antineoplastic or antiviral agents [ 1 , 2 ]. These compounds belong to secondary metabolites (SMs)—metabolites that are not engaged in the internal economy of the producing organism, but are essential for adaptation to specific environments, especially in situations that reflect survival probability [ 3 , 4 ]. Fungal SMs play an important role in protection from UV light damage, communication and signaling, defense against toxic molecules, and creating biological interactions—competition, symbiosis, or pathogenicity [ 2 , 4 ]. Importantly, SMs can be retained inside the cells or secreted into the surrounding environment, as well as exuded by guttation [ 5 , 6 ].

Guttation is a well-known phenomenon that involves the active exudation of water and dissolved substances, without tissue injury [ 7 , 8 ]. The formation of guttation droplets, which is primarily known from plants, is also widely observed among fungi [ 9 , 10 , 11 ]. Its ecological role, however, was undervalued and ignored in research for a long time. The first study on its putative functions was provided by McPhee and Colotelo [ 12 ]. They suggested that guttation enables the accumulation of metabolite reserves and removal of SMs or toxic byproducts of metabolism [ 12 ]. It was also suggested that the guttation process is linked to mycelium maturation [ 13 ], and that formation of exudates might serve as a water reservoir, allowing constant growth of aerial hyphae from afar (of their substrates) [ 14 ]. Deeper research into the composition and biological function of exudates have revealed that they may contain a wide range of bioactive compounds [ 5 , 15 ].

Here, we review reports on biologically active substances found in fungal exudates, with emphasis on molecules that have potential for practical applications, which are significant for human health and safety, and for uncovering putative roles of the guttation phenomenon in filamentous fungi. We also briefly summarize past and present views on fungal guttation from an ecological perspective, and conditions that promote secretion of guttation droplets. We provide an overview on this fascinating topic, which has still not been fully explored.

2. Conditions and Factors Promoting Guttation

Droplet exudation occurs during defined external conditions; it is different for every fungus and appears only during a certain period of culture duration. Although guttation is observed in nature, laboratory culture is most convenient for the elucidation of all promoting factors and parameters [ 10 , 15 , 16 ]. Fungal guttation is an “everyday experience” when practicing mycology ( Figure 1 ); standard culture media are often suitable to induce the phenomenon [ 14 , 16 ]. Among the studies focused on exudate investigations, the following media were utilized: potato dextrose agar [ 17 , 18 ], malt extract agar [ 19 , 20 ], and potato sucrose agar [ 21 ]. These were rarely specialized media, and involved synthetic, natural, and combined [ 15 , 22 , 23 , 24 ]. Hutwimmer et al. [ 15 ] indicated how big impact on a fungal guttation has the composition of sugars in growth medium. The study showed that a combination of more than one carbon sources, well-metabolized, and non-preferred sugars, could promote exudation [ 15 ]; thus, nutritional condition establishments were important in the experimental design. Culture temperature was of similar importance to culture media composition. The temperature range in which guttation occurred, most often, was from 20 °C to 30 °C [ 10 , 25 , 26 ]. A short summary of the described cultivation parameters, as well bioactive compounds found in fungal exudates, is presented in Table 1 . The structural diversity of secondary metabolites found in the exudates is presented in Figure 2 .

Fungal guttation—liquid droplets exuded on the fungi colony surface. ( a – c ) are the different strains belonging to Aspergillus genus; ( d ) strain belonging to Gliomastix genus.

The structural diversity of SMs reported in fungal exudates. ( a ) communesin A; ( b ) gliotoxin; ( c ) griseofulvin; ( d ) macrocyclic trichothecene (satratoxin H); ( e ) mycophenolic acid; ( f ) ochratoxin A; ( g ) phomopsinone A; ( h ) sclerotioramine; ( i ) epipyrone A.

Reports on bioactive compounds found in fungal exudates and culture conditions enabling guttation.

n —number of compounds, QS—quorum sensing, RT—room temperature, “-”—no data; CYA—Czapek yeast extract agar, DCA—dextrose casein agar, ISP-2—International Streptomyces Project-2 medium, MEA—malt extract agar, PDA—potato dextrose agar, PSA—potato sucrose agar, SDA—Sabouraud dextrose agar.

In some cases, specific factors are required to trigger guttation. They act by introducing a necessary signal, e.g., mechanical, such as fungivores, or chemical, like specific growth medium composition [ 29 , 43 ]. Moreover, culture conditions impact the content of metabolites in the exudates [ 11 , 34 ]. For instance, exudates droplets of the Aspergillus ochraceus strain accumulated high concentrations of ochratoxin A (OTA) when grown on a wheat-based medium, whereas at malt extract agar OTA was not detected at all [ 34 ]. Aliferis and Jabaji studied the overall composition of guttation droplets [ 17 ] on Rhizoctonia solani , and there are several previous, fragmentary analyses [ 42 , 44 , 45 , 46 ]. As a result, the researchers have identified the main components of exudates: SMs, carboxylic acids, carbohydrates, followed by less intensively represented fatty acids and amino acids [ 17 ]. Predominantly, chemical characteristics are highly individual, and various conditions induce guttation, which raises questions about the purpose of this phenomenon.

3. Ecological Role of Fungal Exudates

The general biological functions of guttation in fungi remain speculative. At times, it is observed that exudate’s droplets are forming in laboratories, conditionally, but not under field conditions, suggesting that, in these cases, they constitute “the image” of secretory activity [ 15 , 23 , 32 ]. In other cases, especially when fungus has no specific “lifestyle” with the development of specialized ecological relations, we can only suspect some of the general purposes of guttation (e.g., participation in the growth) [ 14 ]. However, these general purposes may be equally important; for instance, in young parts of aerial hyphae, threats of desiccation are noticeable, so retaining suitable moisture via exudates should help maintain a constant growth rate, even with unfavorable water potential [ 14 , 47 ]. The same refers to the conception of exudates as a metabolite reservoir, which is supported by the discovery of large amounts of carbohydrates and fatty acids in droplets of some fungi [ 18 , 28 , 34 ]. Excretion of nutrients collected outside of mycelium, e.g., inositol, mannitol, trehalose, lauric or heptadecanoic acid, is expected to regulate internal physiological mechanisms, and accompany the development of structures, such as sclerotia [ 42 , 48 ]. Therefore, guttation seems to be an important step in the colony maturation process, e.g., linked to cell death [ 12 , 13 ]. Another hypothesis is that fungi remove metabolic byproducts by their secretion, which partially explains a complex composition of exudates, illustrated in biochemical investigations [ 8 , 12 , 18 , 34 ].

The idea of exudates as a reservoir of SMs is attracting much more attention due to diverse and specific activities of the metabolites secreted in them [ 1 ]. Moreover, identification of SMs and their bioactivities could explain the importance of exudates for the producing strain. Hence, a convincing role of exudates from an entomopathogen, Metarhizium anisopliae , was demonstrated by Hutwimmer et al. [ 15 ]. The presence of insecticidal destruxins in Metarhizium droplets informs researchers about the mechanism of pathogenesis; namely, poisonous fluid is exuded during infection into the host, resulting in its death, which facilitates ingrowth of the fungus [ 15 , 49 ]. The ecological role of exudate droplets, produced by phytopathogenic fungi, such as Fusarium culmorum and Sclerotinia sclerotiorum , is quite clear. Their exudates, containing lytic enzymes, likely help with invasion and development in the plant [ 10 , 12 ]. The enzymes present in fungal exudates are covered in more detail in Section 5 .

Furthermore, virulence and defense reactions are shaped by substances secreted in the exudates. For instance, Aspergillus nidulans , after being exposed to prolonged grazing by the fungivore Collembola , intensifies guttation and biosynthesis of toxic SMs to discourage further foraging. This likely occurs in response to mechanic hyphae damages or chemical signals [ 43 , 50 ]. Complementing previous suspicions, it is worth noting that, in this case, guttation ran in parallel with the formation of sexual fruiting bodies, called cleistothecia [ 43 ]. Likewise, Pandey et al. [ 37 ] assumed that SM microfilm, growing around sclerotia of Sclerotium rolfsii after drying off the exudates, had a protective function, as it counteracted the degradation of these structures by microorganisms, and supported their survival in soil [ 37 ]. Another example of an inducible defensive strategy showed Xylaria cubensis FLe9. The FLe9 strain did not exhibit guttation activity in standard culture conditions, whereas after the addition of antifungal amphotericin B to the growth medium, it started to exude mycelial guttates, containing fungistatic metabolites: griseofulvin and dechlorogriseofulvin [ 29 ]. Because the microorganisms commonly interact with each other via metabolic exchange and their metabolites act as mediators of many interactions, it is suspected that amphotericin B, being a microbial product present in nature, simulated the presence of a competitor. Such a chemical signal induced a response that, in vivo, helped to outcompete other microorganisms [ 28 , 29 ].

Specific interactions are not always caused by SMs. For example, in Trichoderma guizhouense and Fusarium oxysporum co-culture, oxidative stress alone might be enough to exert the effect [ 26 ]. The growing Trichoderma colony extrudes droplets with a large amount of hydrogen peroxide, generated due to the activity of NADPH oxidase and a short-chain dehydrogenase/reductase TgSDR1. This results in poisoning the competitor, which leads to the overgrowth of developmentally arrested F. oxysporum [ 26 , 51 ]. Interestingly, the strongest guttation was noticed near to colonies’ contact zone [ 26 ]. An analogous situation occurred in the culture of Pseudoxylaria sp., paired with other fungal species, where an enhanced exudation rate of the droplets was observed in proximity to the competitor. Moreover, the exudates showed an arsenal of not-yet fully identified SMs [ 27 ]. As we can see, more specialized guttation roles often emerge directly from certain SM biological properties ( Table 1 ). In spite of that, some activities that are not connected to the fungus environment, such as antineoplastic, seem to be accidental “side effects”, while these more obvious simply take part in the formation of ecological relationships.

4. Secondary Metabolites Present in Fungal Exudates

4.1. antimicrobials.

Filamentous fungi tend to be a nearly inexhaustible source of antimicrobial compounds due to their participation in various antagonistic interspecific interactions [ 1 , 52 ]. In this context, the guttation is an attractive “selector” of enormous fungal metabolome, as exudate droplets can serve, in vivo, as a tool in such environmental reactions [ 19 , 24 , 42 ].

4.1.1. Antibacterial and Antiviral Compounds

There is a strong need for new, biological antimicrobials, because of the increasing resistance to antibiotics and antimicrobial agents among pathogens [ 53 ]. In the past few decades, the number of multidrug-resistant bacterial strains noticeably increased, while at the same time, the range of effective antibiotics introduced to the market diminished [ 53 , 54 , 55 ]. Indeed, prior to the approval of the first siderophore-cephalosporin conjugate in 2020, the latest, previously uncovered class of antibiotics was lipopeptides, represented by daptomycin, discovered in 1986 [ 53 , 55 ]. However, secondary metabolism of environmental microorganisms is a potential source of new drugs, as demonstrated by the discovery of the peptide-like teixobactin [ 53 , 56 ].

One of the most potent groups of antibacterials seems to be the peptaibols family, members of which have been found in fungal exudates [ 19 , 57 ]. The peptaibols are short, linear peptides, containing between 5 and 20 residues, enriched in non-proteinogenic amino acids, such as α-aminoisobutyrate and isovaline [ 57 , 58 ]. The N-terminal group is usually acetylated, and the C-terminus ends with aminoalcohol: mostly phenylalaninol, but seldom valinol, leucinol, isoleucinol, or tryptophanol [ 58 ]. A typical molecular structure of these compounds presents alamethicin—the first isolated and most extensively studied peptaibol ( Figure 3 a) [ 57 ]. Generally, peptaibols belong to a widely represented group of antimicrobial peptides (AMPs), biosynthesized by non-ribosomal peptide synthetases [ 57 , 59 ]. The AMPs are host–defense peptides, produced in bacteria, fungi, plants, and animals, to protect them against foreign attacks [ 59 ]. Although the scope of peptaibol producers is wide, their most prominent sources are fungi of the Trichoderma genus [ 57 , 58 ]. The biological activity of peptaibols is attributed to the formation of ion channels in cell membranes [ 58 , 59 ]. More precisely, they adopt α-helical conformation and possess an amphipathic nature, which enable self-aggregation into oligomeric channel assemblies, spanning across the lipid bilayer [ 47 , 50 , 51 ]. Apart from antibacterial properties, peptaibols can display antiviral, antifungal, or cytotoxic activity [ 51 , 52 , 53 ].

Antimicrobial compounds of the exudates. Molecular structures of: ( a ) peptaibols—on the example of alamethicin F-50 (acetyl group marked in yellow; aminoalcohol marked in blue; red arrows indicate α-aminoisobutyrate residues) [ 58 , 60 ]; ( b ) polyhydroxyanthraquinones—ω-hydroxyemodin [ 18 ]; ( c ) pseudoxylallemycins—derivative B (the homoallenyl moieties marked in purple) [ 27 ].

An alternative strategy to search for new antibiotics to combat antibiotic-resistant bacteria is to block the expression of their virulence factors. Since the production of these factors is often controlled by quorum sensing, the agents interfering with that signal cascade are appealing tools for antiviral therapy [ 61 , 62 ]. Figueroa et al. [ 18 ] isolated a series of known and new polyhydroxyanthraquinones from the exudates of endophytic fungus, Penicillium restrictum . The compounds acted as quorum-sensing inhibitors. They were shown to inhibit a functional accessory gene regulator quorum-sensing system in a clinical isolate of methicillin-resistant Staphylococcus aureus , leading to the lack of expression of toxins and exoenzymes required to cause an infection [ 18 , 63 ]. As confirmation, the decrease in δ toxin production was noted [ 18 ]. Further experiments on the modes of action were conducted on the derivative, ω-hydroxyemodin ( Figure 3 b), having a relatively strong suppressive effect. They indicated its direct binding to the response regulator AgrA, which subsequently could not associate to agr promoters and indirectly upregulate the expression of virulence factors [ 63 ].

Not less interest is connected with search for new antiviral substances. Worth describing here is another AMPs group of compounds found in fungal exudates—destruxins [ 15 ]. Similar to peptaibols, the destruxins exhibit a variety of biological activities, some of which will be discussed later. They are cyclic hexadepsipeptides composed of an α-hydroxy acid and five amino acids ( Figure 4 a) [ 64 ]. Individual derivatives differ on the hydroxy acid, N-methylation, and specific R-group patterns of the amino acid residues [ 64 , 65 ]. The main components of M. anisopliae exudate droplets are destruxins A, B, and E [ 15 ], presented in Figure 4 a. In vitro tests implied that some of the destruxins possess anti-hepatitis B activity. Examined derivatives have exerted inhibitory effects on the expression of the hepatitis B surface antigen in human hepatoma cells carrying an integrated viral gene [ 66 , 67 ]. Additionally, destruxins of Beauveria felina , along with isaridins and isariins, have been evaluated for anti-Zika virus activities [ 68 ]. Some of the isolated compounds revealed inhibitory activity against Zika virus RNA replication and, interestingly, the observed effect in the infected A549 cell line model was stronger than for ivermectin, used due to its high antiviral efficacy as a positive control. Moreover, tested cyclohexadepsipeptides blocked virus entry and downregulated the production of NS5, an essential protein for viral replication [ 68 ]. Furthermore, some destruxins are antibacterial agents [ 69 ], and possess similar structure pseudoxylallemycins ( Figure 3 c), which have antibacterial and antineoplastic properties (see Section 4.4 ) [ 27 ].

Exuded compounds and agriculture. The structure of: ( a ) destruxins (A, B, E) [ 70 ]; ( b ) mevalocidin [ 71 ].

4.1.2. Antifungal Compounds

Fungitoxic metabolites are recognized as the central points of antagonistic relationships between fungi, e.g., competition or mycoparasitism [ 4 , 42 , 66 ]. Pandey et al. [ 37 ] showed that the exudates collected from S. rolfsii had antifungal activity against other plant parasites. The exudates affected spore germination of all 26 tested fungi in vitro and significantly reduced disease incidence in infected plants under field conditions [ 37 ]. Chemical analysis of the S. rolfsii exudate droplets revealed the presence of phenolic compounds: high concentrations of ferulic acid, as well as tannic, gallic, caffeic, vanillic, chlorogenic, cinnamic, and oxalic acids [ 37 ]. Analogically, phenolic compounds turned out to be the major fractions of R. solani exudates, with ferulic acid and ethyl ester as the most abundant components [ 17 ]. The presence of these compounds contributed to the antifungal effects, since a part of them, e.g., ferulic acid, were reported to be fungitoxic [ 17 , 37 ]. Apart from that, Olsen et al. [ 38 ] discovered a new antifungal protein, denoted “ bubble protein ”, in the exudate droplets of Penicillium brevicompactum strain (see Section 5 ). This abundantly exuded constituent of the guttates inhibited the growth of Saccharomyces cerevisiae yeasts in a dose-dependent manner [ 38 , 39 ]. Similarly, the Penicillium chrysogenum antifungal protein C (PAFC), present in exudates of the Q176 strain, was proven to effectively inhibit Candida albicans growth [ 24 ].

Experimental reports highlight the importance of the induction of SM biosynthesis gene expression during screening procedures of natural products, particularly in regard to antifungal discovery [ 2 , 26 , 69 ]. The significance of this was emphasized in the work by Wang et al. [ 36 ] on Penicillium citreonigrum . The fungus SM profile underwent profound changes in response to chemical epigenetic manipulation [ 36 ]. When this Atlantic Forest-soil derived fungus was cultured on an untreated growth medium, it produced colorless exudates containing a simple assemblage of SMs, whereas on a medium with addition of the DNA methyltransferase inhibitor, the exuded droplets became a dark-red color, and were highly enriched in compounds representing distinct biosynthetic families. Six azaphilones and two new meroterpenes were detected. Among them, the sclerotioramine had antifungal properties (it was active against a panel of Candida strains) and showed a modest antibacterial effect [ 36 ]. Except for one compound, a pencolide, which was detected in both cultures, all others were found exclusively in the exudates of the epigenetically modified fungus [ 36 ]. This confirms that epigenetic alterations promote the transcription of silent SM biosynthetic pathways in fungi and impact the metabolite composition of the exudates.

More direct induction was applied in work by Caraballo-Rodríguez et al. [ 29 ]. The researchers triggered production and exudation of two antifungal metabolites in X. cubensis , by the addition of an antifungal compound to the culture medium [ 29 ]. However, both induced metabolites, griseofulvin used as a fungistatic drug, or its derivative dechlorogriseofulvin, are well-known molecules, and were reported earlier in Xylaria isolates [ 72 , 73 ]. This includes X. cubensis exudates droplets, in which high griseofulvin contents were detected [ 28 ]. Sica et al. [ 28 ] went a step further in their study, examining X. cubensis co-cultured with another fungus instead of introducing a one-compound inductor. The precise influence of the competitor on X. cubensis was checked afterwards by Knowles et al. [ 74 ]. After growth in co-culture, they established SM profiles of the mycelium surface. As a result, two additional antifungal derivatives of griseofulvin were identified, dechloro-5′-hydroxygriseofulvin and 5′-hydroxygriseofulvin [ 74 ]. Importantly, both of these works were aimed at sampling the colony surface, which included exudate chemistry characterization and facilitated dynamic changes monitoring [ 28 , 74 ]. The method, called droplet-based liquid microjunction surface sampling probe, or in short “droplet probe”, was described more broadly in the review by Oberlies et al. [ 75 ].

The examples mentioned above do not cover all of the reports. Other works describe antifungal polyene compounds [ 32 , 33 ], unidentified substances that likely grant fungitoxicity to exudates [ 25 , 27 ], or accompanying constituents, such as some fatty acids, that are not discussed here [ 17 ].

4.2. Bioinsecticides, Bioherbicides

In terms of plant protection, bioinsecticides and bioherbicides are, undoubtedly, significant for agriculture. Efforts made towards their discovery involve the search for new SMs, especially those produced by plant and pest pathogens. This approach is built on the hypothesis that they are the best candidates for biocontrol products [ 76 , 77 , 78 ]. Some toxins (e.g., mevalocidin) secreted by pathogenic fungi, might present special properties that enable their utilization [ 71 , 78 ]. A few studies on fungal exudates revealed that they accumulated compounds which were implemented successfully. That include both phytotoxins from plant pathogens and toxins of entomopathogenic fungi [ 15 , 30 ].

Secretion of highly insecticidal destruxins by Metarhizium or Beauveria fungi makes them promising pest biocontrol agents, stimulating their usage [ 59 , 79 , 80 , 81 , 82 ]. The insecticidal activity of destruxins was tested on a variety of pests, proving them to be effective [ 64 ]. Insect lethality was a result of the tetanic paralysis and was attributed to opening of ion channels in the plasma membrane. This caused Ca 2+ influx, which in turn induced muscle depolarization [ 64 , 65 ]. Importantly, both fungi genera are considered safe to human health and environmentally harmless because of neutrality to organisms other than insects [ 79 , 80 ]. These features resulted in extensive exploitation of the strains in agricultural pest control programs, as an alternative to chemical insecticides. M. anisopliae or Beauveria bassiana -derived formulations had already been registered for commercial use to control tobacco whiteflies, locusts and grasshoppers, spittlebug of sugarcane, red spider mites, thrips, fruit flies, and many others [ 59 , 81 , 82 ]. Moreover, they may become tools in combating arthropod vectors of human diseases, such as malaria-causing mosquitoes or ticks, a vector of Lyme borreliosis, or tick-borne encephalitis [ 59 , 83 , 84 ]. The described fungi can be employed in two forms—predominantly, as mycoinsecticide, when their conidia are dispersed, or by application of a mixture of isolated destruxins [ 81 , 82 ].

Mevalocidin is a compound that has a good prospects for its commercial application as a new herbicide. This unique, non-host specific phytotoxin is found in two Coniolariella sp. strains and is present in their guttates; it is also actively exuded into the surrounding environment [ 30 , 71 ]. The structure of this toxin ( Figure 4 b) consists of a pentenoic acid backbone with attached methyl, hydroxy, and hydroxymethyl functional groups. The conformationally-preferred, open chain form exists in equilibrium with the circular, lactone form [ 30 , 71 ]. Mevalocidin has beneficial features. It acts on a wide spectrum of weeds and was observed to cause lethality on all tested grass and broadleaf plant species [ 71 ]. It is rapidly absorbed after treatment, achieves a high concentration level, and efficiently translocates through phloem and xylem to other plant parts, including the roots. Moreover, mevalocidin demonstrates broad-spectrum post-emergence activity, stronger than weakly appearing pre-emergence effects, which suggests its rapid degradation in soil. The set of post-emergent symptoms, such as stunting, meristematic inhibition, or anthocyanin accumulation, is unlike those of any commercial herbicide or known phytotoxin, suggesting a novel mode of action [ 71 ]. The interference with new targets is an especially valuable feature because weeds become resistant to herbicides, often having the same target sites as older ones [ 77 ]. This clearly shows that new biological control agents are needed and that examining fungal guttation may bring real applicative benefits. Additionally, exudates can be potential sources of plant growth and development promoting factors [ 83 , 84 ].

4.3. Mycotoxins

Mycotoxins constitute the main health threat among fungal SMs. These compounds, defined as filamentous fungi products, pose health hazards to human and vertebrates by exerting high toxicity on cells [ 85 , 86 ]. Due to the chemical and toxic heterogeneity, mycotoxins are characterized by a wide range of adverse effects, including hepatotoxins, neurotoxins, immunosuppressants, nephrotoxins, hormone analogues (mycohormones), mutagens, carcinogens, or teratogens [ 86 , 87 ].

The pivotal issue connected with mycotoxins is contamination of either farmland or stored crops and food products [ 86 , 88 ]. There are several studies [ 11 , 34 ] on exudates from strains known to biosynthesize OTA, a common toxin of food stock stored in unsuitable conditions [ 87 ]. According to Muñoz et al. [ 34 ], the Aspergillus and Penicillium ochratoxigenic strains, cultured on coffee- and wheat-based media, showed different OTA production intensities. Their biomasses contained much more OTA levels in the wheat-based medium than in coffee-based. On wheat-based medium, Aspergillus strains formed exudate droplets, which coincided with the high OTA amounts formed by these fungi. The exudate droplets accumulated even higher OTA concentrations than mycelium [ 34 ]. Similarly, OTA and ochratoxin B (OTB) level measurements in Penicillium strains showed that, in exudates, their content was higher, compared to corresponding mycelia and underlying post-culture medium. The differences reached, respectively, up to 11 and 176 times higher concentrations in exudates than in the mycelium and agar for OTA, and 47.5 and 132 times higher for OTB [ 11 ]. The same tendency between the toxicity of exudate droplets and biomass extracts was reported by Salo et al. [ 20 ]. Moreover, large amounts of gliotoxin were detected in the exudates of marine-derived Aspergillus fumigatus strains [ 40 , 41 ]. Ongoing emissions of this mycotoxin into the seawater can result in its accumulation inside mussels [ 40 ]. Infestation of shellfish farming areas by A. fumigatus could therefore cause health risks for shellfish consumers [ 40 ].

Intake of mycotoxins is also related to their “liberation” into the air. This was studied in Penicillium expansum , a strain isolated from indoor building material, by Salo et al. [ 20 ]. The strain produced exudate droplets containing chaetoglobosins and communesins. Natural air convection simulating room conditions was induced in the agar Petri dishes, after fungus inoculation, by cooling the dish lids. Both exudate and liquid condensed on the lid were compared, and proven to contain similar patterns of mycotoxins, confirming the transfer of the toxins from exudates into the air. The role of the guttation in a transit of mycotoxins from mold to air cannot be neglected as it is a crucial factor in airborne respiratory toxicity [ 20 , 23 ]. This topic was analyzed deeper on a set of common indoor molds [ 23 ]. Metabolites secreted in exudates by isolates of Aspergillus , Chaetomium , Penicillium , Trichoderma , Rhizopus, and Stachybotrys genera were analyzed. Most of the strains, except for Aspergillus and Rhizopus , emitted mycotoxins in the exudate droplets. Additionally, T. atroviride , Rhizopus, and Stachybotrys sp. released biosurfactants in this way, which may influence the spread of microbial pollutants [ 23 ]. Moreover, the high toxicity only referred to the fungal biomass of young, actively growing, and guttating colonies. In comparison, over 6-month-old cultures displayed more than 10 times weaker toxic effects on mammalian cells [ 23 ].

There is no clear separation between food and air mycotoxins, rather they are intertwined. One example comes from a macrocyclic trichothecenes producing fungi, such as Stachybotrys genus, which can be responsible for serious contamination of crops, food reserves, or buildings [ 5 , 89 ]. These trichothecenes were observed to be secreted into the environment via guttation by some Stachybotrys chartarum strains [ 5 ]. However, not all of the macrocyclic trichothecenes are harmful to the human organism; they possess additional activities, e.g., antifungal and anticancer [ 90 , 91 ]. On the other hand, mycotoxins can be found among the peptaibols family. A good example involves peptaibols from the exudates of Trichoderma strains, isolated from contaminated buildings, where occupants reported indoor air-related disease symptoms [ 19 ]. The above examples illustrate that there are SM families with compounds that differ in biological activity, and can exert various effects on humans, from harmful to beneficial, making them interesting objects for further investigations.

4.4. Anticancer Substances

It is imperative to establish new, more specific, antineoplastic therapeutics, as cancerous diseases cause critical problems in modern societies. For example, hepatocellular carcinoma (HCC), one of the most malignant and widespread cancers, is the third most frequent cause of cancer-related death worldwide and shows high chemoresistance to many available drugs [ 92 ]. Therefore, HCC cells were recently targeted with peptaibols [ 93 , 94 ]. Trichokonin VI was found to suppress growth in the HCC HepG2 line, by the induction of calcium-mediated apoptosis and autophagy [ 93 ]. More precisely, it triggered the influx of extracellular calcium, inducing a calpain-dependent, intrinsic mitochondrial pathway [ 94 ]. It may be a universal mechanism of peptaibols action, because of their ability to form ion, Ca 2+ -permeable channels in lipid bilayer membranes [ 94 , 95 ].

As the peptaibols family is structurally diverse, trichokonin subclasses have been investigated as well [ 96 ]. Anticancer activity against selected cell lines showed also: culicinin D on breast tumor cells [ 97 ], alamethicin F50 derivative on a panel of cancer lines [ 60 ], emericellipsin on HepG2 [ 98 ], and potentially trilongins, as proteasome inhibitors [ 99 ]. It is worth noticing that members of different peptaibol subclasses have been found in fungal exudates [ 19 ]. Castagnoli et al. [ 19 ] identified toxins belonging to several peptaibol groups, such astrichorzianines, trilongins, and trichostrigocin-like peptaibols, in the exudates of various Trichoderma strains. In research by Rivera-Chávez et al. [ 60 ], aimed at SMs occurring directly on the surface of a fungal culture, new peptaibol derivatives were identified. The research was based on earlier, in situ, searching strategy, enabling surface sampling that included exudates [ 31 , 75 , 100 ].

The next broad class of anticancer molecules that can be found in exudate droplets are short cyclic peptides. Examples include previously-mentioned pseudoxylallemycins or destruxins [ 27 , 70 ]. Some of the pseudoxylallemycins, tetrapeptides from Pseudoxylaria sp. X802 exudates, demonstrated to exhibit antiproliferative activity against human umbilical vein endothelial cells and the K-562 cell line, as well as cytotoxic activity towards HeLa cells [ 27 ]. Despite that, the overall molecular mechanism of their anticancer effects remains unknown hitherto. However, their structure characterizations suggested a contribution of rare allenyl modifications in the compound activity [ 27 , 101 ]. Moreover, homoallenyl-tyrosine moieties ( Figure 3 c) are amenable sites for chemical alterations, enabling easy creation of new derivatives [ 101 ].

Interestingly, some compounds among the destruxin mixture exuded by Metarhizium fungi have strong antineoplastic properties [ 70 , 102 , 103 ]. The anticancer action mechanisms of the three most common destruxin derivatives, A, B, and E, have been investigated on colon cancer cell models [ 70 ]. All of them were found to cause an imbalance of the cell cycle and cytotoxicity based on intrinsic apoptosis induction, as well as an associated with phosphoinositide-3-kinase/Akt signaling pathway inhibition. Moreover, destruxins inhibit the migration and tube formation of human endothelial cells, which indicates antiangiogenic potential [ 70 ]. At the same time, only destruxin E caused intensive disturbance of the intracellular redox balance and showed the strongest antiproliferative activity among them, already at a nanomolar range [ 70 ]. In another study, Huynh et al., (2014) confirmed the effectiveness of destruxin B against HCC. In that case, the cell proliferation inhibition was associated mainly with attenuation of the Wnt/β-catenin pathway, fundamental for HCC carcinogenesis and progression [ 103 ]. This observation is largely consistent with earlier experiments [ 102 , 104 ] and likely also refers to the E derivative, which exerts anchorage-independent growth inhibition connected with decreased expression of cyclin D1, on the immortalized cell line [ 102 ]. Other reports, on different cancer cell lines, highlighted the role of apoptosis induction by destruxin B in investigated cancer cells [ 105 , 106 , 107 ]. Thus, as the molecular mechanisms behind such compounds vary, both cyclic peptides and linear peptaibols represent promising multifunctional anticancer drug candidates for preclinical development.

5. Proteins Excreted by Guttation

The specific properties of fungal exudates could be determined not only by small-molecule SMs—some reports indicate that various proteins are secreted via guttation [ 10 , 16 ]. Jones [ 108 ] noticed that S. sclerotiorum exudates showed activity of phenol oxidase [ 108 ]. Colotelo et al. [ 42 ] measured the protein content and presence of selected groups of enzymes in S. sclerotiorum exudate. As a result, they additionally confirmed β-glucosidase, catalase, peroxidase, and polyphenoloxidase activities [ 42 ]. Furthermore, in exudates of S. sclerotiorum and S. rolfsii , P. claviforme and F. culmorum polygalacturonase (pectinase), and cellulolytic activities were detected. Because these fungi are known phytopathogens, observations listed above should be caused by specific enzymes, playing a vital role in pathogenesis by plant tissue lysis [ 10 , 42 ].

Another example of bioactive protein present in fungal exudates constitutes the earlier mentioned bubble protein [ 38 , 39 ]. This defensin occurs in high concentrations in the exudates of the P. brevicompactum strain. It revealed antifungal effects during inhibition studies [ 39 ]. Similar to other members of defensins family, bubble protein can be characterized as small-sized protein, enriched in basic amino acids and cysteines. It is stabilized by the framework of disulfide-bridges and mainly consists of beta-sheet structures [ 39 , 109 ]. One general mode of the antimicrobial action of defensins relies on disrupting cell membrane functions by forming channels, resulting in membrane permeabilization, or by modifying membrane transporter activities [ 109 ]. High amino acid sequence similarity with the bubble protein shares PAFC, one of three PAF proteins that have been isolated from P. chrysogenum exudates [ 24 ].

A more comprehensive, proteomic study on fungal exudate composition was conducted by Wang et al. [ 16 ]. In the exudate of phytopathogenic fungi, Sclerotinia ginseng , they found 122 different proteins; 59 of them were identified and classified into six categories: carbohydrate metabolism, oxidation-reduction process, transport and catabolism, amino acid metabolism, proteins performing other functions, and those with unknown roles [ 16 ]. Part of the proteins in the carbohydrate metabolism group were associated with the sclerotium development process while the other was involved in virulence. These results are consistent with earlier observations of closely related S. sclerotiorum [ 16 , 35 ]. The identified carbohydrate metabolism proteins were, particularly, polysaccharide-degrading enzymes, either acting with fungal specific polymers, such as glucan, or the hydrolyzing plant sugars. The first group is responsible for modifications of a fungal cell wall architecture, whereas the second group catalyzes depolymerization of the plant-host cell wall structural components during invasion [ 16 ]. Moreover, in both works, among the detected proteins, those belonging to groups associated with primary metabolism were present, e.g., energy metabolism, but also factors crucial for signal transduction, SM biosynthesis, etc. [ 16 , 35 ].

Recent reports showed even larger numbers of secreted proteins. In exudate droplets of S. sclerotiorum , researchers identified a total of 258 proteins [ 22 ], in Cercospora armoraciae —576 proteins [ 25 ], while in exudates of Ustilaginoidea virens— 650 various proteins were detected [ 21 ]. Proteomic analysis of S. sclerotiorum exudates overlapped to some degree with earlier observations—four proteins were recognized as being related to plant cell wall degradation, contributing to host tissue necrosis [ 22 ]. Two works by Wang et al. [ 21 , 25 ] reported a number of metabolically relevant protein groups, covering almost the entire process of fungal growth and development, suggesting participation of exudates in the whole strain life cycle. Among the reported proteins, there were cell cycle proteins, ones responsible for signaling, nutrient catabolism, xenobiotics biodegradation, posttranslational modifications, and transport [ 21 , 25 ]. Moreover, many exuded proteins, especially those involved in peroxisome metabolism and biosynthetic pathways, might confer antifungal, antioxidant, and antimicrobial activity upon the exudates [ 25 ]. It shows how abundant the fungal exudate proteome is, and how far it impacts the strain features. The exact mechanisms of the protein delivery to the exudates are not known; further research is required. The exudate droplets can either contain proteins characteristic for secretome, whose activity is specifically extracellular, or those connected with intracellular processes [ 25 , 35 ].

6. Conclusions

Guttation in fungi occurs at different conditions, and its ecological role is sometimes elusive. At the moment, we can only speculate that guttation is a process occurring from whole mycelium and the droplets are forming on the intersection of environments with different state of matter e.g., solid/liquid and air intersection. On such intersection water evaporates and droplets are formed with higher concentration of metabolites. At the same time in liquid or solid media/environment the exuded substances diffuse or interact with surrounding matter. The wealth of metabolites, possessing specific bioactivities in exudates, is enormous. For example, we can find molecules with antagonistic activities against other organisms, some of which have biotechnological and biomedical potential, i.e., as new antibiotics or antitumor agents. Others display risks, as they can be harmful to humans or live-stock animals. The multitudes of interactions and activities of the exuded compounds are reflected in their structural and chemical diversity. The research discussed here sheds new light on the significance and real nature of the guttation phenomenon. Nevertheless, many aspects of the phenomenon still require research. It would be interesting to see how the composition of the exudates change with culture conditions. Moreover, elucidation of delivery mechanisms, of metabolites and proteins to the exudates, requires more research. It would be of interest to investigate whether the exudate droplets contain extracellular vesicles, as these could be carriers of large varieties of molecules [ 110 ]. In our work, we outlined fungal guttation, an interesting (yet, still largely unknown) research subject. We also highlighted its essential importance to the natural product research community and other branches of science.

Acknowledgments

A.K. was supported by the Doctoral School at the University of Silesia in Katowice, Poland.

Author Contributions

Conceptualization, A.K. and P.S.; investigation, A.K. and P.S.; writing—original draft preparation, A.K.; writing—review and editing, P.S.; visualization, A.K. and P.S.; supervision, P.S.; funding acquisition, P.S. All authors have read and agreed to the published version of the manuscript.

This work was supported by the National Science Centre (Poland), grant no.2018/02/X/NZ9/01838. APC was funded by the University of Silesia in Katowice.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Data availability statement, conflicts of interest.

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

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5.4 Wilting and guttation

5.4 Wilting and guttation (ESG7P)

Wilting and Guttation

This section explains to the learners how excessive loss of water can cause plants to wilt and lose some of their structural support.

During transpiration the learners learnt how the leaves are constantly losing water vapour to the environment. However, what happens when there is not enough water in the soil to replace the water that was lost? Similarly, what happens when there is too much water? In this unit we discuss wilting, and why plants wilt and get floppy in hot weather or after a long drought. We will also look at ways that plants can rid themselves of extra water when there is too much water in the environment and the plant has to cope with high root pressure and a low transpiration rate.

We just discussed transpiration, and how leaves are constantly losing water vapour to the environment. However, what happens when there is not enough water in the soil to replace the water that was lost? Similarly, what happens when there is too much water? In the next section we discuss wilting, and why plants wilt and get `floppy' in hot weather or after a long drought. We will also look at ways that plants can rid themselves of extra water when there is too much water in the environment and the plant has to cope with high root pressure and a low transpiration rate.

Wilting (ESG7Q)

Plants need water to maintain turgor pressure. Turgor pressure is what provides the plant with much of its structural support. Have a look at Figure 5.24 which shows the effect of osmosis on the turgidity of cells.

Figure 5.24: Cells in solutions with different concentrations

Wilting refers to the loss of rigidity or structure of non-woody parts of plants ( Figure 5.25 ). It occurs when turgidity of plant cells is lost. When a cell absorbs water, the cell membrane pushes against the cell wall. The rigid cell wall pushes back on the cell making the cell turgid. If there is not enough water in the plant, the large central vacuole of the cell shrinks and the cytoplasm decreases, resulting in decreased pressure being exerted on the cell membrane, and in turn, on the cell wall. This results in the cell becoming flaccid (floppy). When the cells of a plant are flaccid, the entire plant begins to wilt.

Figure 5.25: Crops wilt due to a lack of water.

Wilting occurs due to lower availability of water which may be due to:

• Drought conditions : where the soil moisture drops below conditions that allow plants to grow.
• Low temperatures : which prevent the plants vascular transport system from functioning;
• High salinity (salt concentration): which causes water to diffuse from plant cells to the soil, thus inducing shrinking of cells.
• Bacterial or fungal infections : that block the plant's vascular system.

Guttation (ESG7R)

Guttation is the "oozing out" or exuding of drops of water on the tips or edges of leaves of some vascular plants. An example of guttation is visible in Figure 5.26 .

Figure 5.26: Guttation in plant leaves

Below is an explanation of how guttation occurs:

• At night, when it is dark, less transpiration occurs since the stomata are closed.
• When soil moisture is very high, water will enter the plant roots because the water potential of the roots is lower than that of the surrounding soil.
• Thus, water accumulates in the plant, resulting in root pressure.
• The root pressure forces some water to exit the leaf tip or edge structures called hydathodes or water glands, forming drops.
• Root pressure is what drives the flow of water out of the plant leaves, rather than transpirational pull.

For guttation to occur there must be a high water content in the soil to create the root pressure. The transpiration rate must be slow in order for the root pressure to be higher than the transpirational pull. Guttation must not be confused with transpiration. Table 5.3 highlights the differences between guttation and transpiration.

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Book contents

• Frontmatter
• List of Figures
• List of Tables
• Acknowledgments
• List of Abbreviations
• 1 Phenomenon of Guttation and Its Machinery
• 2 Principles of Guttation and Its Quantification
• 3 Mechanism of Guttation
• 4 Regulation of Guttation
• 5 Chemistry of Guttation
• 6 Plant Microbiology and Phytopathology of Guttation
• 7 Significance of Guttation in Soil–Plant–Animal–Environment Systems
• 8 Significance of Guttation, Associated Structures, and Root Secretion in the Production of Pharmaceuticals and Other Commercial Products
• 9 General Conclusions and Future Perspectives
• Bibliography

4 - Regulation of Guttation

Published online by Cambridge University Press:  12 May 2020

Introduction

The phenomenon of guttation, like other physiological phenomena, is regulated by a number of internal and external factors. These factors mainly include the genetic makeup, growth and phenology of plants, hormonal and solute balance, temperature, humidity, light, and wind, which may conveniently be classified into the following heads and subheads.

Internal factors

These factors originate within the plants themselves and play a significant role in influencing guttation from leaves. These factors are briefly categorized and described below.

Genetic factors

Species variability

As stated earlier in Chapter 1, the phenomenon of guttation occurs in a wide range of plant species, which include herbaceous mesophytes, shrubs, and woody trees in angiosperms; gymnosperms; pteridophytes; algae; and fungi (Chen and Chen 2005; Lersten and Curtis 1991; Raleigh 1946a,b; Singh et al. 2009a; Sperry 1983; Stocking 1956a). Normally, significant guttation occurs in grass species including rice, wheat, barley, oats, and maize and other plant species such as tomato, balsam, Nasturtium , Colocasia , and Saxifraga and in some plants of Cucurbitaceae family as well; however, there is a high variability in guttate volume. Plants that exhibit guttation are seen to guttate through leaf tips, but in some plants, like the rice plant, guttation mainly occurs through the edges of the leaf, along with the surface, especially during the late hours of the day (Singh et al. 2008, 2009a). Few plant species exhibit profuse guttation under highly humid conditions, which appear as if water droplets are falling from the leaves (Feild et al. 2005). A single leaf of Colocasia antiquorum is capable of exuding up to 100–250 mL guttation water per day (Stocking 1956a). Guttation may also occur sometimes from the stems, generally through leaf scars or lenticels and flowers. The fungus Pilobolus is well known for its abundant guttation (Tarakanova et al. 1985; Tarakanova and Zholkevich 1986). Similarly, the fungus Polyporus squamosus also exudes droplets of water through its polypores profusely, which are similar to guttation in higher plants (Figure 1.2). Thus, these species of fungi, among others, present good examples of the occurrence of guttation.

As for guttation variabilities, it is worth mentioning that the exudation from Moso bamboo shoots during spring, in Southeast Queensland of Australia, can be sighted by the wet patches they create, having considerable agronomic and economic significance.

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• Regulation of Guttation
• Sanjay Singh
• Book: Guttation
• Online publication: 12 May 2020
• Chapter DOI: https://doi.org/10.1017/9781108487023.006

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Top 10 Experiments on Plants (With Diagram)

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Are you researching on experiments on Plants ? You are in the right place. The below mentioned article includes a collection of ten experiments on plants: 1. Plant Pigment Distribution 2. Ascent of Sap in Plants 3. Guttation in Plants 4. Transpiration in Plants 5. Mineral Nutrition in Plants 6. Photosynthesis 7. Respiration in Plants 8. Growth Rate in Plants 9. Growth of Plants by Promoting Substances 10. Biotechnology.

• Experiments on Biotechnology

1. Experiments on Plant Pigment Distribution:

Aim of the Experiment:

To detect the presence of anthoxanthin in plant tissues.

Requirements:

White-coloured flowers of any plant, concentrated ammonia, water bath, alcohol, alkali, HCl, basic lead acetate, ferric chloride.

1. White flowers or petals of white flowers of the given plant (e.g., Phlox or Chrysanthemum) are placed in contact with a few drops of concentrated ammonia. A yellow colour is obtained.

2. Extract white flowers on a water bath with aqueous alcohol.

3. Decant the extract and divide it in three portions:

(i) To one portion add an alkali. The colour changes to yellow. Acidify this by adding a few drops of HCl. The colour disappears.

(ii) To the second portion add basic lead acetate solution. A yellow or orange precipitate is produced.

(iii) To the third portion of the extract add ferric chloride solution. A green or brown colour appears.

All these three tests indicate the presence of anthoxanthins in the material.

2. Experiments on Ascent of Sap in Plants:

To demonstrate that water moves up through the xylem of the plant.

A Balsam plant, big test tube, test-tube stand, water, cotton, eosin stain, razor, slides, glycerine, microscope, cover-slip.

1. Take a complete balsam plant with roots, stem, leaves and flowers.

2. Keep the plant in a big test tube containing eosin solution.

3. Fix a cotton plug at the mouth of test tube and keep the experiment undisturbed for 2-3 hours (Fig. 14).

4. Cut the transverse section of stem with a razor, place it on slide and study under the microscope.

Observations:

It is observed that the petiole bases and the petals have become pink coloured. In the transverse section of the stem only xylem has taken the stain.

Pink stain of the petiole bases and the petals indicates that eosin stain has reached up to petiole bases and flowers through root stem and leaves. Study of the transverse section under the microscope reveals that only xylem cells are stained, thus indicating that the solution moved through the xylem.

3. Experiments on Guttation in Plants:

To demonstrate the process of guttation with entire potted plant.

A potted plant of garden nasturtium, water, bell jar (Instead of garden nasturtium other plants like oat seedlings, wheat seedlings, tomato, Colocasia, etc. may also be taken).

1. Take a potted plant of garden nasturtium and water it copiously.

2. Cover the pot along the plant with a bell jar and place it in a cool and dark place.

3. Connect the apparatus to an aspirator and make it air-tight (Fig. 17).

4. Keep the experiment a for a few hours and observe the changes.

Slow exudation of water begins at the tip of each leaf. These water drops gradually enlarge and may fall off or run down the side of the leaf.

This exudation of water is due to the phenomenon of guttation. When the plant is copiously watered then water is forced from the xylem vessels through intercellular spaces and out of plant from pore-­like structures (called hydathodes, water pores or water stomata’s, Fig. 19) present at the margins of the leaves.

Water exudes through hydathodes with the help of a pressure developed in the sap of the xylem elements. It is believed to be a pressure identical with the root pressure. The exuded water also contains amino acids, mineral salts, sugars and traces of other solutes.

Guttation occurs abundantly when the conditions are such that absorption of water by the roots is very high and the rate of transpiration is very slow. Guttation can also be demonstrated with a single freshly cut leaf of garden nasturtium when it is fixed on one end of a U-tube fitted with a cork and filled with water. From the other end of the U-tube add a little amount of mercury which helps in forcing the water in the petiole.

4. Experiments on Transpiration in Plants:

To compare the stomatal and cuticular transpiration of the leaves of different plants by cobalt chloride method.

Leaves of the plants to be compared for transpiration (preferably they should be worked out in the attached condition), 3% solution of cobalt chloride, filter paper, slides, forceps, clips, stop watch, desiccator, anhydrous calcium chloride and vaseline.

(a) Preparation of cobalt chloride discs:

1. Prepare a 3% solution of cobalt chloride and soak the filter papers in it.

2. Remove the excess of cobalt chloride solution from filter papers by squeezing them with a rubber roller and let them dry.

3. Cut the filter paper into small discs of definite diameter, make them absolutely dry in an oven at 30°-40°C and preserve them in a desiccator. Dry discs are of blue colour.

(b) Comparison of water loss from both the leaf surfaces:

4. Take a leaf of the plant and place one disc of cobalt chloride paper on its upper surface and one on Lower surface. Press them with clean glass slides.

5. Clip the two slides together with two separate clips, make them air-tight with vaseline and start the stop watch (Fig. 24).

6. Note the time in which blue colour of disc changes into pink.

7. Repeat the same experiment with the leaves of the other plants to be compared for the rate of transpiration.

Above-mentioned observations indicate that the time required for a change from blue to pink on lower surface of leaves is less than that of upper surface.

Because the colour changes rapidly on the lower surface than the upper surface in all the leaves worked out, so it can be concluded that more water was transpired from the lower surface, and hence more stomata are present on this surface than the upper surface.

5. Experiments on Mineral Nutrition in Plants:

To demonstrate water culture experiment of showing mineral nutrition in plants.

Seven large glass jars, split cork, seedlings of nearly same size (either of maize, oat, tomato or tobacco), Sach’s nutrient solution (normal solution as well as solutions with calcium deficiency, nitrogen deficiency, potassium deficiency, phosphorus deficiency, iron deficiency and magnesium deficiency), black paper.

(A) Preparation of Normal Sach’s Nutrient Solution:

Following composition makes the normal Sach’s nutrient solution:

KNO 3 – 2gm

MgSO 4 – 1 gm.

NaCl – 0.5 gm.

CaSO 4 – 1 gm.

Ca 3 (PO 4 ) 2 – 1 gm.

FeSO 4 – Only traces

Water – 2 litres

(B) Preparation of Sach’s nutrient solution with different deficiencies:

(a) Solution for calcium deficiency:

Instead of calcium sulphate and calcium phosphate use potassium sulphate and sodium phosphate.

(b) Solution for nitrogen deficiency:

Instead of potassium nitrate use potassium chloride.

(c) Solution for phosphorus deficiency:

In place of calcium phosphate use calcium nitrate.

(d) Solution for potassium deficiency:

In place of potassium nitrate use sodium nitrate.

(e) Solution for iron deficiency:

Do not use ferrous sulphate.

(f) Solution for magnesium deficiency:

In place of magnesium sulphate use potassium sulphate.

1. Take seven large glass jars and make them clean thoroughly with hot water and finally with distilled water.

2. In one jar fill the normal Sach’s nutrient solution and in the remaining six jars, fill the solutions having the deficiency of calcium, nitrogen, phosphorus, potassium, iron and magnesium, respectively. Mark all these jars as Normal, Ca, N, P, K, Fe and Mg with glass-marking pencil (Fig. 33).

3. Take young seedlings of almost equal size of the plants (either of oat, maize, tomato or tobacco), fit them in seven different split corks and fix one split cork in each of the jar in a way that the roots of the seedlings are immersed in the solutions.

4. Wrap the jars with black paper to check the growth of algae and keep them in bright, warm conditions.

5. Change the liquid almost every day with a fresh one and note the changes for about a month.

The growth and general health of the seedlings is absolutely normal in the normal solution while it is different, stunted or checked in many ways in solutions with the deficiency of some or other element.

The effects of the deficiency of different minerals is different in different plants.

6. Experiments on Photosynthesis:

To show that carbon dioxide is necessary for photosynthesis.

Two bell jars, potted plant, aspirator, beakers, soda lime, caustic potash, glass plate (2), some inert material, two wide tubes ending into fine tube, grease, iodine.

1. Take two potted plants and place them in darkness for two days to make them de-starched.

2. Place the pots on glass plate and cover them with a bell jar.

3. The mouth of both the bell jars is fitted with a cork having two holes. Through one hole is inserted a wide-mouthed tube ending into fine tube and through the other hole a bent tube is fitted which remains connected with an aspirator (Fig. 35).

4. The wide-mouthed tube of one bell jar is filled with soda lime. In the bell jar place two beakers containing caustic potash.

5. The wide-mouthed tube of other bell jar is filled with some inert material like pebbles, and in this bell jar place two beakers containing water in place of caustic potash. This functions as a control.

6. Apply grease at the base of the bell jar to prevent the air to pass in, and keep both the apparatuses in sunlight for a few hours, and observe.

Test the leaves of both the plants for starch separately. The leaves of the plant, placed under a bell jar having caustic potash in beaker and soda lime in the tube show negative test for starch while the leaves of the other bell jar (in which beakers contain water and tube is filled with pebbles) show positive test for starch.

Negative test for starch in the leaves of one plant indicates that there is no starch formation in its leaves because of the absence of CO 2 . All other conditions for photosynthesis (i.e., light, chlorophyll, water and temperature) are normal.

Only CO 2 is not present in the surroundings of the plant because the CO 2 of the air entering through the wide-mouthed tube is absorbed by the soda lime and the entering air is free from CO 2 . On the other hand the CO 2 , which is coming out in the process of respiration of plant, is absorbed by the caustic potash placed in the beakers.

The leaves of the other plant show positive test for starch because ail the essential requirements for photosynthesis, i.e., light, chlorophyll, water, temperature and also CO 2 , are present in its surrounding.

So, CO 2 is necessary for photosynthesis.

7. Experiments on Respiration in Plants:

To measure and compare rate of respiration of various plant parts by volumetric method using Pettinkoffer’s tubes.

Jars, respiratory substrate, Pettinkoffer’s apparatus, barium hydroxide solution, wooden stand, pressure regulator (suction pump), grease, soda lime, oxalic acid, phenolphpthalein, barium carbonate, caustic potash, burette, beakers, measuring cylinder, balance with weighing box.

1. Fill the jars with soda lime and place about 100 gm. respiratory materials in U-tube chamber.

2. Now fill the long and narrow Pettinkoffer’s tubes with solution of barium hydroxide of known concentration (N/10). Place the Pettinkoffer’s tubes in such a way on a wooden stand that they are oriented obliquely.

3. Connect the tubes with a suction pump or pressure regulator.

4. Make the entire apparatus air-tight by applying grease.

5. Now allow the pressure regulator to function. Due to this the air current rushes into the jars filled with soda lime which absorbs carbon dioxide of the air. The air now passes through the plant material placed in the U-shaped respiratory chamber (Fig. 53).

6. From the U-shaped chambers, the air is now bubbled through the Pettinkoffer’s tubes filled with barium hydroxide solution.

7. For regulating a slow movement of air and bubbles through the soda lime, respiratory substrate and barium hydroxide solution, the pressure regulator is allowed to work. The air first passes through one of the Pettinkoeffer’s tube and then it is allowed to flow through the second tube.

8. Now remove the first tube and titrate its contents. Due to the presence of precipitated barium carbonate (BaCO 3 ) the contents become turbid.

9. Measure about 25 ml. of contents of Pettinkoffer’s tube, i.e., barium carbonate and titrate it against N/10 solution of oxalic acid.

10. Phenolphthalein drops are used as indicator in the beaker containing barium carbonate and note the end point.

Observations and results:

Observations and results may be noted in the form of following table:

N 1 V 1 =N 2 V 2 , where

(a) N 1 = Known normality of oxalic acid.

It is calculated as follows:

Molecular weight of oxalic acid = 126

Equivalent weight 126/2 = 63

Therefore, N = 63

N/10= 6.3 gm. of oxalic acid dissolved in 1000 cc of water

So, N, = 6.3.

(b) V 1 = Known volume of oxalic acid used = 10 cc

(c) N 2 = Normality of barium hydroxide solution, which is to be determined.

(d) V 2 = Volume of barium carbonate =25 cc

In this way N 1 V 1 = N 2 V 2 may be calculated as follows:

6.3 × 10 = N 2 × 25

Therefore, N 2 = 6.3 × 10 / 25= 2.52

Conclusion:

The amount of CO 2 produced by 100 gm. of given plant material (respiratory substrate) is 2.5 mg/litre in one hour. In the same way, rate of respiration of different respiratory substrates or different plant parts can be determined.

8. Experiments on Growth Rate in Plants:

Aim of the Experiment: To measure the growth rate of plant by a horizontal microscope.

Horizontal microscope with a vertical stand fitted with sliding linear scale, pen, plant or twig of the plant to be measured.

In horizontal microscope (Fig. 57), the optical remain in horizontal position. It is held by a vertical stand fitted with a sliding linear scale. Its optical tube can be moved both upwards and downwards with the help of a screw. With the help of a linear scale, the vertical movement can be measured.

The growth from this microscope is measured in the following manner:

1. Make a small point on the shoot apex with the help of a pen.

2. Bring this ink point in focus of the microscope by observing through its eyepiece.

3. After 24 hours again observe the same ink point which has now moved up due to the growth in the plant. Move the microscope upwards, focus it and note the distance between the initial and the final readings.

4. Note the readings daily for 10 days after a definite interval of 24 hours.

An increase in the readings is observed daily. This indicates that the plant is growing daily.

9. Experiments on Growth of Plants by Promoting Substances:

Bioassay of auxin, gibberellin, cytokinin, abscisic acid (ABA) and ethylene using appropriate plant material.

What is bioassay?

Bioassay means the quantitative determination of a substance by measuring its biological effects on e.g., growth, that is the use of an organism to test the environment, Or, it is the determination of the power of a biological product by testing its effect on an organism.

Appropriate plant materials or bioassay materials mentioned in following Table.

Method, observations and results:

See the following table:

10. Experiments on Biotechnology:

Aim of the Experiment :

To work out the generalized steps used in the methodology of tissue culture in a plant material.

Plant material (e.g. mature carrot plant), water, scalpel or razor, cork borer, sterile petri dishes, callus initiation medium (e.g. Murashige-Skoog’s medium) with 2, 4-D, shoot development medium, pot with soil.

1. Take a mature carrot plant (Fig. 2A) with its tap root intact, remove its leaves and wash its tap root thoroughly (Fig. 2B).

2. Cut the tap root into 3 or 4 pieces (Fig. 2C) with a sharp scalpel or razor.

3. Insert the cork borer into a tap root piece (Fig. 2D) and take out the desired regions of root.

4. Put such a removed tap root piece in a sterile petridish and cut it transversely into small pieces as shown in (Fig. 2E).

5. Take some callus initiation medium (e.g. Murashige-Skoog’s medium or MS medium) with 2, 4-D in a sterile petridish, place some disks or cut pieces of tap root on it and incubate for 6-8 weeks. Callus formation starts within 4-6 weeks (Fig. 2 F).

6. Transfer the calli to another petridish containing shoot development medium. Young plants with roots and shoots (Fig. 2G) start to develop within 4- 8 weeks.

7. These young plants are transferred to pots containing soil (Fig. 2 H) where they develop into mature plants (Fig. 2A).

Related Articles:

• Experiments on Mineral Nutrition in Plants | Botany
• Conduction of Water in Plants: 4 Experiments

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Guttation: Hydathodes & Mechanism

Arpita Srivastava

Content Writer | Updated On - May 3, 2024

Key Highlights

• Guttation is the release of water in the form of water droplets of xylem sap at the ends or edges of small herbaceous plants.
• At night, when root pressure is high, water droplets leave the vessels with the help of openings called "hydathodes".
• Water loss in the form of vapor is transpiration, whereas in guttation, water is lost in the form of water droplets.
• It allows plants to remove excess water content stored by leaf margins.
• Chemicals in guttation provide an opportunity to determine soil nutrient status and plants. 

Guttation is a process in which plants release water on the leaf edges in the form of droplets. It is mainly observed at night when the rate of transpiration is low.

• The process is carried out to remove  water from the roots of the plants, stems , and leaves.
• Some common examples of guttation involve  wheat, tomatoes, barley and strawberries.

Key Terms: Guttation, Transpiration, Xylem, Sap, Plants, Hydathodes, Nutrients, Stomata

What is Guttation?

[Click Here for Sample Questions]

Guttation is the secretion of water in the form of water droplets of xylem sap on the tips or edges of small herbaceous plants such as grasses. These plants that don't have any kind of woody branches above the ground.

• Guttation usually occurs as a consequence of a combination of high root pressure and a low evaporation rate/too high humidity.
• This occurs just after sunrise when the plant becomes active and the humidity is high.
• It takes place when the cell vacuole is filled, because the plant will first replenish any water shortages in the plant cells.
• Since it requires a lot of pressure, hence it can’t happen in huge plants since pressure necessary to drive the water out is high.
• Guttation involve selection of natural and inorganic substances, the most common of which can be sugars and potassium.

Mechanism of Guttation

Guttation is carried out when soil is flooded with rainwater, and humidity is high. This results in the absorption of extra water by the roots of the plants. Water will gather within the plant, resulting in a minor root pressure.

• Few water droplets are forced to leak through leaf tips, water glands, generating drops due to the base pressure. 
• Due to hydrostatic pressure, root pressure will push the xylem upwards through the stem of the plants.
• This results in the release of liquid through specialised leaf structures called hydathodes.
• Water released during guttation consists of a solution obtained from the internal  vascular system of plants . 
• The solution obtained will contain components like  water, minerals, and organic compounds . 
• Droplets contain minerals like  potassium, calcium, and magnesium .
• Guttation helps regulate water level and soil nutrient status, releasing excess water and dissolved substances in plants.

Role of Hydathodes in Guttation

Plants have small organs that connect their vasculature (veins) to the external world. At night, root pressure in plants is quite high, water droplets leave the vasculature with the help of openings called hydathodes.

• These organs are in the form of small pores, which also serves as a safe entry passage for the vascular pathogens.
• Hydathodes, also called water stomata, forms a similar structure to stomata in which they are porous.
• It  allow water to escape from the plant through secretion since hydathodes remain in a constantly state.
• Due to this excess water accumulates in the plants and water is secreted out of the leaf.
• Guttation is often confused with transpiration and mist.
• Transpiration takes place through stomata, lenticel and cuticle, while dew is the condensation of atmospheric water droplets.
• Guttation is a different anatomy altogether and is caused by root pressure.

Guttation vs Transpiration

The difference between guttation and transpiration are as follows:

Sample Questions

Ques: What is guttation?  (2 marks)

Ans: Guttation is the secretion of water in the form of water droplets of xylem sap on the tips or edges of small herbaceous plants such as grasses or such plants that don't have any kind of woody branches above the ground. It usually occurs as a consequence of a combination of high root pressure (which may be caused by different factors) and a low evaporation rate/too high humidity. This often occurs just after sunrise when the plant becomes active and the humidity is high.

Ques: How is guttation different from transpiration? (4 marks)

Ans : Perspiration occurs through the stomata, lenticels, and cuticles, while guttation is facilitated by "hydathodes". Transpiration usually occurs during the day and has a cooling effect (this is the main focus), while guttation occurs mainly at night and has no cooling effect.

• The state of lost water is vapor in transpiration while in guttation the lost water is in the form of water droplets (liquid).
• While transpiration is beneficial to plants by helping them regulate their body temperature; Guttation is a less favourable process for plants and in some cases, even harmful due to the deposition of salts on the tips of the leaves after evaporation of the excreted water.
• Water lost through transpiration is in the form of vapor and is therefore pure, while water lost through guttation is made up of many organic and inorganic compounds.
• Transpiration is not dependent on humidity, while guttation is dependent on humidity because guttation is a direct function of root pressure, which in turn is a direct function of humidity.

Ques: What are hydathodes? What role do they play in Guttation? (2 marks)

Ans: Plants have small organs that connects their vasculature (veins) to the external world. These are called hydathodes. These organs are in the form of small pores, which also serves as a safe entry passage for the vascular pathogens (mainly disease-causing microbes). Guttation mainly occurs at night. At night when the root pressure is high water droplets ooze out of vasculature with the help of openings called “hydathodes".

Ques: What kind of plants are more prone to guttation and why is it harmful? (2 marks)

Ans: Herbaceous plants are more prone to go through Guttation. Guttation water often contains some organic and inorganic molecules that remain as a coating on the leaves after evaporation of water. This slows down the photosynthesis process which is harmful for the plants as well as exuding of water infused with minerals may be injurious to the  plants' vascular system as well.

Ques: Why does guttation affect the population of the bees and what are its impacts?  (3 marks)

Ans: It was observed that guttation drops from miticide seed corn plants could contain amounts of insecticide continually greater than 10 mg/l, and as much as 2 hundred mg/l for the imidacloprid neonicotinoids. Concentrations this excessive correspond to, if not higher than, lively ingredients utilized in pest control sprays. It was observed that bees die inside a  couple of minutes of consuming guttation drops collected from vegetation grown from neonicotinoid-coated seeds. This has widespread impacts such as pollination. Less pollination means a smaller number of flowers, fruits etc. This is a serious impact on the ecosystem.

Ques: When is the guttation most prominently visible? Name the suitable factors for the process?  (3 marks)

Ans: There is usually no perspiration at night because the stomata of most plants are closed. With high soil moisture, water penetrates the roots of plants, since the water the potential of the roots is less than that of the soil solution.

• Water accumulates in the plant, causing low root pressure.
• Some water droplets are forced to escape through the tip of the blade or unique looking systems, hydathodes or water glands, creating droplets due to pressure from the base.
• Root stress, now without perspiration force, is the force behind this flow.
• While perspiration is suppressed and the relative humidity is high, which consists in the at night, the evisceration is maximally strong.

Ques: What are the uses of Guttation?  (3 marks)

Ans: The chemicals in guttation water provides opportunity for non-invasive tests to determine the nutritional status of soil and plants provided some interesting observations on the impact soil fertility.

• Guttation water is believed to exert governance over the solubility of organic and inorganic nutrients and polymerization of organic compounds, which aid and add to soil fertility.
• The importance of guttation for plants can be understood by the fact that it serves as a pressure-release valve in precipitation and continuous absorption of water, with resultant progressive development of hydrostatic pressure that pumps water up in the leaves.

Ques: What is the difference between guttation and exudation? (3 marks)

Ans : The difference between guttation and exudation are as follows:

Ques: How guttation is carried out in banana plant? (2 marks)

Ans:  Guttation in banana plants is a natural phenomenon in which banana plants absorb water through their roots. This ater travels up the xylem due to root pressure and transpiration. During nights with high humidity, the transpiration process slows down significantly. However, root pressure might still be high, which can lead to an excess of water building up within the plant.

Ques: What is the importance of guttation? (3 marks)

Ans: The importance of guttation are as follows:

• Guttation helps remove excess water from the plants due to high root pressure by leaf margins.
• It happens only during the night as it prevents the risk of damage to cells and overhydration.
• The process helps regulate internal pressure within the plant’s vascular system.
• It helps plants release water with the help of a process called hydathodes.
• This provides a balanced environment for cellular processes.

Ques: What is the consequences of guttation? (4 marks)

Ans:  The consequences of guttation, a phenomenon in which water escapes and accumulates in droplets along the leaf margins under high humidity conditions in many plants growing in moist soil, have been little studied and remain largely unknown.

• Therefore, leaf gas exchange and chlorophyll fluorescence were examined, using two experimental approaches, in Alchemilla mollis plants under conditions that favour guttation and prevent this phenomenon.
• These results partially support the previously hypothesized guttation function and prevention of excess water in the leaves but contradict many other studies.
• More work is needed to understand the function of guttation properly.

Ques: What is root pressure? (2 marks)

Ans:  Root pressure refers to the pressure applied in the xylem when water and other ions are transmitted from soil to the vascular tissues. It helps provide water and nutrients to plants and also pushes water and nutrients out of the plant.

Ques: How can we demonstrate the process of guttation? (3 marks)

Ans: We can demonstrate the process of guttation as follows:

• In this experiment, we will require a plant tomato, a bell jar and an aspirator.
• First, water the plant and then cover it with a bell jar.
• Keep the plant in a cool environment and apply an aspirator.
• After leaving for a few hours, water starts to secrete from the tips of the leaves.
• Hydathodes are found on the edge of leaves by releasing excess water inside the plant.

Ques: How does temperature affect guttation? (2 marks)

Ans:  Temperature plays a significant role in guttation by influencing the rate of transpiration, which in turn affects the pressure buildup within the plant. Along with temperature, humidity also plays a role. High humidity further reduces transpiration, making guttation more likely on cool and humid nights.

Ques: What is transpiration? (2 marks)

Ans:  Transpiration is the process in which plants will lose water in the form of water vapour through stomata. It involves the evaporation of water from the leaves of the plant. The process helps cool plants, changes the osmotic pressure of cells, and enables the flow of mineral nutrients.

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