GuttationBy

Halala Rahman Qadir

Guttation• Guttation is the appearance of drops

of xylem sap on the tips or edges of leaves of some vascular plants, such as grasses. Guttation is not to be confused with dew, which condenses from the atmosphere onto the plant surface Secretion of water on to the surface of leaves through specialized pores, or hydathodes.

Showing guttation fluid in leaves

W h at is th e m ain cau se o f gu tt ati o n in p lan ts?

• The main cause of guttation in plants is root pressure,during night when root pressure is high sometimes den due to this pressure watery drops ooze out with the assistance of special structures which help in guttation called the hydathodes.

Transpiration• Transpiration is a process similar to

evaporation. It is a part of the water cycle, and it is the loss of water vapor from parts of plants (similar to sweating), especially in leaves but also in stems, flowers and roots. Leaf surfaces are dotted with openings which are collectively called stomata, and in most plants they are more numerous on the undersides of the foliage. The stomata are bordered by guard cells that open and close the pore. Leaf transpiration occurs through stomata.

The differences between guttation and transpiration

Trans piration Guttation 1.Takes place through cuticle, lenticel and stomata.

1.Takes place through hydathodes

2.It usually occurs in the day 2. It usually occurs in the night

3. Water lost in the form of water vapour 3. Water lost in the form of droplets

4. The water lost is pure 4.Guttation droplets contain organic and inorganic solvent.

5. It gives a cooling effect 5. It does not give a cooling effect.

6. Its benefial to plants as its maintains body tempreture by cooling effects.

6. Its less significant to ;plant and some time causes injury to plant by deposition to of salts on the leaf tips after evaporation.

7.Occure during dry day 7.ocuure during humid periods .

Transpiration

(Moisture loss is a pull due to evaporation) Evaporation of water through stomata.Loss of moisture from leaves and stems. Occurs usually during the day. Stomata are on the underside of leaves 90% of moisture loss is through Transpiration.

Guttation Shown is a compound leaf of strawberry (Fragaria).

HYDATHODESA hydathode is a type of secretory tissue in leaves, usually of Angiosperms, that secretes water through pores in the epidermis or margin of leaves, typically at the tip of a marginal tooth or serration. They probably evolved from modified stomata. It is involved in guttation, where water is released from the top in order to transport the nutrients in the water from the roots to the leaves. Hydathodes are connected to the plant vascular system by a vascular bundle.

Figure (a) Nasturtium leaf showing guttation at the margin of leaf(b) A vertical section of a leaf showing hydathode.

Hydathodes

Stomata• In botany a stoma (also stomate; plural stomata) is a pore,

found in the leaf and stem epidermis that is used for gas exchange. The pore is bordered by a pair of specialized parenchyma cells known as guard cells that are responsible for regulating the size of the opening. The term stoma is also used collectively to refer to an entire stomatal complex, both the pore itself and its accompanying guard cells. Air containing carbon dioxide and oxygen enters the plant through these openings where it is used in photosynthesis and respiration, respectively. Oxygen produced by photosynthesis in the spongy layer cells (parenchyma cells with pectin) of the leaf interior exits through these same openings. Also, water vapor is released into the atmosphere through these pores in a process called transpiration.

Leaf showing stomata

SHOWING STOMATA

Differences between stomata &Hydathodes Stomata

Hydathodes

1.Occure in epiderm of leaves ,young stems .

1.Occure at the tip or margin of leves that grown in moist shady place .

2.Stomatal aperture is guarded by two kidney shaped guard cells.

2.Aperture of hydathodes is surround by a ring of cuticularized cells

3.The two guard cells are generally surrounded by subsidiary cell.

3.Subsidary cells are absent

4.Opening and closing of the stomatal aperture is regulated by guard cells .

4.Hydathode pores remain always open .

5.These are involved in transpiration and exchange of gases .

5.These are involved guttation .

Hydathodes may be active or passive

1-Active Hydathodes are specialized epidermal cells which do not have a cuticle on the outside and are not connected directly with vascular strand directly.2-Passive Hydathode comprises loosely arranged ,colourless and parenchymatous cells known as epithem.it lies inside the leaf below the vein end.

Chemical content

• Guttation fluid may contain a variety of organic and inorganic compounds, mainly sugars, and mineral nutrients, and potassium. On drying, a white crust remains on the leaf surface.

• The water that is lost in this process is not pure but contains minerals, , organic acids, sugars and even enzymes.  The estimation of solutes lost in this process, reveal that certain plants loose about 200-500 mg of solutes per liter of water.

 

Guttation fluid

Guttation fluid contain various and noticeable amount of micro&macro molecules .

The guttation fluid may rill off,evaporate, or reabsorbed.

Guttation play a role in tip burn of leaves.Guttation fluid as its easly collectable

sollutions can be used in production of recombinant protiens.

Analysis

• If high levels of nitrogen appear in the fluid, it is a sign of fertilizer burn .Excess nitrogen must be leached from the soil by addition of large quantities of water. This may result in water pollution, but is the best way to restore soil fertility.

Fertilizer burn on a leaf

MECHANISM OF GUTTATION

• Under certain conditions like soil flooded with overnight rain water and with high relative humidity of the day atmosphere, the root system of some plants like tomato, potato, etc., absorb excess of water by active uptake. As a result, hydrostatic pressure develops in the root system which actually pushes water upwards.  So the water along with other soluble components of the cells is forced out of the xylem elements located into Epithem tissue. 

• As result, the space behind the water stomata gets filled with the water and with more root pressure operating; the liquid is virtually pushed out of the pore, where the stomata do not offer any resistance.  Probably transfer cells may also help in the retrieval of minerals and other components from the xylem elements and secreting out along with water. 

• However, it has been speculated that active hydathodes may directly secrete the minerals and organic acids out of the passive stomata.  Such active secretion of the above said substances creates a  diffusion gradient and water is just withdrawn from the cells into exterior surface so guttation takes place.  In spite of the borderline between active and passive mechanisms of guttation is not much, the concepts are attractive.

Guttation injuries

The injuries of concentrated gutted solution are related to three kinds of casual bases.

• First, injuries are connected with loss and depletion of usual amounts of vital nutrient substances.

• Secondly,injuries are caused by the accumulation and concentration of guttation products on localized areas of the plants.

• Finally, the entrance of various foreign agents and pathogen causes injuries since they go through water pore into the hydathodes during active guttation periods.

Guttation injuries

• Chlorosis and necrosis, two guttation injury symptoms, are usually observed on leaves whose injuries are generally caused by direct action of concentrated guttation solution and microorganisms’ infection.

The condition where the process of guttation occure

• At night, transpiration usually does not occur because most plants have their stomata closed. When there is a high soil moisture level, water will enter plant roots, because the water potential of the roots is lower than in the soil solution. The water will accumulate in the plant, creating a slight root pressure. The root pressure forces some water to exude through special leaf tip or edge structures, hydathodes, forming drops. Root pressure provides the impetus for this flow, rather than transpirational pull.

Why Does Guttation Take Place at Night?

The conditions must be right for guttation to occur. Transpiration stops at night when the stomata on leaves close. Water in the soil is absorbed by the roots of vascular plants by osmosis when the water potential in the roots is lower than the water potential in the soil. Root pressure forces the water up through the roots into the stems and leaves of plants.

Gutation on grass, photographed soon after sunrise

The related studies regarding to guttation

• Table 1- following show that some experiment about the composition of guttation fluid from Rye, Wheat, and Barley Seedlings it show that total sugar content is about equal in rye and barley fluids, but lower in xvheat. Glucose is the principal sugar component of the rye and barley fluids and galactose highest in wheat. Most of the amino acid in all 3 fluids is aspartic acid or asparagine.

Barley fluid is far higher than the other 2 in total amino acids, with wheat the lowest.

Most inorganic elements are found to be highest in barley and lowest in wlheat, with the exception of iron where rye is highest and barley lowest. Barley fluid is highest in choline, paminobeuizoic acid. thiamine, and uracil, while rye is highest in inositol and pyridoxine. Wheat is mutch lower than the other 2 in choline and inositol.

Advantages and disadvantages of guttation

• The significance of guttation is not clear. It is of less importance to plants. Sometimes it may cause injury to leaf margins by salt deposits which is left by evaporation of guttation water. The salt deposits at the margin of pore of hydathode may plasmolyse and kill the entering pathogenic bacteria and fungi. the process of guttation important nutrients and water may be lost,which may in turn lead to the dehydration and wilting of the plant.

Showing dew

Condition ocuring guttation

Guttation depend on many enviromental conditions among these factors that favor guttation are high water absorption ,high root pressure ,and reduced transpiration .

The wind velocity. soil moisture stress, as external factors,

played dominant roles in the regulation of guttation.

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