Water droplets on leaves

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 stoma are bordered by guard cells (together known as stomata) that open and close the pore. Leaf transpiration occurs through stomata, and can be thought of as a necessary “cost” associated with the opening of the stomata to allow the diffusion of carbon dioxide gas from the air for photosynthesis. Transpiration also cools plants, changes cell’s osmotic pressure, and enables mass flow of mineral nutrients and water from roots to shoots.

Transpiration from the aerial parts of a plant occurs from three different regions

  1. From the leaves through the stomata (stomatal transpiration),
  2. Directly from the surface of the leaves and stems (cuticular transpiration)
  3. From the lenticels which are the minute openings on the surface of old stems (lenticular transpiration).

The major part of the transpiration occurs through the stomata, the other two types of transpiration contribute very little.

Guttatuion

Guttatuion

  1. 1. Guttation By Halala Rahman Qadir
  2. 2. 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.
  3. 3. Showing guttation fluid in leaves
  4. 4. What is the main cause of guttation in plants? • 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.
  5. 5. 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.
  6. 6. 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. 6. Its benefial to plants as its maintains body tempreture by cooling effects. 7.Occure during dry day It does not give a cooling effect. 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.ocuure during humid periods .
  7. 7. 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.
  8. 8. Guttation Shown is a compound leaf of strawberry (Fragaria).
  9. 9. HYDATHODES A 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.
  10. 10. Figure (a) Nasturtium leaf showing guttation at the margin of leaf (b) A vertical section of a leaf showing hydathode.
  11. 11. Hydathodes
  12. 12. 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.
  13. 13. Leaf showing stomata
  14. 14. SHOWING STOMATA
  15. 15. 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 .
  16. 16. 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.
  17. 17. 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.
  18. 18. 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.
  19. 19. 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
  20. 20. 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.
  21. 21. • 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.
  22. 22. • 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.
  23. 23. 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.
  24. 24. 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.
  25. 25. 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.
  26. 26. 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.
  27. 27. Gutation on grass, photographed soon after sunrise
  28. 28. 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.
  29. 29. 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.
  30. 30. 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.
  31. 31. Showing dew
  32. 32. 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.
  33. 33. Thank you

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: A Pressure Relief for Plants

Christopher J. Starbuck
University of Missouri
(573) 882-9630

Published: June 1, 2009

Guttation droplets on blades of fescue.

Have you ever noticed tiny water droplets uniformly spaced around the margins of a leaf on a dewy morning? If so, you might have wondered what would cause dew drops to form in such a regular pattern. In fact, you have observed a phenomenon called “guttation”, by which plants exude water from structures called ‘hydathodes” on margins or tips of leaf blades. In a sense, guttation is Mother Nature’s way of allowing plants to relieve water pressure that can build up in their tissues under certain conditions.

The processes by which plants take up water from the soil are fairly straight forward. Assuming that there is ample water stored in capillary pores in the soil, a plant pulls most of its water from the ground through suction created by transpiration (evaporation from stomata on the lower leaf surfaces). Over 90 percent of water used by most temperate zone plants is lost to the atmosphere through transpiration. While this may seem inefficient, transpiration is necessary for two mainreasons; cooling of the leaf surface and pulling minerals from the soil into the plant.

Guttation droplet on ‘Strawberries and Cream’ ribbon grass.

Thinking back to high school biology, you may remember that roots have a layer of cells surrounding their central vascular tissues (xylem and phloem) called an endodermis. Water can not move through the endodermis without going through cellular membranes because the cell walls perpendicular to water flow are sealed with suberin (remember the casparian strip?). As roots take up fertilizer and other solutes from the soil, these can accumulate in cells inside the endodermis. Then, when transpiration stops at night, pressure may build up as water moves through the endodermis by osmosis. This is when guttation comes into play.

Guttation droplets on a tomato leaf in a greenhouse.

Under night time conditions of high humidity, cool air and warm soil, root pressure can move water to the leaves. Since the stomata are closed at night, transpiration can not remove water from the leaf as it does during the day. Hydathodes, located on leaf margins near the ends of tiny veins, exuded droplets of water to relieve the pressure. Even though water lost to guttation contains minerals and sugars, the losses are inconsequential. In rare cases, bacteria can grow in guttation droplets and be pulled back into the leaf when the sun comes up, leading to disease infection. In other cases, guttation may reduce the incidence of a non-infectious disorder called edema, in which tiny blisters appear on leaves during long periods of high humidity and excess soil moisture. Edema can be a problem when growing geraniums in the greenhouse. Regardless of its effects on plants, guttation provides entertainment to plant lovers. Check it out on your next dewy garden walk.

Water droplets on leaves

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