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Water stress (drought and salt stress) is one of the major environmental problems causing severe losses in agriculture and in nature. Drought tolerance of plants is mediated by several mechanisms that work together, including stabilizing and protecting the plant from damage caused by desiccation and also controlling how much water plants lose through the stomatal pores during drought.
Stoma in a tomato leaf shown via colorized scanning electron microscope image A stoma in horizontal cross section The underside of a leaf. In this species (Tradescantia zebrina) the guard cells of the stomata are green because they contain chlorophyll while the epidermal cells are chlorophyll-free and contain red pigments.
English: Opening and Closing of Stomata 1-Epidermal cell 2-Guard cell 3-Stoma 4-K+ ions 5-Water 6-Vacuole a. Open stoma: stomata are the small pores in the epidermis of leaves. They are bordered by guard cells. The stomata open when the turgor pressure increases in the guard cells, causing the cells to buckle outward.
Stomatal conductance, usually measured in mmol m −2 s −1 by a porometer, estimates the rate of gas exchange (i.e., carbon dioxide uptake) and transpiration (i.e., water loss as water vapor) through the leaf stomata as determined by the degree of stomatal aperture (and therefore the physical resistances to the movement of gases between the air and the interior of the leaf).
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Metabolic inhibitors reduce the stomatal opening and increase the leaf resistance to water vapour diffusion without affecting carbon dioxide uptake. Examples include phenylmercury acetate, abscisic acid (ABA), and aspirin. Film-forming antitranspirants form a colorless film on the leaf surface that allows diffusion of gases but not of water vapour.
Turgor pressure within the stomata regulates when the stomata can open and close, which plays a role in transpiration rates of the plant. This is also important because this function regulates water loss within the plant. Lower turgor pressure can mean that the cell has a low water concentration and closing the stomata would help to preserve water.
The closing of pome lenticels can arise when the cuticle over the stomata opening or the substomatal layer seals. Closing can also begin if the substomatal cells become suberized , like cork . The number of lenticels usually varies between the species of apples, where the range may be from 450 to 800 or from 1500 to 2500 in Winesap and ...