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Transpiration
Published in Yeqiao Wang, Fresh Water and Watersheds, 2020
Stomata are embedded in the leaf epidermis and are formed by a pair of cells called guard cells. The guard cells in monocots plants, as shown in Figure 27.2, tend to resemble barbells with bulbous structures at each end. The guard cells of dicot plants shown in Figure 27.3, have a kidney shape. In both cases, the pair of guard cells is attached to each other at both ends. Swelling of the bulbous end of guard cells in monocots causes the cylindrical midsections to move apart increasing the aperture of the pore. The entire kidney-shaped cells of dicots swell and, as a result of a specialized cell wall structure bordering the pore, the aperture of the pore increases. Conversely, a decrease in the size of guard cells in both cases results in a decrease in pore aperture.
Air pollution impacts
Published in Abhishek Tiwary, Ian Williams, Air Pollution, 2018
The first site of action for ozone, as for other oxidative gaseous pollutants, is believed to be the cell plasma membrane. The integrity and full functioning of this membrane is particularly important for guard cells, because it controls water flow into and out of the cells, cell turgor and hence shape and stomatal aperture. If the guard cells do not function efficiently, there are several possible consequences: for well-watered plants, stomata will not open to their full capacity so that photosynthesis is reduced; for drought-stressed plants, they will not close as tightly so that water loss is increased; neither will they close as tightly when the plant is ozone-stressed, so that the ozone flux through the stomata is increased. Hence the ozone-exposed plant is in a lose-lose situation – it cannot photosynthesise as strongly when water is in good supply, and it cannot restrict water loss as effectively when water is scarce. Looked at from the opposite perspective, there are many experimental observations that stomata close in response to ozone exposure, potentially reducing gas exchange, photosynthesis and growth. There is a much smaller number of observations that suggest the opposite – that at low concentrations, ozone can stimulate stomatal opening.
Effects on plants, visual range and materials
Published in Abhishek Tiwary, Jeremy Colls, Air Pollution, 2017
The first site of action for ozone, as for other oxidative gaseous pollutants, is believed to be the cell plasma membrane. The integrity and full functioning of this membrane is particularly important for guard cells, because it controls water flow into and out of the cells, cell turgor and hence shape and stomatal aperture. If the guard cells do not function efficiently, there are several possible consequences: for well-watered plants, stomata will not open to their full capacity so that photosynthesis is reduced; for drought-stressed plants, they will not close as tightly so that water loss is increased; neither will they close as tightly when the plant is ozone-stressed, so that the ozone flux through the stomata is increased. Hence the ozone-exposed plant is in a lose-lose situation – it cannot photosynthesise as strongly when water is in good supply, and it cannot restrict water loss as effectively when water is scarce. Looked at from the opposite perspective, there are many experimental observations that stomata close in response to ozone exposure, potentially reducing gas exchange, photosynthesis and growth. There is a much smaller number of observations that suggest the opposite – that at low concentrations, ozone can stimulate stomatal opening.
Diffusional and Thermal Resistances of Substomatal Cavity and Its Application on Wick
Published in Heat Transfer Engineering, 2022
Transpiration is the most important physiological activity of plant and the stoma plays an essential role as the terminal in this activity. Some interesting phenomena, such as the phase change and heat and mass transfer, keep happening within the stoma and substomatal cavity, just like that happens within the wick. It was found that the abscisic acid triggered a signal in the guard cells that led to stomatal closure for reducing the water loss in response to the drought [14]. The guard cell controls the stomatal aperture through its expansion and contraction by the osmotic potential [15]. To indicate the extent of stomatal opening, a parameter named stomatal conductance was used, which relates to the net photosynthetic rate and CO2 concentration [16, 17]. There were some classical theoretical models of the stomatal conductance, such as the Jarvis model [18], Ball-Berry model [19] and Leuning model [20].
Photosynthesis, lipid peroxidation, and antioxidative responses of Helianthus annuus L. against chromium (VI) accumulation
Published in International Journal of Phytoremediation, 2022
Dharmendra Kumar, Chandra Shekhar Seth
SEM analysis of leaf surface revealed that Cr(VI) stress promotes stomata closure along with damaged guard cells and epidermal cells (Figure 1(b–d)). The fully flaccid and normal shape and size of epidermal and guard cells were observed in the control plant leaf (Figure 1(a)). The degree of damage to guard cells and epidermal cells intensified with the increasing concentrations of Cr(VI). A lower [15 mg Cr(VI) kg−1 soil] concentration of Cr(VI) caused partially closed stomata with marginally shrinked guard cells and intact epidermal cells (Figure 1(b)). However, in higher [30 and 60 mg Cr(VI) kg−1 soil] concentrations of Cr(VI) completely closed stomata, shrank and damaged guard and epidermis cells were observed; epidermal cells looked fragile and fused with guard cells at some point in the 30 and 60 mg Cr(VI) kg−1 soil (Figure 1(c,d)). The stomata were partially to completely closed which directly affects the CO2/H2O exchange and in turn, affects photosynthesis. The change in stomata physiology is largely governed by ABA-mediated efflux of K+ ion from guard cells which leads to the stomata closure. Closed stomata hampers the leaf CO2/H2O exchange and cause the inhibition in gas exchange parameters viz, A, E, and GH2O. The Pb exposure has been reported to inhibit the leaf gaseous exchange parameters by damaging the guard cells and stomata in Brassica juncea (Agnihotri and Seth 2020).