Little is known about the morphological variations or differences in stomatal characteristics of Pistaciaspecies. How these variations may be related to the environment is also unknown. This paper describes the diverse stomatal morphology recorded among the Algerian representatives of Pistacia atlanticaDesf.(Atlas pistachio).
Leaf Samples of eight Algerian sites of Pistacia atlanticawere characterised according to their stomatal type, distribution and position in the epidermis, shape, size and density by the mean of light microscopy and scanning electron microscopy.
The leaves are amphistomatic in all the sites. However the abaxial stomatal densities are much higher. The mean number of stomata per square millimeter was 30.5 on the adaxial face and 308.5 on the abaxial face. The stomata were elliptical and slightly sunken in the epidermis, of the actinocytic or anomocytic types with a mean length of 29.1µm and a mean width of 19.5µm.
However, the variations in the aperture of stomata did not reveal a clear pattern in response to the ecological gradient tested, suggesting that it is a genotypic character. Onlythe stomatal density showed agreement with the environmental conditions for the areas where the trees were grown. Especially up to 900 m in altitude ecological conditions abaxial leaf stomata density decreases significantly compared to that of lowland habitats. The best discriminating traits recorded in this study were the stomata size and the stomatal density. These characteristics may afford an initial screening method for classifying P. atlanticain terms of drought resistance
Spring barley (Hordeum vulgare L. cv. Klaxon) plants were exposed to mixtures of SO2+ NO2(at concentrations of 24–35 nl l−1of each gas, depending upon fumigation system), or to charcoal-filtered, or unfiltered ambient air during the period in which the second, and subsequent, leaves were emerging. The ability of individual detached leaves to regulate water loss was then examined after terminating the pollutant treatment.
Observations of diurnal changes in stomatal resistance of well-watered plants, using a viscous flow porometer, failed to indicate any major alterations which could be attributed to prior exposure to SO2+ NO2. By contrast, when an ABA solution (10−1mol m−3) was applied to detached leaves, the stomata of polluted plants were less responsive than plants previously exposed to control air.
The dynamics of the observed responses strongly implicated impaired physiology of the guard cells rather than mechanical changes in the epidermis that might, for example, result from damage to the cuticle. Stomatal closure was considerably slower in polluted leaves compared with the controls. This decline in responsiveness to ABA was observed using leaves excised from well-watered plants and in the absence of any externally visible injury.
The ability of stomata to respond to a range of CO2 concentrations from 195–735 μmol mol−1was also examined using individual leaves, attached to the plant, in an environmentally controlled cuvette. Here the stomata of leaves which had been fumigated with SO2+ NO2 behaved in a similar manner to the non-fumigated leaves, both showing closure in elevated CO2 concentrations.
Upon incubation of epidermal peels of Commelina communis in 1 millimolar KCl, a synergistic effect of light and low fusicoccin (FC) concentrations on stomatal opening is observed. In 1 millimolar KCl, stomata remain closed even in the light. However, addition of 0.1 micromolar FC results in opening up to 12 micrometers. The same FC concentration stimulates less than 5 micrometers of opening in darkness.
The synergistic effect (a) decreases with increasing FC or KCl concentrations; (b) is dark-reversible; (c) like stomatal opening in high KCl concentrations (120 millimolar) is partially inhibited by the K+ channel blocker, tetraethyl-ammonium+ (20 millimolar).
In whole-cell patch-clamp experiments with guard cell protoplasts of Vicia faba, FC (1 or 10 micromolar) stimulates an increase in outward current that is essentially voltage independent between – 100 and +60 millivolts, and occurs even when the membrane potential is held at a voltage (−60 millivolts) at which K+ channels are inactivated.
These results are indicative of FC activation of a H+ pump. FC effects on the magnitude of inward and outward K+ currents are not observed. Epidermal peel and patch clamp data are both consistent with the hypothesis that the plasma membrane H+ ATPase of guard cells is a primary locus for the FC effect on stomatal apertures.
Stomata, functionally specialized small pores on the surfaces of leaves, regulate the flow of gases in and out of plants. The pore is opened by an increase in osmotic pressure in the guard cells, resulting in the uptake of water. The subsequent increase in cell volume inflates the guard cell and culminates with the opening of the pore. Although guard cells can be regarded as one of the most thoroughly investigated cell types, our knowledge of the signaling pathways which regulate guard cell function remains fragmented.
Recent research in guard cells has led to several new hypotheses, however, it is still a matter of debate as to whether guard cells function autonomously or are subject to regulation by their neighboring mesophyll cells.
This review synthesizes what is known about the mechanisms and genes critical for modulating stomatal movement. Recent progress on the regulation of guard cell function is reviewed here including the involvement of environmental signals such as light, the concentration of atmospheric CO2 and endogenous plant hormones. In addition we re-evaluate the important role of organic acids such as malate and fumarate play in guard cell metabolism in this process.
Transgenic tomato (Solanum lycopersicum) plants expressing a fragment of the Sl SDH2-2 gene encoding the iron sulfur subunit of the succinate dehydrogenase protein complex in the antisense orientation under the control of the 35S promoter exhibit an enhanced rate of photosynthesis.
The rate of the tricarboxylic acid (TCA) cycle was reduced in these transformants, and there were changes in the levels of metabolites associated with the TCA cycle. Furthermore, in comparison to wild-type plants, carbon dioxide assimilation was enhanced by up to 25% in the transgenic plants under ambient conditions, and mature plants were characterized by an increased biomass.
Analysis of additional photosynthetic parameters revealed that the rate of transpiration and stomatal conductance were markedly elevated in the transgenic plants. The transformants displayed a strongly enhanced assimilation rate under both ambient and suboptimal environmental conditions, as well as an elevated maximal stomatal aperture.
By contrast, when the Sl SDH2-2 gene was repressed by antisense RNA in a guard cell-specific manner, changes in neither stomatal aperture nor photosynthesis were observed. The data obtained are discussed in the context of the role of TCA cycle intermediates both generally with respect to photosynthetic metabolism and specifically with respect to their role in the regulation of stomatal aperture.
Solute content of stomata from intact onion cotyledons grown under either greenhouse or growth chamber conditions was followed over the course of a daily light cycle to determine patterns of osmoregulation.
Initial opening of stomata was well correlated with guard cell potassium accumulation under both growth conditions. Subsequently, however, there was a consistent decrease in guard cell potassium content despite constant or increasing aperture. Although a secondary increase in potassium was sometimes observed during the second half of the light cycle, guard cell potassium content was poorly correlated with aperture.
Sucrose levels in guard cells increased 60% during the period of declining potassium content, suggesting its use as an alternate osmoticum. Guard cells are postulated to use multiple pathways for the production of osmotica over the course of a complete daily cycle of stomatal movements.
Glutathione (GSH) has been shown to negatively regulate methyl jasmonate (MeJA)-induced stomatal closure.
We investigated the roles of GSH in MeJA signaling in guard cells using an Arabidopsis mutant, cad2–1, that is deficient in the first GSH biosynthesis enzyme, γ-glutamylcysteine synthetase. MeJA-induced stomatal closure and decreased GSH contents in guard cells. Decreasing GSH by the cad2–1 mutation enhanced MeJA-induced stomatal closure. Depletion of GSH by the cad2–1 mutation or increment of GSH by GSH monoethyl ester did not affect either MeJA-induced production of reactive oxygen species (ROS) or MeJA-induced cytosolic alkalization in guard cells.
MeJA and abscisic acid (ABA) induced stomatal closure and GSH depletion in atrbohD and atrbohF single mutants but not in the atrbohD atrbohF double mutant. Moreover, exogenous hydrogen peroxide induced stomatal closure but did not deplete GSH in guard cells.
These results indicate that GSH affects MeJA signaling as well as ABA signaling and that GSH negatively regulates a signal component other than ROS production and cytosolic alkalization in MeJA signal pathway of Arabidopsis guard cells.