The influence of altered water availability on stomatal patterns of leaves
The aim of this research was to study the influence of altered water availability on stomatal patterns of leaves. A baseline study of leaves stomatal indices, (stomatal as a proportional of all epidermal cells) stomatal density, (number of stomatal per unit area of epidermis) epidermal cell density, epidermal cell length and stomatal length and width was made in wheat, and sorghum cultivars; Saudi Red, Funk, Indian White, Morgon 854, Morgon 856 and Pioneer 8ss in relation to water limitation. Seedlings of wheat and sorghum cultivars grown under water limitation showed increases in their stomatal density, epidermal cell density and trichome index in response to reduced watering frequency. Stomatal index of the two species, however, were not altered in the same way. In sorghum there was no apparent change in stomatal index in relation to water limitation treatment but stomatal density and trichome index increased. In wheat there was a marked reduction in the stomatal index in response to water limitation but there were increases in trichome indices and stomatal densities of all parts of the leaves. Wheat plants grown under water limitation imposed by polyethylene glycol (PEG) treatments to roots showed marked reductions in their growth compared with controls. Stomatal density was found to increase in response to PEG treatments while stomatal index decreased. Incubation of newly-germinated wheat seedlings in PEG resulted in an inhibition of growth of coleoptiles. However, the density of stomata decreased, unlike what was seen in leaf tissues. When wheat coleoptiles were subjected to conditions of limited water availability guard mother cell (GMC) production appeared not to be influenced by water status of the tissues. Wheat coleoptiles grown under different periods of light showed slight decreases in stomata density compared to the controls. Abscisic acid treatment was able to substitute for water limitation treatments by reducing stomatal index in both leaves and coleoptiles whilst increasing the production of trichomes in leaves. However, in coleoptile the same treatment reduced both the GMC index as well as stomata index. Salinity treatments, inhibited seed germination and were found to decrease stomatal index. Incubation of wheat seedlings in PEG resulted in a yellow pigmentation of the roots. The pigment was tentatively identified. However, it was not possible to distinguish whether the pigment was a specific metabolite of PEG in the roots or was produced by a non-biological conversion of PEG.