Salt stress influence on stomatal and hydraulic conductivity, as well as on the level of aquaporins in leaf cells of barley plants, differing in salt tolerance

We studied participation of aquaporins in the regulation of leaf hydraulic conductivity and relationship of hydraulic conductivity with accumulation of ABA and stomatal closure during salt stress. Using the method of immunohistochemical localization we showed that salinity led to greater decline in the level of aquaporins in the region of the vascular leaf bundles of the more salt-tolerant Prairia cultivar, accompanied by a noticeable decrease in hydraulic conductivity of the leaf. In the less salt-tolerant plants of the Mikhailovsky cultivar, significant changes in the level of aquaporins under the influence of salt stress were not found. The degree of decrease in the hydraulic conductivity of the leaf in plants of two cultivars under the influence of salt stress correlated with a decrease in transpiration. Immunohistochemical localization of abscisic acid (ABA) in leaf cells showed that during salt stress this hormone accumulated in leaf mesophyll cells and stomata. The uptake of exogenous hormone from the nutrient solution and its entry into the leaf through the vascular bundles was accompanied by an increase in staining for aquaporins and the hydraulic conductivity of the leaves, which is characteristic of the ABA action. Differences in the localization of exogenous and endogenous hormones were obviously the cause of the opposite directions of changes in hydraulic conductivity: its increase under the influence of an exogenous ABA and a decrease - under the influence of salt stress. ABA concentration assessment in xylem showed the absence of its increase during salt stress, which explains the absence changes of staining for this hormone in the region of the leaf vascular bundles and indicates that accumulation of ABA in a short-term salt stress is not the result of its delivery from the roots, but the result of its synthesis in the shoot itself.