Hormonal signaling to control stomatal movement during drought stress

When a plant experiences water stress, one of the early signs is the control of water loss through its stomata. These responses are more closely linked to soil moisture content than to leaf water status, which remains constant. Stomata actually respond to chemical or hormonal signals produced by the dehydrating roots. The most important hormonal signal in this regard is ABA, which has been very well observed in dehydrating roots and circulating in plants under water deficit conditions. ABA is thought to produce its effect through its interaction with other chemicals like jasmonic acid (JA), cytokinins, auxin and ethylene. They produce their effect through ion exchange, cytoskeletal reorganization, metabolite production, modulation of gene expression and post-translational modification of proteins. ABA and JA are positive regulators of stomatal closure, auxins and cytokinins are negative regulators and the role of ethylene dependent on the tissue and its condition. Here, we would like to give a brief account of various signaling components involved in opening and closing of stomata during water deficit, especially with reference to the hormonal signals. We will also discuss the role of various ion channels, transporters, and pumps localized in the plasma membrane for influx and efflux of solutes and thus providing help in stomatal function. The role of ER proteins calnexin (CNX) and calreticulin (CRT) as Ca2 + binding chaperones in mediating drought stress signaling has also been discussed.