May play a role in signal transduction of hyperosmotic response. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Activated by hyperosmotic stress. Expressed in leaf blades, leaf sheaths and roots. Expressed in shoots and roots of young seedlings. By hyperosmotic stress and abscisic acid (ABA) in leaf blades. May be phosphorylated. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family.