Involved in early responses to osmotic stress. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Activated by osmotic stress and by abscisic acid (ABA). Activation by NaCl is dependent on ABA. Up-regulated in response to NaCl treatment. Significantly reduced levels of SnRK2 proteins activated by NaCl or abscisic acid (ABA) compared with wild-type. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family.