Plants can adapt to osmotic stress by rapidly expressing genes that will counter imbalances in ions, cell volume, and turgor pressure. Hoyos and Zhang show that two kinases are rapidly expressed and activated upon exposure to high salt conditions. One kinase appears to be a MAP kinase family member that was previously identified as a salicylic acid-induced kinase (SIPK). A 40-kD protein kinase was also activated and called high osmotic stress-activated kinase (HOSAK). Unlike other stress-activated pathways in plants that rapidly activate gene expression, SIPK and HOSAK are stimulated independently of calcium or expression of abscisic acid, a plant hormone that increases in response to water deficit. The roles of SIPK and HOSAK in the plant's response to change in osmolarity remain to be defined.
Hoyos, M.E., and Zhang, S. (2000) Calcium-independent activation of salicylic acid-induced protein kinase and a 40-kilodalton protein kinase by hyperosmotic stress. Plant Physiol. 122: 1355 -1364. [Abstract] [Full Text]