Guard Cells Possess a Calcium-Dependent Protein Kinase That Phosphorylates the KAT1 Potassium Channel

Jiaxu Li, Yuh Ru Julie Lee, Sarah M. Assmann

Research output: Contribution to journalArticlepeer-review

157 Scopus citations


Increasing evidence suggests that changes in cytosolic Ca2+ levels and phosphorylation play important roles in the regulation of stomatal aperture and as ion transporters of guard cells. However, protein kinases responsible for Ca2+ signaling in guard cells remain to be identified. Using biochemical approaches, we have identified a Ca2+-dependent protein kinase with a calmodulin-like domain (CDPK) in guard cell protoplasts of Vicia faba. Both autophosphorylation and catalytic activity of CDPK are Ca2+ dependent. CDPK exhibits a Ca2+-induced electrophoretic mobility shift and its Ca2+-dependent catalytic activity can be inhibited by the calmodulin antagonists trifluoperazine and N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide. Antibodies to soybean CDPKα cross-react with CDPK. Micromolar Ca2+ concentrations stimulate phosphorylation of several proteins from guard cells; cyclosporin A, a specific inhibitor of the Ca2+-dependent protein phosphatase calcineurin enhances the Ca2+-dependent phosphorylation of several soluble proteins. CDPK from guard cells phosphorylates the K+ channel KAT1 protein in a Ca2+-dependent manner. These results suggest that CDPK may be an important component of Ca2+ signaling in guard cells.

Original languageEnglish (US)
Pages (from-to)785-795
Number of pages11
JournalPlant physiology
Issue number2
StatePublished - Feb 1998

All Science Journal Classification (ASJC) codes

  • Physiology
  • Genetics
  • Plant Science


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