PT  - JOURNAL ARTICLE
AU  - Li, J.
AU  - Assmann, S. M.
TI  - An Abscisic Acid-Activated and Calcium-Independent Protein Kinase from Guard Cells of Fava Bean.
AID  - 10.1105/tpc.8.12.2359
DP  - 1996 Dec 01
TA  - The Plant Cell
PG  - 2359--2368
VI  - 8
IP  - 12
4099  - http://www.plantcell.org/content/8/12/2359.short
4100  - http://www.plantcell.org/content/8/12/2359.full
SO  - Plant Cell1996 Dec 01; 8
AB  - Abscisic acid (ABA) regulation of stomatal aperture is known to involve both Ca2+-dependent and Ca2+-independent signal transduction pathways. Electrophysiological studies suggest that protein phosphorylation is involved in ABA action in guard cells. Using biochemical approaches, we identified an ABA-activated and Ca2+- independent protein kinase (AAPK) from guard cell protoplasts of fava bean. Autophosphorylation of AAPK was rapidly (~1 min) activated by ABA in a Ca2+- independent manner. ABA-activated autophosphorylation of AAPK occurred on serine but not on tyrosine residues and appeared to be guard cell specific. AAPK phosphorylated histone type III-S on serine and threonine residues, and its activity toward histone type III-S was markedly stimulated in ABA-treated guard cell protoplasts. Our results suggest that AAPK may play an important role in the Ca2+-independent ABA signaling pathways of guard cells.