DefinePK

Abstract

Calcium chelatorsantagonist effectively blocked the jasmonic acid JA induced accumulation of
a basic 28 kDa Bowman-Birk proteinase inhibitor and an acidic 17 kDa pathogenesis-related class
1 protein in rice seedling leaf sheaths. In gel kinase assays revealed rapid changes in the
phosphorylation activities of a 46 and 56 kDa Myelin Basic Protein Kinase MBPK and a 48 kDa
putative Ca2-dependent protein kinase CDPK by JA and leaf sheath cutting and these changes
were determined to be cytosolic in nature. In vitro protein phosphorylation of crude and cytosolic
protein extracts, followed by two-dimensional polyacrylamide gel electrophoresis showed
considerable enhancement in the Ca2-dependent phosphorylation of certain proteins as early as 15
min after JA treatment, particularly a 56 kDa phosphoprotein. Hydrogen peroxide a potent reactive
oxygen species, ROS and oxyfluorfen a lipid peroxidizing agent caused a significant increase in
the levels of these two proteins over the cut control. Whereas, when JA was co-applied with 3-3,
4-dichlorophenyl-1,1-dimethylurea, a photosystem II electron transport inhibitor and n-propyl
gallate, a free radical scavenger, the accumulation of these induced proteins were considerably
reduced. These results suggest an involvement of kinase-signaling cascades and the ROS in JA
elicited accumulation of these defensestress-related proteins in rice.