Involvement of calcium-dependent protein kinase in rice (Oryza sativa L.) lamina inclination caused by brassinolide

Promotive effect of brassinolide (BL) on green lamina inclination was concentration-dependent when excised rice (Oryza sativa, L,) lamina was floated on BL solution under continuous light conditions. Protein kinase inhibitor staurosporine and Ca2+ channel blocker LaCI3 could completely, while Ca2+ chelator EGTA could partially inhibit the lamina inclination caused by BL, Two protein kinases with apparent molecular masses of 45 and 54 kDa were detected using an in-gel kinase assay with histone III-S as a substrate. in particular the changes in 45 kDa protein kinase activity correlated with lamina inclination caused by BL. The 45 kDa kinase activity was inhibited by Ca2+ chelator EGTA, protein kinase inhibitor, staurosporine and calmodulin antagonist W-7. Therefore, this 45 kDa protein kinase was Identified as a Ca2+-dependent protein kinase (CDPK), Patterns of 2-dimensional PACE after in vitro phosphorylation of crude extracts showed, that the phosphorylation of 56 and 41 kDa proteins, which,vas Ca2+-dependent, was strongly increased by BL treatment. These results suggested that CDPK and Ca2+-dependent protein phosphorylation are involved in BL-induced rice lamina inclination,.