Calcium mediated cytokinin action on chlorophyll synthesis in isolated embryo of Scots pine

Abstract

Chlorophyll (Chl) synthesis in isolated Scots pine embryos depended on exogenous application of cytokinin (CK) and Ca2+. At a constant benzyladenine (BA) level (4.4×10-5 M) 10-4 to 10-2 M Ca2+ concentrations in mineral medium were optimum for Chl biosynthesis under both light and dark. At a zero or very low (10-6 M) concentration of external Ca2+, Chl synthesis was relatively more Ca2+-dependent in embryos cultured in darkness than in the light, which suggested that the light: (a) stimulated the transport of Ca2+ from external sources to cytosol, and/or (b) interacted with Ca2+ directly in the pathway of Chl biosynthesis. The need of external Ca2+ was evidenced in experiments with modulators of Ca2+-transport systems. The reduction of the inward current of Ca2+ from readily accessible external sites by chelating agent (ethylene glycol-bis (beta-aminoethyl ether-N,N,N'N'-tetraacetic acid, EGTA) and Ca2+-channel blockers canceled the formation of Chl. The effect of EGTA depended on the level of external Ca2+. Inhibitory action of Ca2+-channel blockers depended on their kind and concentration: at the 10-5 M concentration La3+>verapamil>nifedipine inhibited Chl formation. In the presence of Ca2+, the Ca2+-agonist A 23187 mimicked the BA effect and about 92% of Chl was synthesized as compared with the BA variant. Low concentrations of calmodulin antagonists reduced the amounts of Chl. Calmodulin was included in a second messenger system for BA action in promoting Chl biosynthesis in isolated Scots pine embryos.