biologia plantarum

Biologia plantarum 35:53, 1993 | DOI: 10.1007/BF02921119

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

Z. Lechowski¹, J. Białczyk¹

¹ Department of Plant Physiology and Development, Jagiellonian University, Kraków, Poland

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.

Received: February 4, 1992; Accepted: April 2, 1992; Published: March 1, 1993  Show citation