MASTOPARAN INDUCES AN INCREASE IN CYTOSOLIC CALCIUM-ION CONCENTRATIONAND SUBSEQUENT ACTIVATION OF PROTEIN-KINASES IN TOBACCO SUSPENSION-CULTURE CELLS

Mastoparan induced a transient elevation of cytosolic free Ca2+ concen tration ([Ca2+](cyt)) in tobacco suspension culture cells. The mastopa ran-induced [Ca2+](cyt) elevation was inhibited by 8-(N, N-diethylamin o)-octyl 3,4,5-trimethoxybenzoate- HCl and neomycin but not by depleti on of extracellular Ca2+, suggesting that the elevation was the result of Ca2+ release from the intracellular stores caused by stimulation o f phosphoinositide turnover. Hydrogen peroxide which has been shown to induce an oxidative burst in soybean cells by mastoparan treatment [L . Legendre, P.F. Heinstein, P.S. Low, Evidence for participation of GT P-binding proteins in elicitation of the rapid oxidative burst in cult ured soybean cells, J. Biol. Chem., 267 (1992) 20140-20147], also indu ced a transient [Ca2+](cyt) elevation in the tobacco cells. However, m astoparan did not induce an oxidative burst in the tobacco cells. Acti vation of a 50, a 75 and a 80 kDa protein kinases after the mastoparan -induced [Ca2+](cyt) elevation was shown by an in-gel protein kinase a ssay. This activation was inhibited by neomycin, suggesting that the [ Ca2+](cyt) elevation is necessary for the mastoparan-induced activatio n of the protein kinases. The activation was inhibited also by pretrea tment with staurosporine and was sustained by pretreatment with calycu lin A, suggesting that the protein kinase activity is regulated by pro tein phosphorylation/dephosphorylation. The present report shows that mastoparan induces an increase in [Ca2+](cyt) without oxidative burst and subsequent activation of protein kinases in tobacco cells. (C) 199 8 Elsevier Science B.V.