Mastoparan induces an increase in cytosolic calcium ion concentration and subsequent activation of protein kinases in tobacco suspension culture cells.

Mastoparan induced a transient elevation of cytosolic free Ca2+ concentration ([Ca2+]cyt) in tobacco suspension culture cells. The mastoparan-induced [Ca2+]cyt elevation was inhibited by 8-(N,N-diethylamino)-octyl 3,4,5-trimethoxybenzoate-HCl and neomycin but not by depletion of extracellular Ca2+, suggesting that the elevation was the result of Ca2+ release from the intracellular stores caused by stimulation of 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 GTP-binding proteins in elicitation of the rapid oxidative burst in cultured soybean cells, J. Biol. Chem., 267 (1992) 20140-20147], also induced a transient [Ca2+]cyt elevation in the tobacco cells. However, mastoparan did not induce an oxidative burst in the tobacco cells. Activation 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 assay. This activation was inhibited by neomycin, suggesting that the [Ca2+]cyt elevation is necessary for the mastoparan-induced activation of the protein kinases. The activation was inhibited also by pretreatment with staurosporine and was sustained by pretreatment with calyculin A, suggesting that the protein kinase activity is regulated by protein 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.