Induction of wound response gene expression in tomato leaves by ionophores

Three ionophores were used to investigate a potential role of the plasma-membrane (PM) potential in the regulation of systemic wound-response gene expression in tomato (Lycopersicon esculentum Mill.) plants. Valinomycin, nigericin, and gramicidin, which affect the PM potential by dissipating H+ and K+ gradients, respectively, induced the rapid accumulation of wound-response gene transcripts. Transcript induction by gramicidin was kinetically, qualitatively and quantitatively similar to systemin-induced transcript accumulation. On a molar basis, gramicidin and nigericin, which affect gradients of both H+ and K+, were more effective than the K+-selective valinomycin. Hyperpolarization of the PM by fusicoccin, on the other hand, repressed wound-response gene expression and, at the same time, induced salicylic acid (SA) accumulation and the expression of pathogenesis-related proteins. We show here that the inhibition of the wound response after fusicoccin treatment is not mediated by elevated concentrations of SA but is likely a direct effect of PM hyperpolarization. The data indicate a role for the PM potential in the differential regulation of wound and pathogen defense responses.