2-aminoindan-2-phosphonic-acid and fusicoccin

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 escuilentum 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.

Topics: Cell Membrane; Gene Expression Regulation, Plant; Glycosides; Gramicidin; Indans; Ionophores; Leucyl Aminopeptidase; Membrane Potentials; Nigericin; Organophosphonates; Plant Leaves; Plant Proteins; Protease Inhibitors; RNA; Salicylic Acid; Signal Transduction; Solanum lycopersicum; Threonine Dehydratase; Transcription, Genetic; Valinomycin

Treatment of tomato plants (Lycopersicon esculentum Mill.) with fusicoccin (FC), an activator of the plasma-membrane H+-ATPase which maintains an electrochemical gradient across the plasma membrane, resulted in a dose-dependent accumulation of transcripts for intra- and extracellular pathogenesis-related (PR) proteins. The accumulation of PR protein transcripts was paralleled by an increase in leaf salicylic acid (SA) content. Transcripts of PR proteins and SA started to accumulate 3 h after FC treatment. 2-Aminoindan-2-phosphonic acid, an inhibitor of SA synthesis, was used to assess the role of SA in FC-mediated induction of PR gene expression. 2-Aminoindan-2-phosphonic acid was found to suppress the accumulation of SA but not the induction of PR gene expression in response to FC treatment. Furthermore, in transgenic tobacco plants overexpressing a bacterial salicylate hydroxylase gene (nahG-tobacco), PR transcripts accumulated after FC treatment to levels similar to those observed in control tobacco plants. The data indicate a role for the proton gradient across the plasma membrane in the SA-independent induction of PR gene expression.

Topics: Glycosides; Indans; Organophosphonates; Plants, Genetically Modified; RNA, Plant; Salicylic Acid; Solanum lycopersicum