The respiratory burst and electrolyte leakage induced by sulfhydryl blockers in Egeria densa leaves are associated with H2O2 production and are dependent on Ca2+ influx

In leaves of Egeria densa Planchon, N-ethylmaleimide (NEM) and other sulfhy dryl-binding reagents induce a temporary increase in nonmitochondrial respi ration (Delta QO(2)) that is inhibited by diphenylene iodonium and quinacri ne, two known inhibitors of the plasma membrane NADPH oxidase, and are asso ciated with a relevant increase in electrolyte leakage (M. Bellando, S. Sac co, F. Albergoni, P. Rocco, M.T. Marre [1997] Bot Acta 110: 388-394). In th is paper we report data indicating further analogies between the oxidative burst induced by sulfhydryl blockers in E. densa and that induced by pathog en-derived elicitors in animal and plant cells: (a) NEM- and Ag+-induced De lta QO(2) was associated with H2O2 production and both effects depended on the presence of external Ca2+; (b) Ca2+ influx was markedly increased by tr eatment with NEM; (c) the Ca2+ channel blocker LaCl3 inhibited Delta QO(2), electrolyte release, and membrane depolarization induced by the sulfhydryl reagents; and (d) LaCl3 also inhibited electrolyte leakage induced by the direct infiltration of the leaves with H2O2. These results suggest a model in which the interaction of sulfhydryl blockers with sulfhydryl groups of c ell components would primarily induce an increase in the Ca2+ cytosolic con centration, followed by membrane depolarization and activation of a plasma membrane NADPH oxidase. This latter effect, producing active oxygen species , might further influence plasma membrane permeability, leading to the mass ive release of electrolytes from the tissue.