TRANSIENT STIMULATION OF OXYGEN-UPTAKE INDUCED BY SULFHYDRYL-REAGENTSIN EGERIA-DENSA AND POTAMOGETON-CRISPUS LEAVES

A Vigorous and transient increase of O-2 uptake associated with a simu ltaneous release of CO2 was elicited in Egeria dense and in Potamogeto n crispus leaves by treatment with N-ethylmaleimide (NEM) and by other -SH group reagents (iodoacetate, p-(chloromercuri)benzenesulfonate (p -CMBS), Ag+, Hg2+, Cu2+). The NEM-induced respiratory burst was appare nt even in the absence of photosynthesis (darkness, or presence of DCM U) as well as in the presence of the respiration inhibitors cyanide an d propyl gallate or SHAM, separate or in combination. In contrast, a c omplete suppression of the respiratory burst was induced by diphenylen e iodonium and by quinacrine, inhibitors of the plasma membrane NADPH oxidase activated in the pathogen-elicited oxidative burst-in granuloc ytes and in plants,The respiratory burst induced by NEM and by the unc oupler CCCP were additive. The intensity of the respiratory burst was markedly decreased by increasing the pH of: the medium from 5 to 8, an d partially decreased by the presence of K+ in the medium. Azide inhib ited the burst (as well as basal respiration) at pH 6.5 but not at pH 5. The stimulation of QO(2) by SH reagents was associated with an earl y, pronounced membrane depolarization together with a rapid increase o f the release into the medium of K+ and other electrolytes, and with a rapid decrease of the intracellular ATP, ADP and G6P contents. The po ssible relationships between this SH reagent-induced respiratory burst and the associated effects on E-m and electrolyte leakage are discuss ed.