Inhibition of darkness-induced stomatal closure by ethylene involves a removal of hydrogen peroxide from guard cells of Vicia faba

Abstract

Ethylene regulates many aspects of plant growth and development; however, its effect on the behavior of the stomata is still largely obscure. Here, the association between ethylene inhibition of darkness-induced stomatal closure and hydrogen peroxide (H2O2) levels in Vicia faba guard cells was studied. Like ascorbic acid (ASA), the most important reducing substrate for H2O2 removal, catalase (CAT), one of H2O2-scavenging enzymes, and diphenylene iodonium (DPI), an inhibitor of the H2O2-generating enzyme NADPH-oxidase, both ethylene-releasing compound 2-chloroethylene phosphonic acid (ethephon, ETH) and 1-aminocyclopropane-1-carboxylic acid (ACC), the immediate precursor of ethylene, were found to inhibit stomatal closure by darkness and to reduce H2O2 levels in guard cells, indicating that ethylene-caused inhibition of darkness-induced stomatal closure involves reduction in the H2O2 level in guard cells. Additionally, similar to ASA and CAT, ACC/ETH not only suppressed H2O2-induced stomatal closure and H2O2 level in guard cells treated with exogenous H2O2 in the light, but also reopened the stomata, which had been closed by darkness, and reduced H2O2 level that had been generated by darkness, showing that ethylene causes H2O2 removal from guard cells. However, the above-mentioned effect of ACC/ETH was dissimilar from that of DPI, which not only was incapable to reduce H2O2 level induced by exogenous H2O2 but also could not abolish H2O2 that had been generated by darkness. Thus, we suggest that ethylene probably induces H2O2 removal and reduces H2O2 level in guard cells and finally inhibits stomatal closure induced by darkness. Furthermore, the mechanism of H2O2 removal caused by ethylene was also discussed.