Sensitivity of ATPases to silver ions suggests that silver acts outside the plasma membrane to block ethylene action

Abstract

The possibility of inhibition of ATPases, when silver salts are used to inhibit ethylene action in plant tissues, was considered. The vanadate-sensitive ATPase in a plasma membrane preparation was sensitive to 1 μM silver nitrate. Inhibition was reversed by a 20-fold excess of sodium thiosulphate, or dithiothreitol, but not by EDTA. This ATPase was also inhibited by silver nitrate in the presence of a four- or eight-fold excess of sodium thiosulphate. Mitochondrial ATPases appeared to be less sensitive than the plasma membrane enzymes to silver nitrate, but more sensitive to silver thiosulphate mixtures. Dilution of silver thiosulphate increased its inhibitory effect. Silver above 10 μM promoted ion and sugar efflux from corn coleoptile segments, but tissue respiration was only inhibited at 500 μM silver. It is suggested that ethylene action is inhibited by silver acting outside the plasma membrane.