The effect of inhibitors of plasma membrane H+-ATPase and oxidoreductases on NH+4uptake by Pisum arrense roots

Abstract

The effect of inhibitors of plasma membrane oxidoreductases (quinacrine and dicumarol) and H+-ATPase (dicyclohexylcar­bodiimide and orthovanadate) on ammonium uptake by Piswn arve11se seedlings and the activities of H+-ATPase and NADH­ferricyanide oxidoreductase was investigated. The uptake solution contained 50 µM NH4 +. In I h experiments, quinacrine and dicumarol depressed strongly and irreversibly the rate of NH4 + uptake and markedly inhibited the activity of NADH-ferri­cyanide oxidoreductase in the plasma membrane vesicles prepared from root cells. Simultaneously, sodium onhovanadate inhibited the activity of plasma membrane H+-ATPase increased the rate of NH/ uptake. Dicyclohexylcarbodiimide in­hibited H+ -ATPase activity and increased efflux of NH4 + from roots to ambient solution. The results indicate on the lack of direct connection between uptake rate of 50 µM NH4 + and H+-ATPase activity, and suggest thai mem brane redox systems play a predominant role in this process.