The effect of inhibitors of plasma membrane H+ - ATPase and oxidoreductases on NH4+ uptake by Pisum arvense roots

Abstract

The effect of inhibitors of plasma membrane oxidoreductases (quinacrine and dicumarol) and H⁺-ATPase (dicyclohexylcarbodiimide and orthovanadate) on ammonium uptake by Pisum arvense seedlings and the activities of H⁺-ATPase and NADH-ferricyanide 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-ferri-cyanide oxidoreductase in the plasma membrane vesicles prepared from root cells. Simultaneously, sodium orthovanadate inhibited the activity of plasma membrane H⁺-ATPase increased the rate of NH₄⁺ 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 that membrane redox systems play a predominant role in this process.