THE EFFECT OF INHIBITORS OF PLASMA-MEMBRANE H-ATPASE AND OXIDOREDUCTASES ON NH4+ UPTAKE BY PISUM ARVENSE ROOTS()

The effect of inhibitors of plasma membrane oxidoreductases (quinacrin e and dicumarol) and H+-ATPase (dicyclohexylcarbodiimide and orthovana date) on ammonium uptake by Pisum arvense seedlings and the activities of H+-ATPase and NADH-ferricyanide oxidoreductase was investigated. T he uptake solution contained 50 mu M NH4+. In 1 h experiments, quinacr ine and dicumarol depressed strongly and irreversibly the rate of NH4 uptake and markedly inhibited the activity of NADH-ferricyanide oxido reductase in the plasma membrane vesicles prepared from root cells. Si multaneously, sodium orthovanadate inhibited the activity of plasma me mbrane H+-ATPase increased the rate of NH4+ uptake. Dicyclohexylcarbod iimide 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 mu M NH4+ and H+-ATPase activity, and suggest that membrane redox systems play a predominant role in th is process.