Inhibition of Potassium Uptake and Regulation of Membrane-Associated Mg2+-ATPase Activity of Pea Roots by Aluminium

Abstract

The uptake of K⁺ by pea decreased markedly by the treatment with AICl₃. The decrease was alleviated by the co-treatment with Ca²⁺. The membrane associated with ATPase which was isolated from pea roots, was considered to be the plasma membrane enriched by the natures of associated ATPase. The activity was highly dependent on the presence of Mg²⁺, but not Ca²⁺ and the optimum activity was observed at neutral pH. The activity was inhibited by diethylstilbesterol, N,N’ -dicyclohexyl carbodiimide. and vanadate. Rather specific requirement of ATP was observed when ATP acted as a substrate. The membrane-associated ATPase was competitively inhibited by AICl₃ added to the assay medium with respect to ATP. The rate of inhibition by Al at various pHs was parallel with that of the activity in the absence of AI. Various chemicals were tested for the alleviation of the inhibition of membrane-associated ATPase by AI. Tripolyphosphate, citric acid, glucose 6-phosphate, pyrophosphate, glutamic acid, and malic acid restored the activity in this order. The activity of membrane associated ATPase treated with AI in vitro was not changed when the unbound Al was removed by dialysis. In contrast the activity of the membrane-associated ATPase prepared from the roots treated with AI in vivo increased. Furthermore, alkaline phosphatase (p-nitrophenyl phosphatase activity) in pea roots increased after the treatment with AI.