Pisum arvense plants were subjected to 5 days of nitrogen deprivation. Then, in the conditions that increased or decreased the root glutamine and asparagine pools, the uptake rates of 0.5 mM NH₄⁺ and 0.5 mM K⁺ were examined. The plants supplied with 1 mM glutamine or asparagine took up ammonium and potassium at rates lower than those for the control plants. The uptake rates of NH₄⁺ and K⁺ were not affected by 1 mM glutamate. When the plants were pre-treated with 100 µM methionine sulphoximine, an inhibitor of glutamine synthesis, the efflux of NH₄⁺ from roots to ambient solution was enhanced. On the other hand, exposure of plants to methionine sulphoximine led to an increase in potassium uptake rate. The addition of asparagine, glutamine or glutamate into the incubation medium caused a decline in the rate of NH₄⁺ uptake by plasma membrane vesicles isolated from roots of Pisum arvense, whereas on addition of methionine sulphoximine increased ammonium uptake. The results indicate that both NH₄⁺ and K⁺ uptake appear to be similarly affected by glutamine and asparagine status in root cells.
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