Transport of amino acids (L-valine, L-lysine, L-glutamic acid) and sucrose into plasma membrane vesicles isolated from cotyledons of developing pea seeds

Abstract

Transport of the amino acids L-valine, L-lysine, and L-glutamic acid and of sucrose was studied in plasma membrane vesicles isolated from developing cotyledons of pea (Pisum sativum L. cv. Marzia). The vesicles were obtained by aqueous polymer two-phase partitioning of a microsomal fraction and the uptake was determined after the imposition of a H+-gradient (ΔpH, inside alkaline) and/or an electrical gradient (Δψ, inside negative) across the vesicle membrane. In the absence of gradients, a distinct, time-dependent uptake of L-valine was measured, which could be enhanced about 2-fold by the imposition of ΔpH. The imposition of Δψ stimulated the influx of valine by 20%, both in the absence and in the presence of ΔpH. Uptake of L-lysine was more strongly stimulated by Δψ than by ΔpH, and its ΔpH-dependent uptake was enhanced about 6-fold by the simultaneous imposition of Δψ. In the absence of gradients the uptake of L-glutamic acid was about 2-fold higher than that of L-valine, but it was not detectably affected by ΔpH or Δψ. Although the transport of sucrose was very low, a stimulating effect of ΔpH could be clearly demonstrated. The results lend further support to the contention that during seed development cotyledonary cells employ H+-symporters for the active uptake of sucrose and amino acids.