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

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. Martia). 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 (Delta pH, inside alkaline) and/or an electrical gradient (Delta psi, 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 Delta pH. The imposition of Delta psi stimulated the influx of valine by 20%, both in the absence and in the presence of Delta pH. Uptake of L-lysine was more strongly stimulated by Delta psi than by Delta pH, and its Delta pH-dependent uptake was enhanced about 6-fold by the simultaneous imposition of Delta psi. In the absence of gradients the uptake of L-glutamic acid was about 5-fold higher than that of L-valine, but it was not detectably affected by Delta pH or Delta psi. Although the transport of sucrose was very low, a stimulating effect of Delta pH 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.