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...

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.