Uptake of Amino Acids by Barley Leaf Slices: Kinetics, Specificity, and Energetics

Uptake of ¹⁴C-labelled _L-lysine. _L-arginine, _L-glutamic acid, _L-aspartic acid, and glycine was studied in 0.75 mm wide barley (Hordeum vulgare L. cv. Lise) leaf slices. After an initial period (10 min) of rapid accumulation amino acid uptake proceeded at a steady, lower rate for several hours. Uptake was stimulated by 10^?4M Ca^?2+ ions. Uptake was strongly _pH dependent with the following optima: aspartic acid _pH 3.5. glutamic acid _pH 4.1. glycine _pH 5.8, lysine _pH 6–7, and arginine _pH 5–8 (a broad plateau). The optimal temperature was about 30°C. and the temperature coefficient in the range 0–20gGC was 2.3–2.5. Concentration-dependence data gave uptake isotherms which appeared to be multiphasic for all the amino acids used. The amino acids inhibited each other in a competitive fashion, indicating that they were all transported by a single carrier system. Uptake of lysinc was strongly inhibited by 10^?4M 2.4-dinitrophenol. Lysine uptake was not stimulated by light under aerobic conditions. However, it was much reduced in the dark under anaerobic conditions. This reduction was almost compensated for by light. The light-stimulation of uptake under anaerobic conditions was abolished by 10^?5M 3-(3,4-dichlorophenyl) 1.1-dimethylurea.