Transport of amino acids in barley leaf tissue: II. The kinetics of uptake of an unnatural analogue

A detailed analysis is presented of the relationship between external concentration and the rate of uptake of an amino-acid analogue, α-aminoisobutyric acid, by barley leaf strips. The results are compatible with the operation of specific uptake mechanisms in the case of both freshly cut and 'aged' tissue. Determination of the fraction of uptake susceptible of inhibition by a competing amino acid suggested that a parallel diffusion pathway, if any, plays only a minor role. Indications for a dual amino-acid uptake mechanism were obtained. The principal effect of ageing appears to be exerted on uptake in the lower concentration range.