Evidence for distinct amino acid transport systems in cultured tobacco cells.

It is shown by competition experiments that tobacco cell lines have distinct transport systems for L-amino acids. For all tested amino acids the Lineweaver-Burk plots were diphasic indicating the presence of more than one carrier for any one amino acid. Moreover distinct transport systems for neutral, acidic and basic amino acids were kinetically characterized. Based on competition experiments neutral amino acids were absorbed by all transport systems. Aspartic acid entered the cells via its own carrier and via the basic carrier while arginine was taken up only by the basic carrier. Neutral amino acids such as L-leucine or L-phenylalanine were taken up faster than acidic or basic amino acids.