Amino-acid-transport mutant of Nicotiana tabacum L

The uptake rates of 16 amino acids were measured in leaf discs from Nicotiana tabacum L., cv. Xanthi (wild type) and from two valine-resistant mutants, Val(r)-1 and Val(r)-2. For all amino acids tested the uptake rates in Val(r)-1 were similar to those in the wild type. The Val(r)-2 mutant showed a reduced uptake of neutral and acidic amino acids, but uptake of the basic amino acids was only slightly lower than in the wild type. It is argued that two systems for amino-acid transport are present: one for neutral and acidic amino acids and the other for basic amino acids.