The effects of additions of leucine or sucrose to the medium on which chlorotic barley mutant seedlings developed were examined and compared with those of corresponding green segregants. These additions often raised their fresh weight to that of the green segregants grown on basal medium; their protein content was also higher. Although the chlorophyll content of the mutants Xan-b15,18 and Xan-c23 was increased, it remained substantially below that of the green segregants; that of the mutants Xan-b22 and Xan-b54 did not increase.
In addition to these abnormal growth characteristics, the soluble amino acid pools of the mutants grown on all media and of green segregants grown on leucine medium showed characteristics of chlorotic growth with high levels of aspartic acid and asparagine; these levels were less marked in the mutants which responded to sucrose supplementation.
Levels of ribulose-1,5-diphosphate carboxylase remained substantially below those of the green segregants irrespective of the medium supplementation. It was concluded that while these Xantha mutants of barley responded to leucine and sucrose supplementation, this response was different from the pattern associated with strictly auxotrophic growth.