A barley (Hordeum vulgare L.) mutant, R5201, selected for resistance to 4́ mM trans-4-hydroxyproline had a 3-6 fold increase in the soluble proline content of the leaf compared with the parent cultivar, Maris Mink. The mutant converted more [U-4C]glutamic acid to free proline in the leaves than Maris Mink but incorporation into protein proline was similar. Incorporation of radioactivity into proline was inhibited by exogenous proline more in Maris Mink than R5201, suggesting that feedback inhibition of proline biosynthesis is relaxed, but not absent in the mutant. When [1-14C]ornithine was the precursor, both R5201 and Maris Mink incorporated similar small amounts of label into soluble and protein proline. More protein proline was formed by both genotypes from labelled glutamic acid than from labelled ornithine. There may exist two routes of proline formation, where the glutamate pathway is synthetic and the ornithine pathway is catabolic. © 1984.
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