Effects of hydroxyproline on the growth of excised root segments of Pisum sativum under aseptic conditions.

The cis and trans isomers of 4-hydroxy-L-proline stimulated the extension growth of excised 2-4 mm pea root segments during culture. Increase in the uptake and subsequent incorporation of [(14)c]leucine into proteins was inhibited by both L-isomers, and so also were changes in chloride uptake capacity and in protein metabolism measured in terms of invertase and peroxidase activities. Changes in [(14)C]proline uptake and incorporation, and in respiration, were unaffected. Proline had no effect on changes in extension growth or protein metabolism but did prevent the effects of both hydroxyproline isomers. Azetidine-2-carboxylic acid inhibited extension growth and all the aspects of protein metabolism studied, the effects again being all prevented by proline. It is suggested that hydroxyproline enhances growth by interfering with protein synthesis in the cell walls.