Effects of hydroxyproline on the growth and cell-wall protein metabolism of excised root segments of Pisum sativum.

Hydroxyproline, in the presence of sucrose, enhanced the extension growth of excised 2-4 mm pea root segments in aseptic media. About 90% of protein-bound hydroxyproline in the pea root segments was confined to the cell-wall fraction where it occurred as trans-4-hydroxy-L-proline. The amounts of wall-bound hydroxyproline increased dramatically towards the cessation of extension growth, but when the segments were cultured in trans-hydroxyproline, this increase was considerably less.Externally supplied cis and trans-hydroxyproline inhibited the formation of protein-bound [(14)C]hydroxyproline from [(14)C]proline without affecting the total amount of [(14)C]proline incorporated into proteins. Studies with αα'-dipyridyl showed that, although some of the externally supplied trans-[(14)C]hydroxyproline was incorporated directly into cell-wall proteins, most of it was first converted into proline which was then incorporated into proteins and subsequently reconverted, in part, into hydroxyproline. The effect of externally supplied hydroxyproline is discussed in relation to protein-bound proline hydroxylation.