Extraction of hydroxyproline-containing proteins and pectic substances from cell walls of growing and non-growing mung bean hypocotyl segments.

Elongating upper and non-elongating lower segments of mung bean hypocotyls (Phaseolus aureus Roxb.) were compared in their ability to incorporate labelled polymers into their cell walls when fed with [(14)C]proline. The non-growing segments incorporated more amino acids into the walls and showed a higher degree of hydroxylation of the proline residues. The proportion of the [(14)C]polymer solubilized by chaotropic or complexing solutes was lower in the non-growing segments, possibly because of enhanced formation of covalent crosslinks between the glycoprotein and other cell wall constituents.The [(14)C]polymer was extracted from the wall by alkali at room temperature after removal of most of the hemicellulose by alkali at 0°, regardless of whether or not the pectic substances were first removed. The alkali does not extract any of the pectic polyuronide. Similar results were obtained with 6 M guanidine thiocyanate, which solubilizes appreciable amounts of the glycoprotein at room temperature and neutral pH without removing pectic substances.The results are considered to indicate a cell wall structure in mung bean hypocotyl tissue in which at least part of the pectin and some of the glycoprotein are not linked covalently together or to other cell wall constituents.