Glycosylated seryl residues in wall protein of elongating pea stems

The protein content of salt-washed cell walls isolated from etiolated stems of Pisum sativum L. approximately doubled during elongation. In the same period the concentration in the wall of hydroxyproline, hydrazine-labile (= presumably glycosylated) serine, valine, tyrosine, lysine, and histidine increased markedly in comparison with other amino acids. After elongation was completed both the amino acid composition and the protein content of the cell wall changed only slightly. The ratio for the wall of hydrazine-labile seryl residues to hydroxyprolyl residues remained constant during and after elongation and was found to be 0.20. A linear relationship was established between the rate of elongation and the concentration in the wall of the hydroxyproline-rich glycoprotein both in vivo and in cut sections incubated in buffer.