[Polysaccharide metabolism in the cell walls of growing Phaseolus aureus seedlings]

Quantitative determinations of the cell wall constituents (pectin, hemicellulose and α-cellulose) of growing Phaseolus aureus seedlings showed marked changes during early growth. The cell walls of the 2 to 4 days old seedlings were composed of approximately 30% α-cellulose, 50% hemicelluloses and 20% pectin. After four weeks the proportion of the different fractions had changed to approximately 60% α-cellulose, 30% hemicelluloses and 10% pectin. Quantitative sugar determinations on these polysaccharide fractions have shown that mainly the non-cellulosic fractions (hemicelluloses and pectin) underwent considerable changes in sugar composition during growth. The hemicelluloses contained non-cellulosic polysaccharides with a high glucose content, which were not starch. These were broken down in the cell walls during growth.In a series of experiments in which (14)C-glucose was injected into the hypocotyls of four days old Phaseolus aureus seedlings, the transport of radioactivity to the different plant organs and its incorporation into the cell wall polysaccharides of the bean stem were studied. The major part of the radioactivity was incorporated into the cell wall of the stem tissue. Minor amounts were transported to the roots and leaves. Of the cell wall polysaccharides of the stem, the hemicellulosic fraction showed a higher rate of incorporation of the (14)C-glucose than the α-cellulose in the early stages of growth. With increasing age of the plant, radioactivity was transferred from the hemicellulosic fraction to the α-cellulose, suggesting turnover of polysaccharides in the growing cell wall.