TURNOVER OF GALACTANS AND OTHER CELL-WALL POLYSACCHARIDES DURING DEVELOPMENT OF FLAX PLANTS

We investigated the synthesis and turnover of cell wall polysaccharide s of the flax (Linum usitatissimum L.) plant during development of the phloem fibers. One-month-old flax plants were exposed to a 40-min pul se with (CO2)-C-14 followed by 8-h, 24-h, and 1-month periods of chase with ambient CO2, and radioactivity in cell wall sugars was determine d in various plant parts. The relative radioactivity of glucose in non cellulosic polysaccharides was the highest compared with all other cel l wall sugars immediately after the pulse and decreased substantially during the subsequent chase. The relative radioactivities of the other cell wall sugars changed with differing rates, indicating turnover of specific polysaccharides. Notably, after 1 month of chase there was a marked decrease in the proportional mass and total radioactivity in c ell wall galactose, indicating a long-term turnover of the galactans e nriched in the fiber-containing tissues. The ratio of radiolabeled xyl ose to arabinose also increased during the chase, indicating a turnove r of arabinose-containing polymers and interconversion to xylose. The pattern of label redistribution differed between organs, indicating th at the cell wall turnover processes are tissue- and cell-specific.