Breakdown of (1→3), (1→4)-β-D-glucans during development of rice coleoptiles in air and under water

Rice (Oryza sativa L. cv. Koshihikari) coleoptiles grown under water achieved greater length than those grown in air. The content of (1-->3), (1-->4)-beta-D-glucans in the cell wall of coleoptiles as determined with Bacillus glucanase increased rapidly in the early stage of coleoptile growth, then it decreased under both cultural conditions. The relative amount of beta-D-glucans in the cell wall (per cell wall dry mass) of watergrown coleoptiles was larger than that of air-grown ones during the experimental period. The relative beta-D-glucan contents in the cell wall showed a good correlation with the increment of coleoptile length. (1-->3),(1-->4)-beta-D-glucan-hydrolyzing activity was detected in a protein fraction extracted from the cell wall preparation with 1 mol/L NaCl. The activity also increased in the early stage of growth, but then decreased. The relative activity of beta-D-glucan-hydrolysis (per cell wall dry mass) of water-grown coleoptiles was also higher than that of air-grown ones. The peak of beta-D-glucan contents in the cell wall preceded that of beta-D-glucan-hydrolyzing activity by 1 or 2 days. There was good correlation among the increment of coleoptile length, the decrease in relative beta-D-glucan contents and the relative activity of beta-D-glucan-hydrolysis of the two types of coleoptiles, except for those valves in the early stage of coleoptile growth. These results suggest that the level of (1-->3),(1-->4)-beta-D-glucans in the cell wall determines the capacity of rice coleoptiles to elongate and that the degradation of the glucans due to the action of hydrolase is involved in intact coleoptile growth, especially in the later growth phase.