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

Rice (Oryza sativa L. cv. Koshihikari) coleoptiles grown under water achiev ed 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 i t decreased under both cultural conditions. The relative amount of beta-D-g lucans 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-hydr olyzing activity was detected in a protein fraction extracted from the cell wall preparation with 1 mol/L NaCl. The activity also increased in the ear ly stage of growth, but then decreased. The relative activity of beta-D-glu can-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 tho se valves in the early stage of coleoptile growth. These results suggest th at 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 th e glucans due to the action of hydrolase is involved in intact coleoptile g rowth, especially in the later growth phase.