Stress-relaxation analysis of submerged and air-grown rice coleoptiles: Correlations with cell wall biosynthesis and growth

The growth rate of rice coleoptiles grown under water was decreased by expo sure to air. In parameters of the stress-relaxation of cell walls, water-gr own coleoptiles had a larger pre-extension time (Tp) and a smaller stress-r elaxation rate (b) as compared with those exposed to air. Tp and b were sig nificantly correlated with the growth rate of coleoptiles grown under diffe rent conditions The amounts of cell wall components, such as hemicellulose, cellulose, diferulic acid (DFA) and ferulic acid (FA), in air-exposed cole optiles increased rapidly as compared with those in submerged ones. When 7- h air-exposed seedlings were submerged again, the growth rate of re-submerg ed coleoptiles was still lower as compared with that of continuously submer ged ones during the subsequent incubation under water. The decrease in Tp, the increase in b, and the increases in the amounts of those wall component s by air-exposure were not completely recovered even when coleoptiles were re-submerged after 7 h. There were close correlations between the amounts o f cell wall components per unit length of coleoptile and Tp and b. These re sults indicate that Tp and b can represent the ability of rice coleoptiles to grow under different conditions and that those wall components are invol ved in determining Tp and b of cell walls.