ANALYSIS OF THE GROWTH-RESPONSE OF AIR-GROWN RICE COLEOPTILES TO SUBMERGENCE

The effect of submergence of air-grown rice seedlings (Oryza sativa L. var. Sasanishiki) on coleoptile growth and ultrastructure, extensibil ity and chemical composition of the cell walls was investigated. The l ag-time between start of submergence and the onset of the enhancement of growth was less than 4 h. The growth response was associated with a drastic thinning of the cell walls and an increase in wall extensibil ity. At the outer epidermal wall of both air-grown and submerged coleo ptiles electron-dense (osmiophilic) particles were detected. During su bmergence, the net accumulation of cellulose and hemicellulose was red uced, but the increase in pectic substances was unaffected. Submergenc e caused an 80 % inhibition of the net accumulation of wall-bound phen olics (ferulic- and diferulic acid) compared with air-grown controls. The osmotic concentration of the tissue saps was not affected by subme rgence. Our results support the hypothesis that rapid coleoptile elong ation under water is caused by an inhibition of the formation of pheno lic cross-links between matrix polysaccharides via diferulate, which r esults in a mechanical stiffening of the cell walls in the air-grown c oleoptile.