Change of ß - Amylase Activity In Germination and Early Rice Seedlings Under Hypoxic and Anoxic Water.

Direct seeded rice, especially water seeding, requires strong hypoxia tolerance for stable seedling establishment under submerged paddy. Water seeding has advantages in weed control and water management but has the problem of poorly germination and standing establishment, which causes uneven rice populations. The relationship between anoxia tolerance and carbohydrates catabolism was studied in japonica rice. Four rice cultivar was experimented as anoxic tolerant rice cultivar (cvs WD-3, PBR) and susceptible rice cultivar (cvs Juanbyeo:JA, Nampyeongbyeo:NP) treated anoxic submergence. The coleoptile elongation and fresh weight were markedly supressed by anoxia than normoxia, however those of WD-3 and PBR was faster than JA and NP. Soluble sugar concentration of WD-3 and PBR (tol var.) was more increased than JA and NP (sus var.) under anoxia. Especially maltose concentration of WD-3 and PBR (tol var.) increased up to 2-fold at 3 days after treatment and was retained until 9 days after treatment however that of JA and NP increased only 1.3-fold. β-Amylase that cleaves maltose from starch, those activities of WD-3 and PBR were increased  up to 10-fold at 9 days after treatment than before treatment. Otherwise α-amylase activity of WD-3 and PBR was rapidly decreased after treatment. These results suggest that β-amylase activity strongly associate with degradation of sugar from starch in endosperm during germination stage and its product as maltose support elongation of rice coleoptiles in anoxia.