RELATIONSHIP BETWEEN COLEOPTILE ELONGATION AND ALCOHOLIC FERMENTATIONIN RICE EXPOSED TO ANOXIA .2. CULTIVAR DIFFERENCES

The relationship between coleoptile elongation and survival vs. alcoho lic fermentation of rice under anoxia is examined using eight cultivar s differing in submergence tolerance. Anoxia was imposed on either 1 o r 4 d aerated seeds either by N-2 flushing submerged tissues or by inc ubating tissues in stagnant deoxygenated agar at 0.1 % w/v; the latter simulated the stagnant conditions of waterlogged soil, Two cultivars that were most tolerant to submergence also had the greatest tolerance to anoxia, while a submergence intolerant cultivar was also intoleran t to anoxia. Coleoptile growth under anoxia was related to rates of et hanol synthesis (R(E)), however differences between growth during anox ia and survival after anoxia indicated that post-anoxic injury may als o be important in rice seeds exposed to anoxia. The correlation betwee n coleoptile growth and R(E) measured on a tissue basis using intact s eeds was r(2) = 0.67 among six varieties over 0-3 d anoxia. This corre lation improved to about r(2) = 0.85 using R(E) of (embryos plus coleo ptiles) over 0-3 d, or coleoptiles at 3 d after anoxia. Coleoptile gro wth of individual seeds was usually poorly correlated to R(E) in these cultivars at 2-3 d after anoxia. When coleoptiles of similar lengths were obtained from different cultivars using 4 d aerated seeds, there were differences in R(E) and coleoptile growth which were related to c oleoptile growth during 3 or 5 d anoxia, either on a tissue (r(2) = 0. 85) or a fresh weight basis (r(2) = 0.70-0.97 respectively). Results a re discussed in relation to factors which may limit ethanol synthesis in rice exposed to anoxia and the importance of growth to the survival of seeds and mature plants during submergence in the natural environm ent.