LEVELS OF ABSCISIC-ACID IN ANOXIA-TREATED OR ETHYLENE-TREATED RICE (ORYZA-SATIVA L) SEEDLINGS

Changes of internal ABA levels in relation to anoxia- or ethylene-induced growth alterations were determined in etiolated rice (Oryza sativa L. cv. Taichung Native 1)seedlings. An inverse relationship between ABA levels and growth was observed at the early growth stages of rice seedlings. When rice seedlings were exposed to anoxia or 10 mu l/l ethylene, coleoptile elongation was enhanced while growth of roots and leaves was inhibited. In contrast, anoxia or ethylene induced a decrease of ABA levels in coleoptiles but an increase in roots and leaves, especially after 48 h of treatment. In addition, the anoxia- or ethylene-enhanced coleoptile elongation was inhibited by ABA ranging from 10(-7) M to 10(-4) M. Thus, results presented here indicate that ABA is an inhibitory modulator in the anoxia- or ethylene-induced morphological changes of etiolated rice seedlings.