Anoxia tolerance in rice roots acclimated by several different periods of hypoxia

Rice (Oryza sativa L.) seedlings were subjected to hypoxic pretreatment (H-PT; incubated in 5 percnt; O2 atmosphere) for various lengths of time followed by an anoxic stress. Anoxia tolerance of rice roots was improved with increasing duration of H-PT, but longer H-PT than 12 h gave no additional improvement. Concentrations of ATP and ethanol, and activities of pyruvate decarboxylase (EC 4.1.1.1) and alcohol dehydrogenase (EC 1.1.1.1) in the roots were increased by H-PT, and the times and patterns of increasing in these concentrations and activities were similar to those of increasing in the anoxia tolerance. These results suggest that the H-PT may increase anoxia tolerance due to maintenance of ATP levels with rapid induction of ethanolic fermentation, and hypoxic acclimation may occur within 12 h.