The effect of oxygen tension on the changes in the level of endogenous ABA corresponding the dormancy-breaking in rice seed.

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The seeds of 3 varieties having the different dormancy periods were tested for germination under 100%, 20%, and 0% oxygen contents with interval of 10 days during the dormancy. The dormancy-breaking was promoted under the high oxygen tension but it was inhibited under the low oxygen tension. Both the degree of the promotion and of the inhibition were positively proportional to the intensities of the dormancy. The soaked seeds treated with high tenperature of 40゜C, for 2 days under the conditions of 20% and 0% oxygen contents were sown in the flasks containing 100%, 20%, and 0% oxygen, respectively. The dormancy of the seeds treated under the condition of 20% oxygen was broken most effectively at the high oxygen tension, but under the condition of 0% oxygen, dormancy-breaking was inhibited exceedingly. On the other hand, the dormancy of seeds treated under the condition of 0% oxygen was broken effectively at the high oxygen tension, but under the condition of 0% oxygen, no dormancy-breaking occurred at all. When artificial treatments such as husking or injury, were given to soaked or dry seeds, the lowering in the level of ABA occurred with both treatments, but the lowering was much more remarkable in soaked seeds than in dry seeds. The level of the ABA in the soaked seeds treated with high temperature was lowered remarkably under the condition of 100% oxygen, but it stayed unchangeably under the condition of 0% oxygen, And the fact that endogenous ABA content stayed unchangeably under the condition of 0% oxygen, was proved more clearly by the quantitative analysis using gas chromatography.