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SummaryTo clarify the mechanism of high temperature-induced floret sterility in rice (Oryza sativa L.), we studied the effects of high temperature at flowering on the ability of thecae to dehisce and on pollen-grain swelling which causes thecae dehiscence. Two japonica rice cultivars, grown in four L pots under submerged soil conditions were subjected to high (39°C) and moderate (34°C) temperatures from 10 : 00 to 16 : 00 for three consecutive days at the flowering stage. The percentage of the thecae dehisced in response to artificial opening of the florets by removing lemma and the mean diameter of the pollen grains measured during four minutes after the artificial opening were examined to determine the ability of the thecae to dehisce and that of the pollen grains to swell, respectively. The high temperature given on the day of flowering decreased both the percentage of the dehisced thecae and the diameter of the pollen grains but did not affect the relationship between them. The thecae of the plants which had been subjected to the high temperature for one or two days before flowering, however, showed a lower dehiscence percentage than those of the plant treated on the day of flowering against the same pollen-grain diameter. We concluded that high temperature given on the day of flowering decreased the ability of the pollen grains to swell resulting in poor thecae dehiscence, and that, besides this decrease, high temperature given just before the days of flowering lowered the function of thecae themselves to dehisce, causing poorer thecae dehiscence.
Matsui et al. (Sat,) studied this question.