Abstract: Taking cold-tolerant rice cultivar 996 and cold-sensitive rice cultivar 4628 as test materials, a growth chamber experiment was conducted to investigate their pollen characters and flag leaf physiological and biochemical characteristics under the effects of low temperature stress. The plants were respectively treated with low temperature ［19 ℃ (06:00-8:00；19:00-23:00)/21 ℃ (08:00-10:00；16:00-19:00)/23 ℃ (10:00-16:00)/17 ℃ (23:00-06:00)］and optimal temperature ［24 ℃ (06:00-8:00; 19:00-23:00)/26 ℃ (08:00-10:00；16:00-19:00）/30 ℃ (10:00-16:00)/22 ℃ (23:00-06:00)］ for seven days after heading. Low temperature stress decreased the anther dehiscence coefficient and pollen germination rate, as well as the sterile pollen rate of spikelets on middle and lower parts of panicles, with the anther dehiscence coefficient and pollen germination rate of cultivar 996 being significantly higher than those of cultivar 4628, indicating that coldtolerant cultivar 996 had the capability to keep better pollination and pollen germination. Under low temperature stress, the flag leaf soluble protein and free proline contents and their increments of cultivar 996 were significantly higher than those of cultivar 4628, while the MDA content and relative conductivity and their increment were in adverse, indicating that cold-tolerant cultivar 996 had more quick and strong protective responses, and was able to keep stable membrane structure and function.

Key words: rice (Oryza sativa), low temperature stress, pollen characters, physiological and biochemical characteristics, flag leaf, food security, resource use, rice planting, dense planting with less nitrogen application, greenhouse gas.