The study was conducted to determine the effects of high temperature stress (37℃ for 08:00-17:00 and 30℃ for 17:00-08:00 in the growth chamber) in heading stage on the nitrogen metabolism of flag leaves of rice with 996, a heat-tolerant line, and 4628, a heat-sensitive line, as the materials. The results showed that, under high temperature stress, total N content and the nitrate reductase (NR) activity of flag leaves of both rice lines decreased while the contents of heat stable protein, proline and free amino acids and the ratio of p...