Abstract: Two japonica rices, Wuyujing 3 and 97.7 were used to study changes in contents of soluble protein, free amino acids and endopeptidase activity during photosynthetic declination. Results showed that the content of soluble protein in flag leaves of Wuyujing 3 was higher than that of 97.7, but decreased faster. Free amino acids in flag leaves and the thirteenth leaves of Wuyujing 3 started to increase 10 days before the turning point of photosynthetic declination (TPPD), while it occurred just 1-2 days before TPPD of 97.7. During reversible phase of photosynthetic declination, endopeptidase activity kept in low level and increased slightly only in the later part of this phase, then they increased sharply at irreversible phase and reached a very high level. For Wuyujing 3, the change in endopeptidase activity in the thirteenth leaf was parallel to that in flag leaf, but for 97.7, the sharp increase of endopeptidase activity came later than that of flag leaf. It implied that, compared with Wuyujing 3, the procedures of protein breakdown and transfer to transportable nitrogen in 97.7 leaves were slower during photosynthetic declination, and this may be one important reason for relatively low seed setting rate and the incomplete use of its high yielding potentiality.

Key words: rice, photosynthetic declination, soluble protein, free amino acid, endopeptidase activity

摘要： 以两个粳稻品种武育粳3号和97-7作材料研究了光合功能衰退进程中叶片中可溶性蛋白质、游离氨基酸和内肽酶活力的变化。武育粳3号剑叶的可溶性蛋白质含量比97-7高,但其含量下降比97-7快。武育粳3号的剑叶和第13叶在光合功能衰老转折点到来之前10 d左右游离氨基酸含量开始上升，而97-7则在转折点之前1～2 d才开始上升。在光合功能衰退的可逆阶段，内肽酶的活力维持在较低水平，只是在可逆阶段的后期内肽酶的活力有轻微的升高。但进入不可逆阶段后，内肽酶的活力则急剧升高，并达到很高的水平。武育粳3号的第13 叶和剑叶中的内肽酶活力变化基本上是平行的，而97-7的第13叶内肽酶的活力急剧上升期却迟于剑叶。这表明，与武育粳3号相比，在97-7叶片衰老过程中，叶片中的蛋白质降解、转化为可输出氮的进程缓慢。这可能是97-7结实率不高、产量潜力不能充分发挥的一个重要原因。

关键词: 水稻, 光合功能衰退, 可溶性蛋白质, 游离氨基酸, 内肽酶活力