中文摘要：

以陆地棉早熟品种中棉所58和中熟品种邯郸109为材料，研究子叶衰老过程中氮素的再利用率（NRE）及氮代谢相关指标的变化。结果表明：子叶衰老过程中，单位面积总N含量（NPA）逐渐降低，中棉所58 NRE为69．26％，邯郸109为54．45％；叶绿素、可溶性蛋白质含量和硝酸还原酶（NR）活性先上升后降低，NR最先降低，中棉所58和邯郸109分别在9d、14d开始下降；中棉所58各指标比邯郸109早下降4～8d。谷氨酸脱氢酶（GDH）活性先下降后上升，表明GDH可能是氮素再利用的关键酶。

英文摘要：

Nitrogen （N） resorption efficiency （NRE） and changes in nitrogen metabolism indices in cotton cotyledons during leaf senescence were studied in two cotton cultivars： CCRI 58 （short season） and Handan 109 （medium season）. The main results were as follows： during the process of leaf growth and senescence, total nitrogen content in unit area （NPA） decreased gradually, NRE in CCRI 58 and Handan 109 is separately 69.26% and 54.45%, N metabolism indices such as chlorophyll and soluble protein content and nitrate reductase （NR） activity, are all increased first, then declined. The first to show a decline was NR activity, 9 d and 14 d in CCRI 58 and Handan 109. The declined times in CCRI 58 are 4-8 days prior to Han 109. Glutamate dehydrogenase （GDH） activity first declined, then increased, indicting that GDH may be the key enzyme involved in N resorption.