Under natural condition and spraying exogenous NO, cotton cultivars with different senescence traits were used to investigate changes in NO contents, anti-oxidative enzymes and related gene expression during the aging process of euphylla and cotyledons. The results indicated that, under field condition, the NO contents showed the highest level in the young leaf and declined gradually with the progression of leaf senescence. The NO content in presenescent cultivar decreased faster and was significantly lower than that of non-presenescent cultivar at the late stage of leaf senescence. Under laboratory condition, the NO content of cotyledons was the highest in young leaf and the lowest at late growth stage. After application of SNP solution, the NO content was significantly higher in the treatment group than that of control group during the whole period of cotyledon development. The activities of catalase (CAT) and ascorbate peroxidase (APX) and their genes expressions were comparatively lower at the seventh day and reached the highest level at the fourteenth day both in the control and treatment groups, then declined with leaf development; at the same stage, the activities of CAT and APX in treatment group were significantly higher than control group, especially at the late stage of cotyledons. The activity of peroxidase (POD) and its gene expression declined significantly by spraying exogenous SNP. Although exogenous NO could inhibit the activity of superoxide dismutase (SOD) at early stage of cotyledon development, the treatment group demonstrated greater SOD activity than that of control group in the process of leaf senescence. The responses of different types of SOD to NO varied, and the Cu/Zn SOD was the most sensitive isoforms, among which cCu/Zn SOD's genes played a more potent role. The physiological and molecular mechanism underlying the delaying effect of NO on leaf senescence is thus revealed by fine coordination of the activity of oxidation and anti-oxidation systems (CAT, APX, POD, and SOD) in plant.%以早衰性状不同的棉花栽培品种为材料,在自然条件下和外施一氧化氮(nitric oxide,NO)的条件下,调查早熟棉花植株真叶和子叶衰老过程中NO含量变化和抗氧化酶活性及相关基因的表达.结果表明,大田条件下,NO含量在幼嫩叶片中最高,随着叶片的衰老含量逐渐降低；在叶片发育后期早衰材料的NO含量下降快,并且显著低于不早衰材料.室内条件下,植株发育过程中,NO含量在幼嫩子叶中最高在生长后期最低；外施硝普纳(SNP)溶液后的植株,其NO含量在子叶的整个生育期都比对照组高,且两者差异显著.对照组和处理组的过氧化氢酶(CAT)和抗坏血酸过氧化物酶(APX)的活性及相关基因的表达第7天较低,第14天最高,随后逐渐下降；在同一时期,处理组显著高于对照组,在生育后期表现的更为明显.外施SNP可显著降低参试品种过氧化物酶(POD)的活性和相关基因的表达.在子叶发育初期,外源NO对超氧化物歧化酶(SOD)的活性有抑制作用,随着叶片衰老,处理组的SOD活性又高于对照组.不同类型的SOD对NO的反应不同,Cu/Zn SOD最敏感,其中又以cCu/ZnSOD基因的作用更突出.NO通过调控植株体内CAT、APX、POD和SOD等氧化/抗氧化系统,延缓叶片的衰老进程.
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