Abstract
Under natural condition and spraying exogenous NO, cotton cultivars with different senescence traits were used to in-vestigate 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.
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