Regulation Effects of Exogenous 6-BA on Photosynthesis and Leaf Senescence in Cotton

Compared to control(CK),the plant height,leaf number,leaf area,and dry weight per plant were all increased in the treatment with exogenous 6-BA in the tested cotton cultivars.The chlorophyll content,soluble protein content and photosynthetic rate in the lower-position leaves of plant were higher in the 6-BA treatment than those in CK,but the 6-BA effects varied on above parameters among the cultivars.The highest effects was found in 33B,the senescent-sensitive cultivar,then in 20B,the mid-senescent type cultivar,and the lowest in Fengkang 6,the senescent-resisting cultivar.6-BA application increased the superoxide dismutase(SOD) activities and peroxidase(POD) activities,and decreased the MDA contents in the tested cultivars,showing that the exogenous 6-BA has a role for plant to enhance the capabilities of active oxygen scavenging and lessen the over-oxidation degree of cytoplasm membrane.Therefore,the improvement of balance level between the process of producing active oxygen species and corresponding scavenging capability during the mid-and late-leaf growth stages,was possibly the important physiological mechanism that the leaf photosynthetic rates were increased and leaf senescences were delayed in the treatment with exogenous 6-BA Thus,in cotton production,exogenous 6-BA has possibly an important role for delaying the senescence of the cultivars with the senescent-sensitive type.