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棉 花 学 报 Cotton Science 2008，20(2)：123-127
Studies on the Characteristics of Leaf Senescence at Different Stem Positions of Cotton Abstract：In recent years, with the generalization of transgenic cotton, premature senescence is aggravated, which has become a main factor for the production of cotton. Characteristics of leaf senescence for main stem of different positions were studied in the later full boll stage of cotton in the field. With Bt-transgenic cotton 33B as experimental plant, by researching into the change trends of contents of chlorophyll and MDA in functional leaves on main stem in the whole growing period, the turning point from blooming to senescence was found in 2005. Hereby in 2006 the physiological characteristics (Chlorophyll, Protein, MDA, SOD, POD) of all leaves at the different stem positions on the cotton plant were researched into in the turning period, and then the differences in senescence between leaves were analyzed. The results showed, (1) The turning point from blooming to senescence is at the later full bolling stage; (2) The Chl content, Pro content and SOD activity decreased with the change of leaf position from stem top to bottom, while the MDA content and POD activity increased; (3) All of the main stem leaves can be separated into three parts on the basis of physiological index changes: bloom leaves (the first leaf and the second leaf on the top), light senescence leaves (the third leaf to the eighth leaf ), heavy senescence leaves (the ninth leaf and the tenth leaf), (4) The middle leaves (light senescence leaves) should be mainly diagnosed and regulated at the full bolling stage, which can postpone the leaf senescence, even the whole plant senescence.
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