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Studies on the Changes of Kinetics of Chlorophyll Fluorescence from Intact Leaves During Senescence and the Mechanism of Inhibiting Aging by 6-BA

SONG Chunpeng, MEI Huisheng (Department of Biology, Peking University)CHU Zhongxi (Institude of Botany Academia Sinica, Beijing)  
The kinetics of 685 nm chlorophyll fluorescence emission from wheat (Triticum aestivum L.) leaves were measured during senescence. It were found that the second peak (S to M rise) in induction curves disappered firstly, variable fluorescence (Fv:Fp-Fo), Fp-Ft and the ratio of Fv/Fo were decreased rapidly, and the time taken to reach P posnt of the curve reduced. All these indicated that fewer plastoquinone (PQ) molecules in old leaves were responsible for this decline in photosynthetic capability. Treatments of detached wheat and maize (Zea mays L.) leaves with 6-BA, not only could strongly inhibit the decrease of the ratio of Fv/Fo and Fv, but also sustain the second peak. In addition, the second peak disappered when the leaves were treated with riboflavin after 3 days in darkness, but BA + riboflavin kept it. Meanwhile the decrease of superoxide dismutase activity and the increase of lipid peroxidation was also delayed. Thus, the possible mechanism of BA in preventing senescence as the scavenger of free radicals was discussed.
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