Effects Of Plant Growth Regulators On Physiological And Biochemical Changes During Leaf Senescence Of Tree Peony

In this study Paeonia suffruticosa ‘Luoyanghong’ and ‘Huhong’ were used as the test material. Effects of different plant growth regulators on the senescence of peony leaves were studied by using the method of foliar spraying. We selected two ways of spraying: First, we used the single spraying method on 2 varieties of peony leaves by different concentrations of 6-BA and GA3. Second, with three times spraying on ‘Luoyanghong’ leaves with different concentrations of NAA, 6-BA, GA3 and KT, the period of spraying was carried out once a per five days. By observing the changes of peony leaves photosynthetic characteristics, active oxygen metabolism, and other relevant physiological and biochemical changes in the process of aging, to investigate the effects of different concentrations and types plant growth regulators on the senescence of peony leaves. The main results are as follows:(1) A single spraying of 6-BA and GA3 could improve ‘Luoyanghong’ and ‘Huhong’ leaves’ soluble sugar, soluble protein and chlorophyll contents, increased SOD and POD activity, while MDA accumulation in leaves was inhibited, and the relative cell membrane permeability was reduced. The appropriate concentration of the two kinds of growth regulator was 300 mg·L-1. The best spraying time was middle to late July. The effect of 6-BA is better than GA3.(2) Sprayed three times to ‘Luoyanghong’ leaves, NAA, 6-BA, GA3 and KT could increase the net photosynthetic rate(Pn), stomatal conductance(Cond), intercellular CO2 concentration(Ci), transpiration rate(Tr) at different degree, delayed the decomposition of chlorophyll in leaves, promoted the synthesis of soluble sugar, soluble protein, maintained SOD, POD activity and inhibited MDA accumulation, the raise of cell membrane permeability and oxygen free radicals producing rate in peony leaves. The most suitable concentrations were NAA 200 mg·L-1, 6-BA 200, 300 mg·L-1, GA3 300 mg·L-1 and KT 50 mg·L-1, these treatments can significantly delay the leaf senescence of ‘Luoyanghong’.(3) The physiological and biochemical dynamics change during leaf senescence in ‘Luoyanghong’ were: the net photosynthetic rate and chlorophyll contents decreased, SOD, POD activity increased slightly and then decreased gradually, MDA contents, cell membrane permeability and oxygen free radical producing rate is gradually rising trend, soluble sugar, soluble protein and free amino acid contents were increased firstly and then decreased.(4) During ‘Luoyanghong’ leaves senescence process, the indexes of active oxygen metabolism correlation were: SOD, POD activity showed a significant negative correlation with MDA content, oxygen free radical generation rate. MDA content showed a significantly positive correlation and cell membrane permeability, oxygen free radical generation rate.