Effects Of Drought Stress On Photosynthesis And Fluorescence Chlorophyll Parameters Of Apple Leaves And Leaf Senescence Characteristics

Drought is a common problem that existing in agricultural production. Fruits are subjected to drought stress in the Northwest of china. We take three apple cultivars including M. pumila cv. Keziaerma, M. niedzwetzkyana cv. Kalaaerma and M. pumila cv. Redchief Delicious, to studied the effects of drought stress on leave photosynthesis and chlorophyll fluorescence parameters of apple under different water stress, and also studied the changes of leave photosynthesis, activities of SOD,POD,CAT in leaf senescence. evaluate the relationships of leaf senescence and reactive oxygen metabolites from different apple varieties. discuss The changes of photosynthesis and chlorophyll fluorescence parameters of different apple leaves under drought stress were explored as well as their adaptive response to drought stress. discuss the physiological responses of apple to drought stress. It provides theoretical basis for drought resistance mechanism research of fruit.The results were as follows:1. The growth of the three cultivars leaves was obviously inhibited under the drought stress. The results showed that non-photochemical quenching coefficient(qN), the actual photosynthesis efficiency of PSⅡin the light (ΦPSⅡ), the maximum photochemical efficiency of PSⅡ(Fv/Fm) and photochemical quenching coefficient(qP) decreased gradually with the increase of drought stress level. By contrast, the primary fluorescence(Fo) increased obviously. But each parameter varied differently between different cultivars under drought stress.2. The growth of the three cultivars was inhibited under the drought stress, The decline of photosynthesis was considered as a result of stomatal restriction under moderate stress, but non-stomatal restriction was the dominant under severe stress. There was a close relationship between the effects of drought stress on chlorophyll fluorescence parameters in different cultivars and their drought resistance.3. The observations indicated that net photosynthetic rate(Pn),transpiration rates(Tr), stomatal conductance(Gs) declined on the period of leaf senescence. The photosynthetic capabilities of the leaves decreased rapidly with plant gradual consenescence. The net photosynthetic rates of M. pumila cv. Redchief Delicious were greater than other two varieties, It able to keep a relatively high photosynthetic capability at the late stage of leaves growth.4.The activities of CAT,SOD and chlorophyll content in apple leaves declined under drought stress, but the activity of MDA increased, and the activity of POD increased earlier and followed by a decline. CAT,SOD activity can prevented the damages on leaf membrane structures and physiological capability, and prolonged the functional duration of leaves.