Effects Of Drought Stress On Antioxidant System And Photosynthetic Characteristics In Cucumber Seedlings

Drought stress is an agricultural problem in many areas in the world, which seriously affectsplant growth and development and may lead to a drastic reduction in economic yield. Cucumber(Cucumis sativus L.) is one of the important vegetable crops worldwide, and also is the main type ofvegetables cultivated in protected condition in China. In the growth period cucumber need a lot ofwater and is particularly sensitive to water deficit. When the relative soil water content is less than70%, cucumber will be slow growth, and its production will decline. In recent years, growing interesthas focused on the subject that the effect of drought stress on cucumber. The information of droughtstress in plant physiology in a short period of time is very limited.In the present study, cucumber cultivar ‘Jinyou No.1’was used in climate chambers andhydroponics. Cucumbers were selected for PEG6000-simulated drought stress experiments. wedetermined the effects of different drought stress on the plant growth, membrane lipid peroxidation,antioxidant enzymes activity, ascorbate-glutathione cycle, photosynthesis and chlorophyllfluorescence and so on. We also investigated on the drought resistance of cucumber seedlings in ashort period of time. The main results are as follows:1. Effects of drought stress on oxidation resistance in cucumber seedlings: Under drought stress,membrane lipid peroxidation was significantly increased in leaves and roots of cucumber seedlings,showing the relative conductivity and MDA content were significantly increased, ROS levels(including O￣2ˉproduction rate and H2O2content) were remarkably raised. Expose to drought stress,in antioxidant enzyme system, CAT, POD and APX activity of cucumber seedlings were higher thanthe control; compared with the control, SOD activity first increased and then decreased. In AsA-GSHcycle, MDHAR activity was lower than control in medium drought stress, but its activity wasincreased after24h in severe drought stress. DHAR and GR activity were inhibited under droughtstress, contents of AsA and GSH were lower than the contral.2. Effects of drought stress on photosynthetic characteristics in cucumber seedlings: Underdrought stress, carotenoid content chlorophyll a content, chlorophyll b content and chlorophyll a/bdeclined, net photosynthetic rate, stomatal conductance and transpiration rate significantly decline, PSII photochemical efficiency, photochemical quenching were also decreased. However,non-photochemical quenching was significantly increased under drought stress.