Physiological And Biochemical Mechanism Of Exogenous Nitric Oxide Mitigates Seed Germinantion And Seedling Growth Of Cucumber Under Eupatorium Adenophorum Spreng. Extract Stress

Protected vegetable production plays an important role in annual balanced supply of vegetables in China. However, its unique characteristics, such as annual cultivation, soil continuous cropping, low temperature and high humidity in winter, which always results in frequent weeds, pests and diseases and pesticide control, finally leading to environmental and product contamination. Eupatorium adenophorum Spreng. contains natural grass, insecticidal and fungicidal active substance, therefore it has a positive significance in research and development of new botanical pesticides and herbicides. Nitric oxide (NO) has an important impact on plant growth development and adversity response, however, it is still unclear how NO effects on cucumber seed germination and seedlings growth under Eupatorium adenophorum Spreng. extract stress. In this study, we exlpored physiological and biochemical mechanism of exogenous nitric oxide effects seed germinantion and seedling growth of cucumber under Eupatorium adenophorum Spreng. extract stress. The results showed that:1. Seed germinantion and seedling growth of cucumber was inhibited differently under different concentrations of Eupatorium adenophorum Spreng. extract (ZL), such as the inhibition of seed germination, germination rate, vigor index and seedling fresh weight. Seedling growth depended on concentration of ZL, for instance, low concentrations promoted seed germination and seedling growth of cucumber, high concentrations was the opposite.2. ZL injured apical cell and structure, leading to shrink and loss of root tip cells, change of cell morphology and random arrangement. These finally inhibited root activity, which negatively affected seed germination and seedling growth of cucumber.3. ZL caused oxidative stress in cucumber seedling roots. It significantly increased the activity of super oxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), ascorbic acid (AsA) and malondialdehyde (MDA).4. NO effectively alleviatived the stress of ZL. It increased cucumber seed vigor index, main root length and fresd weight of seedling, alleviatived apical damage, enhanced antioxidant enzyme SOD, POD, CAT, APX activity, increased antioxidant AsA content and reduce MDA content.5. In all, NO promoted cucumber seed germanition and seedling growth, increased antioxidant enzyme activity and antioxidant content, decreased reactive oxygen species, alleviatived Mebranelipid peroxidation under ZL stress. NO successfully alleviatived the stress of ZL and improved its ability against ZL stress. NO would provide expected application value in cucumber cultivation under ZL stress.