Effects Of Cinnamic Acid Stress On Physiological And Biochemical Of Cucumber Seedlings, And Exogenous NO On The Mitigation Of Cinnamic Acid

Greenhouse vegetables have become indispensable to China's agriculture component. Cucumber (Cucumis sativus L.) is a favourable vegetable for Chinese and has become the main variety of greenhouse vegetables. However, the contradiction between limited land for vegetable production and year-round demand for the supply leads to monocropping as the popular cropping system, resulting in a reduction both in productivity and the food quality. Autotoxicity is one of the most important factors responsible for the continuous cropping obstacles. It was well documented that cucumber plant has autotoxic potential, and more than 10 kinds of growth inhibitory substances including benzoic and cinnamic acids from its root exudates have been isolated and identified. These substances could significantly inhibit plant growth by influencing physiological metabolism process such as ion absorption, water utilization, photosynthesis and respiration etc. Nitric oxide (nitric oxide, NO) is a widespread biological activity of molecules in vivo. NO as a plant intracellular and intercellular messenger molecule that can regulate plant growth, development, and in Plants of various biological and abiotic stress response to the transmission of information play an important role. Since the majority of toxicity studies to alleviate stay in farming methods and reasonable fertilization, lack of exogenous substances and self-understanding of the interaction between toxic substances. In a clear toxic substances, an autotoxin in root exudates, from the growth of cucumber seedlings, enzyme activity and membrane permeability on the basis of the impact study of exogenous NO on the role of cinnamic acid and mitigation. Furthermore, study to alleviate the impact of toxic substances on the feasibility of cucumber, to reduce or eliminate barriers to continuous cropping cucumber and provide a theoretical basis and solution. The main results are as follows:1) In order to evaluate tolerant capacity of different cucumber genotype to cinnamic acid stress, the effects of exogenous cinnamic acid stress on cucumber seedlings were studied by using plug seedlings of 18 cucumber varieties as testing material. The results indicated that the cinnamic acid has obvious inhibitory action to growth of cucumber seedlings. The concentration of 100μmol·L^-1 is adopted to screen cucumber genotypes with tolerant to cinnamic acid stress. For response index (RI), overground fresh and dry weight, root fresh and dry weight, and plant height were more sensitive to cinnamic acid stress, chlorophyll and root volume taken second place, but the stem thickness was little sensitive. By using the cluster analysis based on the absolute value of RI,18 cucumber genotypes were divided into tolerant varieties (8 genotypes), relatively tolerant varieties (8 genotypes) and sensitive varieties (2 genotypes).2) In order to explore the self-cinnamic acid on the toxicity mechanism of cucumber.The effects of exogenous cinnamic acid stress on seedling growth and antioxidant enzyme systems, and active oxygen metabolism of different varieties of cucumber were studied. The results showed that exogenous cinnamic acid has a strong inhibitory effect on seedlings growth of cucumber. This inhibitory effect was stronger when the concentration was higher. Antioxidant enzymes SOD, POD, CAT and APX showed upward trend when the concentration was low (50～100μmol·L^-1), but the effect was downward when the concentration was high (200～400μmol·L^-1).O2^- production rate, H₂O₂, MDA and Pro contents increased with the cinnamic acid concentration level added to the soil, but chlorophyll content was significantly reduced. Above mentioned parameters were different with tested varieties of cucumber.3) Since the toxic effect to ease and breaking the barriers to continuous cropping, and confirmed that exogenous NO on the quality of cucumber from the toxic effects with ease.The effects of exogenous nitric oxide on seedling growth and antioxidant enzyme systems, and active oxygen metabolism under 200μmol·L^-1 cinnamic acid stress. The results showed that 100μmol·L^-1 exogenous sodium nitroprusside can significantly ease the stress on cucumber plants cinnamic acid damage. 100μmol·L^-1 exogenous sodium nitroprusside can increase the amount of seedling growth, enhance seedling leaf antioxidant enzymes SOD, POD, CAT and APX activity, increased leaf chlorophyll and Pro content, reduced leaf MDA, H₂O₂ content and O2^- production rate. we observed a diminishing stimulative effect on cucumber seedling growth and the oxidative damage to leaves sustained and the protective enzyme activities decreased when treated with 50 or 200 or 400μmol·L^-1 of SNP. 100μmol·L^-1 exogenous sodium nitroprusside can increase cucumber seedlings of patience under cinnamic acid stress.