Alleviative Effect Of Selenium On Pakchoi Cabbage Under Salt-Stress And Its Mechanism

Soil salinization is one of main limiting factors for agricultural production. It is important to reduce the damage of salt-stress to plant with chemical method, enhance the adapt ability of plant to brinetreated environment, stimulate crops with high and stable yields and strengthen the harness and the synthetical develop and use of saline soil. Selenium is an important bioelement, which can decrease the harm of stress to plant. It is an important biological approach of enhancing the salt-enduring ability of plant to use selenium to allevate the salt-stress. Pakchoi cabbage is used as the tested material in this research to study the effects of selenium on the salt-stress to pakchoi cabbage, determine the allevated effect of selenium on salt-stess to pakchoi cabbage, analyze the mechinism of selenium on oxidation resistance, membrane stability, photosynthesis and energy metagolism variation of pakchoi cabbage under salt-stress, using the combined methods of culture experiment, field plot experiment and chemical analysis. The alleviation effect and its mechanism of selenium on pakchoi cabbage under salt stress are systematically clarified from cell physiology, biochemistry and ultrastructure, which can supply scientific basis of the enhancement of selenium on the adaptability of plant to salt stress.The main conclusions in the study are shown as follows:1. Selenium can enhance seed germination ability and the emergence percentag of pakchoi cabbage under salt-stress. Emergence percentage can be increased 17.91%-34.92% under low salt-stress while 65.20%-94.76% under high salt-stress when selenium is applied as basal application. Presoaking with selenium can enhance emergence percentage 20.65%-40.28% under low salt-stress while 123.02%-146.71% under high salt-stress.2. Selenium promotes absorption of N, P, K, Ca and Mg nutrients in pakchoi cabbage are suppressed under salt stress. Selenium increases the yield of pakchoi cabbage under salt-stress.Biomass of pakchoi cabbage tends to decrease with the increase of the degree of salt-stress. To applicate selenium can markedly increase the biomass of pakchoi cabbage, basal application can increase 7.66%, spraying selenium can enhance 5.96% and presoaking increases 4.85% under low salt-stress; Under high salt-stress, selenium of basal application and spraying both markedly increase the yields of pakchoi cabbage 10.27% and 8.07%, respectively. Biomass of pakchoi cabbage is markedly enhanced 7.17% with applicating selenium in plot experiment. It explains that selenium has the effect of increasing yield of pakchoi cabbage under salt-stress. 3. Selenium suppresses the increase of plasma membrane permeability of pakchoi cabbage under salt-stress. Without applicating selenium, plasma membrane penetrability of pakchoi cabbage is gradually increased with the degree of salt-stress increased, relative electrical conductivity of leaves in pakchoi cabbage was increased obviously 21.82%-41.43% under salt-stress. While that was markedly decreased with applicating selenium, selenium of basal application can decrease 21.61%-25.61% and selenium spraying decreases 12.05%-18.55%. It shows that selenium plays a good protective function on plasma membrane penetrability of pakchoi cabbage under salt-stress. Selenium can alleviate the damage to protoplasmic membrane and the effusion of ions, which effectively prenvent the injury of salt-stress to plasma membrane and maintain well penetrable function of membrane.4. Selenium enhances the osmoregulatory function and promotes water metabolism of pakchoi cabbage under salt-stress. Selenium improves osmoregulatory function, inhibits the accumulation of Cl- and Na+ ions, enhance the absorption of K+ and Ca2+ ions, increases the value of K+/Na+ and Ca2+/Na+, increases soluble sugar accumulation while decreases proline accumulation in pakchoi cabbage under salt-stress. It is shown that selenium can maintain balanced osmotic pressure of cells, alleviate physiology water stress of pakchoi cabbage, stimulate water metabolism in pakchoi cabbage, and also effectively prevent the poison of single salt.Without selenium, relative water content in leaves of pakchoi cabbage is decreased 7.34%-10.95% under salt-stress. Applicating selenium can markedly increase relative water content in leaves of pakchoi cabbage, basal application can increase relative water content 8.16%-12.37%, selenium spraying increases 6.30%-9.07%, and presoaking increases 5.50% under low salt-stress, but there are no obvious effects under high salt-stress.5. Selenium enhances oxidation resistance ability of pakchoi cabbage under salt-stress. Applicating selenium can increase the contents of GSH, Vc, Se of pakchoi cabbage obviously under salt-stress, which are three oxidation resistance substances and obviously enhance the activities of GSH-Px, GR, POD, SOD, which are four kinds of antioxidant enzyme. It is shown that selenium can increase the contents of oxidation resistance substances and the activities of antioxidase, this establishes the material basis for enhancing oxidation resistance function. Selenium can markedly reduce the accumulation of free radical in pakchoi cabbage under salt-stress. Selenium used as basal application decreases O2-? content 16.61%~ 25.66%,spraying selenium can reduce 11.19%~18.50%. At the same time, selenium can obviously reduce the accumulation of MDA, which is the end product of peroxidation, selenium used as basal application can decrease MDA content 16.96%~ 24.71%,spraying selenium can reduce 12.21%~20.21%. Selenium also can enhance the synthetic oxidation resistance ability of pakchoi cabbage under salt-stress, selenium used as basal application can increase that 16.96%~ 24.71%,while spraying selenium enhances 12.21%~20.21%.6. Selenium maintains the stability of plasma membrane in pakchoi cabbage under salt-stress. Applicating selenium can remarkably improve the structure and function of plasma membrane of pakchoi cabbage under salt-stress. Under salt-stress, applicating selenium can increase the chloroplast, and lamellas of basal granule make them regular stacked in leaves of pakchoi cabbage, and markedly improve the ultrastructure of chloroplast. Selenium can enhances IUFA of membrane lipid fatty acid under salt-stress, selenium used as basal application can increase IUFA 22.49%-43.40% and spraying selenium increases 9.63%-37.94%. Applicating selenium prevents the dematuration of membrane liquid effectively, maintains the balance between membrane liquid and fatty acid, and maintains good fluidity of membrane. Why the physical structure and chemical composition of plasma membrane are maintained at a well status? Because applicating selenium inhibits the accumulation of poisonous ions, enhances the antioxygenation of pakchoi cabbage, alleviates the peroxidization of membrane liquid, effectively protects membrane system and alleviates the damage to membrane system of pakchoi cabbage which was caused by salty adversity.7. Selenium improves the photosynthesis of pakchoi cabbage under salt-stress. Under salt-stress, chlorophyll b and total chlorophyll contents in leaves of pakchoi cabbage are increased remarkably, the elevation of chlorophyll a/b value is suppressed. Photosynthetic rate is markedly enhanced by applicating selenium. Selenium used as basal application enhances chlorophyll b and total chlorophyll contents 16.10%-58.52% and 4.83%-26.41%, respectively, and raises photosynthetic rate 25.40%-68.09%; Spraying selenium increases chlorophyll b and total chlorophyll content 11.69%-35.57% and 4.34%-21.25% respectively, and increases photosynthetic rate 17.46%-63.83%. So this guarantees the photosynthesis of pakchoi cabbage under salt-stress.8. Selenium promotes energy metabolism of pakchoi cabbage under salt-stress. ATP content in pakchoi cabbage is raised and energy metabolism is maintained well under salt-stress with applicating selenium. ATP content in pakchoi cabbage is increased 18.31%-48.16% when selenium is used as basal application, while that is increased 15.53%-35.20% when selenium was sprayed. Selenium can guarantee sufficient energy supply in pakchoi cabbage under salt-stress and maintain the need of motive force for vital activity of organism.