Effects Of Selenium On Physiological Characteristics Of Watermelon Seedlings Under The High Temperature

In order to explore the effects of four different extrinsic Selenium treatments onphysiological characteristic of watermelon seedlings under the high temperature stress,Two cultivars （Zaojia8424and Jingxin2） of watermelon were planted in culture media withdifferent selenium （Se） concentrations(0,0.3,0.6,0.9,1.2mg·kg^-1). When the watermelonseedlings grew up, the plants were transferred into climatic room and exposed to hightemperature stress （38℃,6h）. Then the leaves were harvested tor measurement of the rootactivities, portable Photosynthesis system, Osmotic Adjustment and vary of antioxidantsystem and so on.The results indicate:1. Applying Selenium increased the root activity of watermelon under high temperaturestress. It indicated that Selenium could obviously alleviate and decrease inhibition of hightemperature stress on watermelon growth. The root activity of Zaojia8424and Jingxin2went to the maximum levels, when the Se concentration is0.9mg.kg^-1and0.6mg.kg^-1.2. The photosynthesis of watermelon seedlings was severely refrained and the Pndecreased. Compared to CK, both of the watermelon varieties were damaged. Thephotosynthesis rate of the two watermelon varieties went to the maximum levels when theSe treatment is0.9mg·kg^-1.3. Under the high temperature stress, photosynthesis of watermelon seedlings severelyinhibited and the content of total photosynthetic pigment decreased greatly. Se treatmentscould alleviate differently the effect of high temperature stress on the watermelon seedlingsby increasing the chlorophyll content. Compared to the no-selenium treatment, the contentof chlorophyll b in Zaojia8424had increased by57.6%, and the total content ofchlorophyll had increased by18%.4. Because of the high temperature, several fluorescence parameters including maximumfluorescence, photochemical maximum efficiency of PSⅡ photochemical quenchingcoefficient （qP） were decreased. At the same time, no photochemical quenching coefficient（qN） was increased. Otherwise, the different Se levels treatment could relieve effects ofhigh temperature stress on photosynthesis characteristic and chlorophyll fluorescenceparameters in watermelon seedlings.5. The increase of comparative electrical conductivity showed that the cell had beenbadly damaged. Contrast to no-selenium treatment, application of four Se decreased the rise of comparative electrical conductivity. The best selenium treatment is0.9mg·kg^-1,because in this Se level, the watermelon had stronger resistance to high stress.6. The content of MDA in both of the two watermelon showed that the high temperaturehad damaged the cell. Selenium treatments decreased the MDA content of Jingxin leavesby35.8%(1.2mg·kg^-1). So the treatments with selenium could relieve the damage to thewatermelon seedlings, and improved the tolerance to high temperatures stress.7. Application of different concentration Selenium treatment could effectively enhancedthe activities of GPX （GSH-Px）, POD （peroxides）, SOD （superoxide dismutase） and CAT（catalase） activity in the leaves of watermelon under high temperature stress. The resultsindicated the selenium treatments could increased the ability of sweeping away ReactiveOxygen Species by improving the special antioxidant enzymes and antioxidants. It showedus that Selenium could evidently decrease and alleviate harmness of high stress onwatermelon seedlings.