Effect And Mechanism Research Of Exogenous Spermine Pretreatment Improve The Drought Resistance Of Trifolium Repens L.

In this study we used the cultivar’Ladino’and’Haifa’of white clover (Ttrifolium repens) as.the experimental materials. By using polyethylene glycol (PEG-6000) penetrant to simulate drought stress and applying appropriate concentration of spermine (Spm) into the root to conduct pretreatment, and making the direct drought stress as control. Explore the effect and its mechanism on exogenous spermine inducing drought resistance of white clover. The main results are as follows:1. Exogenous Spm pretreatment could improve white clover drought tolerance by delaying the senescence process of the leaves. During the period of drought stress, relative water content and chloroplast pigment content of two white clover cultivars in the Spm pretreatment were significantly higher than the without pretreatment. while electrolyte leakage and MDA content to the contrary.2. With prolonged drought stress, SOD and APX activity in the two varieties of white clover increased; the change of CAT activity was not obvious; and POD activity increased before it reduced. The activity of four kinds of antioxidant enzymes in the Spm pretreatment were significantly higher than the without pretreatment.3. Soluble sugar content of white clover leaves in different treatment was increasing along with the continuous of drought stress. In addition to the difference between the two treatments of ’Ladino’ was not significant in 6 day. In the rest of the time, soluble sugar content of two varieties in the Spm pretreatment was significantly higher than the without pretreatment. During the period of drought stress, compared with the material without pretreatment, soluble sugar content of’Ladino’in the Spm pretreatment significantly raised in 0 and 9 days; fructose content also increased significantly in 9 day; while sorbitol content significantly reduced in 6 day. For’Haifa’, reducing sugar and glucose contents of 6 and 9 days and fructose, sucrose and sorbitol contents of 9 day increased significantly. Sucrose synthase activity in different treatment didn’t change significantly over time. And sucrose phosphate synthase and sorbitol dehydrogenase activity were on the rise. Spm pretreatment significantly reduced sucrose synthase activity of the two varieties. However it enhanced the activity of sucrose phosphate synthase and sorbitol dehydrogenase.4. Western Blot showed that:22,23 and 33 KDa dehydrins were expressed in ’Ladino’during drought stress. The expression of 33 KDa was enhanced with prolonged stress; and Spm pretreatment on the expression of this protein had a significant role in promoting.22 and 30 KDa dehydrins were expressed in’Haifa’. Spm pretreatment significantly promoted the expression of 30 KDa during drought stress.5. Fluorescence quantitative PCR analysis showed that:Y2SK, Y2K and SK2 gene expression presented a trend of cut during stress, but the Spm pretreatment on the expression of Y2K and SK2 gene had a significant role in promoting. The three dehydrins gene expression of ’Haifa’ in 0 to 6 day basically remained unchanged and only slightly lower in 9 day. Spm pretreatment significantly lowered three kinds of gene expression in 6 day, while significantly raised in 9 day.