Physiological Characteristics Of Trifolium Repens In Response To Freezing-thawing And Acid Deposition Stress

In this paper, Trifolium repens was used as the research object. To study from three kinds of condition, respectively were: simulation of freezing – thawing stress, simulation of freezing-thawing and acid deposition stress, real freezing-thawing in the nature. The content of soluble protein, soluble sugar, proline and malondialdehyde(MDA), and the activity of superoxide dismutase(SOD), catalase(CAT) and peroxidase(POD) were determined and analyzed. The test purpose was to reveal that the physiological characteristics of T. repens in response to acid deposition and freezing-thawing stress. This article hopes to explore the growth of the low latitudes of thermophilic plants, how to adapt to the cold temperature of the high latitudes.In the freezing-thawing tests, the content of leaves and stolons of soluble protein and proline were increasing during the thawing- freezing stress stage reached maximum at-5 ℃, then the temperature continued to reduce, the content reduced. When the temperature fell, the content of MDA increased significantly, and the content of stolons were more than in the leaves, which could show that the degree of stolons damage were bigger. The changes of soluble sugar were not significant during the thawing- freezing stress stage, but the content increased rapidly during the freezing-thawing stress. The content of soluble protein in the leaves were more than in the stolons, and the content of proline and soluble sugar were higher in the stolons. The leaves of activity of SOD, POD, CAT were increasing, reached maximum at-5 ℃ when the temperature was gradually reduced, but the biggest activity of the stolons were at-10 ℃. Three enzymes were cooperated with each other on function. The activity of stolons of SOD, CAT was higher than the activity of leaves, and the activity of leaves of POD was higher. Under the simulation of freezing-thawing and acid deposition stress, the content of proline and MDA,the activity of SOD, POD were all higher than the single freezing-thawing control groups. At the same time, large molecules such as soluble protein and soluble sugar,which were due to the decomposition reaction, content were lower.With the increasing of natural freezing-thawing stress, the content of soluble protein of stolons increased firstly and then decreased. When the stress was aggravating, the content of soluble sugar and MDA increased. No whether in winter or spring, if experienced the freezing-thawing stress(The temperature dipped below zero degree), the content of proline were increased, when the temperature was lowest, content were the most. When real freezing-thawing stress in the nature increased, the activity of SOD and CAT had the similar variation trend, which was increased. The activity of POD decreased firstly and then increased. The SOD was the most dynamic, which could eliminate free radicals. To reduce the membrane lipid peroxidation, protecting the membrane from the damage of free radicals, being maintained the balance of active oxygen metabolism in the body, thus to play the role of protection. Soluble protein, MDA and the antioxidant enzymes, the content of spring were higher than in winter. Sampling time and the content of each index were significant difference(P< 0.05).No matter the simulation freezing-thawing stress or the natural freezing-thawing stress, the content of proline and malondialdehyde had the similar trends, when the temperature reduced, the content of accumulation was increased, but the accumulation of natural freezing-thawing were more than the simulation of freezing-thawing.The activity of antioxidant enzyme system in the condition of natural freezing-thawing always showed higher than simulation freezing-thawing, which showed that T. repens in winter were more resistant to low temperature, to protect the cell membrane system, to reduce the damage of membrane, and cold resistance were stronger. No matter the simulation freezing-thawing stress or the natural freezing-thawing stress, T. repens could respond to environment temperature change. Rapid activation of antioxidant enzyme system and the steady accumulation of osmotic regulation substances were interacted with each other, thus suppressing the function of the membrane lipid peroxidation, this would make the tissue cells adapt to water balance on the freezing-thawing.