| White clover(Trifolium repens L.), also known as white trefoil, belonging to bean clover, is a perennial herbaceous plant. Since white clover had strong ability to resistance to freezing, drought, and a long green leaves period, long florescence, it has become a useful plant in landscaping construction. Due to short-life of the leaves, white clover relies on new leaves growing from the stolons constantly and old leaves dead to maintain the survival of plant. Stolons is the main organ to overwinting. But it not known if leaves of different age and growing from different season had same physiological adaptation mechanism to respond to temperature change and if there were difference in physiological adaptation mechanism among new leaves grown from different season. In this study, the activities of superoxide dismutase(SOD), peroxide(POD), catalse(CAT), the contents of soluble sugar, soluble protein, proline, malondialdehyde in the leaves of different leaf age(young leaves, middle leaves, old leaves) of white clover(Trifolium repens L.) and carbohydrate energy transfer and conversion in white clover leaf and stolon were investigated in different seasons to reveal the role of antioxidant enzymes, osmoregulation, carbohydrate metabolism in white clover stolons survival, overwintering, spread of growth, and regeneration, as to provide theoretical basis for reasonable development and utilization of white clover and management. The results of the study are as follows:(1)Physiological regulation mechanism of white clover leaves growing from different season to adapt to different seasons temperature.The activities of SOD, POD, CAT, the contents of soluble sugar, soluble protein, proline, MDA and chlorophyll in the leaves of different leaf age(young leaves, middle leaves, old leaves) of white clover(Trifolium repens L.) sampled from different season were investigated to understand that physiological regulation mechanism of white clover leaves’ to adapt to different seasons temperature and the ecological role of short-life leaves of white clover in maintaining stolon growth. The result showed that:(1) Young leaves grown in winter, temperature were below zero, had the highest in activities of POD and SOD, and the content of soluble sugar,proline and chlorophyll a in one year, while the content of MDA was rather lower. But young leaves grown in summer, with high temperature, had higher in the content of MDA and chlorophyll b, lower in activities of POD, SOD and in contents of soluble sugar and proline.(2) with leave becoming to mature, the content of chlorophyll b, proline and soluble sugar and the activities of POD and SOD increased, while the MDA content decreased.(3) Old leaves of different season had same physiological characteristics. The contents of soluble sugar and proline in the leaves tended to be higher, while the activities of CAT and the content of MDA decreased. It indicated that antioxidant enzymes and osmoregulation played a important protective role in maintaining oxygen radical metabolism and balance of water metabolism in young leaves adapting to the temperature of different seasons and leaf rapid growth.(2) The variation analysis on physiological response to freezing stress between young leaves from summer and spring.The content of MDA, the activities of antioxidant enzyme(SOD, POD and CAT enzyme) and the content of osmoregulation(soluble sugar, soluble protein and proline) were measured in the young leaves of white clover grown in summer and spring exposed to artificial freezing stress to reveal if there were differences in physiological response to the extreme temperature changes between young leaf grown in different seasonal temperature. Results showed that, in natural environment, the young leaves grown in low temperature in spring(7 ℃) had lower content of MDA by 25% than that of young leaves grown in summer heat(28 ℃), and young leaves grown in springt had higher activities of SOD and CAT and the content of soluble sugar, soluble protein and free praline than that young leaves grown in summer. During freezing-thawing stress, young leaves grown in spring remained higher activities of SOD and CAT enzyme, higher in contents of soluble sugar, soluble protein and free proline than that of young leaves grown in summer. Therefore, young leaves grown in spring with low temperature experiencing cold acclimation obtained physiological adaptations and ability to resistance to freezing. But the young leaf grown in summer had not experienced cold acclimation and had lower frost resistance. Obviously, the experience of cold acclimation played an important in young leaves to adapt the temperature changes. It was reason why leave grown in summer would not grow in autumn and winter.(3) The effect of the carbohydrate in stolons and leaves of white clover on overwintering and regeneration in spring. The carbohydrate content in the different parts of stolons and leaves of in white clover grown in the natural environment were measured in fall and winter and spring to reveal the role of carbohydrate metabolism in overwintering and regeneration of white clover. It showed that, with temperature droping in the late autumn, the content of total soluble sugar, the ratio of soluble sugar to total carbon, the ratio of starch to total carbon increased, while, ratio of fiber content to total carbon decreased in the stolons of white clover. During freezing-period, the ratio of soluble sugar to total carbon, the ratio of starch to total carbon(except for the top of the stem) increased, and the ratio of fiber to total carbon decreased. It presented that nonstructural carbohydrate and structural carbohydrate transferred and converted in the stolons played an important role in adapting to temperature changes in maintaining cell osmotic potential, growth potential, mechanical organizations.Therefore, white clover had various adaptive strategies for the temperature changes in different seasons. it’s a survival strategy that stolons produced new leaves with strong adaptability and made leaf vicarious death in every seasons. White clover maintained the balance of cell oxygen radical metabolism and balance of water under the condition of different seasons by regulating activities of leaf antioxidant enzymes and content of osmoregulation, which was important physiological adaptation strategy for white clover to survival in different season. In the process of overwintering and regeneration, the carbohydrates between the stolons and leaves of white clover were transferred and converted timely to provide energy to cell and osmotic regulation to prevent cell from freezing and maintain the balance of water by transfering and convertion. |
PDF Full Text Request