| White clover (Trifolium repens L.) belongs to Fabaceae family, Trifolium genus, is a perennials fine forage, turf and ground cover plant. It has many features, such as good quality, good Grazing-tolerance, which is an important legume for mixture turfgrass establishment. White clover has beautiful gesture, ornamental, and strong adaptability and the ability of nitrogen fixation. It is also more and more widely used in landscaping, water and soil conservation and ecological construction. But the root of white clover is less developed, which is very sensitive to drought stress. Global climate change, causing frequent occurrence of drought disaster, which has become the important factor limiting use of white clover. This paper researched on the white clover (T. repens cv. Chuanyin Ladino)which is potted with the drought preconditioning, which is under2rounds of pretreatment of drought, and use well-water as untreated group. The paper study the reaction of whiter clover under drought stress, and the drought pretreatment inducing the physiological and molecular mechanism of drought resistance. The results are as follows:(1). Drought pretreatment can obviously increase the tolerance of whiter clover under drought stress. The RWC of two groups continue to decline during drought stress, the untreated group declined faster. Under drought stress after4d, the RWC of pretreatment group was significantly higher than untreated group. The electrolyte leakage (EL) of two groups continued to increase under drought stress, and rapidly declined after re-watering; but the EL of drought pretreatment group was significantly lower than untreated group.(2). Drought pretreatment induced the rise of osmotic adjustment ability in white clover. The pretreatment group had higher osmotic adjustment substance content by drought pretreatment before drought stress, and the amplitude and duration of increased osmotic adjustment substances were significantly higher than the untreated group during drought stress. The soluble sugar content of two groups have continued to rise at early period of drought stress, but the untreated group started to decrease at later period of drought stress, the pretreatment group continued to rise at the same period, both groups have significant difference; The untreated group showed decreased first and then increased trend while the pretreatment group were decreased after re-watering. Two groups of soluble sugar content were at the same level at6d in re-watering. The free proline and betaine content changing trend of two groups show a consistent state, They all increased with harder drought stress, and declined after re-watering. The pretreatment group significantly higher than the untreated group at later period of drought stress. This suggests that soluble sugar content has big effect on maintenance of drought resistance in white clover.3. The drought pretreatment improved the antioxidant enzymes activity of white clover, and reduced the membrane lipid peroxidation (the MDA content). The activity of APX of two groups all had a trend which was first increase then decline, the activity of APX of drought pretreatment group was always higher than untreated group under drought stress, the untreated group decline more slowly, couldn’t recovered to the initial state like pretreatment after re-watering; the activity of SOD of two groups all had a trend which was first increase then decline, then ascend after re-watering,the activity of SOD of drought pretreatment group was always higher than untreated group under drought stress, and two groups recovered to the initial state after re-watering; the activity of CAT and POD of two groups all had a same trend which was rising constantly at the stage of drought stress, then decreased after re-watering, after4d stress, the activity of CAT and POD of drought pretreatment group was significantly higher than untreated group, the activity of CAT and POD of two groups was not significant differences after3d re-watering; The pretreatment group MDA content increased significantly less than the untreated group after8d drought stress and3d re-watering.4. The drought pretreatment improved the Cu/ZnSOD gene expression level of white clover. The gene expression level of two groups at8d was significantly higher than the day before stress, and the drought pretreatment group was significantly higher than the untreated group as well. |
