| White clover (Trifolium repens L) belongs to the bean family Leguminosae and the genus Trifolium. Its high content of proteins and other nutrients makes it a very excellent grazing grass; its beautiful shape and long-lasting green leaves also makes it a major lawn grass. It also has the ability to fix nitrogen. The cultivation of white clover can increase soil fertility and the ground green coverage rate, and control the growth of weeds, maintain soil temperature and reduce the erosion of soil.Poultry industry in China is underdeveloped and there exists great potentials. In addition, with the rapid advancing of urbanization and the New Countryside Construction in China, the prospects of cultivating white clover, both as grazing and as lawn grass, seems promising. However, white clover has a very narrow ecological amplitude, is not very resistant to stresses (e.g. drought and water-logging), and prefer warm and humid climates. In order to promote the development of white clover industry, the physiological and biochemical studies of Trifolium repens Lin stresses are quite necessary.In this paper, the physiological and biochemical responses of drought process of white clover were studied. The growth and physiological indexes, antioxidative enzyme activity and zymograms were measures and analyzed.It has been observed that 19 days after stopping watering of the pot cultivated white clover, parts of the old leaves were withering and the leaf color was bluish gray and lustless; After 27 days, 50% of the plants withered.Changes in physiological and chemical features in response to the drought progress are as follows.1. The daily growth rate after watering stopping was decreasing and ceased to grow after 20 days, whereas the daily growth rate of the normal control after 15 days was still 2.0mm/day. The root system of white clover was highly developed. It has a relatively high R/T ratio of about 0.3); during the drought process, the R/T ratio was observed increasing. Significant changes in R/T ratio were observed after 20 days of watering stopping; the ratio increases by 20% after 30 days of drought, whenthe ratio of the control remains to be around 0.3.2. The relative water content in leaf was decreasing and the deficiency in leaf water saturation was increasing with the advancing of drought;the content of total chloroplast pigments was decreasing; after 30 days of drought, the content of total chloroplast pigments dropped 26%, while the content of caroteniods remains constant; the content of soluble sugar in leaf was observed to rise after 15 days of drought, peaking (increasing onefold plus) after 25 days; The content of proline and MDA was observed to increase significantly with the advancing of drought. At their peaks, Pro (after 20 days of drought) and MDA (after 25 days of drought) increased sixfolds and threefolds respectively; after peaking, there were tendencies to drop for both..3. The activity of SOD and POD during the seedling stage were both higher (both increased to two folds) than those of the leaves. After 15 days of stopping watering, the SOD and POD activity in roots and leaves rose rapidly with the advancing of druoght; After about 25 days of drought, SOD and POD in roots and leaves peak, reached more than threefolds of those of the control; and then tended to drop. At 30 days of drought, levels of SOD and POD returned back to the initial levels, whereas the activity of SOD and POD in the control remained almost unchanged. The CAT activity in roots and leaves increased significantly with the drought progress, but there were not much difference compared with those of the control. It must be noted that after 20 days of drought, the CAT activity was decreasing gradually.4. The comparison of SOD zymogram of 27 days of drought (ca. 50% of withering) with the control showed that the isozyme bands in roots, stems and leaves were identical in number and in mobility, but the relative activity in the drought groug was higher than that of the control. The POD zymogram showed in drought roots had 3 stronger-than-the-control bands(.Rf=0.08,0.21 and 0.39) and one weaker band (Rf=0.34). There was one specific band (Rf=0.56) in the control stems disappeared during drought. One band (Rf=0.08) , shared by both the roots and the stems in the control, evidently increased in activity. CAT zymogam showed that there was only one and identical band in roots , stems and leaves, of both drought and the normal control. However, after drought, GAT activity was slightly decreased compared with the control. |
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