| Clovers with developed roots, dense stems and leaves, bright-coloured flowers, are the most important turf and forage grass species of the temperate regions, used around the world widely. Which show unique role in beautifying cities, roads, mixly protecting dams of rivers and lakes, ect. Especially for the cultivars of Trifolium repens L. Trifolium pratense L. Trifolium hybridum L. In this study, Haifa, Rivendel, Common red clover, Alsike clover as materials to be researched under drought conditions. Potted, with5water gradients, on the basis of drought gradient, measured the dynamic changes of morphological and physiological indexes of the clover. PEG6000treated plants, determined the expression difference of RT2drought-resistant, compared drought-resistant ability of different cultivars under drought stress. The purpose of this study is to provide important theoretical basis on selecting drought tolerance cultivars and cultivating clovers in large areas and in the arid and semi-arid areas. Measurements include: relative water content of soil, leaf relative water content, leaf water potential, leaf free proline content, leaf leaf soluble protein content, leaf soluble sugar content, leaf peroxidase activities, leaf chlorophyll content and leaf relative conductivity rate, stomatal areas、stomatal densities、stomatal opening and closing ratio、stomatal conductance, the cloning and expression of RT2. The results and the innovation were as follows:1Moisture aspects:With the lengthening of stress durations, the trends of the RWC, water potential of leaves, lost water rate of cutting leaves decreased, and appeared differences among clovers in the same moisture gradient. Common red clover was strongest and Haifa was weakest in drought resistance, the others were between them. The correlation was very significant positive between3moisture indexes and soil relative water content of4clovers. The correlation was different among clovers. Showed:soil moisture was a main environmental factor, which caused water changes of clovers. When the soil moisture decreased, plant moisture would be directly affected. The clovers of drought-resistance changed alittle in moisture.2Osmoregulation aspects:with the lengthening of stress duration, free proline contents, soluble protein contents and soluble sugar contents of leaves were presenting obvious trend of increase. They were of different fluctuation due to the different clovers and the degree of water stress during the process. Differences were significant among clovers. But The whole changes rules of three substances were Common red clover> Rivendel> Alsike clover> Haifa during the process. The test results showed:when the soil moisture reducing, the contents of three kinds of soluble substances increased, the more increased, more stronger in drought-resistance.From correlationship between osmoregulation substances and RWC, water potential analysis, three kinds of substances were negatively correlated between RWC and water potential, positive correlativity among three substances in the whole process. T he results showed:4kinds of clovers would increased three osmoregulation substances contents under water stress to ensure to maintain lowly basic penetration of cells, water absorption, and activities of cells, that related to the cultivars drought-resistant ability of a plant. The correlationship amang osmoregulation substances in different cultivars showed the relationship was coordinated and integrated.3The contents of chlorophyll, POD and cytoplasmic membrane permeability: With the increasing of drought stress, chlorophyll contents of leaves increased by slow-fast-slow tendency first, decreased at last. The chlorophyll contents and the relative water contents of leaves negatively correlated in the0d-8d, positive correlation in the8d-16d.The activities of POD in4clovers increased first and then decreaced at last during the treatment process. POD showed high activity in4clovers under water stress, the performance was obvious under mild stress, but the activities decreaced from moderate to severe stress. Activities of PODwere negatively correlated between RWC and water potential in the0d-8d, positive correlation in the8d-16d. The activities of POD in clovers were regulated by the changes of leaf water contents greatly, increased in the early stage of drought, with the increased stress, the activities decreased. The protecting cell membrane abilities of POD were limited, when clovers were under drought stress.With the increasing degree of drought stress, the conductivity of4clovers increased significantly, increased slowly in the mild stress, and fast at the late stage, and showed negative correlation between the RWC, water potential of leaves, positive correlated between the activities of POD, and related significant and a very significant. The drought resistant orders:Common red clover> Rivendel> Alsike clover> Haifa.4Stomatal factors:Stomatal area, opening and closing ratio and stomatal conductance decreased under drought stress, but stotnata density increased. Stomatal area declined slowly in the mild and moderate drought stress, declined fast in the severe stress. Stomatal density increased gently. Stomatal opening and closing ratio declined faster in the first and last stage s, slowly in the interim; Stomatal conductance declined slowly in the first stage, but rapidly in the later stage. Stomata density showed negative correlation between the RWC, water potential of leaves. Stomatal areas, opening and closing ratio correlated positively between the RWC, water potential of leaves. Stomatal conductance correlated positively between water potential of leavesN Relative water contents of soil.5Drought-resistant gene RT2expression:analyzed the changes of RT2expression in Common red clover with the stressed point. The results showed that drought stress could induce the gene RT2expression of Common red clover, that suggested:the drought resistance of clovers might associate with the gene induction and expression of scavenging system of active oxygen. With24h of drought stress, the RT2expression was significant difference among4clovers. RT2expression of Common red clover and Rivendel were significantly higher than those of Alsike clover and Haifa. The results showed that the RT2expression was different among different clovers, the aboundances of RT2expression were relatively higher in stronger drought-resistant clovers. Common red clover and Rivendel displayed stronger tolerance to drought than Alsike clover and Haifa.6Drought resistance comparison in different cultivars:comparatively analyzed the changes of drought-resistant indexes in clovers under drought stress, the drought-resistance orders:Common red clover> Rivendel> Alsike clover> Haifa.7Innovation points of research:1) It was the first that researched comprehensivly stomatal dynamic changes and leaf water status under drought stress in the relationship in the clovers2) It was very comprehensive research on leaf water status, soil moisture status change, cell osmotic regulation substances, cell membrane permeability, protective enzyme activity, and the relationship among them analysised comprehensivly in clover drought resistance3) For the first time, cloned clover RT2under drought condition and compared their expression, revealsed:the close relationship between the drought resistance in clovers and the expression of active oxygen removal system geneof cells... |
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