Study On Drought Resistance And Screening Identification Indexes Of Drought Resistance In Rice

The experiment was carried out in growth chamber under both normal and drought conditions to investigate the effects of water stress on morphological, growth and development indexes and physiological and biochemical characteristics during bud, seedling, heading and grain filling stage. Identification index of drought resistance during bud, seedling and heading stage had been established preliminary. The effects of water stress on morphological, physiological, biochemical and grain yield had been carded out deep research. This paper adequately expounded and proved the relationship between physiological and biochemical characteristics and drought resistance in rice and systematically discussed the key physiological and biochemical mechanism of drought resistance during grain filling. The results followed:1. 25%PEG—6000(w/v) was used to induce water stress, coleoptile length, radicle length, germination length, root number, germination rate, the dry weight of germinations and roots of different of rice at germinating stage were measured. The results showed that relative radicle length, relative germination length and relative dry weight of germinations could be used as indexes of assessing the drought resistance at germinating stage of rice. It was better that total classes from relative classes of the drought resistance was used to screen drought resistance of rice cultivars. The drought resistance of 76 rice cultivars was evaluated with this method. It was proved that the way is reliable.2. To determine the mechanisms and screen identification indexes of drought resistance during seedling stage in rice, the experiments were carried out in growth chamber to investigate the effects of water stress on morphological and physiological characteristics in 15 rice cultivars under both normal and drought conditions during seedling stage. The results showed that relative leaf age, relative the area of first leaf under the central leaf, relative leaf fresh weight, relative root length were significantly and very significantly correlated with the survival percentage under repeated drought condition, and these four indexes could be used as the morphological indexes to identify the drought resistance. Relative activities of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) and relative content of free amino acid (AA), ascorbic acid (AsA), reduced glutathione (GSH), soluble protein, malondialdehyde (MDA) were significantly and very significantly correlated with the survival percentage under repeated drought condition, and these eight indexes could be used as the physiological indexes to identify the drought resistance. Through principal components analysis, an integrated identification index including the relative activity of SOD, relative GSH content, leaf fresh weight and leaf age was established. The drought resistance of 15 rice cultivars was evaluated by stepwise regression equation and the results indicated that it was feasible to predict the drought resistance in rice during seedling stage using integrated identification index.3.The identification indexes of drought resistance at flowering stage under water stress were screened by the main content analysis and the step regression analysis. The results showed that at flowering stage, proline content and relative moisture content in leaf, and leaf stomatal conductance and leaf areas have significant influence on drought resistance and can be selected to identify the drought resistance of rice. The drought resistance of 10 rice cultivars was evaluated by stepwise regression equation and the results were basically consistent with the results in paddy field, which indicated that it was feasible to predict the drought resistance in rice at flowering stage using the four indexes screened out in this study.4.Ten rice cultivars, with different drought resistance were used as experimental materials. Changes in AsA content, AA content, soluble protein content, MDA content and antioxidative enzyme activities were studied under both irrigation and drought conditions at flowering stage. The results indicated that water stress increased contents of AsA, AA, soluble protein and MDA; as well as the activities of SOD, CAT and POD in leaves at flowering stage. Correlation analysis showed that drought tolerant coefficient significantly or very significantly correlated with relative contents of AsA, AA, MDA and SOD activity under both normal and drought conditions. Therefore, they could be selected as identification indexes for drought tolerance at flowering stage.5.Water stress reduced plant height, leaf area and leaf area index, and enhanced senescence in later period, reduced accumulation of dry matter during plant growth period, and dry matter accumulation increased slowly in early period. Water stress decreased panicle length, primary branch number, secondary branch number, Spikelets per panicle, number of filled grains per panicle, seed setting rate and 1000-grain weight, which resulted in decreased yield. The responses of yield and yield components were different among different cultivars because of drought resistance, and it decreased in better drought resistant cultivars were obvious less than those in weaker ones.6.Dry matter weight of stem and sheath at heading and harvest stage under water stress was lower than that of control. The water stress plant had lower export amount of stems and sheath, export and transform percentage of the matter after heading. Dry matter weight of stem and sheath at heading, Export amount of stems and sheath, export and transform percentage of the matter after heading were positively significant and very significant correlation with grain yield. Export and transform percentage of the matter in better drought resistant cultivars was higher than that in weaker drought resistant cultivars, and decreases in better drought resistant cultivars were obvious less than those in weaker ones.7.The water stress decreased grain growth potentiality, the maximum and mean rate of grain filling, and prolonged active grain filling. Time and date of the maximum rate of grain filling was earlier under water stress, especially in weaker drought resistant cultivars. Water stress increased time and rate of grain filling in middle and later growth stages. It suggested that water stress inhibited grain filling and delayed active grain filling. Activity of key enzymes in rice grain including soluble starch synthase (SSS), ADP-glucose pyrophorylase (ADPGPPase)and soluble starch branch enzyme were decreased under water stress.8. During grain filling, water stress aggravated the membrane lipid peroxidation in rice leaves, which was more severe in weaker drought resistant cultivars than that in better ones. Also 0₂ˉand H₂O₂ were accumulated more rapidly in weaker drought resistant cultivars than that in better ones. During the period of water stress, decreases of GSH content, AsA content, chlorophyll content, photosynthetic rate and stomatal conductance in better drought resistant cultivars were obvious less than those in weaker ones. Contents of soluble sugar and amino acid and activities of SOD, CAT and POD in leave increased obviously in 0～14d after anthesis and subsequently decreased rapidly, and those in better drought resistant cultivars were more than those in weaker ones in 0～14d after anthesis. At the same time, the results showed that changes of 0₂ˉcontent, H₂O₂ content, MDA content, GSH content, AsA content, photosynthesis, osmotic regulators and antioxidative enzyme activities correlated significantly to drought resistance of rice cultivars, and better drought resistant hybrids possessed high antioxidation capacity.