| High temperature and drought stress have becoming two major devastating factors on rice production, especially for high quality rice varieties. Elucidating the physiological and biochemical mechanism of rice tolerance to these stresses is therefore significant to rice production. In this study, two rice varieties "yuzhenxiang(YZX)" and"xiangwanxianl2 (XWX12)", the first and third class high quality rice varieties respectively, were used and treated under high temperature (37?) for different times (1?4?7d), also they were treated under heat stress (35?) combined with varying degrees of drought (flooding, moderate drought, severe drought). The yield and quality related traits were investigated. The main results and conclusions are as follows:1. High temperature and drought effect on starch components and contentsCompared to the natural temperature(the average daily temperature 33?), with high temperature(37?,the same below) treatment for 7d in the filling stage, amylopectin and total starch contents decreased 23.37%,13.36% in YZX, and dropped 19.4%,10.53% in XWX12, amylose contents of two cultivars' rose 16.61%,12.44%. In the treatment of high temperature with severe drought, amylose contents of YZX, XWX12. increased 18.04%, 17.84%, amylopectin contents decreased 3.65%,8.38%, and the total starch contents decreased 1.10%,8.63% respectively, compared to the treatment of optimum temperature with flooding in the filling stage. YZX is greater than XWX12 in the change amplitude of starch component.2. High temperature and drought effect on grain protein components and contentsWith extension of high temperature treatment days in the filling stage, the contents of grain globulin, albumin, gluten increased, but those of globumin, gliadin decreased, and that of crude protein of YZX, XWX12 increased significantly by 18.5%,16.7%. Except the treatment of flooding with the optimal temperature in the filling stage, other treatments of temperature and water interaction decreased the contents of grain albumin, globulin and gladin, but increased the contents of gluten and crude protein. Compared with the treatment of flooding with the optimal temperature, the treatment of high temperature with severe drought produced the most significant effects: The contents of albumin, globulin and gliadin dropped biggest, those of gluten and crude protein increased largest, crude protein content increased by 19.2%,16.4% respectively. YZX changed greater than XWX12 in protein components. Water was the first element of affecting the contents of all protein components, and temperature was the second.3.High temperature and drought effect on seed setting rateWith high temperature treated 7d in the heading stage, pollen coloring rates of YZX and XWX12 decreased, pollen germination rates lowered 68.3%,67.5% than the control. In the treatment of high temperature with severe drought, the seed setting rate of YZX, XWX12 were 23.4%,33.1%, lowered 67.22%,60.31% than the control respectively. Effect order to seed setting rate in YZX was as follows:severe drought and high temperature>severe drought and the optimum temperature>the optimum temperature and moderate drought>high temperature and flooding>.the optimum temperature and flooding, but in XWX12 it was as follows:severe drought and high temperature>severe drought and the optimum temperature>moderate drought and high temperature>moderate drought and optimum temperature>high temperature and flooding>the optimum temperature and flooding., High temperature brought little effect on the seed setting rate in the booting stage, but larger effects on seed setting rate in the heading stage and the filling stage. High temperature had greater effect on seed setting rate of YZX than XWX12 in the booting stage and the heading stage.4. High-temperature and drought effects on the rice processing and appearance quality character:With high temperature 37? treated 7d in the filling stage, milled rice rate of YZX and XWX12 decreased 5.1%,3.5%, head milled rice rate fell 5.8%,3.9%, chalkiness increased by 12.2%,17.5%, chalky rate increased by 25.0%,15.7%. High temperature had greater effects on quality characters of YZX than XWX12 in the filling stage. Compared to the treatment of flooding with the optimal temperature, milled rice rate of YZX, XWX12 decreased 4.1%,3.9%. head milled rice rate decreased 4.7%,4.9%, chalky rate increased 0.8%,1.2% respectively, chalkiness decreased by 0.06%,0.05%, gel consistency declined by 7.1%,14.0.% in the treatment of severe drought with high temperature.5. Grain starch related enzyme performance in high temperature and droughtWith increasing aridity in the filling stage, enzyme (SS, AGpase) activity of grain lowered. AGpase activity under the treatment of optimal temperature with flooding has higher peak than the other treatments. SSS activity of XWX12 and YZX reached the maximum after treated 4d,7d, respectively; and decreased slowly in 9d and 15d. After high temperature treated in the filling stage, GBSS activity of YZX has higher peak than XWX12. GBSS activity was the highest in the treatment of optimal-temperature with flooding, and lowest in the treatments of high-temperature with severe-drought. GBSS activity of the optimal-temperature and flooding, high-temperature and flooding, moderate-drought and optimal-temperature was higher than that of moderate-drought and high-temperature, severe-drought and optimal-temperature, severe-drought and high-temperature. Drought was the first effecting factor on enzyme activity, high temperature was the second one.6. Key enzyme activity related protein synthesis performanceDuring treatment of high temperature in the filling stage, NR activity of two cultivars showed a downward trend. After treated, NR activity increased, then fell again. XWX12 had higher NR activity than YZX. In the filling stage, NR activities of two cultivars were affected severely in the condition of high-temperature with severe-drought, but affected little in the treatment of the optimal-temperature and flooding. Influence of high-temperature and drought to YZX was bigger than that of XWX12. GDH activity decreased during high-temperature treatment. Duration of high temperature longed, inactivation of other enzyme in vivo decreased GOGAT activity. YZX had bigger change range on GOGAT activity than XWX12.in the filling stage. In all interaction treatments, YZX had lower GDH activity starting point and greater change-range of activity than XWX12, particularly in the treatments of the high-temperature with flooding and the optimal-temperature with flooding, GDH activity of YZX changed significantly greater than XWX12.7. Effects of high temperature and drought on photosynthetic rate and dry matter accumulation and transportationUnder high-temperature treatment in the booting, heading and filling stages, photosynthetic rate of YZX decreased by 14.0%,19.1%,25.1% than the control., After high-temperature treated Id,4d,7d in the heading stage, photosynthetic rate of YZX was lower 6.60%,9.67%,18.96% than the control, that of XWX12 was lower 3.55%,8.95%, 13.77% than the control. In three periods, especially in the heading stage, the net photosynthetic rate of YZX decreased significantly than XWX12 in high temperature treatment. After high-temperature treated in the booting, heading and filling stages, dry matter content decreased 49.33%,40.3%,21.16% in YZX and 43.41%,39.56%,24.27% in XWX12 compared with the control. Decline in two cultivars had no significant differences. High-temperature period effect on dry matter accumulation was as follow:booting stage>heading stage>filling stage. In the condition of high-temperature, dry matter accumulation of YZX decreased more than XWX12. In the treatment of severe-drought with high-temperature in the filling stage, dry material output, output rate, stem and sheath conversion rate in stem and sheath decreased 34.9%,55.93%70.04%, in YZX and 33.29%, 54,27%?61.56% in XWX12, compared to the treatment of flooding with optimum-temperature, dry material conversion rate of XWX12 was affected significantly less than YZX.8. Overall conclusionsHigh-temperature and drought have the greatest effect on rice starch composition and content, protein composition and grain weight in the filling stage. In the heading stage, high-temperature and drought affected severely on pollen germination rate and seed setting rate. In the booting stage, high-temperature and drought mainly affected flag leaf photosynthetic rate and pollen development. Drought was the first factor in grain quality and yield, and high-temperature was the second one. In the booting, heading and filling stage, YZX tolerance to high-temperature and drought was lower than XWX12.Multi-character (quality, yield, drought resistance and heat resistance) should be united in the popularization in the process of variety improvement. In the application of high-quality-rice cultivars, the adaptability of the ecological quality characters should be strengthened according to suitable promotion areas and season of variety, and measures should be adopted timely to prevent and control the adverse effect on grain quality by drought and high-temperature... |
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