| Wheat is a kind of grain crop which covers the biggest area in the world which is also one of the important staple crops in China.The grouting time is the critical period of forming grain weight and yield, in the northern China, the grouting time of wheat frequently suffers soil and atmospheric drought with the varying degree, which seriously influences wheat's grouting process and limits the enhancement of yield.High crop yield not only requires functional leaves with strong photosynthetic capability, but also requires photosynthate is transported and distributed effectively.Wheat's photosynthetic products mainly exists and transports in the form of sucrose, sucrose phosphate synthase (SPS) controls the synthesis of sucrose in leaves. Photosynthate transported into grain exists in the form of sucrose at first.Therefore by the research of metabolism process of the sucrose in wheat flag leaf, penult stem, grain, it is helpful to grasp the synthesis of each spot photosynthesis product of the wheat and have a comprehensive understanding the transportation and the assignment direction, what more, which has important meaning to discussion the wheat source storehouse relations' adjustment under drought condition.Chang-Wu134, Chang-Han58, and moisture sensitive wheat Xi-Nong 9871, drought-resistance wheat, were selected as experiment material, flag leaves'photosynthetic parameters, sucrose content, sucrose phosphate synthase (SPS) and (SS) sucrose synthase (flag leaf, penult stem, grain), yield index were studied on 6d, 12d, 18d, 24d after flowering during grain filling by pot culture experiment. Main results are as follows:1.With the degree of drought stress increase and the process of grain filling, the changing trends of wheat's flag leaf photosynthetic rate are basically coincident with transpiration rate, stomata conductance and intercellular CO2 concentration after 6 ~ 18 days of flowering. During 24 day after anthesis, Gs, Ci increased, but Pn reduced. It showed that it was stomata factors that influenced photosynthesis during earlier period and the intermediate stage, while the non-stomata factors became the main limiting factors during later period, followed with chloroplast degeneration and the flag leaf's senility.2. As the soil moisture reduction from WCK to SWS, the WUE of Chang-Wu134 were 3.86, 3.96, 3.33 umolCO2/mmolH2O; the WUE of Chang-Han58 were 3.32, 3.53, 3.49 umolCO2/mmolH2O and that of Xi-Nong9871 were 3.31, 3.22, 2.65 umolCO2/mmolH2O. Drought increased wheat's WUE at different level. The drought-resistance wheat Chang-Wu 134 had higher WUE than the other two.3. In the flag leaves, kernels and stems of wheat, sucrose, SPS and SS activity 12d after blossoming were all significantly higher than that after 24d. Under moderate drought ,SPS and SS activity, sucrose synthetic ability of the drought-resistance wheat are all enhanced,and sucrose content increases 12d after blossoming. But for the moisture sensitive wheat under moderate drought, the results are opposite. With the grain filling process and the aging of flag leaf, 24d after blossoming, key enzymes activity in the sucrose metabolism of all wheat varieties is lower than that of the control treatment under moderate drought, and the sucrose content increases or decreases in different degree. In the stems of wheat, moderate drought improves the stem SPS and SS activity of three wheat varieties 12d after blossoming, but reduces the stem SPS and SS activity 24d after blossoming. Moderate drought make the sucrose content of drought-resistance wheat reduced but sucrose content of moisture sensitive wheat increased 12d after blossoming ; However,24d after blossoming, moderate drought reduce the SPS and SS activity in stem., which enhanced sucrose synthetic ability. Under severe drought, sucrose content and the SPS activity and SS activity all decline in the flag leaves, stems and grains of three wheat varieties. These results demonstrate that, whether the sucrose content or SPS and SS activity of the drought-resistance wheat are all higher than that of the moisture sensitive wheat under the moderate drought, except for that the sucrose content in the stem of the moisture sensitive wheat is higher than the WCK while that of the drought-resistance wheat is lower. In grouting process, sucrose metabolism activity of the drought-resistance wheat under drought conditions is higher than that of the moisture sensitive wheat. Lots of carbohydrate accumulated in different parts of the wheat, so as to lay a foundation for grain filling.4. 1000-grain weight of three wheat varieties performance as: Changwu 134 (38g) > Chang-Han58 (32g) > Xinong 9871 (31g); grain number per spike performance as: Chang-Han58 (52 grain per spike) > Xinong 9871 (43 grain per spike) > Changwu 134 (40 grain per spike); Final production performance as: Chang-Han58 (19g/pot) > Changwu 134 (18g/pot) > Xinong 9871 (16g/pot). The above data shows that Changwu 134 wheat yield increases is mainly the result of 1000-grain weight increases, while the Chang-Han58 wheat yield increases mainly because of increased grain number. Xinong 9871 wheat yield decreases because of both the two factors, and it is affected by its genetic factors and drought resistance ability. 5. Moderate water deficit was helpful to increase harvest index of drought-resistance wheat, but reduced the harvest index of moisture sensitive wheat. With the degree of soil moisture deficit aggravating, water use efficiency of two kinds of ecological wheat increased earlier but reduced later. Anyhow, water deficit had less influence on yield and harvest index of drought-resistance wheat than moisture sensitive wheat, but it had bigger influence on water use efficiency of drought-resistance wheat than moisture sensitive wheat, therefore, drought-resistance wheat showed higher drought resistance and water use ability.The above results show that effects of water deficit in filling stage on photosynthetic characteristics of wheat were different because of different varieties. For drought-resistance wheat, Moderate water deficit didn't destroy PSâ…¡and photosynthetic rate increased slightly, but the photosynthetic rate of moisture sensitive wheat would reduce because of water deficit. As the result, effects of water stress on photosynthetic parameters of moisture sensitive wheat were more than drought-resistance wheat. It showed that it was stomata factors that influenced photosynthesis during earlier period and the intermediate stage, while the non-stomata factors became the main limiting factors during later period, followed with chloroplast degeneration and the flag leaf's senility. The carbohydrate produced by plant photosynthesis is transport and storage in the plant in the form of sucrose. Drought-resistance wheat has high Pn in moderate water deficit, which offer enough carbohydrate for the completion of sucrose metabolism. The Sucrose content of Flag leaf, stem and seed in drought-resistance wheat were 75.5mg/g,53.1 mg/g,1.02mg/grain and moisture sensitive wheat were 53.2 mg/g, 49.1 mg/g,0.84mg/grain. Water deficit effects Sucrose metabolism by photosynthesis, all of that Reflected from the yield. The yields of two drought-resistance wheat were higher than moisture sensitive wheat, which were compensated by Grain weight and grain number per panicle.
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