Effects Of Water Deficit On Ear Photosynthesis And Sucrose Synthesis Metabolism In Wheats With Different Drought Resistances

Wheat is one of the main food crops in China. During reproductive stage, drought stressaffects the yield and influences the food security significantly. Ear photosynthesis of wheatmakes great contributions to the grain filling, and the ear has better stress resistance and themore obvious superior of photosynthesis than flag leaf. Study on photosyntheticcharacteristics of wheat ear and source-sink relationship on water deficiency will illustrate thecontribution of ear to grain yield. This research has important implications for breeding fordrought tolerance and high and stable yield of wheat. Two wheat cultivars with differentdrought resistances were selected in this study. Through pot experiment, effects of waterdeficit on photosynthetic characteristics of ear and the transport of photoassimilates in twowheat cultivars with different drought tolerances. The main results are listed as follows:1. At anthesis and early grain stage net photosynthetic rates of flag leaf in two wheatcultivars decreased under water deficit, however, net photosynthetic rates of ear was lessinfluenced by water deficit in drought-tolerance cultivar Xinong1043and net photosyntheticrates of ear decreased by26.7%and15.9%in drought-sensitive cultivar Shan253(P<0.05).At late grain filling stage (18-24d after flowering), the ear of Xinong1043maintainedrelatively high net photosynthetic rates, whether under normal condition or under waterdeficit. At late grain filling stage (24d after flowering), the contents of chlorophyll andsoluble protein decreased strongly (P<0.05) in flag leaf. By contrast, steady trend of thiscomponents in bracts (glume, lemma and palea) delayed ear senescence and maintainedadvantages of photosynthesis during grain filling stage.2. The content of sucrose in flag leaf increased at first and decreased later during grainfilling stage. Instead, the content of sucrose in bracts continued to drop. The ear of wheatprovided a plenty of assimilate supply to the grain development at early grain filling stage. Atmiddle grain filling stage (12d after flowering), the content of sucrose in glume and lemma ofdrought-sensitive cultivar Shan253increased by36.2%and104%under water deficit,respectively. Related enzyme activities in sucrose synthesis metabolism showed the similarphenomenon to sucrose accumulation. At early and middle grain filling stage (0-12d afterflowering), the activities of SPS and SS increased significantly (P<0.05) in drought-sensitive cultivar Shan253. Sucrose content and enzyme activities of bracts was less influenced bywater deficit in drought-tolerance cultivar Xinong1043. The higher content of sucrose inbracts of drought-sensitive cultivar Shan253might be related to high enzyme activities, and itmight also be related to retention assimilate.3. At middle grain filling stage (12d after flowering), content of sucrose in grain ofdrought-tolerance cultivar Xinong1043and drought-sensitive cultivar Shan253increased by26.5%and73.1%under water deficit, respectively. At maturity stage (30d after flowering),content of starch declined in both wheat varieties. At late grain filling stage (18-24d afterflowering), activities of SS and AGPase significantly declined (P<0.05) in drought-sensitivecultivar Shan253and slightly dropped in drought-tolerance cultivar Xinong1043. Water stressdecreased sink activity in drought-sensitive cultivar at middle and late grain filling stage.4. Water use efficiency of drought-tolerance cultivar Xinong1043rose slightly underwater deficit condition, drought-sensitive cultivar Shan253had a significant drop (P<0.05).Under water deficit condition, grain weight and harvest index of Xinong1043decreasedslightly, and Shan253dropped significantly (P<0.05). Water deficit had limited impact ondrought-tolerance cultivar Xinong1043.