Effects Of Water Deficit On C3 And C4 Photosynthesis Enzymes And Primary Carbon Metabolism In Wheat Flag Leaves And Spikes

As one of the major crops in China,wheat is prone to high temperature and other extreme environmental infestation,which affects its yield.Drought is one of the factors limiting wheat yield in China.The filling stage is an important period for wheat yield.Previous studies shown that wheat spike bracts senesced later,more tolerance and the more stable photosynthetic capacity than flag leaves under water deficit.Therefore,it is important to explain the physiological mechanism of drought tolerance and high photosensitivity of wheat spike bracts under drought stress,which could be contributed to create new varieties of drought-tolerant wheat to increase wheat yield.In this study,bioinformatics was used to sequence the C4 photosynthetic enzyme genes of wheat based on wheat genomic data.Pot experiment was carried out and the wheat of Zhengyin 1 was selected as the experimental material to analysis the change of C4 photosynthetic enzyme activities,genes expression and the carbon metabolites in wheat flag leaves and spike bracts(Glumes and lemmas).To determine the different response of C4 photosynthetic key enzymes to drought stress in wheat flag leaf and spike bracts.The main results are as follows:1.The net photosynthetic rate of spikes increased first and then decreased.Under water deficit,the photosynthetic rate of flag leaves decreased significantly,while the did not decrease significantly in spikes.The effect of drought stress on photosynthetic rate of wheat flag leaves was higher than that of spikes.The activity of Rubisco in flag leaves and spike bracts was significantly decreased during the whole filling period under water deficit,which indicated that the photosynthetic capacity decreased significantly.The activity of Rubisco in flag leaves was decreased more than that of spike bracts.C4 photosynthetic enzyme(PEPC,MADP-MDH,NADP-ME,PPDK)activities in the spike bracts were increased in the early filling stage(0-6 DAA),peaked at 6 DAA,and gradually decreased during the late filling stage.Compared with normal water supply,C4 photosynthetic enzyme activities in spike bracts were increased significantly in the middle stage of filling(12 DAA,18 DAA)under drought stress,while the activity of C4 photosynthetic in flag leaves was decreased,which was significantly lower than that in spike bracts.These results indicated that the activity of C4 photosynthetic enzymes in spike bracts was increased by drought stress,which may be an important reason for the spike bracts have physiological advantage than that of flag leaves under water deficit2.We identified the C4 photosynthetic genes in the wheat and comparison with C4 photosynthetic genes in C4 and C3 plants,including rice,maize,Brachypodium distachyon and Setaria italica.Phylogenetic analysis indicated that the C4 photosynthetic genes of wheat had a high correlation with Brachypodium distachyon and rice,and also had some homology with maize C4 photosynthetic genes.These results indicated that wheat C4 photosynthetic enzymes may be play a key role in wheat stress resistance.The expression of Rubisco in flag leaves was significantly downregulated under drought stress,but the gene expression level in spike bracts were upregulated in the early stage of grain filling,indicating that the spike bracts have higher photosynthetic rate under water deficit.In spike bracts,drought stress significantly upregulated the expression of C4 photosynthetic enzyme genes in the early stage of grain filling(1-6 DAA),which maintained a certain level in the middle and late filling stage and was significantly higher than that in flag leaves.The same results were found in the enzymes activity change.Drought stress enhanced the C4 photosynthetic enzymes from the transcriptional level and show different expression patterns in flag leaves and spike bracts.It may be one of the reasons that the effect of water deficit on wheat spike bracts is significantly less than that of flag leaves.3.Drought stress significantly inhibited the metabolism of malic acid,oxaloacetate,citric acid and fumaric acid in wheat flag leaves,and the TCA cycle products decreased.Under water deficit,the organic acid content in spike bracts was significantly increased in the middle of grain filling(12 DAA,18 DAA),while the content in the flag leaves decreased.During the whole filling stage,the contents of organic acid in the early grain filling stage were increased gradually,peaked at 6 DAA,and then gradually decreased in the middle and late filling stage,which showing the same change with enzyme activities.These results indicated that there are significant differences at the metabolic levels in different organs by C4 photosynthetic enzymes induced,which could be reasonable explanation for the spike organs more drought tolerance and stable photosynthetic capacity at grain-filling stage compared to the flag leaves under water deficit.