Comparisn On The Photosynthetic Efficiency And Activities Of Enzymes Involved In The C₄Photosynthesis Pathway Between Common Wheat（triticum Astivum） And Foxtail Millet （setaria Italica）

In order to understand the difference in photosynthetic indexes between C3cropcommonwheat and C4cropfoxtail millet, and also to make clear the physiological and biochemicalbasisthat caused the difference,4common wheat varieties (ChineseSpring, Jinmai47,Mianyang11and Xiaoyan6) and4foxtail millet varieties (Yugu1,Dungu1, Jigu19and Jigu20) were used as experimental materials in this study. The anatomical structure of leaves wasobserved,the activities of fourC4enzymes as MDH, NADO-ME, PEPC and PPDK in theleaves of wheat and foxtail millet were determined at the growth stages of seedling, jointing,heading, flowering and grain filling, respectively, and their photosynthetic rates weremeasured at the corresponding stages using Licor6400portable photosynthesis. In addition, afragment of PEPC genewas cloned from foxtail millet variety Yugu1, the main results were asfollows:1. The leaf anatomical structure of wheat showed that mesophyll cells were composed ofspongy and palisade tissue, which were loosely arranged. While vascular bundle, bundlesheath cells and mesophyll cells in the leaf of foxtail millet were arranged closely to becomethe “Kranz anatomy” structure. This difference is important for their photosyntheticefficiency.2. Investigation on the photosynthetic related traits indicated that at different growthstage, the net photosynthetic rate of foxtail millet was significantly higher than that ofwheat,while the transpiration rate,stomatal conductance and intercellular CO2concentration offoxtail millet were significantly lower than that of wheat.The activities of the four C4keyenzymes were all detected in the leaves of wheat varieties at different growth stages, and theactivity variationof the enzymesat different stage were coincide with the changes of netphotosynthetic rate. The activities of the four C4key enzymes in foxtail millet leaves weremuch higher than those in wheat leaves. The activities of PPDK and NADP-ME in wheatleaves were positively correlated with the net photosynthetic rate at different growthstages.The activity of NADP-ME was positively correlated with stomatal conductance andintercellular CO2concentration,while there wasno significant correlation with transpiration rate. The activities of MDH，PEPC and PPDK in foxtail millet leaves were positivelycorrelated with the net photosynthetic rate at different growth stages;the activity of the4keyenzymes involved inC4photosynthetic pathway were all positively correlated with stomatalconductance, while significant correlations between PEPC, MDH and transpiration ratewereonly observe in the leaves of Yugu1, Dungu1and Jigu20, respectively.3. The partial cDNA sequence ofPEPC gene was obtained in foxtail millet variety Yugu1using homological cloning method, which showed95.11%sequence homologywith thatoffoxtail millet PEPC gene in GenBank(10038607).Phylogenetic analysis of nucleotidesequence and amino acid sequence showed that this cDNA sequence was highly homologouswith barley in C3plant, followed by Panicumin in C4plant.