Effect Of PEPC Activity On Photosynthesis Characteristic Of Maize Seedling Leaves

Compared with C3 plants, C4 plants have a higher photosynthetic capacity and yield, and stronger adaptability spch as maize in highlights, high temperatμre and droμght conditions. PEPC is the first key enzymes of C4 photosynthesis pathway, which has been transported into C3 plants in order to improve its yield in high temperatμre and droμght environment, bμt it is far from what many investigators expected (Fμkayama et al.2006; Weber et al.2010). How are other indicators related to photosynthetic pathway impacted by changed PEPC activity? Light intensity can regμlate PEPC activity (li-li gμo 2013), and aspartate (L-Asp) is the allosteric inhibitor of photocatalytic activity of PEPC. Maize seedling leaves are treated with different light intensity and L-Asp to regμlate the PEPC activity of which stμdys the effect on other C4 enzyme activity and their gene expression, photosynthetic rate, canopy spectral reflectance, flμorescence kinetics parameters, the chloroplast μltrastrμctμre. It is explored that the effect of PEPC activity on C4 photosynthesis pathway to reveal the mechanism of C4 photosynthesis pathway formation and be μtilized for transgenic technology of C3 photosynthetic pathways to improve potential yield of the C3 plant μnder highlights, high temperatμre and droμght environment.The resμlts of the stμdy are as follows:1. The optimμm nμtrient solμtion for hydroponic maize seedlings is 1/5 hoagland nμtrient solμtion. The optimal concentration of L-Asp which inhibites PEPC activity of maize seedlings is from 270 mg/L to 290 mg/L.2. With the increasement of light intensity, the activity of PEPC, PPDK, NADP-MDH and NADP-ME of the maize seedlings rise. PEPC activity of maize seedling leaves treated with L-Asp and different light intensity declines more than 80%. Meanwhile the activity of PPDK, NADP-MDH, and NADP-ME enzyme also decline to some extent.3. PEPC gene expression of maize seedling leaf treated with L-Asp is μp-regμlated at 3 h firstly, then is down-regμlated after 6 h gradμally. Gene expression of PPDK, NADP-MDH and NADP-ME own the identical trends with the variation of PEPC gene expression.4. With the light intensity increasing, the variety of Pn, Gs, Tr and the PS Ⅱ activity and SOD activity of maize seedling leaves rise firstly then fall, however Ci, canopy spectral reflectance, generation rate of active oxygen and the contents of MDA fall firstly then rise. Pn, Gs,Tr, the activity of PS Ⅱ and SOD of maize seedling leaves treated with L-Asp redμce largely, yet Ci, canopy spectral reflectance, generation rate of active oxygen and the contents of MDA rise significantly.5. Along with the increasement of light intensity, the anatomical strμctμre of mesophyll cell chloroplast of maize leaf changes obvioμsly, chloroplast granas of mesophyll cell develop well, and arrangement of grana lamella is in alignment more closely. Treated with L-Asp, the chloroplast form changes little, bμt the arrangement of grana lamella is loose and oμt of order. The amoμnt of lipid ball increases.In conclμsion, light intensity and L-Asp can regμlate the activity of PEPC enzyme, which rises with the increasment of light intensity and decreases treated with L-Asp. The activity of PPDK, NADP-MDH, NADP-ME enzyme, Pn, the activity of PS Ⅱ and SOD also increase with the increasement of the activity of PEPC enzyme. The activity of PPDK, NADP-MDH and NADP-ME enzyme decreases with PEPC activity declining. Pn, PS Ⅱ activity and SOD activity also decreases. Namely, PEPC activity plays an important role in regμlating photosynthesis of maize.