Effects of Nitrogen Fertilizer on Photosynthetic Characteristics, C4 Pathway, and Related Gene Expression of Maize Varieties with Different Nitrogen Efficiency

The regulation mechanism of nitrogen fertilizer on the C4 photosynthetic pathway of different nitrogen-efficient varieties, the Xianyu 335 (XY 335) maize variety of high nitrogen efficient type and the Jingnongke 728 (JNK 728) maize variety of low nitrogen efficient type was investigated.Five nitrogen application levels of 120, 180, 240, 300, 360 kg hm -2 (NCK) were set, and nitrogen application in local field production was used as control (NCK).The photosynthetic characteristics, C4 photosynthetic pathway key activities, non-enzymatic substances, and key enzyme genes of different genotypes of maize were examined in response to nitrogen reduction.The results showed that the yield of XY 335 reached a high level when the nitrogen application rate was 240-300 kg hm -2 ; when the nitrogen application rate was 180-240 kg hm -2 , the yield of JNK 728 reached a high level.Under low nitrogen conditions, compared with XY 335, the phosphoenolpyruvate carboxylase (PEPC), NADP-malase (NADP-ME), malate dehydrogenase (NADP-MDH), and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) of JNK 728 maintained high enzyme activity.At elongation stage, PEPC and NADP-ME3 genes of XY 335 were significantly up-regulated.Except for the big bell stage, the Rubisco gene of XY 335 was significantly increased at all growth stages.The PEPCs and NADP-MEs genes of the two varieties were significantly upregulated from the big bell stage to the filling stage.At the jointing stage, the NADP-MDH6 and PPDK1 genes of JNK 728 were significantly up-regulated.At the filling stage, the NADP-MDH gene of JNK 728 was significantly up-regulated.The photosynthetic response mechanism of different maize genotypes to nitrogen fertilizer regulation differed at different growth stages.In conclusion, the results showed that C4 photosynthetic enzyme activity and key gene expression played an important role in improving the adaptability of plants to nitrogen fertilizer at the photosynthetic physiological level in different nitrogen efficient maize.