Comparative Research Of Nitrogen Metabolism Of The Leading Wheat (Triticum Aestivum L.) Cultivars Released In Shandong Province

In this study, the activities of key enzymes involing in nitrogen metabolism and the relative expression of their encoding genes during developing grain from leading wheat cultivars released in different ages in Shandong Province were analyzed, together with grain protein content, nitrogen transfer efficiency and their correlationships. Hopefully, it would provide further understanding for improving the grain yield and the processing quality.Eight leading cultivars during wheat varieties replacement of Shandong Province since1950were screened and studied. Paramerters relatve to nitrogen metabolism were tested including grain yield, grain protein content, free amino acid and soluble protein content in flag leaves, leaf chlorophyll content in leaves from flag leaf emergence to mature stage, the enzyme activities involving in nitrogen metabolism and the relative expression of their encoding genes.The results showed that wheat grain yield, free amino acids content, chlorophyll content in flag leaf and light utilization efficiency increased obviously with time, especially for the late cultivars such as Jinan17and Jimai22with significant high level in thest parameters. The results above indicated that the group structure and nitrogen transportation efficiency of wheat varieties released in Shandong Province has been improved and leaf senescence slowed down with genetic impeovement. However, it has no obvious improvement in grain protein content, which may be due to dilution of significant increased grain yield.The activities of NR, GS and GOGAT and relative expression level of the coding genes significantly increased with cultivar evolution, while NiR activity and its gene expression level had no obvious changes. This maybe indicates that NR, GS and GOGAT play important roles in the protein synthesis process.Correlation analysis showed that NR, GS and GOGAT activities were significantly positively correlated with soluble protein content in flag leaf and grain protein, while the NiR activity and grain content were not related significantly. It may be deduced that NiR did not regulate the grain protein directly. In addition, no significant relationship between the four key enzymes activities and free amino acid content in flag leaf was found in this study.There were obvious differences in gene expression levels of key enzymes in nitrogen metabolism during different periods from flag emergenc to flowering and grain filling stages. Correlation analysis showed there were significant positive correlations between the activities of NR, NiR, GS and GOGAT, indicating that the enzymes involing in nitrogen metabolim may interacted each other. The relative expression level of GS2encoding GS was significantly positive correlated with the amino acid contetn, soluble protein content and grain protein content in mature stage, while GS1and NiR were not relevant.Therefore, the activities of revelant enzymes closely correlated with protein content or nitrogen metabolism efficiency and protein accumulation can be improved by traditional breeding or genetically modification during breeding program in the future.