The Study On GS Isozymes Expression And Relationship Between N-efficiency And GS Isozymes With Different Wheat Cultivars

In this study,combined with pot experiment and field experiment,eight wheat genotypes were used,they were efficient type under high nitrogen(HH): ZM27 and ZM366;inefficient type under high nitrogen(HL): ZM28 and KM20;efficient type under low nitrogen(LH): LM18 and YM49;inefficient type under low nitrogen(LL): XN509 and AK58.As the research object of these eight genotypes,their components of yield,nitrogen efficiency,nitrogen accumulation and distribution and grain-filling characteristics were compared under three nitrogen level(N0:0 kg/ha,N120:120 kg/ha,N225 : 225 kg/ha).Meanwhile,from the perspective of the source-sink-flow organs(functional leaf,peduncle,outer gulme and kernel),the nitrogen metabolism characteristics of different N efficiency wheat genotypes types were studied,including the content of nitrogen metabolites and the activity of the relevant N metabolic enzymes.At the same time,the gene expression and protein subunit expression of GS isoenzyme were determined.The specific relationship between GS1,GS2 and GS2 m isozymes and N efficiency was studied by using methods of correlation analysis,regression analysis and gray relational analysis.In order to clarify the GS isozymes expression characteristics of different N efficiency wheat genotypes and the temporal and spatial distribution of GS isozymes regulate the N efficiency.And provide reference and theoretical basis for the wheat quality and efficient cultivation and the N efficient wheat varieties breeding.The main findings are as follows:(1)The yield of N efficient cultivars(HH and LH)was higher than that of N inefficient(HL and LL)under the same N level.LM18(LH)and ZM366(HH)had the highest NAE,YM49-198 had the highest NUE.(2)There was a significant positive correlation between NUE and N accumulation and distribution,and N accumulation and distribution of N efficient cultivars was higher than that N inefficient cultivars;(3)The peak of GS activity appeared at 7 days after anthesis in functional leaf,which increased with the amount of nitrogen applied.GS enzyme activity in the organs showed: functional leaf>kernel>peduncle>outer glume.The GS activity of N efficient genotypes were generally higher than that of N inefficient genotypes under the same N level;(4)The content of nitrogen metabolites were significantly different,before anthesis,the nitrogen metabolites content was highest in the functional,but after anthesis,he nitrogen metabolites content was highest in the kernel,N showed a significant transport trend;(5)GS1 isoenzyme activity was generally found in different organs,and was induced by organ senescence;GS2 isoenzyme was only present in green organs,and the activity of GS2 was decreased with the organ senescence;GS2m isozyme activity exists only in the specific developmental stages of green organs.The total GS activity increased with the increasing N application.The ratio of GS2/GS1 was higher in N efficient cultivar than that of N inefficient cultivar,showed a higher assimilation ability before anthesis,GS2 / GS1 after anthesis was lower in N efficient cultivar than that of nitrogen inefficient varieties,showing better transportion ability;(6)There are two GS protein subunits,GS1 and GS2 in wheat,with a molecular weight of 39 KD and 42 KD,respectively.Their expression was similar to GS isozymes activities.The GS2 subunit was more abundant in the functional leaf and outer glume,and the GS1 subunit was dominant in the peduncle,but only the GS1 subunit exists in the kernel.The ratio of GS2/GS1 protein subunits was higher in N efficient cultivar than that of N inefficient cultivar,showed a higher assimilation ability before anthesis,GS2 / GS1 after anthesis was lower in N efficient cultivar than that of nitrogen inefficient varieties;(7)The relative expression of Ta GS1 gene was negatively correlated with the amount of N application,and the expression peak of Ta GS1 gene was after anthesis;the relative expression of Ta GS2 gene was positively correlated with the amount of N application,and the expression peak of Ta GS2 gene was at jointing stage;the expression level of Ta GS1 and Ta GS2 gene in different organs was as follows: outer glume>peduncle>functional leaf?kernel,functional leaf>outer glume>peduncle>kernel,respectively;(8)GS isoenzymes are mainly involved in root uptake,chloroplast assimilation,phloem transportion and grain storage.The temporal and spatial distribution of GS isoenzyme may be involved in the regulation of N metabolites in the source and sink organs of wheat;GS2 / GS1 may be one of the main reasons for GS isoenzyme to regulate N efficiency,which triggered the mobilization of N metabolites;(9)The correlation between GS isoenzyme and nitrogen efficiency in different organs was as follows: functional leaf>peduncle>outer glume>kernel,functional leaf can be used as the major organ to study the relationship between GS isozymes and N efficiency;GS1 isozyme activity was significantly positive correlation with nitrogen use efficiency(NUE)and nitrogen absorb efficiency(NAE),negative correlation with nitrogen physiological use efficiency(NPE)and nitrogen transportion efficiency(NTE)in the functional leaf,and there were not found other GS isozyme to be significantly correlation with N efficiency;There was a significant positive correlation between GS2 isozyme and nitrogen metabolites,and there was a significant positive correlation between GS isozyme indicators;At 14-21 days after flowering,found the most significants between the N efficiency and the GS isozymes.So it is suitable to study the correlation between GS isozymes and N efficiency during this time;(10)The regression equation between GS isozymes,N metabolites and N efficiency in different organs had a high determination coefficient(R2);The determination coefficient of NAE regression equation were the highest in functional leaf;The determination coefficients of yield to NAE,NPE and NTE regression equation reached the extremely significant level;The order of the average coefficient of N efficiency in different growth stages was: WS>MS>JS>7DAF>14DAF>21DAF>FS;(11)GS1 isozyme had the highest correlation coefficient with NUE and NAE,and GS2 isozyme had a higher correlation coefficient with NAE in the leaves;GS1 isozyme had the highest correlation coefficient with NAE in the peduncle;The amount of nitrogen applied,total nitrogen content,dry matter accumulation also had a higher correlation coefficient with N efficiency.Conclusion: GS isozymes had a potential relationship with N efficiency,it affects the N efficiency by influencing the the source and sink pool strength,and had a positive effect on improving the N efficiency of wheat.But it does not constitute the determinants of enhancing N efficiency,which need to be achieved by the interaction and regulation of more complex genes and external environmental conditions.