Studies On Enzyme Activities Of Nitrogen Metabolism And The Content Of Nitrogen-containing Compounds In Roots Of Soybean Varieties Released At Different Age

Although a large number of excellent soybean products have been selected,but the yield level is low.However,with the large use of nitrogen fertilizer,the utilization efficiency of nitrogen fertilizer is low,which not only causes environmental pollution,but also causes huge economic losses.Therefore,it is very important to improve soybean yield and nitrogen use efficiency.In this study,18 soybean varieties released from 1929-2016 in Jilin Province were used as experimental materials and field experiments were carried out.Samples（roots）were extracted during at seedling stage（V₄）,flowering stage（R₂）,seed-filling stage（R₄）,granule stage（R₆）and maturity（R₈）.The key enzyme activities of nitrogen metabolism and the content of nitrogen-containing compounds in roots of soybean varieties in different ages were determined,the change rule of key enzyme activities in root nitrogen metabolism and their relationship with the developed ages of soybean varieties were also analyzed.To explore the change trend of nitrogen metabolism in roots during the evolution of soybean varieties is about to aim to clarify the nitrogen absorption mechanism of soybean roots and provide a physiological basis for improving soybean utilization efficiency and high-yield breeding in the future.The test results were as follows:1.The key enzyme activities of nitrogen metabolism in soybean varieties in different ages were similar at different growth stages.During the whole growth period,NR activity increased first,then decreased and increased again,reaching the maximum at R4 stages.GS activity showed a bi-modal curve,whose peak value appeared at R2 and R6 stages,respectively;GOGAT activity showed a change of gradually increasing and then decreasing in a single-peak curve,reaching a peak at R₄stages.GDH activity gradually decreased after reaching the peak in the R2 stage.The activities of NR,GS and GOGAT in roots of soybean varieties in different ages showed as modern varieties>1960s-2000s>early varieties during the whole growth stages,while the activities of GDH showed as early varieties>1960s-2000s>modern varieties.2.The total nitrogen content of soybean varieties in different ages showed a downward trend,whose content at R₂ stages were higher.The total nitrogen content at V₄-R₆ stages showed as modern varieties>1960s-2000s>early varieties and the total nitrogen content increased with the age.High soluble protein content and total nitrogen also showed the same trend,in which the decline trend at V4-R2 stages were most obvious.Then content of free amino acid showed a single peak curve and reached the maximum at R₂ stages,showing as early varieties>1960s-2000s>modern varieties.The content of free amino acid content decreased with the advancement of ages.During the whole growth stages,the change of nitrate nitrogen content first increased and then decreased,and the content at R₂ and R₄ stages were higher.At R₂-R₆ stages,it showed as,early varieties>1960s-2000s>varieties bred by modern varieties,whose nitrate nitrogen gradually decreased with the advancement of ages and ammonium nitrogen content showed a change trend of first increase-decrease-rise.At R₂-R₆ stages,it showed as a modern variety>1960s-2000s>varieties bred by early varieties,whose ammonium state nitrogen increased with the advancement of ages.3.The relationship between the key enzyme activities of nitrogen metabolism and the developed ages in different soybean varieties.During the whole growth stages,the activities of NR,GS and GOGAT showed linear growth change with the advancement of developed ages.The activities of NR at R2 stages were significantly positively correlated with the developed ages（r=0.724**）and the activity of NR at R₄ stages were significantly positively correlated with that V₄stages（r=0.575*,r=0.504*）.The activities of GS at R2 and R4 stages were significantly positively correlated with the developed ages（r=0.816**,0.741**）,and the activities of GS at V4 stages were significantly positively correlated with the developed ages（r=0.627*）.The activities of GOGAT at R6 stages were significantly positively correlated with the developed ages（r=0.589*）,while the activities of GDH decreased linearly with the advancement of ages and the activities of GDH at R2stages were significantly negatively correlated with the developed times（r=-0.478*）.Nitrogen metabolism enzyme activity has a significant impact on soybean yield There was a significant positive correlation between NR activity and yield at V₄ and R₂ stages（r=0.513*r=0.615*）;The activities of GS at R₂ and R₄ stages were significantly positively correlated with yield（r=0.838**、0.845**）;The activities of GOGAT at R₆ stages were significantly positively correlated with the yield（r=0.513*）Soybean root nitrogen metabolism enzyme activity can significantly reflect the level of yield,but has no significant effect on the content of soybean grain protein.With the succession of soybean varieties,the genetic improvement in roots increased the key enzyme activities of nitrogen metabolism and improved the utilization efficiency of nitrogen by soybeans.