Physiological Characteristics And Metabolomics Reveal The Tolerance Mechanism To Low Nitrogen In Glycine Soja Sieb. Et Zucc. Seedling Leaves

Nitrogen(N)is the main mineral element necessary for plant life activities.Nitrogen deficiency is one of the main limiting factors for high yield of crops.Reducing crop dependence on nitrogen fertilizer and cultivating new varieties of low N(LN)-tolerant crops are effective ways to solve various environmental problems caused by nitrogen deficiency and excessive application of nitrogen fertilizer.Wild soybean is a close wild species of cultivated soybean,and it is a kind of important germplasm resource which has the advantages of high protein content and strong resistance.To explore the regulatory mechanisms involved in the adaption to nitrogen deficiency of wild soybean,common and LN-tolerant wild soybean were selected as test materials,the changes of biomass,ion accumulation and photosynthetic characteristics of two ecotypes of wild soybean seedlings under LN stress were studied,and the metabolome data were analyzed,so as to compare the response of two ecotypes of wild soybean to LN stress from physiological characteristics and metabolic level,and to reveal the LN stress resistance mechanism of wild soybean.The results showed that LN stress had different effects on the growth of two ecotypes of wild soybean,and the inhibition degree of LN-tolerant wild soybean was significantly smaller than that of common wild soybean.Analysis of photosynthetic characteristics and ion content in leaves of two ecotypes of wild soybean seedlings showed that LN-tolerant wild soybean had a stronger ability to maintain photosynthesis and stable ion absorption than common wild soybean under LN stress.Analysis of metabolome data showed that the contents of metabolites involved in glycolysis and TCA cycles,sugar and polyols and fatty acids increased significantly in the leaves of two ecotypes of wild soybean seedlings,and the increase in LN-tolerant wild soybean was significantly higher than that in common wild soybean.These metabolites included glucose,glucose-6-phosphate,pyruvate,raffinose,fructose,maltose,inositol,erythritol,palmitic acid,stearic acid,and linoleic acid.The content of organic acid,secondary metabolites involved in the shikimic acid pathway and amino acid accumulated significantly in the leaves of LN-tolerant wild soybean seedlings,while showing a downward trend in common wild soybean seedlings.These metabolites include muconic acid,threonoic acid,methylmalonic acid,nicotinic acid,maleic acid,gluconic acid,ferulic acid,caffeic acid,shikimic acid,glutamic acid,glutamine,asparagine,proline,arginine,leucine,alanine,and phenylalanine.The results demonstrated LN-tolerant wild soybean could maintain higher chlorophyll content and photosynthetic assimilation ability,as well as better ion absorption to maintain nutritional balance,thus showing a better physiological basis.At the same time,LN-tolerant wild soybean could ensure energy supply by promoting glycolysis and TCA cycle;maintain cell osmotic potential by accumulating more small molecular osmotic regulators of sugar,polyols and fatty acids;promote glutamine synthase/glutamate synthase cycle for nitrogen assimilation and enhance shikimic acid secondary metabolic pathway to resist LN stress.The results of this study can provide theoretical basis for the study of LN tolerance of wild soybean and the breeding of new varieties of LN tolerance soybean,which is of great significance to promote the green sustainable development of agricultural production.At the same time,it provides scientific basis for the development,utilization and evaluation of wild soybean germplasm resources.