| Broussonetia papyrifera is widely grown as an excellent high-protein woody fodder.Nitrogen is an essential nutrient for the growth and development of B.papyrifera,and changes in its concentration not only affect growth and development,but also have a significant impact on the nutritional quality of B.papyrifera.At present,the physiological and molecular levels of how G.lucidum responds to changes in nitrogen availability have not been adequately studied,which limits our ability to accurately understand the mechanisms by which nitrogen changes affect G.lucidum growth and development.Therefore,in this paper,we investigated the physiological,biochemical,and proteomic responses of G.sylvestris under nitrogen excess(high nitrogen)and nitrogen deficiency(low nitrogen)conditions by using hybrid G.sylvestris as the study material and setting three nitrogen levels: high(30 m M),medium(7.5 m M normal nitrogen level),and low(1.87 m M).The main findings were as follows:(1)At the physiological level,nitrogen deficiency resulted in increased malondialdehyde(MDA)and proline(Pro)contents,decreased chlorophyll(Chl),soluble sugars(SS)and soluble protein(SP)contents,increased catalase(CAT),peroxidase(POD)and superoxide dismutase(SOD)activities,increased abscisic acid(ABA),growth hormone(IAA),cytokinin(CTK),gibberellin(GA),nitrate reductase(RN),glutamine synthetase(GS),glutamate dehydrogenase(GDH),and glutamate synthase(GOGAT)enzymes;nitrogen excess led to increased malondialdehyde and proline content,increased chlorophyll,soluble sugars,and soluble protein content,increased catalase,peroxidase,and superoxide dismutase activities The levels of abscisic acid,growth hormone,cytokinin,and gibberellin were increased,and the activities of nitrate reductase,glutamine synthetase,glutamate dehydrogenase,and glutamate synthase were increased.(2)At the proteomic level,nitrogen deficiency led to ubiquitination modification of most of the proteins and nitrogen excess led to ubiquitination modification of a small number of proteins.A total of 1376 proteins and 2890 loci were identified among the ubiquitinated modified proteins with a 1.5-fold difference.22%,and the loci accounted for 83% and 17% of the total ubiquitinated loci at low and high nitrogen levels,respectively.In summary,our results indicate that.(1)At the physiological level,nitrogen deficiency inhibits photosynthesis and reduces the synthesis of soluble sugars and soluble proteins,while nitrogen excess promotes photosynthesis and thus the synthesis and accumulation of soluble sugars and soluble proteins.However,in both nitrogen deficiency and nitrogen excess,cell membranes are injured,prompting the body to synthesize more proline to maintain the intracellular osmotic potential and thus absorb more nitrogen or use nitrogen to synthesize as much nitrogenous compounds as possible.The hormonal changes together regulate the growth and development of the tree by enhancing the activity of enzymes related to nitrogen metabolism to convert inorganic nitrogen to organic nitrogen and thus regulate the growth of the tree.(2)At the level of ubiquitination-modified proteomics: ubiquitination-modified proteins play an important role in response to both low and high nitrogen levels,but the response is stronger at low nitrogen levels.Among the amino acid motifs surrounding the ubiquitination modified sites,14 sequence features were identified: EKub,E**AKub,Kub E,AKub,E***Kub,Kub**E,Kub**D,GKub,Kub***A,Kub***E,A*****Kub,Kub**A,E**Kub,Kub G.Also found to be stress stress-related,amino acid metabolism-related,photosynthesis-and carbohydrate-related,hormone-related,energy-related,and ubiquitination-related proteins were 8,1,17,17,5,and 8,respectively,and 6 proteins related to nitrogen metabolism.These ubiquitinationmodified proteins have modification sites ranging from 1 to 11 on them. |
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