| In China,the application amount of nitrogen fertilizer in Brasscia napus L.(B.napus)is large,while the nitrogen fertilizer use efficiency(NUE)was almost lower than 30%.Meanwhile,the NUE was decreased with the nitrogen fertilizer apply increase.Nitrate(NO3~--N)is the main nitrogen source of B.napus,and its absorption,transportation and metabolism have a significant impact on NUE.In this study,nitrogen efficient variety xiangyou15(H),nitrogen inefficient variety 814(L)and the related Arabidopsis thaliana(A.thaliana)genetic materials were selected as the research objects.Based in physiological and biochemical analysis and molecular biology techniques,the mechanism of NO3~--N absorption,transportation and metabolism in B.napus under normal and low nitrogen treatments were studied.The main conclusions are as follows:1,For NO3~--N uptake,the potential absorption capacity of B.napus was significantly improved on low nitrogen condition.Specifically,the total root length,total root surface area,root tip and crossing numbers increased significantly,and root activity and plasma membrane H~+-ATPase activity significantly enhanced on low nitrogen condition.AUX1 functions in indole-3-acetic acid(IAA)translocation,and played a key role in enhancing absorption capacity for root under low nitrogen condition:(1)AUX1 regulated the IAA distribution and promoted root growth and development under low nitrogen condition.(2)AUX1 up-regulated the root’s NRT1.1and NRT2.1’s expression,and enhanced plasma membrane H~+-ATPase activity under low nitrogen condition.2,For NO3~--N distribution,PLANT DEFENSIN 1 gene PDF1.5 enhanced low nitrogen adoption by optimizing the distribution of NO3~--N.Subcellular localization analysis for A.thaliana revealed that PDF1.5 was cytoplasm and cell wall localized.Histochemical analysis revealed that PDF1.5 was mainly expressed in the nodes and carpopodium.The expression of PDF1.5 was significantly increased under low nitrogen condition in B.napus.PDF1.5 mediated the distribution of NO3~--N by regulating the expression of NRT1.5 up-regulated,NRT1.8 down-regulated,and more NO3~--N was transported to the shoot,so as to improve the low nitrogen adaptability and NUE.3,For NO3~--N assimilation,the photosynthetic nitrogen use efficiency(PNUE)was significantly improved under low nitrogen condition.In order to explore the assimilation influences mechanism for low nitrogen adaptability,and the influence of C/N ratio to nitrogen metabolism.We used isotope labeling,transcriptome and metabolomic methods to further study the mechanism under different CO2(normal CO2 concentration,high CO2 concentration)and different NO3~--N conditions(low NO3~--N,normal NO3~--N).Under low NO3~--N condition,elevated CO2 concentration promoted the absorption of C and N,and the content of glutamine and aspartic acid down-regulated,2-Oxoglutarate analogue up-regulated,which enhanced the pathway’s metabolic efficiency of amino acid biosynthesis and tricarboxylic acid(TCA)cycle.Increasing CO2 concentration on low NO3~--N condition enhanced the carbon and nitrogen metabolism efficiency,and showed better growth potential for B.napus.Under normal NO3~--N condition,increasing CO2 concentration inhibited the absorption of C and N,the content of glutamine and aspartic acid up-regulated,2-Oxoglutarate analogue down-regulated,which decreased the pathway’s metabolic efficiency of amino acid biosynthesis and TCA.Increasing CO2 concentration on normal NO3~--N condition caused the leaf to turn yellow and worse growth potential for B.napus.The potential nitrogen metabolism was significantly enhanced under low nitrogen condition.In summary,low nitrogen enhanced NO3~--N potential absorption capacity,allocation efficiency,PNUE,and nitrogen potential metabolism capacity in B.napus.This study explored the low nitrogen adaptive mechanism of B.napus from the perspective of NO3~--N absorption,transportation,distribution and assimilation,which provided scientific basis in NUE improve. |
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