dep1 improves rice grain yield and nitrogen use efficiency simultaneously by enhancing nitrogen and dry matter translocation

The rice cultivars carrying dep1(dense and erect panicle 1)have the potential to achieve both high grain yield and high nitrogen use efficiency(NUE).However,few studies have focused on the agronomic and physiological performance of those cultivars associated with high yield and high NUE under field conditions.Therefore,we evaluated the yield performance and NUE of two near-isogenic lines(NILs)carrying DEP1(NIL-DEP1)and dep1-1(NIL-dep1)genes under the Nanjing 6 background at 0 and 120 kg N ha^(–1).Grain yield and NUE for grain production(NUEg)were 25.5 and 21.9%higher in NIL-dep1 compared to NIL-DEP1 averaged across N treatments and planting years,respectively.The yield advantage of NIL-dep1 over NIL-DEP1 was mainly due to larger sink size(i.e.,higher total spikelet number),grainfilling percentage,total dry matter production,and harvest index.N utilization rather than N uptake contributed to the high yield of NIL-dep1.Significantly higher NUEg in NIL-dep1 was associated with higher N and dry matter translocation efficiency,lower leaf and stem N concentration at maturity,and higher glutamine synthetase(GS)activity in leaves.In conclusion,dep1 improved grain yield and NUE by increasing N and dry matter transport due to higher leaf GS activity under field conditions during the grain-filling period.

Deciphering the morpho–physiological traits for high yield potential in nitrogen efficient varieties(NEVs):A japonica rice case study

The use of nitrogen(N)-efficient rice(Oryza sativa L.) varieties could reduce excessive N input without sacrificing yields. However, the plant traits associated with N-efficient rice varieties have not been fully defined or comprehensively explored. Here, three japonica N-efficient varieties(NEVs) and three japonica N-inefficient varieties(NIVs) of rice were grown in a paddy field under N omission(0 N, 0 kg N ha^(-1)) and normal N(NN, 180 or 200 kg N ha^(-1)) treatments. Results showed that NEVs exhibited higher grain yield and nitrogen use efficiency(NUE) than NIVs under both treatments, due to improved sink size and filled-grains percentage in the former which had higher root oxidation activity and greater root dry weight, root length and root diameter at panicle initiation(PI), as well as higher spikelet-leaf ratio and more productive tillers during the grain-filling stage. Compared with NIVs, NEVs also exhibited enhanced N translocation and dry matter accumulation after heading and improved flag leaf morpho-physiological traits, including greater leaf thickness and specific leaf weight and higher contents of ribulose^(-1),5-bisphosphate carboxylase/oxygenase, chlorophyll, nitrogen, and soluble sugars, leading to better photosynthetic performance. Additionally, NEVs had a better canopy structure, as reflected by a higher ratio of the extinction coefficient for effective leaf N to the light extinction coefficient, leading to enhanced canopy photosynthesis and dry matter accumulation. These improved agronomic and physiological traits were positively and significantly correlated with grain yield and internal NUE, which could be used to select and breed N-efficient rice varieties.

Forms of nitrogen uptake,translocation,and transfer via arbuscular mycorrhizal fungi:A review

Arbuscular mycorrhizal （AM） fungi are obligate symbionts that colonize the roots of more than 80% of land plants. Experi- ments on the relationship between the host plant and AM in soil or in sterile root-organ culture have provided clear evidence that the extraradical mycelia of AM fungi uptake various forms of nitrogen （N） and transport the assimilated N to the roots of the host plant. However, the uptake mechanisms of various forms of N and its translocation and transfer from the fungus to the host are virtually unknown. Therefore, there is a dearth of integrated models describing the movement of N through the AM fungal hyphae. Recent studies examined Ri T-DNA-transformed carrot roots colonized with AM fungi in ~SN tracer experi- ments. In these experiments, the activities of key enzymes were determined, and expressions of genes related to N assimilation and translocation pathways were quantified. This review summarizes and discusses the results of recent research on the forms of N uptake, transport, degradation, and transfer to the roots of the host plant and the underlying mechanisms, as well as re- search on the forms of N and carbon used by germinating spores and their effects on amino acid metabolism. Finally, a path- way model summarizing the entire mechanism of N metabolism in AM fungi is outlined.

A Critical Role of AMT2;1 in Root-To-Shoot Translocation of Ammonium in Arabidopsis

Ammonium uptake in plant roots is mediated by AMT/MEP/Rh-type ammonium transporters. Out of five AMTs being expressed in Arabidopsis roots, four AMT1-type transporters contribute to ammonium uptake, whereas no physiological function has so far been assigned to the only homolog belonging to the MEP subfamily, AMT2;1. Based on the observation that under ammonium supply, the transcript levels of AMT2;1 increased and its promoter activity shifted preferentially to the pericycle, we assessed the contribution of AMT2;1 to xylem loading. When exposed to ^15N-labeled ammonium, amt2;1 mutant lines translocated less tracer to the shoots and contained less ammonium in the xylem sap. Moreover, in an amtl;1 amtl;2 amtl ;3 amt2;1 quadruple mutant （qko）, co-expression of AMT2;1 with either AMT1;2 or AMT1;3 significantly enhanced ^15N translocation to shoots, indicating a cooperative action between AMT2;1 and AMT1 transporters. Under N deficiency, proAMT2;1-GFP lines showed enhanced promoter activity predominantly in cortical root cells, which coincided with elevated ammonium influx conferred by AMT2;1 at millimolar sub- strate concentrations. Our results indicate that in addition to contributing moderately to root uptake in the low-affinity range, AMT2;1 functions mainly in root-to-shoot translocation of ammonium, depending on its Cell-type-specific expression in response to the plant nutritional status and to local ammonium gradients.

The influence of biological soil crusts on ^(15)N translocation in soil and vascular plant in a temperate desert of northwestern China

Aims Desert ecosystems are often characterized by patchy distribution of vascular plants,with biological soil crusts(BSC)covering interplant spaces.However,few studies have comprehensively examined the linkage between BSC and vascular plants through nitrogen(N)or element translocation.the objective of this study was to evaluate the ecological roles of BSC on N translocation from soil to the domi-nant herb Erodium oxyrrhynchum bieb.(geraniaceae)in a temper-ate desert in China.Methods Isotopes(including 15N-glu,15N-NH4Cl and 15N-NaNo3)were used as a tracer to detect translocation of N in two types of desert soil(BSC covered;bare)to the dominant herb E.oxyrrhynchum.three different forms of 15N-enriched N compounds were applied as a point source to small patches of BSC and to bare soil.and we measured isotopes(14N and 15N)and obtained the concentration of labeled-15N in both vascular plants and soils at different distances from substrate application Important Findings Plants of E.oxyrrhynchum growing in BSC-covered plots accumulated moreδ15N than those growing in the bare soil.similarly,soil from b Ccovered plots showed a higher concentration of labeled-N irrespective of form of isotope,than did the bare soil.the concentration of dissolved organic N(15N-glu)in E.oxyrrhynchum was higher than that of dis-solved inorganic N(15N-NH4Cl and 15N-NaNo3).soil covered by BSC also accumulated considerably more dissolved organic N than bare soil,whereas the dominant form of 15N concentrated in bare soil was dissolved inorganic N.Correlation analysis showed that the concentra-tion of labeled-N in plants was positively related to the concentration of labeled-N in soils and the N%recorded in E.oxyrrhynchum.our study supports the hypothesis that BSC facilitates ^(15)N translocation in soils and vascular plants in a temperate desert of northwestern China.