Search

Under the current rice cropping system, excessive nitrogen application has become a major issue that needs to be changed, and nitrogen reduction has become a hot research topic in recent years. The use of optimum planting density is becoming a common agronomic management system in addition to nitrogen reduction, especially under double cropping rice systems. In this paper, changes in rice yield, nitrogen-use efficiency (NUE) and net N mineralization under dense planting with a reduced nitrogen rate (DPRN) were studied. By comparing DPRN with high-nitrogen sparse planting (SPHN), we found that the population tiller number (tiller number per unit area) increased by 9–27% under DPRN cultivation. Nitrogen accumulation under DPRN treatment of double-cropped rice was basically stable. NUE under DPRN was significantly higher by 1.3–22.7% compared to SPHN. The partial factor productivity of applied N (PFPN) was significantly higher than that of SPHN, with an increase of 4.3–22.8%. The net N mineralized of double-cropped rice under DPRN increased at different stages, and the increase in late-season rice (LSR) was greater than that of early-season rice (ESR). The highest net N mineralized in double cropping rice at different stages was found in the dense planting treatment (DP) and N2 (120 kg N h−1). In conclusion, DPRN cultivation of double-cropped rice could be accepted as a proper management strategy for reducing nitrogen input, improving NUE and promoting soil nitrogen mineralization under given conditions.

Nitrogen fertilization and planting density are two key factors that influence the yield of rice. Reducing nitrogen fertilizer input and increasing planting density will help to improve nitrogen use efficiency and stabilize yield. Field and 15N tracer method in plot experiments were conducted to study the trends of yield, nitrogen use efficiency (NUE) and nitrogen transfer of hybrid rice and conventional rice under dense planting with a reduced nitrogen rate (DPRN) and sparse planting with a high nitrogen rate (SPHN). Among the nitrogen in rice plants, the proportion of nitrogen from fertilizer under the DPRN was reduced by 1.8–13%. The late-season rice (LSR) had a higher rate of decrease compared with the early-season rice (ESR). The uptake efficiency of nitrogen fertilizer was significantly higher under the DPRN than that under the SPHN, with an increase of 7.7–21.9%. The accumulated nitrogen and translocated ratio under the DPRN before the heading stage were 6.1–10.8% and 2.0–9.6% higher than those under the SPHN, respectively. The yield did not change under different treatments. Those findings suggest that the DPRN could guarantee a stabilized yield while increasing the NUE and the amount of translocated nitrogen in the double-cropped rice system.

Purpose Waterlogging stress has a negative influence on agricultural production, particularly for rapeseed yield in a rice-rape rotation field. Calcium peroxide reacts with water to release oxygen, which can serve as an excellent supply. Methods In this field experiment, the conventional rape (Brassica napus L.) variety fengyou958 (FY958) and the early maturing rape variety xiangyou420 (XY420) were used to evaluate the effects of calcium peroxide on waterlogging resistance in a rice-rape rotation field. Waterlogging was imposed from the seedling to flowering stages, and three concentrations of calcium peroxide (0, C1 for the 0.594 kg plot− 1 and C2 for the 0.864 kg plot− 1) were added as basal fertilizer. Results Waterlogging decreased the yield of XY420 and FY958 rapeseed by 74.8% and 87.4%, respectively, while the leaf SPAD values decreased significantly by 17.2% and 21.5%. Treatment with calcium peroxide resulted in an increase of 151%-293% in the yield of rapeseed compared with the waterlogged plants. Moreover, calcium peroxide alleviated the peroxidation of leaves and decreased the activities of catalase and superoxide dismutase by 14.2%-44.4% and 10.9%-19.5%. Compared with the waterlogged plants, the contents of abscisic acid and ethylene in the C2 leaves decreased by 37.3% and 33.4%, while the content of gibberellin increased significantly by 44.9%. The belowground parts of the plants were also significantly affected. The treatments with calcium peroxide reduced the activities of fermentation enzymes in the roots, which significantly reduced the accumulation of fermentation products by 25.0%-57.1% and 16.5%-29.4% for lactate and ethanol, respectively. This reduction was owing to the improved levels of oxygen in the root environment that were released by calcium peroxide. Conclusions The application of a suitable concentration of calcium peroxide enhanced the resistance of rapeseed to waterlogging stress, and this study provides a valid method to prevent damage from flooding in rice-rape rotation fields.

Rapeseed (Brassica napus L.) is a nutritious vegetable, while cadmium (Cd) pollution threatens the growth, productivity, and food security of rapeseed. By studying the effects of iminodisuccinic acid (IDS), an easily biodegradable and environmental friendly chelating agent, on Cd distribution at the organ and cellular level, we found IDS promoted dry matter accumulation of rapeseed and increased the contents of photosynthetic pigment in leaves. Inhibited root-shoot Cd transport resulted in higher activity of antioxidant enzymes and decreased hydrogen peroxide (H2O2) and malondialdehyde (MDA) accumulation in leaves, which indicated that IDS contributed to alleviating Cd-caused oxidative damage in leaf cells. Additionally, IDS increased Cd subcellular distribution in cell wall (CW), especially in covalently bound pectin (CSP), and relieved Cd toxicity in organelle of leaves. IDS also enhanced demethylation of CSP. The Cd content in CSP, demethylation degree, and pectin methylesterase activity of CSP increased by 37.95%, 13.34%, and 13.16%, respectively, while IDS did not change the contents of different CW components. The improved Cd fixation in leaf CW was mainly attributed to enhance demethylation of covalently bound pectin (CSP) and Cd chelation with CSP.

We examined differences in soil metabolites from the rice root rhizosphere of long-term rice-rice-fallow (RRF) and rice-rice-rape (RRR) rotations, and examined the effects of 1,2-benzenediol on nitrogen-use efficiency (NUE) and rice growth. The metabolite composition of rice rhizospheres was analyzed using the gas chromatography-mass spectrometry (GC-MS). A range of 0.2, 2.0 and 200 μmol L−1 concentrations of external 1,2-benzenediol were applied to examine their effects on rice growth, nitrate reductase (NR) and glutamine synthetase (GS) activities, and physiological nitrogen-use efficiency (PNUE). The metabolite composition of rhizospheres differed significantly between RRR and RRF. Soil total N and 1,2-benzenediol concentrations during the early rice season were significantly lower under RRR than RRF. Rice growth and NUE significantly enhanced at 0.20 μmol 1,2-benzenediol L−1, but inhibited at 2.0 μmol L−1 or higher. Changes in root morphology and uptake associated with 1,2-benzenediol possibly had contributed to a higher NUE of the early season rice under RRR. The NR and GS activities in rice roots were significantly higher with 0.2 μmol L−1 1,2-benzenediol than without 1,2-benzenediol treatment. Crop rotation significantly affected rice rhizosphere metabolites. An optimal soil 1,2-benzenediol concentration under long-term RRR rotation may be associated with an enhanced NUE and root N uptake and assimilation, resulting in an increased rice growth and yield.

A multiomics approach encompassing morphophysiology, ionomic profiling, whole-genome resequencing, transcriptomics, and high-resolution metabolomics reveals that differences in cadmium resistance between two rapeseed cultivars is determined by subcellular reallocation., Oilseed rape (Brassica napus) has great potential for phytoremediation of cadmium (Cd)-polluted soils due to its large plant biomass production and strong metal accumulation. Enhanced plant Cd resistance (PCR) is a crucial prerequisite for phytoremediation through hyper-accumulation of excess Cd. However, the complexity of the allotetraploid genome of rapeseed hinders our understanding of PCR. To explore rapeseed Cd-resistance mechanisms, we examined two genotypes, ‘ZS11’ (Cd-resistant) and ‘W10’ (Cd-sensitive), that exhibit contrasting PCR while having similar tissue Cd concentrations, and characterized their different fingerprints in terms of plant morphophysiology (electron microscopy), ion abundance (inductively coupled plasma mass spectrometry), DNA variation (whole-genome resequencing), transcriptomics (high-throughput mRNA sequencing), and metabolomics (ultra-high performance liquid chromatography-mass spectrometry). Fine isolation of cell components combined with ionomics revealed that more Cd accumulated in the shoot vacuoles and root pectins of the resistant genotype than in the sensitive one. Genome and transcriptome sequencing identified numerous DNA variants and differentially expressed genes involved in pectin modification, ion binding, and compartmentalization. Transcriptomics-assisted gene co-expression networks characterized BnaCn.ABCC3 and BnaA8.PME3 as the central members involved in the determination of rapeseed PCR. High-resolution metabolic profiles revealed greater accumulation of shoot Cd chelates, and stronger biosynthesis and higher demethylation of root pectins in the resistant genotype than in the sensitive one. Our comprehensive examination using a multiomics approach has greatly improved our understanding of the role of subcellular reallocation of Cd in the determination of PCR.

Cadmium (Cd) is a toxic metal element and the mechanism(s) underlying Cd tolerance in plants are still unclear. Increasingly more studies have been conducted on Cd binding to plant cell walls (CW) but most of them have focused on Cd fixation by CW pectin, and few studies have examined Cd binding to cellulose and hemicellulose. Here we found that Cd binding to CW pectin, cellulose, and hemicellulose was significantly higher in Tor-1, a Cd tolerant A. thaliana ecotype, than in Ph2-23, a sensitive ecotype, as were the concentrations of pectin, cellulose, and hemicellulose. Transcriptome analysis revealed that the genes regulating CW pectin, cellulose, and hemicellulose polysaccharide concentrations in Tor-1 differed significantly from those in Ph2-23. The expressions of most genes such as pectin methyl esterase inhibitors (PMEIs), pectin lyases, xyloglucan endotransglucosylase/hydrolase, expansins (EXPAs), and cellulose hydrolase were higher in Ph2-23, while the expressions of cellulose synthase-like glycosyltransferase 3 (CSLG3) and pectin ethyl esterase 4 (PAE4) were higher in Tor-1. The candidate genes identified here seem to regulate CW Cd fixation by polysaccharides. In conclusion, an increase in pectin demethylation activity, the higher concentration of cellulose and hemicellulose, regulated by related genes, in Tor-1 than in Ph2-23 are likely involved in enhanced Cd CW retention and reduce Cd toxicity.

Nitrogen (N) is essential for plant growth and crop productivity. Organic N is a major form of remobilized N in plants&rsquo, response to N limitation. It is necessary to understand the regulatory role of N limitation adaption (NLA) in organic N remobilization for this adaptive response. Transcriptional and proteomic analyses were integrated to investigate differential responses of wild-type (WT) and nla mutant plants to N limitation and to identify the core organic N transporters targeted by NLA. Under N limitation, the nla mutant presented an early senescence with faster chlorophyll loss and less anthocyanin accumulation than the WT, and more N was transported out of the aging leaves in the form of amino acids. High-throughput transcriptomic and proteomic analyses revealed that N limitation repressed genes involved in photosynthesis and protein synthesis, and promoted proteolysis, these changes were higher in the nla mutant than in the WT. Both transcriptional and proteomic profiling demonstrated that LHT1, responsible for amino acid remobilization, were only significantly upregulated in the nla mutant under N limitation. These findings indicate that NLA might target LHT1 and regulate organic N remobilization, thereby improving our understanding of the regulatory role of NLA on N remobilization under N limitation.

Rapeseed (Brassica napus L.) is a major oil crop in China, with the world’s largest planted area and total yield. Rapeseed has a high demand for nitrogen (N), and nitrogen deficiency in soil is an important limiting factor for rapeseed production. However, rapeseed responds to N deprivation by regulating its own morphology, structure, and physiology. We carried out the current experiment by utilizing low N (LN: 0.3 mM NO3−) and normal N (CK: 6.0 mM NO3−) treatments using Brassica napus as the experimental material. The study results showed that low N induced root elongation in rapeseed, and the root length of LN treatment was 2.37 times that of HN treatment. The dry matter of roots also significantly increased due to low N treatment. Meanwhile, low N treatment decreased photosynthetic pigment (including chlorophyll a, chlorophyll b, and carotenoids) contents and dry mass accumulation of leaves. A higher root/shoot ratio and N physiological efficiency were observed under low N treatment. The changes in cell wall components (pectin, cellulose, hemicellulose, and lignin), related enzymes, and genes’ transcription levels in roots were determined and the results suggested that low N promoted the demethylation of ion-bound pectin (ISP) and covalently bound pectin (CSP), the content of CSP and cellulose. The promoted pectin methylesterase (PME) activity, inhibited pectin and cellulose degradation enzymes, and up/downregulation of related genes also confirming the results of cell wall components. The low N-increased demethylation degree of pectin and content of pectin and cellulose in cell walls was conducive to cell wall loosening and cell wall synthesis during cell division and elongation, ultimately promoting root-adaptive elongation. The study revealed a possible mechanism in which the alteration of cell wall component content and structure participates in cell elongation and expansion, which directly induces root elongation under N deficiency. The successful implementation of this research may be conducive to facilitating the development of rapeseed cultivars with high N use efficiency through root-based genetic improvements and improving plant adaptability to low N.

Background Nitrogen (N) is a macronutrient that is essential for optimal plant growth and seed yield. Allotetraploid rapeseed (AnAnCnCn, 2n = 4x = 38) has a higher requirement for N fertilizers whereas exhibiting a lower N use efficiency (NUE) than cereal crops. N limitation adaptation (NLA) is pivotal for enhancing crop NUE and reducing N fertilizer use in yield production. Therefore, revealing the genetic and molecular mechanisms underlying NLA is urgent for the genetic improvement of NUE in rapeseed and other crop species with complex genomes. Results In this study, we integrated physiologic, genomic and transcriptomic analyses to comprehensively characterize the adaptive strategies of oilseed rape to N limitation stresses. Under N limitations, we detected accumulated anthocyanin, reduced nitrate (NO3−) and total N concentrations, and enhanced glutamine synthetase activity in the N-starved rapeseed plants. High-throughput transcriptomics revealed that the pathways associated with N metabolism and carbon fixation were highly over-represented. The expression of the genes that were involved in efficient N uptake, translocation, remobilization and assimilation was significantly altered. Genome-wide identification and molecular characterization of the microR827-NLA1-NRT1.7 regulatory circuit indicated the crucial role of the ubiquitin-mediated post-translational pathway in the regulation of rapeseed NLA. Transcriptional analysis of the module genes revealed their significant functional divergence in response to N limitations between allotetraploid rapeseed and the model Arabidopsis. Association analysis in a rapeseed panel comprising 102 genotypes revealed that BnaC5.NLA1 expression was closely correlated with the rapeseed low-N tolerance. Conclusions We identified the physiologic and genome-wide transcriptional responses of oilseed rape to N limitation stresses, and characterized the global members of the BnamiR827-BnaNLA1s-BnaNRT1.7s regulatory circuit. The transcriptomics-assisted gene co-expression network analysis accelerates the rapid identification of central members within large gene families of plant species with complex genomes. These findings would enhance our comprehensive understanding of the physiologic responses, genomic adaptation and transcriptomic alterations of oilseed rape to N limitations and provide central gene resources for the genetic improvement of crop NLA and NUE. Electronic supplementary material The online version of this article (10.1186/s12870-018-1507-y) contains supplementary material, which is available to authorized users.

A high concentration of ammonium (NH4+) as the sole source of nitrogen in the growth medium often is toxic to plants. The nitrate transporter NRT1.1 is involved in mediating the effects of NH4+ toxicity; however, the mechanism remains undefined. In this study, wild-type Arabidopsis (Arabidopsis thaliana Columbia-0 [Col-0]) and NRT1.1 mutants (chl1-1 and chl1-5) were grown hydroponically in NH4NO3 and (NH4)2SO4 media to assess the function of NRT1.1 in NH4+ stress responses. All the plants grew normally in medium containing mixed nitrogen sources, but Col-0 displayed more chlorosis and lower biomass and photosynthesis than the NRT1.1 mutants in (NH4)2SO4 medium. Grafting experiments between Col-0 and chl1-5 further confirmed that NH4+ toxicity is influenced by NRT1.1. In (NH4)2SO4 medium, NRT1.1 induced the expression of NH4+ transporters, increasing NH4+ uptake. Additionally, the activities of glutamine synthetase and glutamate synthetase in roots of Col-0 plants decreased and soluble sugar accumulated significantly, whereas pyruvate kinase-mediated glycolysis was not affected, all of which contributed to NH4+ accumulation. By contrast, the NRT1.1 mutants showed reduced NH4+ accumulation and enhanced NH4+ assimilation through glutamine synthetase, glutamate synthetase, and glutamate dehydrogenase. Moreover, the up-regulation of genes involved in ethylene synthesis and senescence in Col-0 plants treated with (NH4)2SO4 suggests that ethylene is involved in NH4+ toxicity responses. This study showed that NH4+ toxicity is related to a nitrate-independent signaling function of NRT1.1 in Arabidopsis, characterized by enhanced NH4+ accumulation and altered NH4+ metabolism, which stimulates ethylene synthesis, leading to plant senescence.

Soil in short-term crop rotation systems (STCR) is still in the initial development stage of farmland soil, whereas after long-term crop rotation treatment (LTCR), soil properties are significantly different. This study compares STCR (4 years) and LTCR (30 years) rice-rice-fallow, rice-rice-rape rotation practices under the same soil type background and management system. To reveal ecosystem mechanisms within soils and their effects on rice yield following LTCR, we analyzed the physical, chemical, and microbiological properties of soils with different rotations and rotation times. Relative to STCR, LTCR significantly reduced soil water-stable aggregate (WSA) content in the 2 mm WSA content significantly increased. Soil organic matter increased in fields under LTCR, mainly in > 2 mm, 2–0.25 mm, and

Nitrogen (N) is a non-mineral macronutrient essential for plant growth and development. Oilseed rape (AnAnCnCn, 2n = 4x = 38) has a high requirement for N nutrients whereas showing the lowest N use efficiency (NUE) among crops. The mechanisms underlying NUE regulation in Brassica napus remain unclear because of genome complexity. In this study, we performed high-depth and -coverage whole-genome re-sequencing (WGS) of an N-efficient (higher NUE) genotype “XY15” and an N-inefficient (lower NUE) genotype “814” of rapeseed. More than 687 million 150-bp paired-end reads were generated, which provided about 93% coverage and 50× depth of the rapeseed genome. Applying stringent parameters, we identified a total of 1,449,157 single-nucleotide polymorphisms (SNPs), 335,228 InDels, 175,602 structure variations (SVs) and 86,280 copy number variations (CNVs) between the N-efficient and -inefficient genotypes. The largest proportion of various DNA polymorphisms occurred in the inter-genic regions. Unlike CNVs, the SNP/InDel and SV polymorphisms showed variation bias of the An and Cn subgenomes, respectively. Gene ontology analysis showed the genetic variants were mapped onto the genes involving N compound transport and ATPase complex metabolism, but not including N assimilation-related genes. On basis of identification of N-starvation responsive genes through high-throughput expression profiling, we also mapped these variants onto some key NUE-regulating genes, and validated their significantly differential expression between the N-efficient and -inefficient genotypes through qRT-PCR assays. Our data provide genome-wide high resolution DNA variants underlying NUE divergence in allotetraploid rapeseed genotypes, which would expedite the effective identification and functional validation of key NUE-regulating genes through genomics-assisted improvement of crop nutrient efficiency.

The two-component high-affinity nitrate (NO3-) transport system (THATS) proteins (NRT2/NAR2) play key roles in the efficient nitrogen (N) uptake and transport under N limitations. We aimed at uncovering the core THATS gene(s) regulating N use efficiency (NUE) in allotetraploid rapeseed (Brassica napus L.). Genomic information, high-throughput transcriptome sequencing and gene co-expression network were integrated to identify and characterize the core THATS genes. We identified 17 BnaNRT2 and eight BnaNAR2.1 homologs spanning across the rapeseed genome. Copy number and gene presence/absence variations of BnaNRT2s/BnaNAR2.1 s, undergoing strong purifying selection, occurred. The over-representation of Dof, MYB and WRKY cis-regulatory elements and the enrichment of CpG islands, and protein phosphorylation sites indicated the importance of transcriptional and epigenetic regulation in the BnaNRT2 activities, respectively. qRT-PCR assays and high-throughput RNA-seq revealed that both BnaNRT2s and BnaNAR2.1 s were expressed preferentially in the roots; and they showed significantly differential expression under different N forms or different levels of NO3- supply. A gene co-expression network identified BnaC8.NRT2.1a and BnaC2.NAR2.1 as the core THATS genes. The core THATS members can serve as elite gene resources for crop NUE improvement. The transcriptomics-assisted gene co-expression network analysis provides novel insights regarding the rapid identification of central members within large gene families of plant species with complex genomes.

The effect of exogenous abscisic acid (ABA) on the nitrogen use efficiency (NUE) of Brassica napus was studied by pot experiments using ABA (1 mg L−1) daubed on the leaves at the early siliquing stage. The results showed that activities of proteases and glutamine synthetase (GS) were significantly promoted by the ABA treatment, which increased the capacity of degradation of foliar proteins and biosynthesis of glutamine (N-transport compounds), both of which promote decreased N in leaves of the ABA treatment. L-glutamine, other free amino acids, and soluble sugar content in the phloem sap of the ABA treatment were significantly higher than those of the control. A 15N label trial showed that more 15N was distributed from leaves to the grain by the ABA treatment, which resulted in a significantly higher NUE in the ABA treatment relative to the control.

Plant vacuoles are unique compartments that play a critical role in plant growth and development. The vacuolar H+-ATPase (V-ATPase), together with the vacuolar H+-pyrophosphatase (V-PPase), generates the proton motive force that regulates multiple cell functions and impacts all aspects of plant life. We investigated the effect of V-ATPase activity in the vacuole on plant growth and development. We used an Arabidopsisthaliana (L.) Heynh. double mutant, vha-a2 vha-a3, which lacks two tonoplast-localized isoforms of the membrane-integral V-ATPase subunit VHA-a. The mutant is viable but exhibits impaired growth and leaf chlorosis. Nitrate assimilation led to excessive ammonium accumulation in the shoot and lower nitrogen uptake, which exacerbated growth retardation of vha-a2 vha-a3. Ion homeostasis was disturbed in plants with missing VHA-a2 and VHA-a3 genes, which might be related to limited growth. The reduced growth and excessive ammonium accumulation of the double mutant was alleviated by potassium supplementation. Our results demonstrate that plants lacking the two tonoplast-localized subunits of V-ATPase can be viable, although with defective growth caused by multiple factors, which can be alleviated by adding potassium. This study provided a new insight into the relationship between V-ATPase, growth, and ammonium accumulation, and revealed the role of potassium in mitigating ammonium toxicity.

The nitrate transporter NRT1.1 is involved in plant NH4+ toxicity; however, its mechanism remains undefined. In this study, wild-type Arabidopsis (Col-0) and NRT1.1 mutants (chl1-1 and chl1-5) were grown hydroponically in NH4NO3 and (NH4)2SO4 media to evaluate NRT1.1 function in NH4+ stress responses. All plants grew normally in mixed N sources, but Col-0 displayed more chlorosis, and lower biomass and photosynthesis than the NRT1.1 mutants in the (NH4)2SO4 condition. Grafting experiments between Col-0 and chl1-5 further confirmed that NH4+ toxicity is NRT1.1-dependent. In (NH4)2SO4 medium, NRT1.1 facilitated the higher expression of NH4+ transporters, increasing NH4+ uptake. Additionally, glutamine synthetase (GS) and glutamate synthetase (GOGAT) in roots of Col-0 plants decreased and soluble sugar accumulated significantly, whereas pyruvate kinase (PK)-mediated glycolysis was not affected, all of which contributed to NH4+ accumulation. In contrast, the NRT1.1 mutants reduced NH4+ accumulation and enhanced NH4+ assimilation through glutamate dehydrogenase (GDH) and glutamate-oxaloacetate transamination (GOT) activity. In addition, the upregulation of genes involved in senescence in Col-0 plants treated with (NH4)2SO4 suggests that ethylene could be involved in NH4+ toxicity responses. Our results indicate that NH4+ toxicity is dependent on NRT1.1 in Arabidopsis, characterized by enhanced NH4+ accumulation and by perturbed NH4+ metabolism, which stimulated ethylene-induced plant senescence.

Oilseed rape (Brassica napus L.) is a crucial source of edible oil and livestock feeding, and is a promising biofuel crop. The increasing demand for oilseed rape requires strategies to increase yield while retaining quality. Field experiments were performed in southern China to evaluate the impacts of fertiliser level and planting density on dry matter accumulation, seed oil and protein content (%) and yield (per ha), oil quality, and the profitability of oilseed rape. Fertiliser treatments contained nitrogen (N), phosphorus (P), potassium (K), sulfur (S) and boron (B) at four increasing rates, compared with nil fertiliser, and there were six planting densities (range 7.5–45 × 104 plants ha–1). Dry matter accumulation significantly (P < 0.05) increased in response to increasing plant population and fertiliser level, whereas harvest index decreased, suggesting that increasing the production of oilseed rape is limited to improvement of population quality. Seed oil and protein contents were significantly affected by fertiliser level rather than planting density. Increasing the fertiliser rate increased seed protein content, simultaneously slightly decreasing oil content. Glucosinolate content of rapeseed slightly decreased with increasing fertiliser but erucic and oleic acid contents were not affected, indicating that increasing the fertiliser rate might not reduce oilseed rape quality. Manipulation of fertiliser level was more effective than altering planting density for increasing seed oil and protein yields. Highest seed oil and protein yields resulted from the highest fertiliser application of 240 kg N, 52.4 kg P, 174.3 kg K, 15 kg S and 1.2 kg B ha–1, under a planting density of 22.5 × 104 plants ha–1. Maximum economic gain occurred with the two highest fertiliser levels, whereas planting density has no significant effect on profitability. A balanced application of NPKSB fertilisers should be employed with direct-sowing cultivation of oilseed rape, aimed at building a suitable population structure that balances plant population density and individual growth.

Nitrate, once taken up by plants, can either be stored in vacuoles or reduced by nitrate reductase in the cytoplasm. High accumulation of NO3 − in the vacuole occurs when assimilation into the cytoplasm is saturated. This study elucidates how proton pumps at the tonoplast (V-ATPase and V-PPase) affect the NO3 − content of Brassica napus by controlling the distribution of NO3 − between the cytoplasm and vacuole. Pot experiments were conducted in a greenhouse under normal N (15.0 mM nitrate) conditions using B. napus genotypes that demonstrated either high (Xiangyou15) or low (814) nitrogen use efficiency (NUE). The NO3 − content of the high NUE genotype was significantly lower than that of the low NUE genotype, whereas the total N per plant of the two genotypes was almost the same, suggesting that the different NUE between the two genotypes is not due to the difference of NO3 − uptake. The relative expression levels of V-ATPase (vha-a3) and V-PPase (avp1) genes in the high NUE genotype were significantly lower than in the low NUE genotype, resulting in lower V-ATPase and V-PPase activities in the high NUE genotype. The transport of NO3 − and protons from the cytoplasm to the vacuole is powered by V-ATPase and V-PPase, so their lower activities increase H+ efflux from and reduce NO3 − influx into the vacuoles of the high NUE genotype. We conclude that the lower activity of proton pumps at the tonoplast is the main reason the high NUE genotype possesses lower NO3 − content and higher N-use efficiency.

The relationship between nitrogen efficiency (NE), defined as seed yield per unit nitrogen (N) application, and seed quality was examined in two oilseed rape (Brassica napus L.) varieties at 5 N application levels, 0.6, 3, 6, 12, 15 mmol L−1, N1, N2, N3, N4 and N5, respectively. Seed yield, oil yield and protein content were increased with the increase in N application level, but NE and oil content were decreased, and the fatty acid composition in seed was hardly changed. Analysis of seven fatty acids revealed aslight decrease in the contents of erucic acid and arachidonic acid with the increase in N application level, but no obvious change in the contents of palmitic acid, stearic acid, oleic acid, linoleic acid and linolenic acid. Compared with the low NE variety H29, the seed yield and contents of erucic acid and arachidonic acid in the high NE variety bin270 were more markedly increased with the increase in N application level, and the oil content was hardly changed. The seed yield, oilcontent and oil yield were higher in the high NE variety than in the low NE variety at all 5 N application levels. There were no significant differences in protein, palmitic acid, stearic acid and oleic acid contents between the varieties at any of the 5 N application levels, but there were slight differences in the linoleic acid and linolenic acid contents between the two varieties. In brief, N application improved oil yield more greatly in the high NE variety than in the low NE variety, but hardly affected the fatty acid composition. Therefore, the seed quality and oil content of oilseed rape may not be decreased by breeding of a high NE variety with a high N absorption efficiency and high N use efficiency.

The study was conducted to investigate the effects of applying different concentrations of the macronutrients K+, Ca2+, and Mg2+ on the responses of contrasting rice (Oryza sativa L.) genotypes under salt stress. A solution culture experiment was conducted in a phytotron at the International Rice Research Institute (IRRI), under controlled temperature and humidity and natural sunlight. When subjected to salt stress of 100 mmol L-1 using NaCl, the salt tolerant genotypes FL478 and IR651, accumulated less Na+ and maintained lower ratios of Na+/K+, Na+/Ca2+, and Na+/Mg2+ than the sensitive genotypes IR29 and Azucena. These tolerant genotypes also had higher concentrations of K+ in their shoots and greater root and shoot biomass and green leaf area. Tolerant genotypes also maintained much lower concentration of Na+ and lower and more favorable ratios of Na+/K+, Na+/Ca2+, and Na+/Mg2+ in their active and developing tissues. Salt tolerance and shoot and root growth of both tolerant and sensitive genotypes were enhanced considerably when higher concentrations of Ca2+ and Mg2+ were applied in culture solution. The concentration of Na+ and the ratios of Na+/K+, Na+/Ca2+, and Na+/Mg2+ in shoots also declined significantly. The beneficial effects of higher calcium were greater than that of magnesium and application of higher concentration of K+ seems to have minor effects. Responses to salinity in rice can therefore be considerably enhanced through proper nutrient management, by increasing the concentrations of nutrient elements that have favorable effects such as Ca2+ and Mg2+. Calcium is particularly more effective than both magnesium and potassium, and can be applied at relatively larger quantities in salt affected soils.

To determine the relationship between nitrogen (N) redistribution of oilseed rape (Brassica napus L.) varieties and N-use efficiency during later growth stages, the differences in N-use efficiency between two varieties (X-36 and X-50) were studied using the 15N labeling method with sand culture under complete nutrient solution conditions. Results showed that X-36 had greater grain yield not because of greater N uptake but because of greater grain yield per unit N in the plant and N-harvesting index. The average proportion of N in the two varieties that was redistributed from the vegetative organs to the grain was 65.1%. The redistribution amount and the proportion of N absorbed at the stem elongation stage and redistributed into the grain of two varieties were the greatest; the least were amounts absorbed at the siliquing stage. The high-N-use-efficiency variety (X-36), when compared with the low-N-use-efficiency variety (X-50), had slower redistribution speed of N before the siliquing stage, which then b...

Differences of nitrogen efficiency of oilseed rape (Brassica napus L.) cultivars and their physiological properties were studied in a pot experiment, and the ratio of seed yield with no nitrogen supplied to that with normal nitrogen supply was adopted as a nitrogen efficiency coefficient. Results showed that the nitrogen efficiency coefficient determined for eight oilseed rape cultivars varied from 0.37 to 0.69, the ratio of nitrogen uptake amounts per plant, nitrogen transfer velocity from stems and leaves to seeds, and nitrogen physiological efficiency of oilseed rape cultivars under nitrogen stressed condition differed from with normal nitrogen supply. The higher the nitrogen efficiency of a cultivar, the higher the ratio of N uptake in no nitrogen to with N supplied. Under low nitrogen-supplying conditions, high nitrogen efficiency cultivars had longer roots, more lateral roots, higher amounts of reuse of nitrate from stem and leaves, and higher nitrate reductase activities in leaves.

Nitrate (NO3−) can accumulate in high concentrations in plant cell vacuoles if it is not reduced, reutilized or transported into the cytoplasm. Such accumulation of NO3− in the vacuole occurs when mechanisms for NO3− assimilation in the cytoplasm are saturated. Moreover, other processes such as efflux across the plasma membrane might affect NO3− accumulation in the vacuole. These are the main reasons limiting nitrogen use efficiency (NUE) in plants. This study elucidates mechanisms for NO3− transport from the cytoplasm to vacuoles by the V-proton pump (V-ATPase and V-PPase) and their relationship with different NUE in four Brassica napus genotypes. Pot experiments were conducted in a greenhouse under normal (15.0 mmol L−1) and limited N (7.5 mmol L−1) concentrations of nitrate using B. napus genotypes that demonstrated either high (742 and Xiangyou 15) or low (814 and H8) NUE (g g−1). Specific inhibitors of V-ATPase and V-PPase increased nitrate reductase (NR) activity, resulting in greatly decreased NO3− in plant tissues. Nitrate reductase activity and NO3− content correlated more highly to V-PPase activity than they did to V-ATPase activity, and correlation between V-PPase activity and NO3− content was significantly higher than it was to V-ATPase. Genotypes with high NUE had significantly lower activities of V-ATPase and V-PPase than those with low NUE. In the high-NUE plants, lower activities of V-proton pump underlie mechanisms that result in significantly lower NO3− content in plant tissues of the high-NUE genotypes than those found in plant tissues of the low-NUE genotypes. Our results show that the tonoplast proton pumps V-PPase and V-ATPase strongly negatively affect NR activity and positively affect NO3− content. V-PPase contributed more to this regulatory mechanism than did V-ATPase.