Differences between winter oilseed rape (Brassica napus L.) cultivars in nitrogen starvation-induced leaf senescence are governed by leaf-inherent rather than root-derived signals

Identification of two postharvest ripening regulatory models in kiwifruit: based on plant hormones, physiology, and transcriptome analysis

Kiwifruit (Actinidia spp.), celebrated for its unique flavor and rich nutritional content, is a globally popular fruit. This fruit requires post-harvest ripening before consumption. However, the unpredictable ripening pace significantly impacts consumer acceptance and sales, thereby hindering the commercial growth of kiwifruit. To address this, understanding the key molecular mechanisms and metabolites governing postharvest ripening and senescence could offer valuable insights for developing storage strategies and breeding techniques in yellow-fleshed kiwifruits. We constructed two models that integrated these findings with existing theories. The first model suggests that, unlike the T6P-sucrose regulatory mechanism observed in plant leaves, the separation of harvested kiwifruit from the mother plant leads to an insufficient supply of T6P, which activates the SnRK1 kinase. This, in turn, inhibits the TOR kinase signaling pathway, regulating starch metabolism. The T6P-SnRK1-TOR-starch metabolism pathway plays a regulatory role during postharvest ripening, limiting excessive starch degradation that could accelerate aging and decay in yellow-fleshed kiwifruit. The second model highlights the role of abscisic acid (ABA), cytokinins (CKs), and ethylene in regulating the process, inducing the activation of ERFs and cell wall-degrading enzymes, promoting fruit postharvest softening. These findings indicate that at least two models, the T6P-SnRK1-TOR-starch metabolism model and the ABA-CKs-ethylene-cell wall degradation model, regulate postharvest fruit ripening, offering new insights into the artificial regulation of yellow-fleshed kiwifruit ripening speed.

Preharvest Application of Sodium Nitroprusside Alleviates Yellowing of Chinese Flowering Cabbage via Modulating Chlorophyll Metabolism and Suppressing ROS Accumulation

Chinese flowering cabbage is prone to senescence and yellowing after harvest, leading to a huge postharvest loss. Nitric oxide (NO) is a multifunctional plant growth regulator, but the effect of preharvest application of NO on the storage quality of Chinese flowering cabbage remains unclear. Preharvest application of 50 mg L^-1 sodium nitroprusside (SNP, a NO donor) to the roots obviously reduced leaf yellowing in Chinese flowering cabbage during storage. Proteomic analysis reveals 198 differentially expressed proteins (DEPs) in SNP-treated plants compared to the control. The main DEPs were significantly enriched in chlorophyll metabolisms, phenylpropanoid synthesis, and antioxidant pathways. SNP treatment enhanced chlorophyll biosynthesis and suppressed chlorophyll-degradation-related proteins and genes. It also modulated flavonoid-biosynthesis-related genes, and 21 significantly regulated flavonoids were identified in SNP-treated plants. The enhanced antioxidant capacity in SNP-treated plants was able to decrease chlorophyll catabolism by inhibiting peroxidase-mediated chlorophyll bleaching. Collectively, preharvest SNP treatment modulated chlorophyll metabolism and preserved chlorophyll content in leaves during storage. Moreover, SNP treatment enhanced flavonoid synthesis, suppressed reactive oxygen species accumulation, and delayed the senescence process, thereby maintaining leaf greening in Chinese flowering cabbage. These findings highlight the role of exogenous NO in alleviating yellowing of leafy vegetables.

An integrated nitrogen utilization gene network and transcriptome analysis reveal candidate genes in response to nitrogen deficiency in Brassica napus

Nitrogen (N) is an essential factor for crop yield. Here, we characterized 605 genes from 25 gene families that form the complex gene networks of N utilization pathway in Brassica napus. We found unequal gene distribution between the A_n- and C_n-sub-genomes, and that genes derived from Brassica rapa were more retained. Transcriptome analysis indicated that N utilization pathway gene activity shifted in a spatio-temporal manner in B. napus. A low N (LN) stress RNA-seq of B. napus seedling leaves and roots was generated, which proved that most N utilization related genes were sensitive to LN stress, thereby forming co-expression network modules. Nine candidate genes in N utilization pathway were confirmed to be significantly induced under N deficiency conditions in B. napus roots, indicating their potential roles in LN stress response process. Analyses of 22 representative species confirmed that the N utilization gene networks were widely present in plants ranging from Chlorophyta to angiosperms with a rapid expansion trend. Consistent with B. napus, the genes in this pathway commonly showed a wide and conserved expression profile in response to N stress in other plants. The network, genes, and gene-regulatory modules identified here represent resources that may enhance the N utilization efficiency or the LN tolerance of B. napus.

Distinct metabolite classes in root exudates are indicative for field- or hydroponically-grown cover crops

Introduction

Plants release a large variety of metabolites via their roots to shape physico-chemical soil properties and biological processes in the rhizosphere. While hydroponic growth conditions facilitate accessibility of the root system and recovery of root exudates, the natural soil environment can alter root metabolism and exudate secretion, raising the question to what extent the quantity and composition of root exudates released in hydroponic growth systems reflect those recovered from soil-grown roots.

Methods

Using a root washing method, we sampled root exudates from four field-grown cover crop species with wide taxonomic distance, namely white mustard, lacy phacelia, bristle oat, and Egyptian clover. A set of primary metabolites and secondary metabolites were analysed in a targeted and untargeted LC-MS-based approach, respectively, for comparison with exudates obtained from hydroponically cultured plants.

Results and discussion

We found that hydroponically cultivated plants released a larger amount of total carbon, but that the recovery of total carbon was not indicative for the diversity of metabolites in root exudates. In the field, root exudates from phacelia and clover contained 2.4 to 3.8 times more secondary metabolites, whereas carbon exudation in hydroponics was 5- to 4-fold higher. The composition of the set of metabolites identified using the untargeted approach was much more distinct among all species and growth conditions than that of quantified primary metabolites. Among secondary metabolite classes, the presence of lipids and lipid-like molecules was highly indicative for field samples, while the release of a large amount of phenylpropanoids, organoheterocyclic compounds or benzenoids was characteristic for clover, mustard or oat, respectively, irrespective of the cultivation condition. However, at the compound level the bulk of released metabolites was specific for cultivation conditions in every species, which implies that hydroponically sampled root exudates poorly reflect the metabolic complexity of root exudates recovered from field-grown plants.

Cytokinins and auxins in organs of aquatic carnivorous plants: what do they reflect?

BACKGROUND AND AIMS

Aquatic carnivorous plants have typical rootless linear shoots bearing traps and exhibit steep physiological polarity with rapid apical growth. The aim was to analyse auxin and cytokinin metabolites in traps, leaves/shoots and shoot apices in several species of genera Aldrovanda and Utricularia to elucidate how the hormonal profiles reflect the specific organ functions and polarity.

METHODS

The main auxin and cytokinin metabolites were analysed in miniature samples (>2 mg dry weight) of different organs of Aldrovanda vesiculosa and six Utricularia species using ultraperformance liquid chromatography coupled with triple quadrupole mass spectrometry.

KEY RESULTS

Total contents of biologically active forms (free bases, ribosides) of all four main endogenously occurring cytokinin types were consistently higher in traps than in leaves in four Utricularia species with monomorphic shoots and/or higher than in shoots in two Utricularia species with dimorphic shoots. In Aldrovanda traps, the total content of different cytokinin forms was similar to or lower than that in shoots. In U. australis leaves, feeding on prey increased all cytokinin forms, while no consistent differences occurred in Aldrovanda. In four aquatic Utricularia species with monomorphic shoots, the content of four auxin forms was usually higher in traps than in leaves. Zero IAA content was determined in U. australis leaves from a meso-eutrophic site or when prey-fed.

CONCLUSIONS

Different cytokinin and auxin profiles estimated in traps and leaves/shoots of aquatic carnivorous plants indicate an association with different dominant functions of these organs: nutrient uptake by traps versus photosynthetic function of traps. Interplay of cytokinins and auxins regulates apical dominance in these plants possessing strong polarity.

Molecular basis of nitrogen starvation-induced leaf senescence

Nitrogen (N), a macronutrient, is often a limiting factor in plant growth, development, and productivity. To adapt to N-deficient environments, plants have developed elaborate N starvation responses. Under N-deficient conditions, older leaves exhibit yellowing, owing to the degradation of proteins and chlorophyll pigments in chloroplasts and subsequent N remobilization from older leaves to younger leaves and developing organs to sustain plant growth and productivity. In recent years, numerous studies have been conducted on N starvation-induced leaf senescence as one of the representative plant responses to N deficiency, revealing that leaf senescence induced by N deficiency is highly complex and intricately regulated at different levels, including transcriptional, post-transcriptional, post-translational and metabolic levels, by multiple genes and proteins. This review summarizes the current knowledge of the molecular mechanisms associated with N starvation-induced leaf senescence.

Oilseed Rape Cultivars Show Diversity of Root Morphologies with the Potential for Better Capture of Nitrogen

The worldwide demand for vegetable oils is rising. Oilseed rape (Brassica napus) diversifies cereal dominated crop rotations but requires important nitrogen input. Yet, the root organ is offering an untapped opportunity to improve the nitrogen capture in soil. This study evaluates three culture systems in controlled environment, to observe root morphology and to identify root attributes for superior biomass production and nitrogen use. The phenotypic diversity in a panel of 55 modern winter oilseed rape cultivars was screened in response to two divergent nitrate supplies. Upon in vitro and hydroponic cultures, a large variability for root morphologies was observed. Root biomass and morphological traits positively correlated with shoot biomass or leaf area. The activities of high-affinity nitrate transport systems correlated negatively with the leaf area, while the combined high- and low-affinity systems positively with the total root length. The X-ray computed tomography permitted to visualize the root system in pipes filled with soil. The in vitro root phenotype at germination stage was indicative of lateral root deployment in soil-grown plants. This study highlights great genetic potential in oilseed rape, which could be manipulated to optimize crop root characteristics and nitrogen capture with substantial implications for agricultural production.

Do nitrogen- and sulphur-remobilization-related parameters measured at the onset of the reproductive stage provide early indicators to adjust N and S fertilization in oilseed rape (Brassica napus L.) grown under N- and/or S-limiting supplies?

Specific combinations of physiological and molecular parameters associated with N and S remobilization measured at the onset of flowering were predictive of final crop performances in oilseed rape. Oilseed rape (Brassica napus L.) is a high nitrogen (N) and sulphur (S) demanding crop. Nitrogen- and S-remobilization processes allow N and S requirements to reproductive organs to be satisfied when natural uptake is reduced, thus ensuring high yield and seed quality. The quantification of physiological and molecular indicators of early N and S remobilization could be used as management tools to correct N and S fertilization. However, the major limit of this corrective strategy is to ensure the correlation between final performances-related variables and early measured parameters. In our study, four genotypes of winter oilseed rape (OSR) were grown until seed maturity under four nutritional modalities combining high and/or low N and S supplies. Plant final performances, i.e., seed production, N- and S-harvest indexes, seed N and S use efficiencies, and early parameters related to N- or S-remobilization processes, i.e., photosynthetic leaf area, N and S leaf concentrations, leaf soluble protein and leaf sulphate concentrations, and leaf RuBisCO abundance at flowering, were measured. We demonstrated that contrasting final performances existed according to the N and S supplies. An optimal N:S ratio supply could explain the treatment-specific crop performances, thus justifying N and S concurrent managements. Specific combinations of early measured plant parameters could be used to predict final performances irrespective of the nutritional supply and the genotype. This work demonstrates the potential of physiological and molecular indicators measured at flowering to reflect the functioning of N- and S-compound remobilization and to predict yield and quality penalties. However, because the predictive models are N and S independent, instant N and S leaf analyses are required to further adjust the adequate fertilization. This study is a proof of a concept which opens prospects regarding instant diagnostic tools in the context of N and S mineral fertilization management.

Effect of breeding on nitrogen use efficiency-associated traits in oilseed rape

Oilseed rape is one of the most important dicotyledonous field crops in the world, where it plays a key role in productive cereal crop rotations. However, its production requires high nitrogen fertilization and its nitrogen footprint exceeds that of most other globally important crops. Hence, increased nitrogen use efficiency (NUE) in this crop is of high priority for sustainable agriculture. We report a comprehensive study of macrophysiological characteristics associated with breeding progress, conducted under contrasting nitrogen fertilization levels in a large panel of elite oilseed rape varieties representing breeding progress over the past 20 years. The results indicate that increased plant biomass at flowering, along with increases in primary yield components, have increased NUE in modern varieties. Nitrogen uptake efficiency has improved through breeding, particularly at high nitrogen. Despite low heritability, the number of seeds per silique is associated positively with increased yield in modern varieties. Seed weight remains unaffected by breeding progress; however, recent selection for high seed oil content and for high seed yields appears to have promoted a negative correlation (r= -0.39 at high and r= -0.49 at low nitrogen) between seed weight and seed oil concentration. Overall, our results reveal valuable breeding targets to improve NUE in oilseed rape.

Nitrogen Supply Drives Senescence-Related Seed Storage Protein Expression in Rapeseed Leaves

In general, yield and fruit quality strongly rely on efficient nutrient remobilization during plant development and senescence. Transcriptome changes associated with senescence in spring oilseed rape grown under optimal nitrogen supply or mild nitrogen deficiency revealed differences in senescence and nutrient mobilization in old lower canopy leaves and younger higher canopy leaves [1]. Having a closer look at this transcriptome analyses, we identified the major classes of seed storage proteins (SSP) to be expressed in vegetative tissue, namely leaf and stem tissue. Expression of SSPs was not only dependent on the nitrogen supply but transcripts appeared to correlate with intracellular H₂O₂ contents, which functions as well-known signaling molecule in developmental senescence. The abundance of SSPs in leaf material transiently progressed from the oldest leaves to the youngest. Moreover, stems also exhibited short-term production of SSPs, which hints at an interim storage function. In order to decipher whether hydrogen peroxide also functions as a signaling molecule in nitrogen deficiency-induced senescence, we analyzed hydrogen peroxide contents after complete nitrogen depletion in oilseed rape and Arabidopsis plants. In both cases, hydrogen peroxide contents were lower in nitrogen deficient plants, indicating that at least parts of the developmental senescence program appear to be suppressed under nitrogen deficiency.

The involvement of cytokinin and nitrogen metabolism in delayed flag leaf senescence in a wheat stay-green mutant, tasg1

In the present study on a wheat stay-green mutant, tasg1, we found that its delayed senescence at the late filling stage was related to the high cytokinin (CK) and N contents. RNA sequencing suggested that several genes may be responsible for the different senescence processes between wild-type (WT) and tasg1 plants. WT and tasg1 seedlings were treated with NH₄NO₃, lovastatin, and 6-benzylaminopurine (BAP), and the results suggested that the feedback of CK with N content regulated the leaf senescence in the tasg1 plants. Furthermore, a knock-out of the candidate gene cisZOGT1 (catalytic O-glucosylation in cis-zeatin) in the wheat mutant pool 'Kronos' exhibited delayed senescence at the late grain filling stage. Overall, our results suggested the cisZOGT1 gene has an important role in regulating wheat leaf senescence by regulating CK and N metabolism. At the same time, CK and N metabolism involved in delayed flag leaf senescence of tasg1 may be by a feedback pattern.

Blue light suppression alters cytokinin homeostasis in wheat leaves senescing under shading stress

Blue light (BL) suppression accelerates the senescence rate of wheat (Triticum aestivum L.) leaves exposed to shading. In order to study whether this effect involves the alteration of different cytokinin (CK) metabolites, CK-degradation, as well as the expression profile of genes responsible of CK-perception, -inactivation, -reactivation and/or -turnover, leaf segments of 30 day-old plants were placed in boxes containing bi-distilled water and covered with blue (B) or green (G) light filters, which supplied a similar irradiance but differed in the percentage of BL transmitted (G << B). A neutral (N) filter was used as control. When appropriate, different CK metabolites or an inhibitor of CK-degradation were added in order to alter the endogenous CK levels. A rapid decrement of trans-zeatin (tZ) and cis-zeatin (cZ) content was observed after leaf excision, which progressed at a higher rate in treatment G than in the control and B treatments. Senescence progression correlated with an accumulation of glycosylated forms (particularly cZ-derivatives), and an increment of CK-degradation, both of which were slowed in the presence of BL. On the contrary, CK-reactivation (analyzed through TaGLU1-3 expression) was delayed in the absence of BL. When different CK were exogenously supplied, tZ was the only natural free base capable to emulate the senescence-retarding effect of BL. Even though the signaling components involved in the regulation of senescence rate and CK-homeostasis by BL remain elusive, our data suggest that changes in the expression profile and/or functioning of the transcription factor HY5 might play an important role.

Integration of multi-omics techniques and physiological phenotyping within a holistic phenomics approach to study senescence in model and crop plants

The study of senescence in plants is complicated by diverse levels of temporal and spatial dynamics as well as the impact of external biotic and abiotic factors and crop plant management. Whereas the molecular mechanisms involved in developmentally regulated leaf senescence are very well understood, in particular in the annual model plant species Arabidopsis, senescence of other organs such as the flower, fruit, and root is much less studied as well as senescence in perennials such as trees. This review addresses the need for the integration of multi-omics techniques and physiological phenotyping into holistic phenomics approaches to dissect the complex phenomenon of senescence. That became feasible through major advances in the establishment of various, complementary 'omics' technologies. Such an interdisciplinary approach will also need to consider knowledge from the animal field, in particular in relation to novel regulators such as small, non-coding RNAs, epigenetic control and telomere length. Such a characterization of phenotypes via the acquisition of high-dimensional datasets within a systems biology approach will allow us to systematically characterize the various programmes governing senescence beyond leaf senescence in Arabidopsis and to elucidate the underlying molecular processes. Such a multi-omics approach is expected to also spur the application of results from model plants to agriculture and their verification for sustainable and environmentally friendly improvement of crop plant stress resilience and productivity and contribute to improvements based on postharvest physiology for the food industry and the benefit of its customers.

Divergent N Deficiency-Dependent Senescence and Transcriptome Response in Developmentally Old and Young Brassica napus Leaves

In the spring oilseed rape (OSR) cultivar 'Mozart' grown under optimal N supply (NO) or mild N deficiency (NL) the transcriptome changes associated with progressing age until early senescence in developmentally old lower canopy leaves (leaf #4) and younger higher canopy leaves (leaf #8) were investigated. Twelve weeks old NO and NL plants appeared phenotypically and transcriptomically identical, but thereafter distinct nutrition-dependent differences in gene expression patterns in lower and upper canopy leaves emerged. In NO leaves #4 of 14-week-old compared to 13-week-old plants, ∼600 genes were up- or downregulated, whereas in NL leaves #4 ∼3000 genes were up- or downregulated. In contrast, in 15-week-old compared to 13-week-old upper canopy leaves #8 more genes were up- or downregulated in optimally N-supplied plants (∼2000 genes) than in N-depleted plants (∼750 genes). This opposing effect of N depletion on gene regulation was even more prominent among photosynthesis-related genes (PSGs). Between week 13 and 14 in leaves #4, 99 of 110 PSGs were downregulated in NL plants, but none in NO plants. In contrast, from weeks 13 to 16 in leaves #8 of NL plants only 11 PSGs were downregulated in comparison to 66 PSGs in NO plants. Different effects of N depletion in lower versus upper canopy leaves were also apparent in upregulation of autophagy genes and NAC transcription factors. More than half of the regulated NAC and WRKY transcription factor, autophagy and protease genes were specifically regulated in NL leaves #4 or NO leaves #8 and thus may contribute to differences in senescence and nutrient mobilization in these leaves. We suggest that in N-deficient plants the upper leaves retain their N resources longer than in amply fertilized plants and remobilize them only after shedding of the lower leaves.

Cultivar Differences in Root Nitrogen Uptake Ability of Maize Hybrids

Although, considerable differences in root size in response to nitrogen (N) application among crop species and cultivars have been widely reported, there has been limited focus on the differences in root N uptake ability. In this study, two maize (Zea mays L.) hybrids, Zhenghong 311 (ZH 311, N-efficient) and Xianyu 508 (XY 508, N-inefficient), were used to compare differences in root N uptake ability. The two cultivars were grown in field pots Experiment I (Exp. I) and hydroponic cultures Experiment II (Exp. II) supplemented with different concentrations of N fertilizer. In both experiments, the levels of accumulated N were higher in ZH 311 than in XY 508 under low- and high-N supply, and the increment in accumulated N was greater under N deficiency. The maximum N uptake rate (V_m) and average N uptake rate (V_a) in Exp. I, the root N kinetic parameter maximum uptake rate (V_max) per fresh weight (FW) and V_max per plant in Exp. II, and the root N uptake rate in both experiments were significantly higher for ZH 311 than for XY 508. In contrast, the root-to-shoot N ratio in both experiments and the root N kinetic parameter Michaelis constant (K_m) in in Exp. II were markedly higher in XY 508 than in ZH 311, particularly under N-deficient conditions. Higher root N kinetic parameters V_max per FW and V_max per plant and lower K_m values contributed to higher N affinity and uptake potential, more coordinated N distribution in the root and shoot, and higher root N uptake rates throughout the growth stages, thus enhancing the N accumulation and yield of the N-efficient maize cultivar. We conclude that the N uptake ability of roots in the N-efficient cultivar ZH 311 is significantly greater than that in the N-inefficient cultivar XY 508, and that this advantage is more pronounced under N-deficient conditions. The efficient N acquisition in ZH 311 is due to higher N uptake rate per root FW under optimal N conditions and the comprehensive effects of root size and N uptake rate per root FW under N deficiency.

Root morphology and seed and leaf ionomic traits in a Brassica napus L. diversity panel show wide phenotypic variation and are characteristic of crop habit

BACKGROUND

Mineral nutrient uptake and utilisation by plants are controlled by many traits relating to root morphology, ion transport, sequestration and translocation. The aims of this study were to determine the phenotypic diversity in root morphology and leaf and seed mineral composition of a polyploid crop species, Brassica napus L., and how these traits relate to crop habit. Traits were quantified in a diversity panel of up to 387 genotypes: 163 winter, 127 spring, and seven semiwinter oilseed rape (OSR) habits, 35 swede, 15 winter fodder, and 40 exotic/unspecified habits. Root traits of 14 d old seedlings were measured in a 'pouch and wick' system (n = ~24 replicates per genotype). The mineral composition of 3-6 rosette-stage leaves, and mature seeds, was determined on compost-grown plants from a designed experiment (n = 5) by inductively coupled plasma-mass spectrometry (ICP-MS).

RESULTS

Seed size explained a large proportion of the variation in root length. Winter OSR and fodder habits had longer primary and lateral roots than spring OSR habits, with generally lower mineral concentrations. A comparison of the ratios of elements in leaf and seed parts revealed differences in translocation processes between crop habits, including those likely to be associated with crop-selection for OSR seeds with lower sulphur-containing glucosinolates. Combining root, leaf and seed traits in a discriminant analysis provided the most accurate characterisation of crop habit, illustrating the interdependence of plant tissues.

CONCLUSIONS

High-throughput morphological and composition phenotyping reveals complex interrelationships between mineral acquisition and accumulation linked to genetic control within and between crop types (habits) in B. napus. Despite its recent genetic ancestry (<10 ky), root morphology, and leaf and seed composition traits could potentially be used in crop improvement, if suitable markers can be identified and if these correspond with suitable agronomy and quality traits.

CN-Wheat, a functional-structural model of carbon and nitrogen metabolism in wheat culms after anthesis. I. Model description

Background and Aims Improving crops requires better linking of traits and metabolic processes to whole plant performance. In this paper, we present CN-Wheat, a comprehensive and mechanistic model of carbon (C) and nitrogen (N) metabolism within wheat culms after anthesis. Methods The culm is described by modules that represent the roots, photosynthetic organs and grains. Each of them includes structural, storage and mobile materials. Fluxes of C and N among modules occur through a common pool and through transpiration flow. Metabolite variations are represented by differential equations that depend on the physiological processes occurring in each module. A challenging aspect of CN-Wheat lies in the regulation of these processes by metabolite concentrations and the environment perceived by organs. Key Results CN-Wheat simulates the distribution of C and N into wheat culms in relation to photosynthesis, N uptake, metabolite turnover, root exudation and tissue death. Regulation of physiological activities by local concentrations of metabolites appears to be a valuable feature for understanding how the behaviour of the whole plant can emerge from local rules. Conclusions The originality of CN-Wheat is that it proposes an integrated view of plant functioning based on a mechanistic approach. The formalization of each process can be further refined in the future as knowledge progresses. This approach is expected to strengthen our capacity to understand plant responses to their environment and investigate plant traits adapted to changes in agronomical practices or environmental conditions. A companion paper will evaluate the model.

CN-Wheat, a functional-structural model of carbon and nitrogen metabolism in wheat culms after anthesis. II. Model evaluation

Background and Aims Simulating resource allocation in crops requires an integrated view of plant functioning and the formalization of interactions between carbon (C) and nitrogen (N) metabolisms. This study evaluates the functional-structural model CN-Wheat developed for winter wheat after anthesis. Methods In CN-Wheat the acquisition and allocation of resources between photosynthetic organs, roots and grains are emergent properties of sink and source activities and transfers of mobile metabolites. CN-Wheat was calibrated for field plants under three N fertilizations at anthesis. Model parameters were taken from the literature or calibrated on the experimental data. Key Results The model was able to predict the temporal variations and the distribution of resources in the culm. Thus, CN-Wheat accurately predicted the post-anthesis kinetics of dry masses and N content of photosynthetic organs and grains in response to N fertilization. In our simulations, when soil nitrates were non-limiting, N in grains was ultimately determined by availability of C for root activity. Dry matter accumulation in grains was mostly affected by photosynthetic organ lifespan, which was regulated by protein turnover and C-regulated root activity. Conclusions The present study illustrates that the hypotheses implemented in the model were able to predict realistic dynamics and spatial patterns of C and N. CN-Wheat provided insights into the interplay of C and N metabolism and how the depletion of mobile metabolites due to grain filling ultimately results in the cessation of resource capture. This enabled us to identify processes that limit grain mass and protein content and are potential targets for plant breeding.

Protocol: optimisation of a grafting protocol for oilseed rape (Brassica napus) for studying long-distance signalling

BACKGROUND

Grafting is a well-established technique for studying long-distance transport and signalling processes in higher plants. While oilseed rape has been the subject of comprehensive analyses of xylem and phloem sap to identify macromolecules potentially involved in long-distance information transfer, there is currently no standardised grafting method for this species published.

RESULTS

We developed a straightforward collar-free grafting protocol for Brassica napus plants with high reproducibility and success rates. Micrografting of seedlings was done on filter paper. Grafting success on different types of regeneration media was measured short-term after grafting and as the long-term survival rate (>14 days) of grafts after the transfer to hydroponic culture or soil.

CONCLUSIONS

We compared different methods for grafting B. napus seedlings. Grafting on filter paper with removed cotyledons, a truncated hypocotyl and the addition of low levels of sucrose under long day conditions allowed the highest grafting success. A subsequent long-term hydroponic cultivation of merged grafts showed highest survival rates and best reproducibility.