Nutritional and tissue-specific regulation of cytochrome P450 CYP711A MAX1 homologues and strigolactone biosynthesis in wheat

Strigolactones (SLs) are a class of phytohormones regulating branching/tillering, and their biosynthesis has been associated with nutritional signals and plant adaptation to nutrient-limiting conditions. The enzymes in the SL biosynthetic pathway downstream of carlactone are of interest as they are responsible for structural diversity in SLs, particularly cytochrome P450 CYP711A subfamily members, such as MORE AXILLARY GROWTH1 (MAX1) in Arabidopsis. We identified 13 MAX1 homologues in wheat, clustering in four clades and five homoeologous subgroups. The utilization of RNA-sequencing data revealed a distinct expression pattern of MAX1 homologues in above- and below-ground tissues, providing insights into the distinct roles of MAX1 homologues in wheat. In addition, a transcriptional analysis showed that SL biosynthetic genes were systematically regulated by nitrogen supply. Nitrogen limitation led to larger transcriptional changes in the basal nodes than phosphorus limitation, which was consistent with the observed tillering suppression, as wheat showed higher sensitivity to nitrogen. The opposite was observed in roots, with phosphorus limitation leading to stronger induction of most SL biosynthetic genes compared with nitrogen limitation. The observed tissue-specific regulation of SL biosynthetic genes in response to nutritional signals is likely to reflect the dual role of SLs as rhizosphere signals and branching inhibitors.

Arabinogalactan Protein-Like Proteins From Ulva lactuca Activate Immune Responses and Plant Resistance in an Oilseed Crop

Natural compounds isolated from macroalgae are promising, ecofriendly, and multifunctional bioinoculants, which have been tested and used in agriculture. Ulvans, for instance, one of the major polysaccharides present in Ulva spp. cell walls, have been tested for their plant growth-promoting properties as well as their ability to activate plant immune defense, on a large variety of crops. Recently, we have characterized for the first time an arabinogalactan protein-like (AGP-like) from Ulva lactuca, which exhibits several features associated to land plant AGPs. In land plant, AGPs were shown to play a role in several plant biological functions, including cell morphogenesis, reproduction, and plant-microbe interactions. Thus, isolated AGP-like proteins may be good candidates for either the plant growth-promoting properties or the activation of plant immune defense. Here, we have isolated an AGP-like enriched fraction from Ulva lactuca and we have evaluated its ability to (i) protect oilseed rape (Brassica napus) cotyledons against Leptosphaeria maculans, and (ii) its ability to activate immune responses. Preventive application of the Ulva AGP-like enriched fraction on oilseed rape, followed by cotyledon inoculation with the fungal hemibiotroph L. maculans, resulted in a major reduction of infection propagation. The noticed reduction correlated with an accumulation of H₂O₂ in treated cotyledons and with the activation of SA and ET signaling pathways in oilseed rape cotyledons. In parallel, an ulvan was also isolated from Ulva lactuca. Preventive application of ulvan also enhanced plant resistance against L. maculans. Surprisingly, reduction of infection severity was only observed at high concentration of ulvan. Here, no such significant changes in gene expression and H₂O₂ production were observed. Together, this study indicates that U. lactuca AGP-like glycoproteins exhibit promising elicitor activity and that plant eliciting properties of Ulva extract, might result not only from an ulvan-originated eliciting activities, but also AGP-like originated.

Two Carbohydrate-Based Natural Extracts Stimulate in vitro Pollen Germination and Pollen Tube Growth of Tomato Under Cold Temperatures

To date, it is widely accepted by the scientific community that many agricultural regions will experience more extreme temperature fluctuations. These stresses will undoubtedly impact crop production, particularly fruit and seed yields. In fact, pollination is considered as one of the most temperature-sensitive phases of plant development and until now, except for the time-consuming and costly processes of genetic breeding, there is no immediate alternative to address this issue. In this work, we used a multidisciplinary approach using physiological, biochemical, and molecular techniques for studying the effects of two carbohydrate-based natural activators on in vitro tomato pollen germination and pollen tube growth cultured in vitro under cold conditions. Under mild and strong cold temperatures, these two carbohydrate-based compounds significantly enhanced pollen germination and pollen tube growth. The two biostimulants did not induce significant changes in the classical molecular markers implicated in pollen tube growth. Neither the number of callose plugs nor the CALLOSE SYNTHASE genes expression were significantly different between the control and the biostimulated pollen tubes when pollens were cultivated under cold conditions. PECTIN METHYLESTERASE (PME) activities were also similar but a basic PME isoform was not produced or inactive in pollen grown at 8°C. Nevertheless, NADPH oxidase (RBOH) gene expression was correlated with a higher number of viable pollen tubes in biostimulated pollen tubes compared to the control. Our results showed that the two carbohydrate-based products were able to reduce in vitro the effect of cold temperatures on tomato pollen tube growth and at least for one of them to modulate reactive oxygen species production.

K Deprivation Modulates the Primary Metabolites and Increases Putrescine Concentration in Brassica napus

Potassium (K) plays a crucial role in plant growth and development and is involved in different physiological and biochemical functions in plants. Brassica napus needs higher amount of nutrients like nitrogen (N), K, phosphorus (P), sulfur (S), and boron (B) than cereal crops. Previous studies in B. napus are mainly focused on the role of N and S or combined deficiencies. Hence, little is known about the response of B. napus to K deficiency. Here, a physiological, biochemical, and molecular analysis led us to investigate the response of hydroponically grown B. napus plants to K deficiency. The results showed that B. napus was highly sensitive to the lack of K. The lower uptake and translocation of K induced BnaHAK5 expression and significantly declined the growth of B. napus after 14 days of K starvation. The lower availability of K was associated with a decrease in the concentration of both S and N and modulated the genes involved in their uptake and transport. In addition, the lack of K induced an increase in Ca2+ and Mg2+ concentration which led partially to the accumulation of positive charge. Moreover, a decrease in the level of arginine as a positively charged amino acid was observed which was correlated with a substantial increase in the polyamine, putrescine (Put). Furthermore, K deficiency induced the expression of BnaNCED3 as a key gene in abscisic acid (ABA) biosynthetic pathway which was associated with an increase in the levels of ABA. Our findings provided a better understanding of the response of B. napus to K starvation and will be useful for considering the importance of K nutrition in this crop.

Characterization of physiological and molecular responses of Zea mays seedlings to different urea-ammonium ratios

Despite the wide use of urea and ammonium as N-fertilizers, no information is available about the proper ratio useful to maximize the efficiency of their acquisition by crops. Ionomic analyses of maize seedlings fed with five different mixes of urea and ammonium indicated that after 7 days of treatment, the elemental composition of plant tissues was more influenced by ammonium in the nutrient solution than by urea. Within 24 h, similar high affinity influx rates of ammonium were measured in ammonium-treated seedlings, independently from the amount of the cation present in the nutrient solution (from 0.5 to 2.0 mM N), and it was confirmed by the similar accumulation of ¹⁵N derived from ammonium source. After 7 days, some changes in ammonium acquisition occurred among treatments, with the highest ammonium uptake efficiency when the urea-to-ammonium ratio was 3:1. Gene expression analyses of enzymes and transporters involved in N nutrition highlight a preferential induction of the cytosolic N-assimilatory pathway (via GS, ASNS) when both urea and ammonium were supplied in conjunction, this response might explain the higher N-acquisition efficiency when both sources are applied. In conclusion, this study provides new insights on plant responses to mixes of N sources that maximize the N-uptake efficiency by crops and thus could allow to adapt agronomic practices in order to limit the economic and environmental impact of N-fertilization.

Responses of hydroponically grown maize to various urea to ammonium ratios: physiological and molecular data

To date urea and ammonium are two nitrogen (N) forms widely used in agriculture. Due to a low production cost, urea is the N form most applied in agriculture. However, its stability in the soil depends on the activity of microbial ureases, that operate the hydrolysis of urea into ammonium. In the soil ammonium is subjected to fast volatilization in form of ammonia, an environmental N loss that contributes to the atmospheric pollution and impacts on farm economies. Based on these considerations, the optimization of N fertilization is useful in order to maximize N acquired by crops and at the same time limit N losses in the environment. The use of mixed nitrogen forms in cultivated soils allows to have urea and ammonium simultaneously available for the root acquisition after a fertilization event. A combination of different N-sources is known to lead to positive effects on the nutritional status of crops. It is plausible suppose that N acquisition mechanisms in plants might be responsive to N forms available in the root external solution, and therefore indicate a cross connection among different N forms, such as urea and ammonium.

This DIB article provides details about the elemental composition and transcriptional changes occurring in maize seedlings when ammonium and urea mixture is applied to nutrient solution. An extensive and complete characterization of seedling response to urea and ammonium treatments is shown in the research article “Characterization of physiological and molecular responses of Zea mays seedlings to different urea-ammonium ratios” Buoso et al. [1].

Maize seedlings were grown under hydroponic system with N applied to nutrient solution in form of urea and or ammonium, hence five different urea (U) to ammonium (A) ratios were tested (100U, 75U:25A, 50U:50A, 25U:75A, 100A). As control maize were fed with nitrate as sole N source, or were maintained in N deficiency (-N). After 1 or 7 days of N-treatment, maize seedlings were collected, and physiological and transcriptional analyses were performed on maize roots.

Depending on nutritional treatment, no significant changes in seedling biomass were observed comparing N treatments. At both sampling times, an overall higher N accumulation in shoots and roots were detected when the inorganic N sources were applied to nutrient solutions (as ammonium or nitrate). ¹⁵N experiments indicated that in comparison to -N seedlings, urea fed seedlings showed an increase of N accumulation and data showed that ureic-N was taken up by seedlings in lower amounts than inorganic N-forms. Through EA-IRMS, ICP-OES and ICP-MS a multielemental composition of maize tissues was performed as well as gene expression analyses by Real-time RT-PCR that allowed to monitor the expression profile of genes most involved in urea and ammonium nutritional pathways.

Fine tuning of hormonal signaling is linked to dormancy status in sweet cherry flower buds

In temperate trees, optimal timing and quality of flowering directly depend on adequate winter dormancy progression, regulated by a combination of chilling and warm temperatures. Physiological, genetic and functional genomic studies have shown that hormones play a key role in bud dormancy establishment, maintenance and release. We combined physiological and transcriptional analyses, quantification of abscisic acid (ABA) and gibberellins (GAs), and modeling to further investigate how these signaling pathways are associated with dormancy progression in the flower buds of two sweet cherry cultivars. Our results demonstrated that GA-associated pathways have distinct functions and may be differentially related with dormancy. In addition, ABA levels rise at the onset of dormancy, associated with enhanced expression of ABA biosynthesis PavNCED genes, and decreased prior to dormancy release. Following the observations that ABA levels are correlated with dormancy depth, we identified PavUG71B6, a sweet cherry UDP-GLYCOSYLTRANSFERASE gene that up-regulates active catabolism of ABA to ABA glucosyl ester (ABA-GE) and may be associated with low ABA content in the early cultivar. Subsequently, we modeled ABA content and dormancy behavior in three cultivars based on the expression of a small set of genes regulating ABA levels. These results strongly suggest the central role of ABA pathway in the control of dormancy progression and open up new perspectives for the development of molecular-based phenological modeling.

Arabinogalactan-like Glycoproteins from Ulva lactuca (Chlorophyta) Show Unique Features Compared to Land Plants AGPs

Arabinogalactan proteins (AGPs) encompass a diverse group of plant cell wall proteoglycans, which play an essential role in plant development, signaling, plant-microbe interactions, and many others. Although they are widely distributed throughout the plant kingdom and extensively studied, they remain largely unexplored in the lower plants, especially in seaweeds. Ulva species have high economic potential since various applications were previously described including bioremediation, biofuel production, and as a source of bioactive compounds. This article presents the first experimental confirmation of AGP-like glycoproteins in Ulva species and provides a simple extraction protocol of Ulva lactuca AGP-like glycoproteins, their partial characterization and unique comparison to scarcely described Solanum lycopersicum AGPs. The reactivity with primary anti-AGP antibodies as well as Yariv reagent showed a great variety between Ulva lactuca and Solanum lycopersicum AGP-like glycoproteins. While the amino acid analysis of the AGP-like glycoproteins purified by the β-d-glucosyl Yariv reagent showed a similarity between algal and land plant AGP-like glycoproteins, neutral saccharide analysis revealed unique glycosylation of the Ulva lactuca AGP-like glycoproteins. Surprisingly, arabinose and galactose were not the most prevalent monosaccharides and the most outstanding was the presence of 3-O-methyl-hexose, which has never been described in the AGPs. The exceptional structure of the Ulva lactuca AGP-like glycoproteins implies a specialized adaptation to the marine environment and might bring new insight into the evolution of the plant cell wall.

Hatching Induction of Cyst Nematodes in Bare Soils Drenched With Root Exudates Under Controlled Conditions

Cyst nematodes account for substantial annual yield losses in crop production worldwide. Concerns over environmental and health issues due to the use of chemical nematicides mean alternative sustainable and integrated solutions are urgently required. Hatch induction of encysted eggs in the absence of host plants, i.e., 'suicide-hatching,' could be a sustainable alternative in reducing population densities of cyst nematodes in infested soils. Here we examined in situ hatching of encysted eggs of Globodera pallida, Heterodera carotae, and Heterodera schachtii at varying soil depths, following exogenous applications of host root exudates in repeated glasshouse experiments. Cysts were retrieved 30 or 43 days post-incubation depending on the nematode species and assessed for hatching rates relative to the initial number of viable eggs per cyst. Hatching of the potato cyst nematode G. pallida depended on both soil moisture and effective exposure to root exudates, and to a lesser extent on exudate concentration. The carrot cyst nematode H. carotae had over 75% hatched induced by root exudate irrespective of the concentration, with better hatch induction at 20 cm as compared with 10 cm soil depth. Hatching of the beet cyst nematode H. schachtii largely depended on the soil moisture level at constant temperature, rather than the type or concentration of root exudates applied. As a conclusion, exogenously applied host root exudates may play a major role in inducing in situ hatch of encysted eggs of potato and carrot cyst nematodes in the absence of host plant under favorable soil temperature/moisture conditions. To improve such strategy, the characterization of chemical profiles of the root exudate composition and field validation are currently ongoing.

Hatching of Globodera pallida Induced by Root Exudates Is Not Influenced by Soil Microbiota Composition

Plant-parasitic nematodes are among the most harmful pests of cultivated crops causing important economic losses. The ban of chemical nematicides requires the development of alternative agroecological approaches to protect crops against nematodes. For cyst nematodes, egg hatching is stimulated by host plant root exudates. Inducing "suicide hatching" of nematode second-stage juveniles (J2), using root exudates in the absence of the host plant, may constitute an effective and innovative biocontrol method to control cyst nematodes. However, before considering the development of this approach, understanding the effect of soil biotic component on cyst nematode hatching by root exudates is a major issue. The effectiveness of this approach could be modulated by other soil organisms consuming root exudates for growth as soil microbiota, and this must be evaluated. To do that, four different native agricultural soils were selected based on their physicochemical properties and their microbiota composition were characterized by rDNA metabarcoding. To disentangle the effect of microbiota from that of soil on hatching, four recolonized artificial soils were obtained by inoculating a common sterile soil matrix with the microbiota proceeding from each agricultural soil. Each soil was then inoculated with cysts of the potato cyst nematode, Globodera pallida, and low or high doses of potato root exudates (PREs) were applied. After 40 days, viable J2 remaining in cysts were counted to determine the efficiency of root exudates to stimulate hatching in different soils. Results showed that (i) when physicochemical and microbiota compositions varied among native soils, the hatching rates remained very high albeit small differences were measured and no dose effect was detected and (ii) when only microbiota composition varied among recolonized soils, the hatching rates were also high at the highest dose of PREs, but a strong dose effect was highlighted. This study shows that abiotic and biotic factors may not compromise the development of methods based on suicide hatching of cyst nematodes, using root exudates, molecules inducing J2 hatch, or trap crops.

Potassium Application Boosts Photosynthesis and Sorbitol Biosynthesis and Accelerates Cold Acclimation of Common Plantain (Plantago major L.)

Potassium (K) is essential for the processes critical for plant performance, including photosynthesis, carbon assimilation, and response to stress. K also influences translocation of sugars in the phloem and regulates sucrose metabolism. Several plant species synthesize polyols and transport these sugar alcohols from source to sink tissues. Limited knowledge exists about the involvement of K in the above processes in polyol-translocating plants. We, therefore, studied K effects in Plantago major, a species that accumulates the polyol sorbitol to high concentrations. We grew P. major plants on soil substrate adjusted to low-, medium-, or high-potassium conditions. We found that biomass, seed yield, and leaf tissue K contents increased in a soil K-dependent manner. K gradually increased the photosynthetic efficiency and decreased the non-photochemical quenching. Concomitantly, sorbitol levels and sorbitol to sucrose ratio in leaves and phloem sap increased in a K-dependent manner. K supply also fostered plant cold acclimation. High soil K levels mitigated loss of water from leaves in the cold and supported cold-dependent sugar and sorbitol accumulation. We hypothesize that with increased K nutrition, P. major preferentially channels photosynthesis-derived electrons into sorbitol biosynthesis and that this increased sorbitol is supportive for sink development and as a protective solute, during abiotic stress.

A comparison of PTI defense profiles induced in Solanum tuberosum by PAMP and non-PAMP elicitors shows distinct, elicitor-specific responses

The induction of general plant defense responses following the perception of external elicitors is now regarded as the first level of the plant immune response. Depending on the involvement or not of these molecules in pathogenicity, this induction of defense is called either Pathogen-Associated Molecular Pattern (PAMP) Triggered Immunity or Pattern Triggered Immunity-both abbreviated to PTI. Because PTI is assumed to be a widespread and stable form of resistance to infection, understanding the mechanisms driving it becomes a major goal for the sustainable management of plant-pathogen interactions. However, the induction of PTI is complex. Our hypotheses are that (i) the recognition by the plant of PAMPs vs non-PAMP elicitors leads to specific defense profiles and (ii) the responses specifically induced by PAMPs target critical life history traits of the pathogen that produced them. We thus analyzed, using a metabolomic approach coupled with transcriptomic and hormonal analyses, the defense profiles induced in potato foliage treated with either a Concentrated Culture Filtrate (CCF) from Phytophthora infestans or two non-PAMP preparations, β-aminobutyric acid (BABA) and an Ulva spp. Extract, used separately. Each elicitor induced specific defense profiles. CCF up-regulated sesquiterpenes but down-regulated sterols and phenols, notably α-chaconine, caffeoyl quinic acid and rutin, which decreased spore production of P. infestans in vitro. CCF thus induces both defense and counter-defense responses. By contrast, the Ulva extract triggered the synthesis of a large-spectrum of antimicrobial compounds through the phenylpropanoid/flavonoid pathways, while BABA targeted the primary metabolism. Hence, PTI can be regarded as a heterogeneous set of general and pathogen-specific responses triggered by the molecular signatures of each elicitor, rather than as a uniform, non-specific and broad-spectrum set of general defense reactions.

Extensin arabinosylation is involved in root response to elicitors and limits oomycete colonization

BACKGROUND AND AIMS

Extensins are hydroxyproline-rich glycoproteins thought to strengthen the plant cell wall, one of the first barriers against pathogens, through intra- and intermolecular cross-links. The glycan moiety of extensins is believed to confer the correct structural conformation to the glycoprotein, leading to self-assembly within the cell wall that helps limit microbial adherence and invasion. However, this role is not clearly established.

METHODS

We used Arabidopsis thaliana mutants impaired in extensin arabinosylation to investigate the role of extensin arabinosylation in root-microbe interactions. Mutant and wild-type roots were stimulated to elicit an immune response with flagellin 22 and immunolabelled with a set of anti-extensin antibodies. Roots were also inoculated with a soilborne oomycete, Phytophthora parasitica, to assess the effect of extensin arabinosylation on root colonization.

KEY RESULTS

A differential distribution of extensin epitopes was observed in wild-type plants in response to elicitation. Elicitation also triggers altered epitope expression in mutant roots compared with wild-type and non-elicited roots. Inoculation with the pathogen P. parasitica resulted in enhanced root colonization for two mutants, specifically xeg113 and rra2.

CONCLUSIONS

We provide evidence for a link between extensin arabinosylation and root defence, and propose a model to explain the importance of glycosylation in limiting invasion of root cells by pathogenic oomycetes.

Impacts of low-level liming on soil respiration and forage production in a fertilized upland grassland in Central France

Liming is a common agricultural practice for improving acidic soils, but the addition of liming materials may also promote soil carbon dioxide (CO₂) emissions, with adverse effects for climate regulation. In grasslands, current understanding of liming impacts on greenhouse gas emissions is limited by a lack of field data on liming and soil respiration. Here we used a two-year field trial and in situ chamber measurements to evaluate the effects of repeated, low-level liming on soil CO₂ emissions from an acidic managed grassland with high soil organic matter content. Soil pH, temperature and moisture were measured during the experiment, as well as microbial and plant biomass, in order to assess possible liming-induced changes to drivers of grassland carbon cycling. Soil CO₂ emissions showed significant variation during the two-year study, driven primarily by fluctuations in soil temperature. Soil respiration rates were unaffected by liming treatment, despite significant lime-induced increases in soil pH. Liming was associated with a decrease in biomass produced per gram nitrogen, as well as a decrease in forage C:N in the second year and transient decreases in microbial C:N, but neither plant nor microbial biomass showed significant responses to liming addition. Collectively, our results suggest that positive effects of low-level liming on plants and soil are not offset by increases in soil CO₂ emissions in situ, highlighting the potential for sustainable liming practices in fertilized grasslands.

From bud formation to flowering: transcriptomic state defines the cherry developmental phases of sweet cherry bud dormancy

Background

Bud dormancy is a crucial stage in perennial trees and allows survival over winter to ensure optimal flowering and fruit production. Recent work highlighted physiological and molecular events occurring during bud dormancy in trees. However, they usually examined bud development or bud dormancy in isolation. In this work, we aimed to further explore the global transcriptional changes happening throughout bud development and dormancy onset, progression and release.

Results

Using next-generation sequencing and modelling, we conducted an in-depth transcriptomic analysis for all stages of flower buds in several sweet cherry (Prunus avium L.) cultivars that are characterized for their contrasted dates of dormancy release. We find that buds in organogenesis, paradormancy, endodormancy and ecodormancy stages are defined by the expression of genes involved in specific pathways, and these are conserved between different sweet cherry cultivars. In particular, we found that DORMANCY ASSOCIATED MADS-box (DAM), floral identity and organogenesis genes are up-regulated during the pre-dormancy stages while endodormancy is characterized by a complex array of signalling pathways, including cold response genes, ABA and oxidation-reduction processes. After dormancy release, genes associated with global cell activity, division and differentiation are activated during ecodormancy and growth resumption. We then went a step beyond the global transcriptomic analysis and we developed a model based on the transcriptional profiles of just seven genes to accurately predict the main bud dormancy stages.

Conclusions

Overall, this study has allowed us to better understand the transcriptional changes occurring throughout the different phases of flower bud development, from bud formation in the summer to flowering in the following spring. Our work sets the stage for the development of fast and cost effective diagnostic tools to molecularly define the dormancy stages. Such integrative approaches will therefore be extremely useful for a better comprehension of complex phenological processes in many species.

Silicon Promotes Agronomic Performance in Brassica napus Cultivated under Field Conditions with Two Nitrogen Fertilizer Inputs

To limit the environmental pollution associated with intensive nitrogen (N) fertilizer usage, alternative cultural practices must be considered for crops requiring high N inputs such as rapeseed. In this context, the effects of silicon (Si) supply on the agronomic performance of rapeseed cultivated under field conditions with two N fertilizer levels (60 and 160 kg ha⁻¹) were studied. Results showed that Si supplied in the form of silicic acid (12 kg ha⁻¹) has no effect on the agronomic performance of plants cultivated with the lower N input. In contrast, in plants fertilized with 160 kg N ha⁻¹, Si supply promotes the preservation of green leaves (until the flowering stage) and at harvest stage, increases biomass, yield, and seed micronutrient concentrations (especially cobalt and iron). The agronomic indexes show that the increase in seed yield is related to a better uptake of N from the soil by Si-treated plants, but is not an improvement in N mobilization towards the seeds. This study showed that Si supply combined with high N inputs (160 kg ha⁻¹) improves usage of N fertilizer and yield. The possibility that a Si supply could allow for a reduction in N input without altering the yield of rapeseed is discussed.

Silicon supply affects the root transcriptome of Brassica napus L

Modulation of gene expression in roots of Brassica napus by silicon (Si) supply could allow plants to cope with future stresses. The origin of the beneficial effects of silicon (Si) in plants, especially when they are subject to stress, remains poorly understood. Some authors have shown that Si alleviates plant stress and consider that this is mainly due to a mechanical effect on the cell wall. In addition, the other studies have shown that Si can also affect gene expression and modulate a number of metabolic pathways, especially in plants cultivated under stress conditions. Previously, Haddad et al. (Front Plant Sci 9:5-16, 2018) showed that a pretreatment of Brassica napus plants with Si (1.7 mM) for 1 week alleviated the stress induced by N privation. These results suggest that this improved resistance in Si-treated plants might be due to the establishment of defense mechanisms prior to exposure to the N stress. The aim of the current work was to test this assumption in Brassica napus roots (where Si is mainly stored) using a transcriptomic approach via the RNA sequencing. Our results indicated that the Si supply leads to a modulation of the expression of genes in Brassica napus roots. Functional categorization of the differentially expressed genes demonstrated that numerous genes are involved in different metabolic pathways and especially in cell wall synthesis, phytohormone metabolism, and stress responses. All these results show that Si modifies the root metabolism of B. napus, which could allow a better adaptation to future stresses.

Microsatellite markers reveal two genetic groups in European populations of the carrot cyst nematode Heterodera carotae

The cyst nematode Heterodera carotae, which parasitizes carrot roots, has been recorded in many countries in Europe (Italy, The Netherlands, Switzerland, France, Denmark, …), in South Africa and in North America (Canada, USA). To date, there is a lack of knowledge about the genetic structure of the populations of this economically important nematode. The aim of this work was to study the structuration of the genetic diversity of the carrot cyst nematode at the European scale. We have developed a set of thirteen polymorphic microsatellite markers and used it to genotype seventeen European populations of H. carotae coming from France, Switzerland, Italy, Denmark and one non-European population from Canada. As previously showed for other cyst nematode species, the H. carotae populations were characterised by a strong heterozygote deficit. A Bayesian clustering analysis revealed two distinct genetic clusters, with one group located in the north of Europe and a second one located in the south of Europe. Moreover, our results highlighted rather limited gene flow at small spatial scale and some events of long distance migration. This first investigation of the genetic diversity of H. carotae populations would be useful to develop sustainable control strategies.

Assessment of Sulfur Deficiency under Field Conditions by Single Measurements of Sulfur, Chloride and Phosphorus in Mature Leaves

Determination of S status is very important to detect S deficiency and prevent losses of yield and seed quality. The aim of this study was to investigate the possibility of using the ([Cl⁻]+[NO₃⁻]+[PO₄³⁻]):[SO₄²⁻] ratio as an indicator of S nutrition under field conditions in Brassica napus and whether this could be applied to other species. Different S and nitrogen (N) fertilizations were applied on a S deficient field of oilseed rape to harvest mature leaves and analyze their anion and element contents in order to evaluate a new S nutrition indicator and useful threshold values. Large sets of commercial varieties were then used to test S deficiency scenarios. As main results, this study shown that, under field conditions, leaf ([Cl⁻]+[NO₃⁻]+[PO₄³⁻]):[SO₄²⁻] ratio was increased by lowering S fertilization, indicating S deficiency. The usefulness of this ratio was also found for other species grown under controlled conditions and it could be simplified by using the elemental ([Cl]+[P]):[S] ratio. Threshold values were determined and used for the clustering of commercial varieties within three groups: S deficient, at risk of S deficiency and S sufficient. The ([Cl]+[P]):[S] ratio quantified under field conditions, can be used as an early and accurate diagnostic tool to manage S fertilization.

Simultaneous untargeted and targeted metabolomics profiling of underivatized primary metabolites in sulfur-deficient barley by ultra-high performance liquid chromatography-quadrupole/time-of-flight mass spectrometry

BACKGROUND

Metabolomics based on mass spectrometry analysis are increasingly applied in diverse scientific domains, notably agronomy and plant biology, in order to understand plants' behaviors under different stress conditions. In fact, these stress conditions are able to disrupt many biosynthetic pathways that include mainly primary metabolites. Profiling and quantifying primary metabolites remain a challenging task because they are poorly retained in reverse phase columns, due to their high polarity and acid-base properties. The aim of this work is to develop a simultaneous untargeted/targeted profiling of amino acids, organic acids, sulfur metabolites, and other several metabolites. This method will be applied on sulfur depleted barley, in order to study this type of stress, which is difficult to detect at early stage. Also, this method aims to explore the impact of this stress on barley's metabolome.

RESULTS

Ultra-high performance liquid chromatography-high resolution mass spectrometry-based method was successfully applied to real samples allowing to discriminate, detect, and quantify primary metabolites in short-runs without any additional sampling step such as derivatization or ion pairing. The retention of polar metabolites was successfully achieved using modified C18 columns with high reproducibility (relative standard deviation below 10%). The quantification method showed a high sensitivity and robustness. Furthermore, high resolution mass spectrometry detection provided reliable quantification based on exact mass, eliminating potential interferences, and allowing the simultaneous untargeted metabolomics analysis. The untargeted data analysis was conducted using Progenesis QI software, performing alignment, peak picking, normalization and multivariate analysis. The simultaneous analysis provided cumulative information allowing to discriminate between two plant batches. Thus, discriminant biomarkers were identified and validated. Simultaneously, quantification confirmed coherently the relative abundance of these biomarkers.

CONCLUSIONS

A fast and innovated simultaneous untargeted/targeted method has successfully been developed and applied to sulfur deficiency on barley. This work opens interesting perspectives in both fundamental and applied research. Biomarker discovery give precious indication to understand plant behavior during a nutritional deficiency. Thus, direct or indirect measurement of these compounds allows a real time fertilization management and encounter the challenges of sustainable agriculture.

Silicon Promotes Growth of Brassica napus L. and Delays Leaf Senescence Induced by Nitrogen Starvation

Silicon (Si) is the second most abundant element in soil and has several beneficial effects, especially in plants subjected to stress conditions. However, the effect of Si in preventing nitrogen (N) starvation in plants is poorly documented. The aim of this work was to study the effect of a short Si supply duration (7 days) on growth, N uptake, photosynthetic activity, and leaf senescence progression in rapeseed subjected (or not) to N starvation. Our results showed that after 1 week of Si supply, Si improves biomass and increases N uptake and root expression of a nitrate transporter gene. After 12 days of N starvation, compared to -Si plants, mature leaf from +Si plants showed a high chlorophyll content, a maintain of net photosynthetic activity, a decrease of oxidative stress markers [hydrogen peroxide (H₂O₂) and malondialdehyde (MDA)] and a significant delay in senescence. When N-deprived plants were resupplied with N, a greening again associated with an increase of photosynthetic activity was observed in mature leaves of plants pretreated with Si. Moreover, during the duration of N resupply, an increase of N uptake and nitrate transporter gene expression were observed in plants pretreated with Si. In conclusion, this study has shown a beneficial role of Si to alleviate damage associated with N starvation and more especially its role in delaying of leaf senescence.

Regulatory Role of Silicon in Mediating Differential Stress Tolerance Responses in Two Contrasting Tomato Genotypes Under Osmotic Stress

Previous studies have shown the role of silicon (Si) in mitigating the adverse effect of drought stress in different crop species. However, data are lacking on a comparison of drought tolerant and drought sensitive crop cultivars in response to Si nutrition. Therefore, the aim of this study was to elucidate the mechanism (s) by which two contrasting tomato genotypes respond to Si nutrition under osmotic stress condition. Two tomato lines contrasting in their response to drought stress were hydroponically grown under polyethylene glycol (PEG, 6000) and two regimes of Si (0 and 1.5 mM). Metabolite profiling was performed in two lines. Growth and relevant physiological parameters, and expression levels of selected genes were also measured. Si application resulted in improved osmotic stress tolerance in both drought tolerant line LA0147 and drought sensitive line FERUM. In the drought tolerant line, Si enhanced uptake of sulfur (S) and ammonium ( NH 4 + ) which led to a significantly higher production of amino acids arginine, methionine, serine, and glycine. While in the drought sensitive line, Si significantly increased production of amino acids proline and GABA which further lowered the level of GSSG to GSH ratio and thus balanced the redox homeostasis under osmotic stress. The higher significant production of amino acids arginine, methionine, GABA, and proline enhanced production of free polyamines putrescine and spermidine and improved osmotic stress tolerance. Therefore, we conclude that Si distinctively regulated osmotic stress tolerance in two contrasting tomato genotypes by differential accumulation of relevant amino acids which eventually led to enhanced polyamine metabolism.

Induction of Barley Silicon Transporter HvLsi1 and HvLsi2, increased silicon concentration in the shoot and regulated Starch and ABA Homeostasis under Osmotic stress and Concomitant Potassium Deficiency

Drought is one of the major stress factors reducing cereal production worldwide. There is ample evidence that the mineral nutrient status of plants plays a critical role in increasing plant tolerance to different biotic and abiotic stresses. In this regard, the important role of various nutrients e.g., potassium (K) or silicon (Si) in the mitigation of different stress factors, such as drought, heat or frost has been well documented. Si application has been reported to ameliorate plant nutrient deficiency. Here, we used K and Si either solely or in combination to investigate whether an additive positive effect on barley growth can be achieved under osmotic stress and which mechanisms contribute to a better tolerance to osmotic stress. To achieve this goal, barley plants were subjected to polyethylene glycol (PEG)-induced osmotic stress under low or high K supply and two Si regimes. The results showed that barley silicon transporters HvLsi1 and HvLsi2 regulate the accumulation of Si in the shoot only when plant suffered from K deficiency. Si, in turn, increased the starch level under both osmotic stress and K deficiency and modulated the glycolytic and TCA pathways. Hormone profiling revealed that the beneficial effect of Si is most likely mediated also by ABA homeostasis and active cytokinin isopentenyl adenine (iP). We conclude that Si may effectively improve stress tolerance under K deficient condition in particular when additional stress like osmotic stress interferes.

Non-Specific Root Transport of Nutrient Gives Access to an Early Nutritional Indicator: The Case of Sulfate and Molybdate

Under sulfur (S) deficiency, crosstalk between nutrients induced accumulation of other nutrients, particularly molybdenum (Mo). This disturbed balanced between S and Mo could provide a way to detect S deficiency and therefore avoid losses in yield and seed quality in cultivated species. Under hydroponic conditions, S deprivation was applied to Brassica napus to determine the precise kinetics of S and Mo uptake and whether sulfate transporters were involved in Mo uptake. Leaf contents of S and Mo were also quantified in a field-grown S deficient oilseed rape crop with different S and N fertilization applications to evaluate the [Mo]:[S] ratio, as an indicator of S nutrition. To test genericity of this indicator, the [Mo]:[S] ratio was also assessed with other cultivated species under different controlled conditions. During S deprivation, Mo uptake was strongly increased in B. napus. This accumulation was not a result of the induction of the molybdate transporters, Mot1 and Asy, but could be a direct consequence of Sultr1.1 and Sultr1.2 inductions. However, analysis of single mutants of these transporters in Arabidopsis thaliana suggested that other sulfate deficiency responsive transporters may be involved. Under field conditions, Mo content was also increased in leaves by a reduction in S fertilization. The [Mo]:[S] ratio significantly discriminated between the plots with different rates of S fertilization. Threshold values were estimated for the hierarchical clustering of commercial crops according to S status. The use of the [Mo]:[S] ratio was also reliable to detect S deficiency for other cultivated species under controlled conditions. The analysis of the leaf [Mo]:[S] ratio seems to be a practical indicator to detect early S deficiency under field conditions and thus improve S fertilization management.

Nutrient deficiencies modify the ionomic composition of plant tissues: a focus on cross-talk between molybdenum and other nutrients in Brassica napus

The composition of the ionome is closely linked to a plant's nutritional status. Under certain deficiencies, cross-talk induces unavoidable accumulation of some nutrients, which upsets the balance and modifies the ionomic composition of plant tissues. Rapeseed plants (Brassica napus L.) grown under controlled conditions were subject to individual nutrient deficiencies (N, K, P, Ca, S, Mg, Fe, Cu, Zn, Mn, Mo, or B) and analyzed by inductively high-resolution coupled plasma mass spectrometry to determine the impact of deprivation on the plant ionome. Eighteen situations of increased uptake under mineral nutrient deficiency were identified, some of which have already been described (K and Na, S and Mo, Fe, Zn and Cu). Additionally, as Mo uptake was strongly increased under S, Fe, Cu, Zn, Mn, or B deprivation, the mechanisms underlying the accumulation of Mo in these deficient plants were investigated. The results suggest that it could be the consequence of multiple metabolic disturbances, namely: (i) a direct disturbance of Mo metabolism leading to an up-regulation of Mo transporters such as MOT1, as found under Zn or Cu deficiency, which are nutrients required for synthesis of the Mo cofactor; and (ii) a disturbance of S metabolism leading to an up-regulation of root SO₄^2- transporters, causing an indirect increase in the uptake of Mo in S, Fe, Mn, and B deficient plants.

Mg deficiency affects leaf Mg remobilization and the proteome in Brassica napus

In order to cope with variable mineral nutrient availability, higher plants have developed numerous strategies including the remobilization of nutrients from source to sink tissues. However, such processes remain relatively unknown for magnesium (Mg), which is the third most important cation in plant tissues. Using Mg depletion of Brassica napus, we have demonstrated that Mg is remobilized from old leaves to young shoot tissues. Moreover, this study showed that Mg depletion induces modification of nutrient uptake, especially Zn and Mn. Finally, comparative proteomic analysis of old leaves (source of Mg) revealed amongst other results that some proteins requiring Mg for their functionality (isocitrate dehydrogenase for example) were up-regulated. Moreover, down-regulation of proteases suggested that mobilization of Mg from old leaves was not associated with senescence.

Nitrogen transfer from Lupinus albus L., Trifolium incarnatum L. and Vicia sativa L. contribute differently to rapeseed (Brassica napus L.) nitrogen nutrition

Nitrogen (N) transfer is well documented in legume-cereal intercropping but this is less often reported for legume-Brassica intercrops even though Brassica crops require higher levels of N fertilizers. The present study was carried out to quantify N transfer from legumes (Lupinus albus L., Trifolium incarnatum L. or Vicia sativa L.) to rapeseed (Brassica napus L.) using the split-root (15)N-labelling method. After three months we observed that legumes did not alter the growth of rapeseed. Vetch showed the lowest growth and demonstrated low (15)N shoot to root translocation and no significant N transfer to rapeseed. In contrast, significant (15)N enrichment was found in lupine and clover and (15)N was transferred to the associated rapeseed plants (around 6 and 4 mg N plant(-1), respectively), which contributed 2 to 3% of the rapeseed total N. Additionally, the data revealed that N2 fixation dominated the N nutrition in lupine despite the high N level provided in the donor compartment, suggesting a greater niche segregation between companion plants. Based on the results of this study we suggest that intercropping can be a relevant contributor to rapeseed N nutrition. Among the three legumes tested, clover and lupine seemed to be the best intercropping candidates.

Effect of sulphur deprivation on osmotic potential components and nitrogen metabolism in oilseed rape leaves: identification of a new early indicator

Identification of early sulphur (S) deficiency indicators is important for species such as Brassica napus, an S-demanding crop in which yield and the nutritional quality of seeds are negatively affected by S deficiency. Because S is mostly stored as SO4 (2-) in leaf cell vacuoles and can be mobilized during S deficiency, this study investigated the impact of S deprivation on leaf osmotic potential in order to identify compensation processes. Plants were exposed for 28 days to S or to chlorine deprivation in order to differentiate osmotic and metabolic responses. While chlorine deprivation had no significant effects on growth, osmotic potential and nitrogen metabolism, Brassica napus revealed two response periods to S deprivation. The first one occurred during the first 13 days during which plant growth was maintained as a result of vacuolar SO4 (2-) mobilization. In the meantime, leaf osmotic potential of S-deprived plants remained similar to control plants despite a reduction in the SO4 (2-) osmotic contribution, which was fully compensated by an increase in NO3 (-), PO4 (3-) and Cl(-) accumulation. The second response occurred after 13 days of S deprivation with a significant reduction in growth, leaf osmotic potential, NO3 (-) uptake and NO3 (-) reductase activity, whereas amino acids and NO3 (-) were accumulated. This kinetic analysis of S deprivation suggested that a ([Cl(-)]+[NO3 (-)]+[PO4 (3-)]):[SO4 (2-)] ratio could provide a relevant indicator of S deficiency, modified nearly as early as the over-expression of genes encoding SO4 (2-) tonoplastic or plasmalemmal transporters, with the added advantage that it can be easily quantified under field conditions.

Prophylactic effects of humic acid-glucan combination against experimental liver injury

Aim:

Despite intensive research, liver diseases represent a significant health problem and current medicine does not offer a substance able to significantly inhibit the hepatotoxicity leading to various stages of liver disease. Based on our previously published studies showing the protective effects of a glucan-humic acid (HA) combination, we focused on the hypothesis that the combination of these two natural molecules can offer prophylactic protection against experimentally induced hepatotoxicity.

Materials and Methods:

Lipopolysaccharide, carbon tetrachloride, and ethanol were used to experimentally damage the liver. Levels of aspartate aminotransferase, alanine transaminase, alkaline phosphatase, glutathione, superoxide dismutase, and malondialdehyde, known to correspond to the liver damage, were assayed.

Results:

Using three different hepatotoxins, we found that in all cases, some samples of HA and most of all the glucan-HA combination, offer strong protection against liver damage.

Conclusion:

Glucan-HA combination is a promising agent for use in liver protection.

Leaf mineral nutrient remobilization during leaf senescence and modulation by nutrient deficiency

Higher plants have to cope with fluctuating mineral resource availability. However, strategies such as stimulation of root growth, increased transporter activities, and nutrient storage and remobilization have been mostly studied for only a few macronutrients. Leaves of cultivated crops (Zea mays, Brassica napus, Pisum sativum, Triticum aestivum, Hordeum vulgare) and tree species (Quercus robur, Populus nigra, Alnus glutinosa) grown under field conditions were harvested regularly during their life span and analyzed to evaluate the net mobilization of 13 nutrients during leaf senescence. While N was remobilized in all plant species with different efficiencies ranging from 40% (maize) to 90% (wheat), other macronutrients (K-P-S-Mg) were mobilized in most species. Ca and Mn, usually considered as having low phloem mobility were remobilized from leaves in wheat and barley. Leaf content of Cu-Mo-Ni-B-Fe-Zn decreased in some species, as a result of remobilization. Overall, wheat, barley and oak appeared to be the most efficient at remobilization while poplar and maize were the least efficient. Further experiments were performed with rapeseed plants subjected to individual nutrient deficiencies. Compared to field conditions, remobilization from leaves was similar (N-S-Cu) or increased by nutrient deficiency (K-P-Mg) while nutrient deficiency had no effect on Mo-Zn-B-Ca-Mn, which seemed to be non-mobile during leaf senescence under field conditions. However, Ca and Mn were largely mobilized from roots (-97 and -86% of their initial root contents, respectively) to shoots. Differences in remobilization between species and between nutrients are then discussed in relation to a range of putative mechanisms.

Humic acid and glucan: protection against liver injury induced by carbon tetrachloride

Humic acids (HAs) have a rather pleiotropic presence, however, their biological effects are still unclear. In this study, we focused on possible hepatoprotective effects of either HA alone or in combination with β-glucan. Using a model of experimental hepatotoxicity caused by carbon tetrachloride (CCL4), we showed that both HA and the glucan-HA combination offered significant protection against hepatotoxicity, with the combination offering superior effects. Our biochemical observations were confirmed by histological evaluation. Based on the experimental data, we conclude that whereas HA has significant effects, the synergy with glucan offers superior effects.

Leaf mineral nutrient remobilization during leaf senescence and modulation by nutrient deficiency

Higher plants have to cope with fluctuating mineral resource availability. However, strategies such as stimulation of root growth, increased transporter activities, and nutrient storage and remobilization have been mostly studied for only a few macronutrients. Leaves of cultivated crops (Zea mays, Brassica napus, Pisum sativum, Triticum aestivum, Hordeum vulgare) and tree species (Quercus robur, Populus nigra, Alnus glutinosa) grown under field conditions were harvested regularly during their life span and analyzed to evaluate the net mobilization of 13 nutrients during leaf senescence. While N was remobilized in all plant species with different efficiencies ranging from 40% (maize) to 90% (wheat), other macronutrients (K-P-S-Mg) were mobilized in most species. Ca and Mn, usually considered as having low phloem mobility were remobilized from leaves in wheat and barley. Leaf content of Cu-Mo-Ni-B-Fe-Zn decreased in some species, as a result of remobilization. Overall, wheat, barley and oak appeared to be the most efficient at remobilization while poplar and maize were the least efficient. Further experiments were performed with rapeseed plants subjected to individual nutrient deficiencies. Compared to field conditions, remobilization from leaves was similar (N-S-Cu) or increased by nutrient deficiency (K-P-Mg) while nutrient deficiency had no effect on Mo-Zn-B-Ca-Mn, which seemed to be non-mobile during leaf senescence under field conditions. However, Ca and Mn were largely mobilized from roots (-97 and -86% of their initial root contents, respectively) to shoots. Differences in remobilization between species and between nutrients are then discussed in relation to a range of putative mechanisms.

Zn deficiency in Brassica napus induces Mo and Mn accumulation associated with chloroplast proteins variation without Zn remobilization

The importance of zinc (Zn) has been of little concern in human nutrition despite a strong decrease of this element in crops since the rise of high yielding varieties. For better food quality, Zn biofortification can be used, but will be optimal only if mechanisms governing Zn management are better known. Using Zn deficiency, we are able to demonstrate that Zn is not remobilized in Brassica napus (B. napus). Thus, remobilization processes should not be targeted by biofortification strategies. This study also complemented previous work by investigating leaf responses to Zn deficiency, especially from proteomic and ionomic points of view, showing for example, an increase in Manganese (Mn) content and of the Mn-dependent protein, Oxygen Evolving Enhancer.

β-(1→3)-Glucan-mannitol conjugates: scope and amazing results

It is well known that β-(1→3)-Glucans present high applicative potential in human health as immunostimulating agents. Numerous studies have highlighted this, but mainly used native polysaccharides extracted from various natural sources. These compounds are therefore inevitably polydisperse but also present structures that are not homogeneous, in an analytical point of view. This is the reason why we have achieved the chemical synthesis of small glucan-mannitol derivatives especially found in brown seaweeds. The targets differ from each other by the nature of the conjunction between the laminaribiose and the mannose or mannitol, i.e., (1→6) or (1→3). We established that (I) these molecules were efficiently obtained from glucose, laminaribiose and/or mannose derivatives; (II) the synthetic plan has to be adapted to the first connection between a glucosyl entity and the mannosyl residue; and (III) resulting pure compounds may be used as the standard for analytical purposes.

Copper-deficiency in Brassica napus induces copper remobilization, molybdenum accumulation and modification of the expression of chloroplastic proteins

During the last 40 years, crop breeding has strongly increased yields but has had adverse effects on the content of micronutrients, such as Fe, Mg, Zn and Cu, in edible products despite their sufficient supply in most soils. This suggests that micronutrient remobilization to edible tissues has been negatively selected. As a consequence, the aim of this work was to quantify the remobilization of Cu in leaves of Brassica napus L. during Cu deficiency and to identify the main metabolic processes that were affected so that improvements can be achieved in the future. While Cu deficiency reduced oilseed rape growth by less than 19% compared to control plants, Cu content in old leaves decreased by 61.4%, thus demonstrating a remobilization process between leaves. Cu deficiency also triggered an increase in Cu transporter expression in roots (COPT2) and leaves (HMA1), and more surprisingly, the induction of the MOT1 gene encoding a molybdenum transporter associated with a strong increase in molybdenum (Mo) uptake. Proteomic analysis of leaves revealed 33 proteins differentially regulated by Cu deficiency, among which more than half were located in chloroplasts. Eleven differentially expressed proteins are known to require Cu for their synthesis and/or activity. Enzymes that were located directly upstream or downstream of Cu-dependent enzymes were also differentially expressed. The overall results are then discussed in relation to remobilization of Cu, the interaction between Mo and Cu that occurs through the synthesis pathway of Mo cofactor, and finally their putative regulation within the Calvin cycle and the chloroplastic electron transport chain.

The relative abundance of oxygen alkyl-related groups in aliphatic domains is involved in the main pharmacological-pleiotropic effects of humic acids

Despite the rather common presence of humic acid (HA), our full knowledge of its biological effect is still lacking. In this article, we first performed a physicochemical characterization of several HAs, and next, we evaluated their ability to affect interleukin-2 secretion, antibody secretion, wound healing (an in vitro model using HaCaT cells), cancer growth (the Lewis lung carcinoma model), and protection against hepatotoxicity. In all tested reactions, HA showed significant stimulation on immune reactions, including suppression of cancer growth and inhibition of lipopolysaccharide-induced hepatotoxicity. These effects were dependent on its chemical properties. The pleiotropic effects of HA observed in this article suggest the possible role of these compounds in human nutrition.

Hydroponics versus field lysimeter studies of urea, ammonium and nitrate uptake by oilseed rape (Brassica napus L.)

N-fertilizer use efficiencies are affected by their chemical composition and suffer from potential N-losses by volatilization. In a field lysimeter experiment, (15)N-labelled fertilizers were used to follow N uptake by Brassica napus L. and assess N-losses by volatilization. Use of urea with NBPT (urease inhibitor) showed the best efficiency with the lowest N losses (8% of N applied compared with 25% with urea alone). Plants receiving ammonium sulphate, had similar yield achieved through a better N mobilization from vegetative tissues to the seeds, despite a lower N uptake resulting from a higher volatilization (43% of applied N). Amounts of (15)N in the plant were also higher when plants were fertilized with ammonium nitrate but N-losses reached 23% of applied N. In parallel, hydroponic experiments showed a deleterious effect of ammonium and urea on the growth of oilseed rape. This was alleviated by the nitrate supply, which was preferentially taken up. B. napus was also characterized by a very low potential for urea uptake. BnDUR3 and BnAMT1, encoding urea and ammonium transporters, were up-regulated by urea, suggesting that urea-grown plants suffered from nitrogen deficiency. The results also suggested a role for nitrate as a signal for the expression of BnDUR3, in addition to its role as a major nutrient. Overall, the results of the hydroponic study showed that urea itself does not contribute significantly to the N nutrition of oilseed rape. Moreover, it may contribute indirectly since a better use efficiency for urea fertilizer, which was further increased by the application of a urease inhibitor, was observed in the lysimeter study.

31P NMR characterization and efficiency of new types of water-insoluble phosphate fertilizers to supply plant-available phosphorus in diverse soil types

Hydroponic plant experiments demonstrated the efficiency of a type of humic acid-based water-insoluble phosphate fertilizers, named rhizosphere controlled fertilizers (RCF), to supply available phosphorus (P) to different plant species. This effect was well correlated to the root release of specific organic acids. In this context, the aims of this study are (i) to study the chemical nature of RCF using solid-state (31)P NMR and (ii) to evaluate the real efficiency of RCF matrix as a source of P for wheat plants cultivated in an alkaline and acid soil in comparison with traditional water-soluble (simple superphosphate, SSP) and water-insoluble (dicalcium phosphate, DCP) P fertilizers. The (31)P NMR study revealed the formation of multimetal (double and triple, MgZn and/or MgZnCa) phosphates associated with chelating groups of the humic acid through the formation of metal bridges. With regard to P fertilizer efficiency, the results obtained show that the RCF matrix produced higher plant yields than SSP in both types of soil, with DCP and the water-insoluble fraction from the RCF matrix (WI) exhibiting the best results in the alkaline soil. By contrast, in the acid soil, DCP showed very low efficiency, WI performed on a par with SSP, and RCF exhibited the highest efficiency, thus suggesting a protector effect of humic acid from soil fixation.

Glucan and humic acid: synergistic effects on the immune system

Humic acids are compounds resulting from decomposition of organic matter. Despite their common presence, our knowledge of their biological effects is limited, and current findings are controversial. We decided to evaluate the immunological effects of two different types of humic acids, differing in source and biochemical characteristics. Using both components either alone or in combination with the well-established yeast-derived immunomodulator glucan, we measured their effects on both the cellular (phagocytosis and tumor suppression) and humoral (antibody production and cytokine secretion) branches of immune reactions. In summary, our results suggest that humic acids are biologically active immunodulators affecting both the humoral and cellular branches of immune reactions. In addition, the two humic acids studied here are working in synergy in stimulation of the immune reaction, supporting further studies of these natural immunomodulators.

Determination of organic acids in tissues and exudates of maize, lupin, and chickpea by high-performance liquid chromatography-tandem mass spectrometry

This article describes a fast and simple methodology for the extraction and determination of organic acids in tissues and root exudates of maize, lupin, and chickpea by LC/MS/MS. Its main advantage is that it does not require sample prepurification before HPLC analysis or sample derivatization to improve sensibility. The results obtained showed good precision and accuracy, a recovery close to 100%, and no significant matrix effect. Moreover, the sensibility of the method is in general better than that of previously described methodologies, with detection limits between 15 and 900 pg injected.

Enhancing effects of new biological response modifier beta-1,3 glucan sulfate PS3 on immune reactions

Glucans have a long history as non-specific biological modulators; however, but the search for optimal chemical configuration is still on. The objective of this study was to evaluate intraperitoneal application of PS3, a sulfated derivative of a (1-->3)-beta-D-glucan isolated from sporophytes of Laminaria digitata. PS3 showed significant stimulation of phagocytic activity as well as potentiation of synthesis and release of IL-2 by splenocytes. In addition, PS3 increased NK cell-mediated killing of tumor cells both in vitro and in vivo. When combined, our observations suggest that PS3 is similarly effective as native non-sulfated (1-->3)-beta-D-glucan and is generally more active than lentinan.

Orally administered marine (1→3)-β-d-glucan Phycarine stimulates both humoral and cellular immunity

(1-->3)-beta-D-Glucans represent highly conserved structural components of cell walls in yeast, fungi, or seaweed. However, it is still unknown how they mediate their effects. The aim of this study was to evaluate both intraperitoneal and oral application of seaweed-derived (1-->3)-beta-D-glucan Phycarine. Phycarine showed significant stimulation of phagocytosis by peripheral blood cells. In addition, the efficiency of chemotherapy of Lewis lung carcinoma with cyclophosphamide was potentiated by Phycarine administration. Phycarine also strongly shortened the recovery of leucopenia caused either by chemotherapy or irradiation. Besides the role in stimulation of cellular immunity, we also found a significant increase of antibody formation. Using a suckling rat model for evaluation of the absorption and tissues distribution of enterally administered (125)I-Phycarine, we found that the majority of Phycarine was detected in the stomach and duodenum 5 min after the administration. This amount sharply decreased during first 30 min. A significant amount of Phycarine entered proximal intestine in a shortly after the gavage. Its transit through proximal intestine was decreasing with time and simultaneously increasing in the ileum. Systemic blood levels were very low (less than 0.5%). Taken together, these observations suggest that Phycarine is similarly effective both after i.p. and oral application, has very strong stimulating effects on three types of experimentally induced leucopenia and stimulates both humoral and cellular branch of immune reactions. The majority of Phycarine can be detected throughout the gastrointestinal tract, supporting the feasibility of enteral administration of Phycarine in the treatment of gastrointestinal diseases.

Recent Progress in the Field of β-(1,3)-Glucans and New Applications

Beta-(1,3)-glucans are widely distributed within microorganisms or seaweeds in which they act as membrane components or for energy storage, respectively. Since these glucans are not biosynthesized by mammals, they are likely to activate the immune system of their host. Since the discovery of their positive involvement as immunomodulator agents, numerous studies were published all around the glycosciences. These works deal with purification procedures, analytical chemistry, synthetic processes, chemical modification of the natural polysaccharides, determination of their physicochemical properties, and assessment of their biological and medicinal effects through in vitro and in vivo studies. This article aims at presenting some recent results linked to beta-(1,3)-glucans through two closely connected points of view, i.e. biology and chemistry. Biological aspects will be focused more particularly on discovery of some receptors present on immunocompetent cells and scope and limitations of chemical synthesis and/or modifications will be described. Moreover, this paper will also introduce some new chemo-enzymatic synthetic methods using wild-type or mutant glycosidases and will be extended to novel opportunities of applications of beta-(1,3)-glucans in nanotechnology resulting from a better understanding of their self-assembling propensity in aqueous media.

Cloning and biochemical characterization of the fucanase FcnA: definition of a novel glycoside hydrolase family specific for sulfated fucans

Sulfated fucans are matrix polysaccharides from marine brown algae, consisting of an alpha-L-fucose backbone substituted by sulfate-ester groups, masked with ramifications, and containing other monosaccharide residues. We here report on the characterization of a novel glycoside hydrolase (FcnA) specific for the degradation of sulfated fucans. This glycoside hydrolase was purified to electrophoretic homogeneity from a Flavobacteriaceae referred to as SW5. The gene fcnA was cloned and sequenced (3021 nucleotides), and the protein (1007 amino acids) was produced in Escherichia coli. FcnA exhibited a modular architecture consisting of a 400-residue-long N-terminal domain followed by three repeated domains predicted to adopt an immunoglobulin fold and by an 80-amino acid-long C-terminal domain. A truncated recombinant protein encompassing the N-terminal domain and the immunoglobulin-like repeats was shown to retain the enzyme activity. The N-terminal catalytic domain shared approximately 25% of sequence identity with two patented fucanase genes, and these three fucanases delineate a new family of glycoside hydrolases. As shown by size-exclusion chromatography (SEC) and 1H-NMR analyses, the fucanase FcnA proceeds according to an endolytic mode of action and cleaves the alpha-(1-->4) glycosidic linkages within the blocks of repeating motifs [-->4)-alpha-L-fucopyranosyl-2,3-disulfate-(1-->3)-alpha-L-fucopyranosyl-2-sulfate-(1-->]n.

Isolation and culture of a marine bacterium degrading the sulfated fucans from marine brown algae

Fucoidans are matrix polysaccharides from marine brown algae, consisting of an alpha-L-fucose backbone substituted by sulfate-ester groups and masked with ramifications containing other monosaccharide residues. In spite of their interest as biologically active compounds in a number of homologous and heterologous systems, no convenient sources with fucanase activity are available yet for the degradation of the fucalean algae. We here report on the isolation, characterization, and culture conditions of a bacterial strain capable of degrading various brown algal fucoidans. This bacterium, a member of the family Flavobacteriaceae, was shown to secrete fucoidan endo-hydrolase activity. An extracellular enzyme preparation was used to degrade the fucoidan from the brown alga Pelvetia canaliculata. End products included a tetrasaccharide and a hexasaccharide made of the repetition of disaccharidic units consisting of alpha-1-->3-L-fucopyranose-2-sulfate-alpha-1-->4-L-fucopyranose-2,3-disulfate, with the 3-linked residues at the nonreducing end.