Nodule phosphorus requirement and O2 uptake in common bean genotypes under phosphorus deficiency

Abstract

The effect of P deficiency on nodulation, nodule P content, nodule O₂ permeability and N fixation rates in Phaseolus vulgaris–rhizobia symbiosis was studied under glasshouse conditions. Four recombinant inbred lines (L34, L83, L115 and L147) and one variety cultivated in Morocco (Concesa) were inoculated with Rhizobium tropici CIAT 899 in hydroaeroponic culture. Two P levels i.e. 75 (deficient level) and 250 µmol plant^?1 week^?1 P (sufficient level) were applied and the trial was assessed 42 days after transplanting that coincide with plant flowering stage. Under P-deficiency, decrease of plant growth (18%) and nodule biomass (19%) was detected and significantly pronounced in the sensitive line L147 compared with the remaining genotypes. Additionally, under P-deficiency, the efficiency in use of rhizobial symbiosis, estimated by the slope of the regression model of shoot biomass as a function of nodule biomass, was significantly increased in the four lines. This constraint did not significantly influence nodule P content in Concesa, but it was 24 and 41% lower in the tolerant and in the sensitive lines, respectively. Nodule P content was positively correlated to nodule biomass, r=0.75, and shoot N, r=0.92. These genotypic variations were associated with variability in nodule O₂ permeability that was significantly affected by the P level-bean genotype interaction. Under P-deficiency, nodule O₂ permeability was significantly reduced in the tested genotypes and accompanied with a decrease in shoot N content, especially in the sensitive lines (35%). Moreover, the ratios plant N fixed: nodule P content and plant N fixed:nodule dry weight were affected under P-deficiency in four lines with an exception observed in Concesa. Depending on the observed data we concluded that N₂ fixation efficiency could be influenced by nodulation and level of nodule P requirement which depend on both bean genotypes and P level.     

In vitro destruction of Eimeria oocysts by essential oils

This study aims to assess the ability of essential oils (EOs) to destroy Eimeria oocyst in vitro using microscopic counting and 273 nm absorbing material release. A screening for the ability of ten EOs to destroy Eimeria oocyst was carried out in liquid medium. Out of these ten, artemisia, tea tree, thyme and clove EOs were identified as being the most effective. The treatment of Eimeria oocyst with these EOs leads to their lysis as shown by the release of substances absorbing at 273 nm. These results were obtained after approximately three hours contact. Four EOs were proven to destroy Eimeria oocysts in a few hours at low concentration. This destructive effect is a consequence of their lysis. This work is a preliminary contribution aiming to develop a new generation of natural efficient agents for destroying Eimeria oocyst to fight coccidiosis in broiler chicken.     

Nodulation and root growth increase in lower soil layers of water‐limited faba bean intercropped with wheat

Below‐ground niche complementarity in legume–cereal intercrops may improve resource use efficiency and root adaptability to environmental constraints. However, the effect of water limitation on legume rooting and nodulation patterns in intercropping is poorly understood. To advance our knowledge of mechanisms involved in water‐limitation response, faba bean (Vicia faba L.) and wheat (Triticum aestivum L.) were grown as mono‐ and intercrops in soil‐filled plexiglass rhizoboxes under water sufficiency (80% of water‐holding capacity) and water limitation (30% of water‐holding capacity). We examined whether intercropping facilitates below‐ground niche complementarity under water limitation via interspecific root stratification coupled with modified nodulation patterns. While no significant treatment effects were measured in intercropped wheat growth parameters, water limitation induced a decrease in shoot and root biomass of monocropped wheat. Likewise, shoot biomass and height, and root length of monocropped faba bean significantly decreased under water limitation. Conversely, water limitation stimulated root biomass of intercropped faba bean in the lower soil layer (15–30 cm soil depth). Similarly, total nodule number of faba bean roots as well as nodule number in the lower soil layer increased under intercropping regardless of water availability. Under water limitation, intercropping also led to a significant increased nodule biomass (48%) in the lower soil layer as compared to monocropping. The enhanced nodulation in the lower soil layer and the associated increase in root and shoot growth provides evidence for a shift in niche occupancy when intercropped with wheat, which improves water‐limited faba bean performance.     

High‐quality spontaneous spawning in greater amberjack (Seriola dumerili,Risso 1810) and its comparison with GnRHa implants or injections

Production of sufficient high‐quality eggs of greater amberjack (Seriola dumerili) still constitutes the main bottleneck for commercial production of this species. The main objective of this study was to compare the quality of spontaneous spawn of greater amberjack with those obtained by either GnRHa injection or GnRHa implant protocols. Captive amberjack broodstock were distributed in three circular tanks of 40 m³. Broodstock from Tank 1 were not hormonally induced and spawned spontaneously, whereas those of Tank 2 were intramuscularly injected with GnRHa (20 µg/kg body weight) and those of Tank 3 were given EV‐500 µg GnRHa implants. The number of eggs per spawn obtained in the broodstock without hormonal treatment was larger than in those obtained with injections or implants. Egg quality was best in broodstock with spontaneous spawn, followed by GnRHa‐injected fish and then GnRHa implants. Besides, size of larvae from control and injected broodstock was similar between them and significantly higher (p < 0.01) than those from GnRHa implant spawn. Overall, this study showed that it is possible to obtain very high‐quality spontaneous spawn in greater amberjack, providing the adequate conditions. Furthermore, GnRHa weekly injections lead to similar egg viability and hatching rates than spontaneous spawn and higher fertilization rates than GnRHa hormonal implants, which is better than in previous studies.     

Photolysis of the herbicide sulcotrione: formation of a major photoproduct and its toxicity evaluation

BACKGROUND: Sulcotrione is a selective herbicide marketed for use in maize since 1993, but its environmental fate is not yet fully elucidated. A major metabolite resulting from cleavage between the two ring moieties, leading to 2‐chloro‐4‐mesylbenzoic acid (CMBA), has been identified; it presents a rather low toxicity. In photochemical studies this compound has also been claimed to be formed in high proportions. The present authors recently found that, under irradiation, sulcotrione mainly yields a cyclization product (CP). Thus, Sulcotrione photochemistry is still a matter of debate. The aim of the present work was to give an unequivocal answer to this issue. The potential toxicity of CP, CMBA and sulcotrione towards three organisms considered as representative of aquatic ecosystems was also evaluated. RESULTS: The main transformation product of sulcotrione is the cyclization product (CP), and CMBA is formed in smaller amounts. For the toxicological approach, the tested organisms were a bacterium, Vibrio fischeri (Bejerinck) Lehmann & Neumann, an alga, Pseudokirchneriella subcapitata (Korshikov) Hindak, and a protozoan, Tetrahymena pyriformis (Ehrenberg) Lwoff. Sulcotrione is more harmful towards the alga, but CP is more toxic to the bacterium and the protozoan. It must be noted that the measured toxicities are nonetheless rather low. CONCLUSION: On irradiation, sulcotrione mainly gives the photocyclization product, which presents a higher toxicity than sulcotrione and CMBA. This cyclization product should thus be considered in sulcotrione environmental risk assessment. Copyright © 2008 Society of Chemical Industry     

A conserved mutation in an ethylene biosynthesis enzyme leads to andromonoecy in melons

Andromonoecy is a widespread sexual system in angiosperms characterized by plants carrying both male and bisexual flowers. In melon, this sexual form is controlled by the identity of the alleles at the andromonoecious (a) locus. Cloning of the a gene reveals that andromonoecy results from a mutation in the active site of 1-aminocyclopropane-1-carboxylic acid synthase. Expression of the active enzyme inhibits the development of the male organs and is not required for carpel development. A causal single-nucleotide polymorphism associated with andromonoecy was identified, which suggests that the a allele has been under recent positive selection and may be linked to the evolution of this sexual system.     

Inoculation with Phosphate Solubilizing Mesorhizobium Strains Improves the Performance of Chickpea (Cicer aritenium L.) Under Phosphorus Deficiency

The use of phosphate-solubilising bacteria as inoculants increases plant phosphorus (P) uptake and thus crop yield. Strains from the genus Mesorhizobium are among the most powerful phosphate solubilizing microorganisms. In order to study efficiency in P uptake and N₂ fixation in chickpea (Cicer aritenium), forty-two rhizobia strains natively from Tunisian soils were studied in symbiosis with the chickpea variety “Béja1” which is frequently cultivated in Tunisia. Plants were inoculated separately with these strains under controlled conditions in perlite under two sources of P i.e. soluble (KH₂PO₄) and insoluble P (Ca₂HPO₄). At flowering stage, growth, nodulation, P uptake and N₂ fixation were assessed in all symbiotic combinations. The results showed that the S27 strain efficiently mobilized P into plants, observed as a significant increase of plant P content when insoluble P (Ca₂HPO₄) was supplied to the soil. This was associated with a significant increase in plant biomass, nodule number and N content under insoluble P conditions. Additionally, inoculation with the Mesorhizobium strain S27 significantly increased the root acid phosphatase activity under insoluble P. This study also shows significant correlations found between plant P content and acid phosphatase activity under low P conditions which may highlight the contribution of acid phosphatases in increasing P use efficiency. A field experiment also showed that most of the chickpea analyzed parameters were improved when plants inoculated with two selected rhizobia strains (S26 and S27) and supplied with P2O5. Overall, these findings postulate that rhizobial inoculation should not only be based on the effectiveness of strains regarding N fixation, but also to other traits such as P solubilisation potential.     

Cervico-vaginal mucus (CVM) – an accessible source of immunologically informative biomolecules

Cervico-vaginal mucus (CVM), the product of epithelial cells lining the uterus, cervix and vagina, is secreted to facilitate uterine lubrication and microbial clearance. Predominantly composed of water and mucins, CVM also contains high levels of immuno-active proteins such as immunoglobulin A (IgA), lactoferrin and lysozyme which protect against infection by blocking adhesion and mediating microbial killing. The repertoire of cytokines, chemokines and antimicrobial peptides is predominantly generated by the secretions of endometrial epithelial cells into the uterine lumen and concentrated in the CVM. The quantity and relative proportions of these inflammatory biomarkers are affected by diverse factors including the estrus cycle and health status of the animal and therefore potentially provide important diagnostic and prognostic indicators. We propose that measuring molecular signatures in bovine CVM could be a useful approach to identifying and monitoring genital tract pathologies in beef and dairy cows.     

Phaseolus vulgaris-rhizobia symbiosis increases the phosphorus uptake and symbiotic N2 fixation under insoluble phosphorus

Five north Tunisian native rhizobia were tested in symbiosis with ‘Coco-blanc’ variety under two phosphorus (P) supplies [P-sufficient and insoluble P (IP)] at 250 μmol P plant^?1. At flowering stage, responses against IP were assessed and indicated that inoculation with P.Ps.09 produced a high nodule biomass (0.12g). Similarly, P.Tb.09 produced 0.08 g nodule biomass under both P and P.Bj.09 that significantly increased nodule number under IP. Shoot biomass exhibited high dry weight with P.Tb.09 and CIAT899 (1.6 g plant^?1). Inoculation with CIAT899 produced a high root biomass under both P. Analysis of a halo diameter of clear zone rounding each colony under IP indicated that P.Tb.09 has developed high halo Ø (1.7cm). These variations were associated under IP with a decrease of pH by P.Ar.09 and with increase in shoot phosphatase activity by P.Ar.09, P.Bj.09, P.OM.09 and P.Ps.09. The use of P-efficient rhizobia may constitute an adaptive mechanism against P-deficiency tolerance.     

INTERACTIONS BETWEEN COMMON BEAN GENOTYPES AND RHIZOBIA STRAINS ISOLATED FROM MOROCCAN SOILS FOR GROWTH,PHOSPHATASE AND PHYTASE ACTIVITIES UNDER PHOSPHORUS DEFICIENCY CONDITIONS

The improvement of common bean production requires the selection of effective rhizobia strains and Phaseolus vulgaris genotypes adapted to available soil phosphorus limitations. The interactions between bean genotypes and rhizobia were studied in hydroponic culture using six genotypes and four strains, CIAT899 as reference and three strains isolated from nodule of farmer's fields in the Marrakech region. The phosphorus (P) sub-deficiency caused a significant reduction on shoot biomass in some bean genotype-rhizobia combinations. Nodule biomass is significantly more reduced under P limitation for several combinations tested. Bean plants inoculated with these local rhizobial strains showed higher nodulation and an increase of nodules phytase and phosphatase activities under phosphorus sub-deficiency especially for RhM11 strain. It was concluded that the studied bean-rhizobia symbiosis differ in their adaptation to phosphorus sub-deficiency and the nodule phosphatases and phytases activities may constitute a strategy of nodulated bean plants to adapt their nitrogen fixation to P deficiency.