Rhizobial Nodulation Research Articles

The Characteristics of Poral Space as Habitat of Soybean Roots and Rhizobium Nodules

The objective of the paper was to emphasize the characteristics of the poral space (quantified according to their size and shape) of an intensely irrigated soil, representing the habitat for soybean roots and Rhizobium bacteria nodulation. The studied site is located in Southern Bărăgan Plain, Perișoru region. The soil is Vermic Chernozem (according to SRTS-2012) formed in carbonate loess like deposits. The climate is temperate continental with an average annual temperature of 10.8°C, and an average annual precipitation of 480 mm. The poral space was quantitatively evaluated at microscopic scale, using image analysis on oriented soil thin sections with the help of an image-analyzer computer. The image analysis allowed the quantitative evaluation at microscopic scale of the undisturbed structure and the adjacent porosity, in 2-D dimension (in thin sections). The pores were divided according to their shape in three classes (regular, irregular and elongated pores), and further each shape class was divided into seven size classes according to the equivalent pore diameter (ranging between 100 and >1000 µm). The result showed, unspecific conditions in the studied Chernozem, thus: Ap horizon was more compacted than the underlined Apt, consequently the total porosity was lower (0.21 m2 m-2 ) into the top Ap horizon, comparing to the underlined Apt (0.33 m2 m-2 ). In agreement with the data obtained by means of image analysis (pores quantified according to their size and shape), the oriented thin sections gave a clear representation of the genesis, location and the characteristics of the poral space. The soybeans roots developed mainly into the areas with intense biological activity. The soil macro- and mesofauna proved to be good habitat builders for soybean roots and the Rhizobium nodules, even in the conditions of a droughty period with the irrigation application delay.

Illumina sequencing of 16S rRNA tag shows disparity in rhizobial and non-rhizobial diversity associated with root nodules of mung bean (Vigna radiata L.) growing in different habitats in Pakistan

In Rhizobium-legume symbiosis, the nodule is the most frequently studied compartment, where the endophytic/symbiotic microbiota demands critical investigation for development of specific inocula. We identified the bacterial diversity within root nodules of mung bean from different growing areas of Pakistan using Illumina sequencing of 16S rRNA gene. We observed specific OTUs related to specific site where Bradyrhizobium was found to be the dominant genus comprising of 82–94% of total rhizobia in nodules with very minor fraction of sequences from other rhizobia at three sites. In contrast, Ensifer (Sinorhizobium) was single dominant genus comprising 99.9% of total rhizobial sequences at site four. Among non-rhizobial sequences, the genus Acinetobacter was abundant (7–18% of total sequences), particularly in Bradyrhizobium-dominated nodule samples. Rhizobia and non-rhizobial PGPR isolated from nodule samples include Ensifer, Bradyrhizobium, Acinetobacter, Microbacterium and Pseudomonas strains. Co-inoculation of multi-trait PGPR Acinetobacter sp. VrB1 with either of the two rhizobia in field exhibited more positive effect on nodulation and plant growth than single-strain inoculation which favors the use of Acinetobacter as an essential component for development of mung bean inoculum. Furthermore, site-specific dominance of rhizobia and non-rhizobia revealed in this study may contribute towards decision making for development and application of specific inocula in different habitats.

Rarity of monodominance in hyperdiverse Amazonian forests

Tropical forests are known for their high diversity. Yet, forest patches do occur in the tropics where a single tree species is dominant. Such “monodominant” forests are known from all of the main tropical regions. For Amazonia, we sampled the occurrence of monodominance in a massive, basin-wide database of forest-inventory plots from the Amazon Tree Diversity Network (ATDN). Utilizing a simple defining metric of at least half of the trees ≥ 10 cm diameter belonging to one species, we found only a few occurrences of monodominance in Amazonia, and the phenomenon was not significantly linked to previously hypothesized life history traits such wood density, seed mass, ectomycorrhizal associations, or Rhizobium nodulation. In our analysis, coppicing (the formation of sprouts at the base of the tree or on roots) was the only trait significantly linked to monodominance. While at specific locales coppicing or ectomycorrhizal associations may confer a considerable advantage to a tree species and lead to its monodominance, very few species have these traits. Mining of the ATDN dataset suggests that monodominance is quite rare in Amazonia, and may be linked primarily to edaphic factors.

Arbuscular Mycorrhizal Fungus Improves Rhizobium–Glycyrrhiza Seedling Symbiosis under Drought Stress

Rhizobia and arbuscular mycorrhizal (AM) fungi can potentially alleviate the abiotic stress on the legume Glycyrrhiza (licorice), while the potential benefits these symbiotic microbes offer to their host plant are strongly influenced by environmental factors. A greenhouse pot experiment was conducted to investigate the effects of single and combined inoculation with a rhizobium Mesorhizobium tianshanense Chen and an AM fungus Rhizophagus irregularis Walker & Schuessler on Glycyrrhiza uralensis Fisch. seedling performance under different water regimes. Drought stress inhibited rhizobium nodulation but increased mycorrhizal colonization. Furthermore, co-inoculation of rhizobium and AM fungus favored nodulation under both well-watered and drought stress conditions. Glycyrrhiza seedling growth showed a high mycorrhizal dependency. The seedlings showed a negative growth dependency to rhizobium under well-watered conditions but showed a positive response under drought stress. R. irregularis-inoculated plants showed a much higher stress tolerance index (STI) value than M. tianshanense-inoculated plants. STI value was more pronounced when plants were co-inoculated with R. irregularis and M. tianshanense compared with single-inoculated plants. Plant nitrogen concentration and contents were significantly influenced by inoculation treatments and water regimes. R. irregularis inoculation significantly increased plant shoot and root phosphorus contents. AM fungus inoculation could improve Glycyrrhiza plant–rhizobium symbiosis under drought stress, thereby suggesting that tripartite symbiotic relationships were more effective for promoting plant growth and enhancing drought tolerance.

Rhizobium inoculation and phosphate fertilization effects on productive and qualitative traits of guar (Cyamopsis tetragonoloba (L.) Taub.)

Guar (Cyamopsis tetragonoloba (L.) Taub.), a grain legume grown in India, Pakistan and the United States, draws interest for irrigated environments in the Mediterranean areas. A limitation to widespread guar adaptation in this environment is its low capability to develop N-fixing Rhizobium nodulation. A study was conducted in South-Eastern Sicily, Italy in 2005 and 2006, to examine three levels of Rhizobium inoculation (non-inoculated, inoculated at sowing, inoculated at sowing plus at the third true leaf) and two levels of applied phosphorus fertilizer (0 and 40 kg ha−1 P). Plant height, pods per plant, seed yield, number of nodules per plant and seed galactomannan content were measured. No significant difference was found due to year of cultivation. Plant height was not significantly affected by Rhizobium or P fertilizer. Phosphorus fertilizer promoted the number of pods per plant, especially when bacteria inoculation was applied. Seed yield was significantly increased by inoculation and phosphorus levels. Inoculant caused a significant increase in seed yield (by 34%) from 2.2 t ha-1 (I0) to 3.4 t ha-1 (I2), whereas phosphorus application enhanced yields by 18% when P0 (2.7 t ha-1) were compared with P40 plots (3.3 t ha-1). Without inoculant there was no nodulation, whereas the number of nodules per plant increased to 14 in plots with the highest level of inoculation. Fertilizer P application did not affect Rhizobium nodulation. Galactomannan content was not influenced by inoculation and P fertilization, however increased seed yield resulting from inoculation and P fertilization led to increased galactomannan production per hectare.

The Nodule-Specific PLAT Domain Protein NPD1 Is Required for Nitrogen-Fixing Symbiosis.

Symbiotic nitrogen fixation by rhizobia in legume root nodules is a key source of nitrogen for sustainable agriculture. Genetic approaches have revealed important roles for only a few of the thousands of plant genes expressed during nodule development and symbiotic nitrogen fixation. Previously, we isolated >100 nodulation and nitrogen fixation mutants from a population of Tnt1-insertion mutants of Medigaco truncatula Using Tnt1 as a tag to identify genetic lesions in these mutants, we discovered that insertions in a M. truncatula nodule-specific polycystin-1, lipoxygenase, α-toxin (PLAT) domain-encoding gene, MtNPD1, resulted in development of ineffective nodules. Early stages of nodule development and colonization by the nitrogen-fixing bacterium Sinorhizobium meliloti appeared to be normal in the npd1 mutant. However, npd1 nodules ceased to grow after a few days, resulting in abnormally small, ineffective nodules. Rhizobia that colonized developing npd1 nodules did not differentiate completely into nitrogen-fixing bacteroids and quickly degraded. MtNPD1 expression was low in roots but increased significantly in developing nodules 4 d postinoculation, and expression accompanied invading rhizobia in the nodule infection zone and into the distal nitrogen fixation zone. A functional MtNPD1:GFP fusion protein localized in the space surrounding symbiosomes in infected cells. When ectopically expressed in tobacco (Nicotiana tabacum) leaves, MtNPD1 colocalized with vacuoles and the endoplasmic reticulum. MtNPD1 belongs to a cluster of five nodule-specific single PLAT domain-encoding genes, with apparent nonredundant functions.

Effect of Rhizobium Symbiosis on Low-Temperature Tolerance and Antioxidant Response in Alfalfa (Medicago sativa L.).

Low temperature-induced stress is a major environmental factor limiting the growth and development of plants. Alfalfa (Medicago sativa L.) is a legume well known for its tolerance of extreme environments. In this study, we sought to experimentally investigate the role of rhizobium symbiosis in alfalfa’s performance under a low-temperature stress condition. To do this, alfalfa “Ladak+” plants carrying active nodules (AN), inactive nodules (IN), or no nodules (NN) were exposed to an imposed low temperature stress and their survivorship calculated. The antioxidant defense responses, the accumulation of osmotic regulation substances, the cell membrane damage, and the expression of low temperature stress-related genes were determined in both the roots and the shoots of alfalfa plants. We found that more plants with AN survived than those with IN or NN under the same low temperature-stress condition. Greater activity of oxidation protective enzymes was observed in the AN and IN groups, conferring higher tolerance to low temperature in these plants. In addition, rhizobia nodulation also enhanced alfalfa’s ability to tolerate low temperature by altering the expression of regulatory and metabolism-associated genes, which resulted in the accumulation of soluble proteins and sugars in the nodulated plants. Taken together, the findings of this study indicate that rhizobium inoculation offers a practical way to promote the persistence and growth potential of alfalfa “Ladak+” in cold areas.

The modulation of leguminous plant ethylene levels by symbiotic rhizobia played a role in the evolution of the nodulation process

Ethylene plays an important role in regulating the rhizobial nodulation process. Consequently, numerous strains of rhizobia possess the ability to decrease plant ethylene levels by the expression of the enzyme 1-aminocyclopropane-1-carboxylate (ACC) deaminase or via the production of rhizobitoxine, thus, leading to an increased ability to nodulate leguminous plants. Nevertheless, not much is understood about the prevalence of these ethylene modulation genes in different rhizobial groups nor their role in the evolution of the symbiotic process.In this work, we analyze the prevalence and evolution of the enzymes ACC deaminase (AcdS) and dihydrorhizobitoxine desaturase (RtxC) in 395 NodC+ genomes from different rhizobial strains isolated from a wide range of locations and plant hosts, and discuss their importance in the evolution of the symbiotic process.The obtained results show that AcdS and RtxC are differentially prevalent in rhizobial groups, indicating the existence of several selection mechanisms governed by the rhizobial strain itself and its evolutionary origin, the environment, and, importantly, the leguminous plant host (co-evolution). Moreover, it was found that the prevalence of AcdS and RtxC is increased in Bradyrhizobium and Paraburkholderia, and lower in other groups. Data obtained from phylogenetic, evolutionary as well as gene localization analysis support the previous hypotheses regarding the ancient origin of the nodulation abilities in Bradyrhizobium and Paraburkholderia, and brings a new perspective for the importance of ethylene modulation genes in the development of the symbiotic process. The acquisition of AcdS by horizontal gene transfer and a positive selection in other rhizobial groups indicates that this enzyme plays an important role in the nodulation process of many rhizobia. On the other hand, RtxC is negatively selected in most symbioses.Understanding the evolution of ethylene modulation genes in rhizobia may be the key to the development of new strategies aiming for an increased nodulation and nitrogen fixation process.

Identification of Soybean Genes Whose Expression is Affected by the Ensifer fredii HH103 Effector Protein NopP.

In some legume–rhizobium symbioses, host specificity is influenced by rhizobial nodulation outer proteins (Nops). However, the genes encoding host proteins that interact with Nops remain unknown. We generated an Ensifer fredii HH103 NopP mutant (HH103ΩNopP), and analyzed the nodule number (NN) and nodule dry weight (NDW) of 10 soybean germplasms inoculated with the wild-type E. fredii HH103 or the mutant strain. An analysis of recombinant inbred lines (RILs) revealed the quantitative trait loci (QTLs) associated with NopP interactions. A soybean genomic region containing two overlapping QTLs was analyzed in greater detail. A transcriptome analysis and qRT-PCR assay were used to identify candidate genes encoding proteins that interact with NopP. In some germplasms, NopP positively and negatively affected the NN and NDW, while NopP had different effects on NN and NDW in other germplasms. The QTL region in chromosome 12 was further analyzed. The expression patterns of candidate genes Glyma.12g031200 and Glyma.12g073000 were determined by qRT-PCR, and were confirmed to be influenced by NopP.

Exploring the use of legumes as host plant species in Glomus mosseae sporulation

The production of high quality, large scale, pathogen free and homogenous mycorrhizal inoculums are required for research purposes and soil bio-fertility. In the current study, a pot culture technique was followed to produce healthy quality and mass quantity of Glomus mosseae spores for research purposes. Five legumes plants were selected {(pea (Pisum sativum), broad bean, (Vicia faba) black eyed beans (Vigna unguiculata) soybean (Glycine max), and mung beans (Phaseolus aureus)}. The legumes were grown for two months under controlled conditions after pre-inoculated with healthy G. mosseae spores. The highest number of spores was counted in the mung beans rhizosphere and it was the best host in nodules weight production and root colonization rate. Soybeans produced the lowest spore’s number. It was found that the correlation between root colonization rate and spores number in the soil was positive. The rhizobium nodule weight was related positively with arbuscular mycorrhizal fungi spores manipulations in the soil.

Signalling in actinorhizal root nodule symbioses.

Plants able to establish a nitrogen-fixing root nodule symbiosis with the actinobacterium Frankia are called actinorhizal. These interactions lead to the formation of new root organs, called actinorhizal nodules, where the bacteria are hosted intracellularly and fix atmospheric nitrogen thus providing the plant with an almost unlimited source of nitrogen for its nutrition. Like other symbiotic interactions, actinorhizal nodulation involves elaborate signalling between both partners of the symbiosis, leading to specific recognition between the plant and its compatible microbial partner, its accommodation inside plant cells and the development of functional root nodules. Actinorhizal nodulation shares many features with rhizobial nodulation but our knowledge on the molecular mechanisms involved in actinorhizal nodulation remains very scarce. However recent technical achievements for several actinorhizal species are allowing major discoveries in this field. In this review, we provide an outline on signalling molecules involved at different stages of actinorhizal nodule formation and the corresponding signalling pathways and gene networks.

Distinctive Patterns of Flavonoid Biosynthesis in Roots and Nodules of Datisca glomerata and Medicago spp. Revealed by Metabolomic and Gene Expression Profiles.

Plants within the Nitrogen-fixing Clade (NFC) of Angiosperms form root nodule symbioses with nitrogen-fixing bacteria. Actinorhizal plants (in Cucurbitales, Fagales, Rosales) form symbioses with the actinobacteria Frankia while legumes (Fabales) form symbioses with proteobacterial rhizobia. Flavonoids, secondary metabolites of the phenylpropanoid pathway, have been shown to play major roles in legume root nodule symbioses: as signal molecules that in turn trigger rhizobial nodulation initiation signals and acting as polar auxin transport inhibitors, enabling a key step in nodule organogenesis. To explore a potentially broader role for flavonoids in root nodule symbioses across the NFC, we combined metabolomic and transcriptomic analyses of roots and nodules of the actinorhizal host Datisca glomerata and legumes of the genus Medicago. Patterns of biosynthetic pathways were inferred from flavonoid metabolite profiles and phenylpropanoid gene expression patterns in the two hosts to identify similarities and differences. Similar classes of flavonoids were represented in both hosts, and an increase in flavonoids generally in the nodules was observed, with differences in flavonoids prominent in each host. While both hosts produced derivatives of naringenin, the metabolite profile in D. glomerata indicated an emphasis on the pinocembrin biosynthetic pathway, and an abundance of flavonols with potential roles in symbiosis. Additionally, the gene expression profile indicated a decrease in expression in the lignin/monolignol pathway. In Medicago sativa, by contrast, isoflavonoids were highly abundant featuring more diverse and derived isoflavonoids than D. glomerata. Gene expression patterns supported these differences in metabolic pathways, especially evident in a difference in expression of cinnamic acid 4-hydroxylase (C4H), which was expressed at substantially lower levels in D. glomerata than in a Medicago truncatula transcriptome where it was highly expressed. C4H is a major rate-limiting step in phenylpropanoid biosynthesis that separates the pinocembrin pathway from the lignin/monolignol and naringenin-based flavonoid branches. Shikimate O-hydroxycinnamoyltransferase, the link between flavonoid biosynthesis and the lignin/monolignol pathway, was also expressed at much lower levels in D. glomerata than in M. truncatula. Our results indicate (a) a likely major role for flavonoids in actinorhizal nodules, and (b) differences in metabolic flux in flavonoid and phenylpropanoid biosynthesis between the different hosts in symbiosis.

Study on the effect of different levels of organic and inorganic fertilizers on microbial enzymes and soil mesofauna in soybean ecosystem

Soybean (Glycine max (L) Merril). is also called Golden bean belongs to family Fabaceae is native to China having high nutritive value and oil content. Due to usage of inorganic fertilizers the fertility of soil and yield soybean has declined. Organic manures known to increase the soil fertility, structure and also influence the microbial enzymes activity and soil mesofauna. In this context the present investigation was undertaken to study, the different doses of farm yard manure and chemical fertilizers on the soil mesofauna and microbial enzymes at GKVK, Bangalore during the year 2013-2014. The investigation revealed that higher abundance of soil mesofauna (18.53) was recorded in 20 tons of FYMha-1 compared to the treatments with recommended package of practices (12.35) and inorganic fertilizer (10.30) alone. Soil mesofauna exhibited a significant positive relation with the microbial enzymes like dehydrogenase, acid and alkaline phosphtases and urease. The results of the multiple linear regression analysis showed that the influence of exchangeable calcium, available potassium and available phosphorous, exchangeable magnesium, dehydrogenase, alkaline phosphatase and urease on the abundance of soil mesofauna was up to 79 per cent. Higher rhizobium nodule number (64.93/plant) and yield (16.01 q/ha) of soybean found to increase with increase in farmyard manure application.

Towards a better understanding of agronomic and soil basis for possible charcoal root rot control and production improvement in bean

Macrophomina phaseolina causes charcoal root rot (CRR) in numerous crops worldwide. However, structural progression of CRR epidemics in association with bean agro-ecosystems is little understood. Thus, progression of CRR epidemics in interaction with 13 agro-ecological variables was characterised in 48 commercial bean fields. Frequency of pathogen isolated from root was assessed at vegetative (V3), flowering-podding (R6-7) and pod maturity (R9) growth stages. Two principal factors accounting for 89% of total data variance characterised CRR epidemics. Rhizobial nodulation and cultivation–depth, clay–pH, date–preceding crop, urea–bean class and urea–herbicide interactions accounted for 50% CRR epidemic dynamics. Sixty-five percent of production variance was explained by soil clay, bean class, colonisation, planting date and depth, cultivation method, preceding crop, nodulation, herbicide and urea application. The present findings enabled us to explain a noticeable part of variations in productivity among the bean CRR pathosystems with the help of certain agricultural and environmental events for sustainable agriculture purposes.

The expression of an exogenous ACC deaminase by the endophyte Serratia grimesii BXF1 promotes the early nodulation and growth of common bean.

In this work, we studied the effect of ACC deaminase production by the bacterial endophyte Serratia grimesi BXF1, and its impact on the nodulation process of common bean. The results obtained indicate that ACC deaminase is an asset to the synergetic interaction between rhizobia and the endophyte, positively contributing to the overall legume-rhizobia symbiosis by regulating inhibitory ethylene levels that might otherwise inhibit nodulation and overall plant growth. The use of rhizobia together with an ACC deaminase-producing endophyte is, therefore, an important strategy for the development of new bacterial inoculants with increased performance.

Multiple Nodulation Genes Are Up-Regulated During Establishment of Reniform Nematode Feeding Sites in Soybean

The semi-endoparastic reniform nematode (Rotylenchulus reniformis) infects over 300 plant species. Females penetrate host roots and induce formation of complex, multinucleate feeding sites called syncytia. While anatomical changes associated with reniform nematode infection are well documented, little is known about their molecular basis. We grew soybean (Glycine max) in a split-root growth system, inoculated half of each root system with R. reniformis, and quantified gene expression in infected and control root tissue at four dates after inoculation. Over 6,000 genes were differentially expressed between inoculated and control roots on at least one date (false discovery rate [FDR] = 0.01, |log2FC| ≥ 1), and 507 gene sets were significantly enriched or depleted in inoculated roots (FDR = 0.05). Numerous genes up-regulated during syncytium formation had previously been associated with rhizobia nodulation. These included the nodule-initiating transcription factors CYCLOPS, NSP1, NSP2, and NIN, as well as multiple nodulins associated with the plant-derived peribacteroid membrane. Nodulation-related NIP aquaporins and SWEET sugar transporters were induced, as were plant CLAVATA3/ESR-related (CLE) signaling proteins and cell cycle regulators such as CCS52A and E2F. Nodulins and nodule-associated genes may have ancestral functions in normal root development and mycorrhization that have been co-opted by both parasitic nematodes and rhizobial bacteria to promote feeding site and nodule formation.

ИЗУЧЕНИЕ ВЛИЯНИЯ БИОПРЕПАРАТА НА ОСНОВЕ КЛУБЕНЬКОВЫХ БАКТЕРИЙ RHIZOBIUM LUPINI НА БОБОВЫЕ И ЗЛАКОВЫЕ КУЛЬТУРЫ

More and more scientific research has been aimed at studying the fixation of “biological nitrogen”, namely microorganisms-symbionts and biological preparations based on them recently. Many years of experiments and production practice clearly show that the microorganisms that fix nitrogen are of greater importance to enrich the soil with nitrogen and increase yields. Rhizobium nodule bacteria, being in symbiosis with bean plants, are absorbed from the atmosphere and supply the plant with the necessary amount of biologically bound nitrogen. Based on these data, the aim of our study is to study the effect of the biological product on the germination, growth and weight of the vegetative mass of legumes and cereals. A comparative analysis of the biological product based on Rhizobium lupini bacteria RL-1 strain with commercial preparations has been carried out. In the experiment the following agricultural crops have been used: peas, wheat, rapeseed, beans. As a result it has been found that RL-1 has a positive effect on the germination, length and mass of vegetative mass of plants. Thus, the length of pea’s offshoots is more by 73 %, rapeseed – by 44 %, wheat –by 60 %, beans – by 12 %. The preparation has also shown a positive effect to the weight of green mass, for example, the weight of peas plants is 50% higher than the controlled ones, rapeseed – by 12 %, wheat-by 90 %, beans – by 14 %. The study relates to the development of microbiological fertilizer plants. As a result of the analysis it was found that the investigated biopreparation based on nodule bacteria R. lupini promotes growth, better germination, increase the green mass of crops.

Nitrate inhibition of N2 fixation and its effect on micronutrient accumulation in shoots of soybean (Glycine max L. Merr.), Bambara groundnut (Vigna subterranea L. Vedc) and Kersting\u2019s groundnut (Macrotyloma geocarpum\xa0Harms.)

Although nitrate is known to inhibit nodulation and N2 fixation in symbiotic legumes, little is known about its effect on the uptake and accumulation of trace elements such as Fe, Zn, Mn and Cu. The aim of this study was to evaluate the effect of 5 mM NO3− supply, either with or without rhizobial inoculation, on nodulation, nodule functioning and micronutrient levels in the shoots of soybean (Glycine max L.Merr.), Bambara groundnut (Vigna subterranea L. Vedc) and Kersting’s groundnut (Macrotyloma geocarpum Harm). The results showed reduction in plant growth, nodule formation and nodule dry matter by the supply of 5 mM NO3− to inoculated seedlings of all three species. Nitrate inhibition respectively caused 1.2, 1.4, and 1.5-fold decrease in nodule number per plant in Bambara groundnut, soybean and Kersting’s bean, which resulted in 2.3, 3.3 and 4.5-fold reduction in nodule dry weight of the test species (in that order). The application of 5 mM NO3− to soybean plants also resulted in 2.5, 4.0 and 5.4-fold decrease in shoot accumulation of Fe, Zn and Mn, respectively, when compared to the purely symbiotic control plants. Furthermore, we observed 1.3, 1.8 and 1.3-fold decreases in the concentration of Zn, Mn and Cu in shoots of inoculated Bambara groundnut with NO3− supply, levels lower than those found in soybean. With Kersting’s groundnut, shoot concentration of Fe, Zn and Cu were higher with the application of 5 mM NO3− to inoculated plants when compared to the purely symbiotic treatment, which was opposite to soybean. But pure NO3−feeding of this species respectively resulted in 2.0, 1.4 and 1.3-fold decreases in Fe, Zn and Cu relative to inoculated NO3−-fed plants. Clearly, NO3− supply to landraces/genotypes of the three legume species did not only inhibit nodule formation and functioning, it also reduced shoot micronutrient levels in soybean and Bambara groundnut, but not Kersting’s bean.

The effects of planted and plowed Stylosanthes guianensis on degrading soil fertility in hilly countries of dry-hot valley

The development of rural economy and ecological restoration were restricted with high temperature and drought in the dry-hot valley of Yuanmou country. The climate and human practice made a degrading ecosystem, and one marked question here was soil fertility degradation. Leguminous forage Stylosanthes guianensis were introduced for years in degraded mountainous dry-hot valley of Yuanmou. Aims to reveal devotions of planting and plowing S. guianensis to degraded mountainous soil fertility, three soil types and two treatments planting experiment were tested in the dry-hot valley of Yuanmou country. The results show that: 1. S. guianensis could adapt to degraded mountain soil. There was a large number of nodules and root in three soil types, number of root nodule was 174.048–650.667 grain/individual plant, root biomass was 214.667–1710.000kg/hm2. 2. With nitrogen fixation of root nodule, rot and decomposing of dry branches and fallen leaves, organic matter, total nitrogen, pH and germ of degrading soil tended to rising after S. guianensis planting and plowing. Increasing root biomass and rhizobium nodules had been repaired and improved microenvironment of soil, especially made an significant increase for germs, in 0–20cm soil from 0.020×105–1.54×105 to 1.880×105–70×105,and 20–40cm soil from 0.020×105–0.380×105 to 1.100×105–52.5×105. 3. S. guianensis, either planting or plowing into soil as green manure planting, could significantly (P<0.05) improve total nitrogen, organic matter, available phosphorus, available K of degraded soil in the fruit tree canopy drip line.

Cell autonomous sanctions in legumes target ineffective rhizobia in nodules with mixed infections.

To maximize benefits from symbiosis, legumes must limit physiological inputs into ineffective rhizobia that nodulate hosts without fixing nitrogen. The capacity of legumes to decrease the relative fitness of ineffective rhizobia-known as sanctions-has been demonstrated in several legume species, but its mechanisms remain unclear. Sanctions are predicted to work at the whole-nodule level. However, whole-nodule sanctions would make the host vulnerable to mixed-nodule infections, which have been demonstrated in the laboratory and observed in natural settings. Here, we present and test a cell-autonomous model of legume sanctions that can resolve this dilemma. We analyzed histological and ultrastructural evidence of sanctions in two legume species, Acmispon strigosus and Lotus japonicus. For the former, we inoculated seedlings with rhizobia that naturally vary in their abilities to fix nitrogen. In the latter, we inoculated seedlings with near-isogenic strains that differ only in the ability to fix nitrogen. In both hosts, plants inoculated with ineffective rhizobia exhibited evidence for a cell autonomous and accelerated program of senescence within nodules. In plants that received mixed inoculations, only the plant cells harboring ineffective rhizobia exhibited features consistent with programmed cell death, including collapsed vacuoles, ruptured symbiosomes, and bacteroids that are released into the cytosol. These features were consistently linked with ultrastructural evidence of reduced survival of ineffective rhizobia in planta. Our data suggest an elegant cell autonomous mechanism by which legumes can detect and defend against ineffective rhizobia even when nodules harbor a mix of effective and ineffective rhizobial genotypes.