Rhizobium Bacteria Research Articles

Molecular Dialog between Root and Shoot via Regulatory Peptides and Its Role in Systemic Control of Plant Development

Plant developmental processes are very flexible and highly depend on environmental factors. This is largely due to the existence of regulatory mechanisms that systemically control development on the whole plant level. In plants, regulatory peptides produced in the roots have been identified that are activated in response to different factors influencing root system, such as variation in the level of macronutrients (first of all, nitrogen and phosphorus) in the soil, influence of symbiotic microorganisms (soil rhizobial bacteria and arbuscular mycorrhiza fungi), and water deficiency. Among the systemically acting peptides, the most thoroughly investigated are CLE (CLAVATA3/EMBRYO SURROUNDING REGION-related) and CEP (C-TERMINALLY ENCODED PEPTIDES) peptides that are capable of travelling through the xylem from the roots to the shoot and triggering responses via binding to specific receptors operating in the phloem of the leaf. This review focuses on the role of these two groups of peptides in molecular dialog between the root and shoot.

Assessing Mungbean Productivity under Organic Management

Background: Now a day’s demand for organic food has increased. Being leguminous, requirement of nitrogen for mung is low. Soil organic matter could affect the soil microbial community and increase the crop growth and yield. In mungbean, roots have symbiotic rhizobia bacteria, which help in fixing atmospheric nitrogen into the soil. Nitrogen plays a major role in synthesis of protein, chlorophyll and plant enzymes of legume. The chemical fertilizers is used in huge quantity which hazards the soil and environment. Synthetic fertilizers have mainly macronutrients in large quantities and cemented the soil for worsening the soil and also the negative impact on crops, livestock and human being. The application of organic sources of nutrients improves the soil physical-chemical condition by adding macro and micronutrients bothMethods: A field experiment in Kharif season was conducted at Agronomy field of CCSHAU, Hisar, Haryana, to study the yield, quality and physiological parameters of mungbean under different organic sources. The experiment was conducted with nine treatments viz., T1- RDF, T2-FYM @ 5 t/ha, T3-Vermicompost@ 2.5 t/ha, T4-FYM @ 5t/ha + Rhizobium, T5-Vermicompost @ 2.5 t/ha + Rhizobium, T6-Green manuring +FYM @ 5 t/ha, T7- Green manuring + Vermicompost @ 2.5 t/ha, T8-Green manuring + FYM @ 5t/ha + Rhizobium and T9-Green manuring + Vermi-compost @ 2.5 t/ha + Rhizobium in RBD replicated thrice.Result: Application of recommended dose of fertilizer produced 6.93 and 4.04 percent higher yield as compared to green manuring + FYM @ 5t/ha + Rhizobium and green manuring + vermicompost @ 2.5 t/ha, respectively. The data revealed that the SPAD value of chlorophyll, RWC and LWP was higher with the application of various organic sources over to recommended dose of fertilizer.

Population-level variation in host plant response to multiple microbial mutualists.

Multipartite mutualisms are widespread in nature, but population-level variation in these interactions is rarely quantified. In the model multipartite mutualism between legumes, arbuscular mycorrhizal (AM) fungi and rhizobia bacteria, host responses to microbial partners are expected to be synergistic because the nutrients provided by each microbe colimit plant growth, but tests of this prediction have not been done in multiple host populations. To test whether plant response to associations with AM fungi and rhizobia varies among host populations and whether synergistic responses to microbial mutualists are common, we grew 34 Medicago truncatula populations in a factorial experiment that manipulated the presence or absence of each mutualist. Plant growth increased in response to each mutualist, but there were no synergistic effects. Instead, plant response to inoculation with AM fungi was an order of magnitude higher than with rhizobia. Plant response to AM fungi varied among populations, whereas responses to rhizobia were relatively uniform. There was a positive correlation between plant host response to each mutualist but no correlation between AM fungal colonization and rhizobia nodulation of plant roots. The greater population divergence in host response to AM fungi relative to rhizobia, weak correlation in host response to each microbial mutualist, and the absence of a correlation between measures of AM fungal and rhizobia performance suggests that each plant-microbe mutualism evolved independently among M. truncatula populations.

Brassinosteroids play multiple roles in nodulation of pea via interactions with ethylene and auxin.

A comprehensive analysis of the role of brassinosteroids in nodulation, including their interactions with auxin and ethylene revealed thatbrassinosteroids inhibit infection, promote nodule initiation but do not influence nodule organogenesis or function. Nodulation, the symbiosis between legumes and rhizobial bacteria, is regulated by a suite of hormones including brassinosteroids. Previous studies have found that brassinosteroids promote nodule number by inhibiting ethylene biosynthesis. In this study, we examined the influence of brassinosteroids on the various stages of infection and nodule development. We utilise pea mutants, including brassinosteroid mutants lk, lka and lkb, the ethylene insensitive ein2 mutant and the lk ein2 double mutant, along with transgenic lines expressing the DR5::GUS auxin activity marker to investigate how brassinosteroids interact with ethylene and auxin during nodulation. We show that brassinosteroids inhibit the early stages of nodulation, including auxin accumulation, root hair deformation and infection thread formation, and demonstrate that infection thread formation is regulated by brassinosteroids in an ethylene independent manner. In contrast, brassinosteroids appear to act as promoters of nodule initiation through both an ethylene dependent and independent pathway. Although brassinosteroids positively influence the ultimate number of nodules formed, we found that brassinosteroid-deficiency did not influence nodule structure including the vascular pattern of auxin activity or nitrogen-fixation capacity. These findings suggest that brassinosteroids are negative regulators of infection but positive regulators of nodule initiation. Furthermore, brassinosteroids do not appear to be essential for nodule organogenesis or function. Given the influence of brassinosteroids on discreet stages of nodulation but not nodule function, manipulation of brassinosteroids may be an interesting avenue for future research on the optimisation of nodulation.

Cytoplasmic interaction of LysM receptors contributes to the formation of symbiotic receptor complex.

Receptor complex formation at the cell surface is a key step to initiate downstream signaling but the contribution of this process for the regulation of the direction of downstream responses is not well understood. In the plant-microbe interactions, while CERK1, an Arabidopsis LysM-RLK, mediates chitin-induced immune responses, NFR1, a Lotus homolog of CERK1, regulates the symbiotic process with rhizobial bacteria through the recognition of Nod factors. Concerning the mechanistic insight of the regulation of such apparently opposite biological responses by the structurally related RLKs, Nakagawa et al. previously showed that the addition of YAQ sequence, conserved in NFR1 and other symbiotic LysM-RLKs, to the kinase domain of CERK1 switched downstream responses from defense to symbiosis using a set of chimeric receptors, NFR1-CERK1s. These results indicated that such a subtle difference in the cytoplasmic domain of LysM-RLKs could determine the direction of host responses from defense to symbiosis. On the other hand, it is still not understood how such structural differences in the cytoplasmic domains determine the direction of host responses. We here analyzed the interaction between chimeric NFR1s and NFR5, a partner receptor of NFR1, by co-immunoprecipitation (Co-IP) of these proteins transiently expressed in Nicotiana benthamiana. These results indicated that the cytoplasmic interaction between the LysM-RLKs is important for the symbiotic receptor complex formation and the YAQ containing region of NFR1 contributes to trigger symbiotic signaling through the successful formation of NFR1/NFR5 complex.

Effect of Co-Inoculation of Bradyrhizobium and Trichoderma on Growth, Development, and Yield of Arachis hypogaea L. (Peanut)

Cultivation of the peanut (Arachis hypogaea L.) on the same land contributes to the accumulation of root exudates, leading to increased soil pathogens and decreased yield. Trichoderma harzianum is a naturally occurring endophytic biocontrol fungus that can enhance plant growth, nutrient uptake, and tolerance to biotic and abiotic stresses. Separately, Bradyrhizobium spp. is a biological nitrogen-fixing (BNF) bacterium favoring nodule formation in peanut roots which promotes nitrogen fixation. The dynamics of the symbiotic association between these two organisms were evaluated in the laboratory and greenhouse conditions. Peanuts were cultivated in pots inoculated with either Bradyrhizobium or Trichoderma or both to evaluate growth, development, and yield. The in vitro study results showed that seeds treated with Trichoderma had better germination and seedling biomass (p = 0.0008) compared to the other treatments. On the other hand, the results of greenhouse studies showed that seeds inoculated with both microbes, and those inoculated with Bradyrhizobium alone had higher dry biomass (p < 0.0001) as well as higher chlorophyll content (p < 0.0001) compared to the other treatments. Understanding of the interactive effects of fungal endophytes and rhizobial bacteria on plant growth and development will help in both the nutrient and disease management of Arachis hypogaea L.

Gene expression abundance dictated exopolysaccharide modification in Rhizobium radiobacter SZ4S7S14 as the cell's response to salt stress

A molecular and metabolic behaviour of EPS-producing and salt-tolerant bacterium Rhizobium radiobacter SZ4S7S14 along with its practical application in salt-stress was investigated. The research target was identification and expression profiles of a large EPS biosynthesis gene cluster, possible structural modification of EPS under salt-stress effect and analysis of the gene(s) relative expression and structural modification correlation. As expected, transposons insertions were identified within or near the coding regions of exoK and exoM, previously known large gene cluster that is required for EPS I synthesis. Different expression levels of exoK and exoM in different salt-stress models resulted in structural modification of EPS, which was seen basically in monomers molar ratio. As a result of downregulation of the genes the strain produced EPS samples with monomers ratio: (1) Glu:Man:Gal:Xyl:Ara:Rha:Rib = 31.21:3.02:2.77:1:0.91:0.64:0.41 (in 0.25% NaCl); (2) Glu:Man:Gal:Xyl:Ara:Rha:Rib = 7.65:1:0.69:0.22:0.2:0.16:0.1 (in 0.5% NaCl); (3) Glu:Man:Gal:Ara:Xyl:Rha:Rib = 9.39:1.89:1:0.58:0.52:0.46:0.26 (in 1% NaCl); and (4) Glu:Man:Ara:Xyl:Rib:Gal = 7.9:2:2:1.58:1.1:1 (in 2.0% NaCl), whereas in control (without NaCl): Glc:Man:Gal:Xyl:Ara:Rha:Rib = 11.66:1:0.90:0.37:0.37:0.15:0.14. It was found that, salt-stress not only leads to downregulation of a large EPS biosynthesis gene cluster, including exoK and exoM genes, but also impacting on their relative expression degree, re-groups of the monomers within the EPS matrix and dictates molar ratio of the monosaccharides in the final metabolite.

Characterization and symbiotic evalution of rhizobium bacteria from various plants on soybean (Glycine Max L) plants in green house

Rhizobium bacteria are bacteria including Plant Growth Promoting Rhizobacteria (PGPR) that are able to fix nitrogen, solubilise phosphate, produce enzymes of protease, IAA hormone and siderophore so that it plays, an important role in increasing agricultural productivity. Several rhizobia have been successfully isolated from 8 legume plants from various regions, with the aim of obtaining Rhizobium isolates which are potential, effective and efficient as biological fertilizer agents. A total of 8 isolates were successfully isolated using selective media for Rhizobium bacteria, namely YEMA, following their activities were tested qualitatively N fixing, solubilise phosphate, protease, IAA hormone and siderophore production. All isolates thrive on YEMA+CR media and showed fast growth in YEMA + BTB.. A total of 11 inoculation treatments were tested on soybean plants consisting of 1. EKP (3), 2. EKP (4), 3. i (1), 4 (combined 1-3), 5. 1 (2), 6. B (1), 7. H (2), 8 ( combined 5-7), 9. A (2), 10.2 (1), 11 (combined 9-10). As a control plant without inoculation and without N fertilizer (K1) and plants without inoculation and with N fertilizer equivalent to 100 kg/ha (K2). The planting media used for greenhouse experiments were sterile sand media. The experimental design used were a completely randomized design with 3 replications. Plants growth were observed with parameters included plant height and number of leaves (at 1,2,3,4,5,6 and 7 weeks). Soybean plants werw harvested at 50 days after planting, following measurement of dry weight of canopy, roots, root nodules, total plants and chlorophyll content. The results showed that 8 individual isolates and 3 combined isolates inoculated to soybean plants varied, all of which were able to increase growth. Isolates number H(2) and 1(2) (isolates of nodules root of Peanut plants) gave the highest yields on the growth of soybean plants.

Nitrogen Fertilizer and Microbial Inoculations Determined the Nutrient Uptake and Productivity of Soybean

Soybean is an important commodity in Indonesia. This study aimed to identify the application of microbe inoculations with dosage of N in form of urea toward the growth, N uptake and yield in soybean. This research was conducted on October 2017 to January 2018 in Panunggalan village, Pulokulon, Grobogan, Central Java. It used the Randomized Complete Block Design 2 factors: urea dosages (0; 50; 100 kg ha−1) and microbe inoculations (no inoculation; Rhizobium (R); Rhizobium + Trichoderma (R+T); Trichoderma(T)). The result showed that combination of urea dosage and microbe inoculations significantly influenced plant height and number of trifoliate leaves. Urea dosages and microbe inoculations or combination of both factors did not imply nodulation process. Higher N dosage and microbe inoculations increased N uptake of biomass on vegetative period but had no effect on flowering and pod filling periods. The combination of 100 kgHa-1 urea with microbes or without microbes produced the highest productivity. However, treatment without urea and no inoculation also achieved the highest production. This suggested that there was a native population of Rhizobium bacteria strains that effectively supplied N for plants. Besides, application of urea of 100 kg ha-1 or 46 N kg ha-1 was too small to interfere fixation nitrogen by local Rhizobium population. Therefore, N application in form of anorganic fertilizer or microbe for symbiotic N-fixation was not recommended for existing agro climatic conditions of area with soybean history. Thus, it could simultaneously save the cost of agricultural production.

Growth and yield of Mung bean (Vigna radiata L.) as affected by Rhizobium sp. bacteria inoculant and frequence of watering

The aim of the study was to know the influence of the Rhizobium bacteria inoculant doses as biotic fertilizer and the frequence of watering on the growth and yield of the mung bean (Vigna radiata L.). The study was conducted in Green House of Faculty Animal and Agricultural Sciences, Diponegoro University. The experimental design of this research was Completely Randomized Design (CRD) The parameters observed were height of plant, number of leaves, days of blooming, and days of pod. The result showed that the dose of the Rhizobium inoculant had a significant effect on days of blooming. The frequency of watering had significant effect on height of plant, number of leaves, days of the bloom, days of the podded and weight of pods. In conclusion, mung bean that was treatmented by Rhizobium sp. bacteria inoculant (treatments of R2, R3 and R4) and treatment of F3 had same in days of blooming and days of podded with bacteria inoculant RHIZOKA (treatment of R1).

Mass Spectrometric Analysis of Acidic Exo-Oligosaccharides of Root Nodule Bacterium Rhizobium leguminosarum bv. viciae VF39

The structures of exo-oligosaccharides produced by a symbiotic nitrogen-fixing bacterium Rhizobium leguminosarum bv. viciae VF39 were determined using the methods of mass spectrometry and HCD fragmentation of ions. Exo-oligosaccharides were shown to be monomers, dimers and trimers of an octasaccharide repeating unit of the high-molecular-weight acidic exopolysaccharide. The major fraction was represented by octasaccharide monomers with two glucuronic acid residues at the reducing end. Heptasaccharides corresponding to an octasaccharide unit without GlcA-c or Glc-b residues in the main chain were also found in the culture liquid. Heterogeneity of exo-oligosaccharides according to the content of O-acetyl and hydroxybutanoyl substituents was revealed.

Lipo-chitooligosaccharides as regulatory signals of fungal growth and development

Lipo-chitooligosaccharides (LCOs) are signaling molecules produced by rhizobial bacteria that trigger the nodulation process in legumes, and by some fungi that also establish symbiotic relationships with plants, notably the arbuscular and ecto mycorrhizal fungi. Here, we show that many other fungi also produce LCOs. We tested 59 species representing most fungal phyla, and found that 53 species produce LCOs that can be detected by functional assays and/or by mass spectroscopy. LCO treatment affects spore germination, branching of hyphae, pseudohyphal growth, and transcription in non-symbiotic fungi from the Ascomycete and Basidiomycete phyla. Our findings suggest that LCO production is common among fungi, and LCOs may function as signals regulating fungal growth and development.

Microbial Consortium of PGPR, Rhizobia and Arbuscular Mycorrhizal Fungus Makes Pea Mutant SGECdt Comparable with Indian Mustard in Cadmium Tolerance and Accumulation.

Cadmium (Cd) is one of the most widespread and toxic soil pollutants that inhibits plant growth and microbial activity. Polluted soils can be remediated using plants that either accumulate metals (phytoextraction) or convert them to biologically inaccessible forms (phytostabilization). The phytoremediation potential of a symbiotic system comprising the Cd-tolerant pea (Pisum sativum L.) mutant SGECdt and selected Cd-tolerant microorganisms, such as plant growth-promoting rhizobacterium Variovorax paradoxus 5C-2, nodule bacterium Rhizobium leguminosarum bv. viciae RCAM1066, and arbuscular mycorrhizal fungus Glomus sp. 1Fo, was evaluated in comparison with wild-type pea SGE and the Cd-accumulating plant Indian mustard (Brassica juncea L. Czern.) VIR263. Plants were grown in pots in sterilized uncontaminated or Cd-supplemented (15 mg Cd kg−1) soil and inoculated or not with the microbial consortium. Cadmium significantly inhibited growth of uninoculated and particularly inoculated SGE plants, but had no effect on SGECdt and decreased shoot biomass of B. juncea. Inoculation with the microbial consortium more than doubled pea biomass (both genotypes) irrespective of Cd contamination, but had little effect on B. juncea biomass. Cadmium decreased nodule number and acetylene reduction activity of SGE by 5.6 and 10.8 times, whereas this decrease in SGECdt was 2.1 and 2.8 times only, and the frequency of mycorrhizal structures decreased only in SGE roots. Inoculation decreased shoot Cd concentration and increased seed Cd concentration of both pea genotypes, but had little effect on Cd concentration of B. juncea. Inoculation also significantly increased concentration and/or accumulation of nutrients (Ca, Fe, K, Mg, Mn, N, P, S, and Zn) by Cd-treated pea plants, particularly by the SGECdt mutant. Shoot Cd concentration of SGECdt was twice that of SGE, and the inoculated SGECdt had approximately similar Cd accumulation capacity as compared with B. juncea. Thus, plant–microbe systems based on Cd-tolerant micro-symbionts and plant genotypes offer considerable opportunities to increase plant HM tolerance and accumulation.

EKSPLORASI DAN KARAKTERISASI BAKTERI RHIZOBIUM ASAL TANAMAN Mucuna bracteata DI TANAH GAMBUT

The efficiency of fertilizing N on oil palm plants on peatlands in several companies is done by planting legume cover crop, one of which is Mucuna bracteata . This plant can form root nodules because it can symbiosis with rhizobium bacteria which will make fixation of N 2 in the air so that the bound N elements can be utilized by plants. This bacterium grows naturally on legume cover crop. This study aims to explore and characterize adaptive rhizobium bacteria in peatlands. The location of sampling is done at PT. Jatimjaya Perkasa, Kubu District, Rokan Hilir Regency. Sampling of root nodules by stratified random sampling. The results obtained by eight bacterial isolates that have relatively similar macroscopic and microscopic characteristics and belong to rhizobium based on the YEMA + CR and YEMA + BTB tests. Keywords: Peat soil, Oil palm, Legume cover crop, Rhizobium

The Medicago truncatula Vacuolar iron Transporter-Like proteins VTL4 and VTL8 deliver iron to symbiotic bacteria at different stages of the infection process.

Summary The symbiotic relationship between legumes and rhizobium bacteria in root nodules has a high demand for iron, and questions remain regarding which transporters are involved. Here, we characterize two nodule‐specific Vacuolar iron Transporter‐Like (VTL) proteins in Medicago truncatula.Localization of fluorescent fusion proteins and mutant studies were carried out to correlate with existing RNA‐seq data showing differential expression of VTL4 and VTL8 during early and late infection, respectively.The vtl4 insertion lines showed decreased nitrogen fixation capacity associated with more immature nodules and less elongated bacteroids. A mutant line lacking the tandemly‐arranged VTL4–VTL8 genes, named 13U, was unable to develop functional nodules and failed to fix nitrogen, which was almost fully restored by expression of VTL8 alone. Using a newly developed lux reporter to monitor iron status of the bacteroids, a moderate decrease in luminescence signal was observed in vtl4 mutant nodules and a strong decrease in 13U nodules. Iron transport capability of VTL4 and VTL8 was shown by yeast complementation.These data indicate that VTL8, the closest homologue of SEN1 in Lotus japonicus, is the main route for delivering iron to symbiotic rhizobia. We propose that a failure in iron protein maturation leads to early senescence of the bacteroids.

Effects of plant density on yield parameters of cowpea (Vigna unguiculata L.)

Cowpea (Vigna unguiculata L.) is an important pulse, fodder and green manure crop. In symbiotic association with Rhizobium bacteria, cowpea fixes atmospheric dinitrogen in its root nodules. Hence cowpea forms an integral part of the cropping systems in Indian agriculture. A field experiment was conducted during rabi 2018-19 on a sandy loam soil of Bagusala Farm (23039’ N latitude, 87o42’ E longitude), M. S. Swaminathan School of Agriculture, Gajapati District, Odisha, to study the effects of variety, plant spacing and variety x spacing interaction on the yield components of cowpea. The experiment was conducted in a split plot design with three replications. Three cowpea varieties, Ketaki, Kamini, and Gomati, were the main plots and three within row plant spacings of 10, 15 and 20 cm, corresponding to plant population densities of 333333, 222222 and 166666 plants ha-1, were the split plots, forming a total of nine treatment combinations. The seeds of cowpea were sown in rows on ridges spaced 30 cm apart. At harvest the yield attributes, pod length, pods plant-1, grain yield, 100 grain weight, biological yield, stover yield and harvest index were recorded. The three cowpea varieties tested did not differ significantly in pods plant-1 and pod length but differed in 100 grain test weight. Gomati had the highest grain test weight, followed by Ketaki, with Kamini having the least test weight. Higher grain yield was recorded in the widest spacing of 20 cm compared to the closest spacing of 10 cm. Cowpea varieties, plant spacings and variety x spacing interactions did not have significant effects on stover yields and harvest indices. The widest plant spacing of 20 cm had higher benefit-cost ratio (BC ratio) than the closer spacings of 10 and 15 cm which had similar BC ratios. Variety x spacing interactions affected BC ratio.

Plant transcriptome analysis reveals specific molecular interactions between alfalfa and its rhizobial symbionts below the species level

BackgroundLeguminous plants alter patterns of gene expression in response to symbiotic colonization and infection by their cognate rhizobial bacteria, but the extent of the transcriptomic response has rarely been examined below the species level. Here we describe the identification of 12 rhizobial biotypes of Ensifer meliloti, which form nitrogen-fixing nodules in the roots of alfalfa (Medicago sativa L.), followed by a comparative RNA-seq analysis of four alfalfa cultivars each inoculated with two E. meliloti strains varying in symbiotic performance and phylogenetic relatedness.ResultsRhizobial biotypes were identified on the basis of their symbiotic performance, particularly shoot dry weight. Differentially expressed genes (DEGs) and metabolic pathways were determined by comparing the RNA-seq data with that of the uninoculated control plant. Significant differences were found between DEGs generated in each cultivar with the inoculation of two rhizobial strains in comparison (P < 0.01). A total of 8111 genes was differentially expressed, representing ~ 17.1% of the M. sativa genome. The proportion of DEGs ranges from 0.5 to 12.2% for each alfalfa cultivar. Interestingly, genes with predicted roles in flavonoid biosynthesis and plant-pathogen interaction (NBS-LRR) were identified as the most significant DEGs. Other DEGs include Medsa002106 and genes encoding nodulins and NCR peptides whose expression is specifically induced during the development of nitrogen-fixing nodules. More importantly, strong significant positive correlations were observed between plant transcriptomes (DEGs and KEGG pathways) and phylogenetic distances between the two rhizobial inoculants.ConclusionsAlfalfa expresses significantly distinct sets of genes in response to infection by different rhizobial strains at the below-species levels (i.e. biotype or strain). Candidate genes underlying the specific interactions include Medsa002106 and those encoding nodulins and NCR peptides and proteins in the NBS-LRR family.

تأثیر تنش کمآبی بر صفات فیزیولوژیک و عملکرد دانه سویا تحت تأثیر تلقیح و عدم تلقیح با قارچ میکوریزا و باکتری ریزوبیوم

به‌منظور بررسی تأثیر تنش کم‌آبی و تلقیح با قارچ میکوریزا و باکتری ریزوبیوم بر صفات فیزیولوژیک و عملکرد دانه سویا، آزمایشی در سال زراعی 1396 در مزرعه هنرستان کشاورزی شهرستان ارومیه به‌صورت اسپلیت پلات فاکتوریل در قالب طرح بلوک‌های کامل تصادفی با سه تکرار اجرا شد. عامل تنش کم‌آبی در سه سطح شامل آبیاری مطلوب، تنش ملایم و تنش شدید کم‌آبی (به‌ترتیب آبیاری بعد از 70، 110 و 159 میلی‌متر تبخیر از تشتک تبخیر کلاس A)، عامل‌های فرعی قارچ میکوریزا در سه سطح شامل بدون میکوریزا، گونه Funneliformis mosseae و گونه Rhizophagus intraradices و باکتری ریزوبیوم در دو سطح شامل عدم تلقیح و Bradyrhizobium japonicum بود. در این بررسی دمای برگ، محتوای نسبی آب برگ، کلروفیل b، کلروفیل a، پرولین، نشت الکترولیت و عملکرد دانه مطالعه شد. تنش بیشتر کم‌آبی همراه با عدم تلقیح با میکوریزا دمای برگ را افزایش اما محتوی نسبی آب برگ و کلروفیل b را کاهش داد. افزایش تنش کم‌آبی همراه با عدم تلقیح با باکتری دمای برگ را افزایش اما کلروفیل b و عملکرد دانه را کاهش داد. تلقیح با باکتری با یا بدون تلقیح با قارچ دمای برگ را کاهش داد. این شرایط برای صفات محتوای نسبی آب برگ، محتوای کلروفیل b و a نیز وجود داشت. تلقیح با باکتری و میکوریزا بخصوص قارچ F. mosseae باعث شد حداکثر عملکرد دانه با 443.2 گرم در مترمربع به‌دست آید. میزان پرولین و درصد نشت الکترولیت در تیمار تنش کم‌آبی شدید و عدم تلقیح با میکوریزا و باکتری بیشتر از تیمارهای دیگر بود. حداقل میزان پرولین و درصد نشت الکترولیت نیز در تیمار آبیاری مطلوب همراه با تلقیح با باکتری و قارچ F. mosseae مشاهده شد. درمجموع، تنش کم‌آبی باعث ایجاد شرایط نامطلوب برای سویا شد که نتیجه آن کاهش عملکرد بود اما تلقیح با باکتری و قارچ باعث کاهش شرایط نامطلوب و رشد بهتر سویا شد.

Screening and optimization of indole-3-acetic acid production by Rhizobium sp. strain using response surface methodology

BackgroundThe production of indole-3-acetic acid (IAA) is an essential tool for rhizobacteria to stimulate and facilitate plant growth. For this, eighty rhizobial bacteria isolated from root nodules of Acacia cyanophylla grown in different regions of Morocco were firstly screened for their ability to produce IAA. Then, IAA production by a combination of isolates and the inoculation effect on the germination of Acacia cyanophylla seeds was studied using the best performing isolates in terms of IAA production. The best IAA producer bacterial isolate (I69) was selected to optimize IAA production using response surface methodology based on the central composite design. ResultsResults showed that the majority of tested isolates were able to produce IAA with a relatively higher concentration of 135 μg/ml for the isolate I69, followed by isolates I22 and I75 with respective concentrations of 116 μg/ml and 105 μg/ml IAA. The IAA production and the seed germination rate were relatively increased by the synergistic effect of I69 and I22. Later, response surface methodology was used to determine optimal operating conditions leading to IAA production optimization. Thus, an incubation temperature of 36 °C, a pH of 6.5, an incubation time of 1 day, and respective tryptophan and NaCl concentrations of 1 g/l and 0.1 g/l were optimal parameters leading to 166 μg/ml IAA which was the maximal produced concentration. ConclusionThe present study highlighted that IAA-producing rhizobacteria could be harnessed to improve plant growth. Furthermore, their production can be easily controlled using response surface methodology, which represents a very useful tool for optimization.

In Vivo Metabolic Regulation of Alternative Oxidase under Nutrient Deficiency-Interaction with Arbuscular Mycorrhizal Fungi and Rhizobium Bacteria.

The interaction of the alternative oxidase (AOX) pathway with nutrient metabolism is important for understanding how respiration modulates ATP synthesis and carbon economy in plants under nutrient deficiency. Although AOX activity reduces the energy yield of respiration, this enzymatic activity is upregulated under stress conditions to maintain the functioning of primary metabolism. The in vivo metabolic regulation of AOX activity by phosphorus (P) and nitrogen (N) and during plant symbioses with Arbuscular mycorrhizal fungi (AMF) and Rhizobium bacteria is still not fully understood. We highlight several findings and open questions concerning the in vivo regulation of AOX activity and its impact on plant metabolism during P deficiency and symbiosis with AMF. We also highlight the need for the identification of which metabolic regulatory factors of AOX activity are related to N availability and nitrogen-fixing legume-rhizobia symbiosis in order to improve our understanding of N assimilation and biological nitrogen fixation.