Nodule Activity Research Articles

Evaluación de la tolerancia al estrés de fósforo en caupí (Vigna unguiculata L. Walp) en Cuba. I. cultivo en solución nutritiva.

Phosphorus deficiency is a major limitingfactor for symbiotic nitrogen fixation and grain yield oflegume crops in the tropics. Eight cowpea genotypes of wideuse in Cuba, were grown in hydroponics solutions; supplyingfrom 50 to 500 µM of P/plant/week. Nitrogen nutrition wasdependent upon symbiotic N2-fixation on adding of 4mmoles NO3/plant/week. Shoot growth was severely limitedby P deficiency, while dry weight of roots increased in bothgroups of plants. Nodule formation was severely decreasedby P deficiency, while specific nodule activity was increasedin the atmospheric N2 fixing plants. Growth response of N2plants was higher than that of NO3- fed plants due to P useefficiency, and revealed a the great large N2-fixationpotential of the specie.

The effects of Liuwei Dihuang on canonical Wnt/β-catenin signaling pathway in osteoporosis

Ethnopharmacological relevanceThe Liuwei Dihuang (LWDH), a wellknown classic traditional Chinese medicine formula, consists of six herbs including Rehmannia glutinosa Libosch. (family: Scrophulariaceae), Cornus officinalis Sieb. (family: Cornaceae), Dioscorea opposite Thunb. (family: Dioscoreaceae), Alisma orientale (G. Samuelsson) Juz (family: Alismataceae), Poria cocos (Schw.) Wolf (family: Polyporaceae) and Paeonia suffruticosa Andrews (family: Paeoniaceae). It has been used clinically in the treatment of many types of diseases with signs of deficiency of Yin in the kidneys for more than 1000 years in China. The purpose of this study was to observe the effects of LWDH on canonical Wnt/β-catenin signaling pathway in osteoporosis. Materials and methodsOsteoporosis model was induced by ovariectomy (OVX) in 8-week-old female Sprague–Dawley (SD) rats. After 12 weeks of treatment with LWDH by intragastric administration, the rats were put to death in batch. The changes of alkaline phosphatase (ALP), osteocalcin (BGP) and estradiol (E2) in serum were determined, bone mineral density (BMD) and histomorphology of right femur were observed, biomechanics of lumbar vertebra were measured, and the expression of Lrp-5, β-catenin, Runx2, Osx involving the canonical Wnt/β-catenin signaling pathway were detected by RT-PCR. In addition, osteoblasts isolated from neonatal rat calvariae were used in this study to investigate the effects of LWDH on the canonical Wnt/β-catenin signaling pathway. Cell proliferation and differentiation were observed by the MTT test, ALP activity and calcified nodules. The expression of Lrp-5, β-catenin, Runx2, Osx mRNA of cells were also detected. All the data were analyzed by SPSS 13.0. ResultsTwelve weeks of treatment with LWDH could significantly decrease the level of ALP and BGP in serum, increase the BMD of femurs, and improve the biomechanical capabililty of vertebral body in maximum loading and elastic modulus. Concerning histomorphology, we found ordered arrangement of trabeculae, slightly thinning of trabeculae and none obvious slight fractures in femurs after twelve weeks of treatment with LWDH. In osteoblast, serum containing LWDH elicited significantly increase in cell viability (at day 6), alkaline phosphatase activity (at days 2, 4 and 6) and amount of calcified nodules. The expression of Lrp-5, β-catenin, Runx2 and Osx involved in the canonical Wnt/β-catenin signaling pathway were significantly up-regulated in the presence of LWDH both in vivo and in vitro experiment. ConclusionsOur results suggest that Liuwei Dihuang could alleviate osteoporosis induced by ovariectomy, in part, through up-regulation of canonical Wnt/β-catenin signaling pathway of osteoblast.

Inhibition of osteogenic differentiation of mesenchymal stem cells by copper supplementation

Copper has been added to scaffolds when investigating bone repair, as an agent to promote vascularization; however, little is known concerning its effect on mesenchymal stem cells (MSCs), which are considered to be the origin of osteoblasts. In this study, we have aimed to elucidate effects of copper on osteogenic differentiation of MSCs. Rat bone marrow MSCs (rBMSCs) were used as a model. Their viability was assessed by MTT assay and Roche's CASY cell counter test and calcium deposition was evaluated by staining with alizarin red S. Fluorescent phalloidin F-actin stain was used to evaluate cytoskeletal changes, protein expressions were investigated by western blotting and mRNA levels were analysed using Q-PCR. A rat model for ectopic bone formation was used to assess effects of copper on MSCs in vivo. Copper supplementation resulted in inhibition of osteogenesis of rBMSCs, along with reduction in expression of a number of osteogenic genes, alkaline phosphatase activity and formation of bone nodules. Cytoskeletal changes to cells during osteogenesis was inhibited by copper supplementation. In vivo study confirmed that copper could inhibit collagen formation whilst promoting angiogenesis. Our study demonstrated that copper inhibited osteogenic differentiation of rBMSCs in vitro. The findings caution appropriate use of copper and have laid a foundation for further research.

CO-INOCULATION OF SOYBEAN (GLYCINE MAX) WITH ACTINOMYCETES AND BRADYRHIZOBIUM JAPONICUM ENHANCES PLANT GROWTH, NITROGENASE ACTIVITY AND PLANT NUTRITION

The aim of this study was to determine the potential of the endophytic actinomycetes that produce plant growth promoters used as co-inoculants with Bradyrhizobium japonicum to promote the growth of soybean. These endophytes exhibited the potential to enhance plant growth, nitrogenase activity of root nodules and plant nutrient uptake. Co-inoculum of B. japonicum with Nocardia alba conferred the maximum yield of root and shoot dry weight. All single-inoculated actinomycetes strains had the ability to enhance plant growth. Noc. alba and Nonomuraea rubra increased total plant dry weight up to 2.14-fold and 2.11-fold, respectively, when compared to the uninoculated controls. Co-inoculations of B. japonicum with each of Noc. alba, Non. Rubra, and Actinomadura glauciflava increased acetylene reduction activity up to 1.7 to 2.7-fold. For plant mineral composition, all of co-inoculation treatments significantly increased the nutrient levels of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), iron (Fe) and zinc (Zn) within a soybean plant.

Root Distribution and Nitrogen Fixation Activity of Tropical Forage Legume American Jointvetch (Aeschynomene americanaL.) cv. Glenn under Waterlogging Conditions

We investigated the root distribution and nitrogen fixation activity of American jointvetch (Aeschynomene americanaL.) cv. Glenn, under waterlogging treatment. The plants were grown in pots under three different treatments: no waterlogging (control), 30 days of waterlogging (experiment 1), and 40 days of waterlogging (experiment 2). The plants were subjected to the treatments on day 14 after germination. Root dry matter (DM) weight distribution of waterlogged plants was shallower than controls after day 20 of waterlogging. Throughout the study period, the total root DM weight in waterlogged plants was similar to that in the controls. Enhanced rooting (adventitious roots) and nodule formation at the stem base were observed in waterlogged plants after day 20 of waterlogging. The average DM weight of individual nodules on the region of the stem between the soil surface and water surface of waterlogged plants was similar to that of individual taproot nodules in the controls. Waterlogged plants had slightly greater plant DM weight than the controls after 40 days of treatment. The total nitrogenase activity (TNA) of nodules and nodule DM weight were higher in waterlogged plants than in the controls. Waterlogged American jointvetch had roots with nodules both around the soil surface and in the area between the soil surface and water surface after 20 days of waterlogging, and they maintained high nitrogenase activity and net assimilation rate that resulted in an increased growth rate.

How do phosphorus, potassium and sulphur affect plant growth and biological nitrogen fixation in crop and pasture legumes? A meta-analysis

Worldwide, legumes are grown on approximately 250Mha and fix about 90Tg of N2 per year. Plants involved in biological nitrogen fixation (BNF) are particularly sensitive to deficiencies of phosphorus (P), potassium (K) and sulphur (S). These nutrients can affect BNF directly; this is modulating growth of rhizobia, nodule formation and functioning, or indirectly by affecting the growth of the host plant. However, several process and mechanisms remain unclear. We compiled a data set (63 studies) on the effects of P, K, and S deficiency on shoot mass, nodule mass and number, nitrogenase activity (estimated by the acetylene reduction activity test, ARA) and the concentration of N, P, K and S in shoots and nodules. Our aims were (1) to compare the relative sensitivity of these traits to nutrient deficiency and (2) to probe for nutrient-specific patterns in trait responses.Our quantitative analysis confirms that nodule growth and number are more sensitive than shoot mass in response to deficiency of P, K and S. In addition, nodule activity decreases more than both shoot and nodule mass, which indicates a reduction in nodule productivity; this is likely related with direct effects of these nutrients on physiological and metabolic processes of nodules. The conserved shoot N concentration, in comparison to concentration of P, K and S indicates a relatively greater accumulation of N that matches the proposed N-feedback mechanism down-regulating BNF in nutrient-deficient systems. Despite some nutrient-specific differences, i.e. smaller nodules and higher N/K ratio with shortage of P and K, respectively, the patterns of growth, nodule activity and nutrient concentration were similar for all three nutrients P, K and S. This indicates that a unique mechanism could be depressing BNF (N-feedback) in conjunction with direct effects of the nutrients on nodule activity.Scarcity of data related to N, K and S concentration in nodules is a major constrain for deep analysis of the deficiencies of the nutrients. Critical concentrations of P, K and S in plant and nodule tissues are also a major gap. Models are needed that integrate the direct effect of the nutrients on nodule growth and activity with the N-feedback mechanism.

An RNA Sequencing Transcriptome Analysis Reveals Novel Insights into Molecular Aspects of the Nitrate Impact on the Nodule Activity of Medicago truncatula

The mechanism through which nitrate reduces the activity of legume nodules is controversial. The objective of the study was to follow Medicago truncatula nodule activity after nitrate provision continuously and to identify molecular mechanisms, which down-regulate the activity of the nodules. Nodule H2 evolution started to decline after about 4 h of nitrate application. At that point in time, a strong shift in nodule gene expression (RNA sequencing) had occurred (1,120 differentially expressed genes). The most pronounced effect was the down-regulation of 127 genes for nodule-specific cysteine-rich peptides. Various other nodulins were also strongly down-regulated, in particular all the genes for leghemoglobins. In addition, shifts in the expression of genes involved in cellular iron allocation and mitochondrial ATP synthesis were observed. Furthermore, the expression of numerous genes for the formation of proteins and glycoproteins with no obvious function in nodules (e.g. germins, patatin, and thaumatin) was strongly increased. This occurred in conjunction with an up-regulation of genes for proteinase inhibitors, in particular those containing the Kunitz domain. The additionally formed proteins might possibly be involved in reducing nodule oxygen permeability. Between 4 and 28 h of nitrate exposure, a further reduction in nodule activity occurred, and the number of differentially expressed genes almost tripled. In particular, there was a differential expression of genes connected with emerging senescence. It is concluded that nitrate exerts rapid and manifold effects on nitrogenase activity. A certain degree of nitrate tolerance might be achieved when the down-regulatory effect on late nodulins can be alleviated.

Approaches for enhancement of N2 fixation efficiency of chickpea (Cicer arietinum L.) under limiting nitrogen conditions

Chickpea (Cicer arietinum) is an important pulse crop in many countries in the world. The symbioses between chickpea and Mesorhizobia, which fix N₂ inside the root nodules, are of particular importance for chickpea's productivity. With the aim of enhancing symbiotic efficiency in chickpea, we compared the symbiotic efficiency of C-15, Ch-191 and CP-36 strains of Mesorhizobium ciceri in association with the local elite chickpea cultivar 'Bivanij' as well as studied the mechanism underlying the improvement of N₂ fixation efficiency. Our data revealed that C-15 strain manifested the most efficient N₂ fixation in comparison with Ch-191 or CP-36. This finding was supported by higher plant productivity and expression levels of the nifHDK genes in C-15 nodules. Nodule specific activity was significantly higher in C-15 combination, partially as a result of higher electron allocation to N₂ versus H⁺. Interestingly, a striking difference in nodule carbon and nitrogen composition was observed. Sucrose cleavage enzymes displayed comparatively lower activity in nodules established by either Ch-191 or CP-36. Organic acid formation, particularly that of malate, was remarkably higher in nodules induced by C-15 strain. As a result, the best symbiotic efficiency observed with C-15-induced nodules was reflected in a higher concentration of the total and several major amino metabolites, namely asparagine, glutamine, glutamate and aspartate. Collectively, our findings demonstrated that the improved efficiency in chickpea symbiotic system, established with C-15, was associated with the enhanced capacity of organic acid formation and the activities of the key enzymes connected to the nodule carbon and nitrogen metabolism.

Influence of arbuscular mycorrhiza on osmotic adjustment compounds and antioxidant enzyme activity in nodules of salt-stressed soybean (Glycine max)

The influence of the colonization with arbuscular mycorrhizal (AM) fungus, Glomus mosseae (Nicolson and Gerdemann), on characteristics of growth, osmotic adjustment compounds and activity of antioxidant enzymes in nodules of salt-stressed soybean (Glycine max (L.) Merr.) was studied in this experiment. The pot experiment was arranged as a factorial in randomized complete block design with four replications at greenhouse of College of Agriculture, Tehran University, Iran. Results indicated that the contents of glycine betaine and proline in nodules were higher in inoculated than in non-inoculated plants. AM fungal colonization increased the activities of superoxide dismutase, catalase, and peroxidase in the nodules. The results indicate that the AM fungus is capable of alleviating the damage caused by salt stress on symbiotic nitrogen fixation of soybean plants by increasing the accumulation of compatible osmolytes and by increased antioxidant enzyme activity. Consequently, arbuscular mycorrhiza formation highly enhanced the salinity tolerance of soybean plant, which increased symbiotic nitrogen fixation and promoted plant growth.

Amplicon restriction patterns associated with nitrogenase activity of root nodules for selection of superior Myrica seedlings

Trees of Myrica sp. grow abundantly in the forests of Meghalaya, India. These trees are actinorhizal and harbour nitrogen-fixing Frankia in their root nodules and contribute positively towards the enhancement of nitrogen status of forest areas. They can be used in rejuvenation of mine spoils and nitrogen-depleted fallow lands generated due to slash and burn agriculture practiced in the area. We have studied the association of amplicon restriction patterns (ARPs) of Myrica ribosomal RNA gene and internal transcribed spacer (ITS) region and nitrogenase activity of its root nodules. We found that ARPs thus obtained could be used as markers for early screening of seedlings that could support strains of Frankia that fix atmospheric nitrogen more efficiently.

Growth and N2 fixation in an Alnus hirsuta (Turcz.) var. sibirica stand in Japan

To estimate the N2 fixation ability of the alder (Alnus hirsuta (Turcz.) var. sibirica), we examined the seasonal variation in nitrogenase activity of nodules using the acetylene reduction method in an 18-year-old stand naturally regenerated after disturbance by road construction in Japan. To evaluate the contribution of N2 fixation to the nitrogen (N) economy in this alder stand, we also measured the phenology of the alder, the litterfall, the decomposition rate of the leaf litter, and N accumulation in the soil. The acetylene reduction activity per unit nodule mass (ARA) under field conditions appeared after bud break, peaked the maximum in midsummer after full expansion of the leaves, and disappeared after all leaves had fallen. There was no consistent correlation between ARA and tree size (dbh). The amount of N2 fixed in this alder stand was estimated at 56.4 kg ha-1 year-1 when a theoretical molar ratio of 3 was used to convert the amount of reduced acetylene to the amount of fixed N2. This amount of N2 fixation corresponded to the 66.4 percent of N in the leaf litter produced in a year. These results suggested that N2 fixation still contributed to the large portion of N economy in this alder stand.

Localization of hydrogen peroxide accumulation and diamine oxidase activity in pea root nodules under aluminum stress

Aluminum (Al) is one of the environmental stressors that induces formation of reactive oxygen species (ROS) in plants. Hydrogen peroxide (H2O2) and H2O2-generated apoplast diamine oxidase (DAO) activity were detected cytochemically via transmission electron microscopy (TEM), in pea (Pisum sativum L.) root nodules exposed to high (50μM AlCl3, for 2 and 24h) Al stress.The nodules were shown to respond to Al stress by disturbances in infection thread (IT) growth, bacteria endocytosis, premature degeneration of bacteroidal tissue and generation of H2O2 in nodule apoplast. Large amounts of peroxide were found at the same sites as high DAO activity under Al stress, suggesting that DAO is a major source of Al-induced peroxide accumulation in the nodules. Peroxide distribution and DAO activity in the nodules of both control plants and Al-treated ones were typically found in the plant cell walls, intercellular spaces and infection threads. However, 2h Al treatment increased DAO activity and peroxide accumulation in the nodule apoplast and bacteria within threads. A prolonged Al treatment (24h) increased the H2O2 content and DAO activity in the nodule apoplast, especially in the thread walls, matrix and bacteria within infection threads. In addition to ITs, prematurely degenerated bacteroids, which occurred in response to Al, were associated with intense staining for H2O2 and DAO activity.These results suggest the involvement of DAO in the production of a large amount of H2O2 in the nodule apoplast under Al stress. The role of reactive oxygen species in pea-Rhizobium symbiosis under Al stress is discussed.

Influence of Mesenchymal Stem Cells with Endothelial Progenitor Cells in Co-culture on Osteogenesis and Angiogenesis: An In Vitro Study

Bone is a highly vascularized tissue reliant on the close spatial and temporal connection between blood vessels and bone cells to maintain skeletal integrity. Considering the intricate connection between osteogenesis and angiogenesis, it is not surprising that communication between mesenchymal stem cells (MSCs) and endothelial progenitor cells (EPCs) is one of the most important cellular interactions that orchestrates bone formation. The aim of this study was to evaluate the interaction of co-cultured bone marrow-derived endothelial progenitor cells (BM-EPCs) and mesenchymal stem cells (MSCs) in angiogenesis and osteogenesis invitro. MSCs and BM-EPCs were isolated from bone marrow of dogs' iliac crest using density gradient centrifugation combined with adhesion method and identified with surface markers, cell proliferation and immunocytochemistry invitro. We used the direct contact method of MSCs and BM-EPCs in a co-culture system. Co-cultured cells and non-co-cultured cells were examined using the alkaline phosphatase (ALP) activity assay, matrix mineralization assay, Matrigel 2D assay and gene expression. ALP activity and calcification of nodules significantly increased in the co-cultured cells compared with MSCs alone after day 3, and tubulogenic activity of the co-cultured cells was also higher than BM-EPCs alone. Expression of bone and angiogenic markers were enhanced beyond expression levels of MSCs and BM-EPCs cultured alone. BM-EPCs co-cultured with MSCs can promote osteogenesis and angiogenesis. This co-cultured system may be broadly useful in engineering a variety of other tissue types.

Metabolism of nitrogen and carbon: Optimization of biological nitrogen fixation and cowpea development

Although the favorable role of plant growth-promoting bacteria (PGPB) in biological nitrogen fixation (BNF) is well established, their involvement in nodule metabolism is unknown. This study was performed to determine the relationship between C and N metabolism in cowpea nodules inoculated with only Bradyrhizobium sp. or with double and triple combinations of Bradyrhizobium sp., and two PGPB, Paenibacillus graminis and Paenibacillus durus during two critical phases of nodule development (flowering and beginning of senescence). The triple inoculation (Bradyrhizobium sp and two PGPB) induced higher N content in nodules, total-N accumulation per plant and shoot dry weight compared with other combinations at the beginning of senescence. This increased N performance was positively correlated with the nodule sucrose content but not with the content of total soluble carbohydrates, reduced sugars and starch. The higher BNF under triple inoculation conditions was not significantly associated with sucrose synthase activity but was slightly associated with soluble acid invertase activity in nodules at the beginning of senescence. These enzymes exhibited opposite responses between flowering and the beginning of senescence in all treatments. Glutamate synthase, glutamine synthetase and glutamate dehydrogenase were stimulated by double (Bradyrhizobium sp. + P. durus) and triple inoculation compared with other treatments. Our data revealed that inoculation with Bradyrhizobium sp. and PGPB is favorable for BNF activity in cowpeas. This positive interaction requires a complex balance involving enzymes and metabolites related to C and N metabolism.

Performance of some Dalbergia sissoo clones collected from its distribution zones for nodulation and nitrogen fixation behavior under nursery condition

Fourteen Dalbergia sissoo clones collected from its distribution zone in the country and were raised in vegetative multiplication garden at Forest Research Institute, Dehra Dun. Out of the existing plant stock five clones were selected from Rajasthan origin, two from Haryana, six from Uttar Pradesh and one from Uttarakhand for the present study. Plants growth data together with nodules were recorded from roots and further assessed for nodulation and nitrogenase activity. Maximum pl-1 nitrogenase activity and height was recorded from U.P (Clone no 33 and 20), whereas, highest collar diameter, nodule weight and number was recorded from Rajasthan (Clone no 80 and 103). Overall clones collected from Uttar Pradesh showed better performance over others. Further for accurate and real selection of the clones, nitrogen fixation and its seasonal behavior performance of each clone is required to be studied. Secondly, for different Shisham growing area, maintenance of clonal seed orchard and vegetative multiplication garden is recommended to conserve the vigour of individual clonal material on agro-climatic zone basis for the future planting stock improvement program and to combat the Shisham mortality in the field and in near future.

Nodulation in the Legume Biofuel Feedstock Tree Pongamia pinnata

The legume tree Pongamia pinnata (also called Millettia pinnata) is gaining importance as a biofuel feedstock tree because of the abundant annual production of oil-rich seeds, adaptation to a wide range of geoclimatic conditions and significant resistance to abiotic stress, such as water-deficit, salinity and acidity of soils. The major defining benefit of using pongamia as a biofuel feedstock is that it is a legume, enabling biological nitrogen fixation through symbiosis with soil bacteria, collectively called rhizobia, which results in root nodulation. Here, we report preliminary data, (i) indicating the range of rhizobia that can form nodules on pongamia, (ii) demonstrating the measurement of nitrogen fixation activity of pongamia nodules via the classical acetylene reduction assay, (iii) illustrating nodule morphology and development and (iv) demonstrating aspects of nodule regulation by external nitrate as well as internal autoregulation of nodulation. We note that in pongamia most nodulation-related characteristics are similar to those found in other annual crop legumes such as soybean.

Effect of nodule formation in roots of hairy vetch (Vicia villosa) on methane and nitrous oxide emissions during succeeding rice cultivation

Leguminous cover crops like hairy vetch (Vicia villosa) is generally grown as winter cover crop in the rice paddy fields of tropical countries like South Korea and Japan. The leguminous cover crops are preferably cultivated due to their N-fixing ability by nodule formation. However, the interactions of nodule formation in hairy vetch roots and increased soil nitrate-N content due to hairy vetch cultivation with emissions of greenhouse gases especially nitrous oxide (N2O) during successive rice cultivation were not studied before. For this study, hairy vetch was harvested 1 week (204D), 2 weeks (197D), 3 weeks (190D) and 4 weeks (183D) before succeeding rice seedling transplanting and nodule characteristics of hairy vetch were compared with soil nitrate-N content and N2O emission during rice cultivation. Number and weight of nodules were increased with increasing age of hairy vetch and that in turn enhanced nitrogenase activity of nodules. The highest soil NO3-N content of 204D treatment might be attributed to the highest nitrogenase activity in the roots of 204 days old hairy vetch plants. The enhanced N2O emission from rice paddy soil due to longer hairy vetch cultivation as winter cover crop indicated that the age of leguminous cover crops is an important factor to determine the global warming during succeeding rice cultivation. Cultivation of hairy vetch for 197 days was probably the best practice to minimize adverse effect of N-fixation on N2O emission from rice paddy soils.

A phytase gene is overexpressed in root nodules cortex of Phaseolus vulgaris–rhizobia symbiosis under phosphorus deficiency

Phosphorus is an essential nutrient for rhizobial symbioses to convert N2 into NH4 usable for N nutrition in legumes and N cycle in ecosystems. This N2 fixation process occurs in nodules with a high energy cost. Phytate is the major storage form of P and accounts for more than 50% of the total P in seeds of cereals and legumes. The phytases, a group of enzymes widely distributed in plant and microorganisms, are able to hydrolyze a variety of inositol phosphates. Recently, phytase activity was discovered in nodules. However, the gene expression localization and its role in N2-fixing nodules are still unknown. In this work, two recombinant inbred lines (RILs) of common bean (Phaseolusvulgaris L.), selected as contrasting for N2 fixation under P deficiency, namely RILs 115 (P-efficient) and 147 (P-inefficient) were inoculated with Rhizobium tropici CIAT 899, and grown under hydroaeroponic conditions with sufficient versus deficient P supply. With in situ RT-PCR methodology, we found that phytase transcripts were particularly abundant in the nodule cortex and infected zone of both RILs. Under P deficiency, phytase transcripts were significantly more abundant for RIL115 than for RIL147, and more in the outer cortex than in the infected zone. Additionally, the high expression of phytase among nodule tissues for the P-deficient RIL115 was associated with an increase in phytase (33%) and phosphatase (49%) activities and efficiency in use of the rhizobial symbiosis (34%). It is argued that phytase activity in nodules would contribute to the adaptation of the rhizobia-legume symbiosis to low-P environments.

Ecosystem‐level consequences of symbiont partnerships in an N‐fixing shrub from interior Alaskan floodplains

In long‐lived N‐fixing plants, environmental conditions affecting plant growth and N demand vary at multiple temporal and spatial scales, and symbiont assemblages on a given host and patterns of allocation to nodule activities have been shown to vary according to environmental factors, suggesting that hosts may alter partner choice and manipulate symbiont assemblages based on shifting plant needs. This study assessed economic trade‐offs among N‐fixing symbionts of thin‐leaf alder (Alnus tenuifolia) by examining whether alder–Frankia associations change in response to the up‐regulation (P fertilization) and down‐regulation (N‐fertilization) of N‐fixation activities, and whether these changes are associated with differences among Frankia partners in their relative C cost and/or N benefit to A. tenuifolia.Relative to control plots, alder in +P plots had significantly higher nodule biomass and N‐fixation rates; these parameters were significantly lower in +N plots, translating to stand‐level N inputs that were more than an order of magnitude greater in +P than +N plots. Nodule respiration and N‐fixation rates were positively correlated, and analyses revealed that alder employs mechanisms to increase the efficiency of C use when N fixation is up‐regulated. Of the eight Frankia OTUs (operational taxonomic units) identified, two were dominant, with significant differences in Frankia OTU composition across samples being explained by fertilization treatment. Dominant OTUs had similar up‐ and down‐regulatory responses to treatments but differed in C costs of N fixation, while the most abundant sub‐dominant failed to up‐regulate N‐fixation rates in +P plots. Differences among Frankia OTUs in traits relevant to plant performance may form the basis for host choice and explain successional shifts in alder–Frankia assemblages. We suggest that manipulation of Frankia assemblages is an adaptation for a species such as A. tenuifolia that maintains a high dependence on atmospheric N across radically different growth environments. Because of the strong effects of thin‐leaf alder on soil N contents, it appears that host changes in C partitioning to nodule activities, including the physiological consequences of host specificity for Frankia assemblages, results in alder both driving and responding to environmental heterogeneity at small to large spatial scales.

Cysteine protease expression and activity in soybean nodules during development and stress

Cysteine protease expression and activity in soybean nodules during development and stress