Open Access
Local inhibition of nitrogen fixation and nodule metabolism in drought-stressed soybean
(Oxford University Press, 2013) Gil Quintana, Erena; Larrainzar Rodríguez, Estíbaliz; Seminario Huárriz, Amaia; Díaz Leal, Juan Luis; Alamillo, Josefa M.; Pineda, Manuel; Arrese-Igor Sánchez, César; Wienkoop, Stefanie; González García, Esther; Ciencias del Medio Natural; Natura Ingurunearen Zientziak; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa: 735/2008; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa: 134/2012
Drought stress is a major factor limiting symbiotic nitrogen fixation (NF) in soybean crop production. However, the regulatory mechanisms involved in this inhibition are still controversial. Soybean plants were symbiotically grown in a split-root system (SRS), which allowed for half of the root system to be irrigated at field capacity while the other half remained water deprived. NF declined in the water-deprived root system while nitrogenase activity was maintained at control values in the well-watered half. Concomitantly, amino acids and ureides accumulated in the water-deprived belowground organs regardless of transpiration rates. Ureide accumulation was found to be related to the decline in their degradation activities rather than increased biosynthesis. Finally, proteomic analysis suggests that plant carbon metabolism, protein synthesis, amino acid metabolism, and cell growth are among the processes most altered in soybean nodules under drought stress. Results presented here support the hypothesis of a local regulation of NF taking place in soybean and downplay the role of ureides in the inhibition of NF
Open Access
Is N-feedback involved in the inhibition of nitrogen fixation in drought-stressed Medicago truncatula?
(Oxford University Press, 2013) Gil Quintana, Erena; Larrainzar Rodríguez, Estíbaliz; Arrese-Igor Sánchez, César; González García, Esther; Ciencias del Medio Natural; Natura Ingurunearen Zientziak; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa: 735/2008
Drought stress is a major factor limiting nitrogen fixation (NF) in crop production. However, the regulatory mechanism involved and the origin of the inhibition, whether local or systemic, is still controversial and so far scarcely studied in temperate forage legumes. Medicago truncatula plants were symbiotically grown with a split-root system and exposed to gradual water deprivation. Physiological parameters, NF activity, and amino acid content were measured. The partial drought treatment inhibited NF in the nodules directly exposed to drought stress. Concomitantly, in the droughted below-ground organs, amino acids accumulated prior to any drop in evapotranspiration (ET). It is concluded that drought exerts a local inhibition of NF and drives an overall accumulation of amino acids in diverse plant organs which is independent of the decrease in ET. The general increase in the majority of single amino acids in the whole plant questions the commonly accepted concept of a single amino acid acting as an N-feedback signal.
Open Access
Physiological responses of legume nodules to drought
(Global Science Books, 2011) Arrese-Igor Sánchez, César; González García, Esther; Marino Bilbao, Daniel; Ladrera Fernández, Rubén; Larrainzar Rodríguez, Estíbaliz; Gil Quintana, Erena; Ciencias del Medio Natural; Natura Ingurunearen Zientziak
Legumes include important agricultural crops, as their high protein content is of primary importance for human food and animal feed. In addition, the ability of most of them to establish symbiotic relationships with soil bacteria allows them to obtain their N requirements from nitrogen fixation in nodules and, therefore, avoids the use of nitrogen fertilizers. Thus, legumes are also essential to improve the soil fertility and quality of agricultural lands and to reclaim eroded or barren areas, making them crucial for agricultural and environmental sustainability. However, legume nitrogen fixation in crop species is very sensitive to environmental constraints and drought, in particular. The present contribution reviews our current knowledge on the processes involved in this inhibition, with particular emphasis on oxygen, nitrogen and carbon physiology. Emerging aspects such as oxidative damage, C/N interactions and sulphur metabolism together with future prospects are also discussed.
Open Access
Nodule carbohydrate catabolism is enhanced in the Medicago truncatula A17-Sinorhizobium medicae WSM419 symbiosis
(Frontiers Media, 2014) Larrainzar Rodríguez, Estíbaliz; Gil Quintana, Erena; Seminario Huárriz, Amaia; Arrese-Igor Sánchez, César; González García, Esther; Ciencias del Medio Natural; Natura Ingurunearen Zientziak; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
The symbiotic association between Medicago truncatula and Sinorhizobium meliloti is a well-established model system in the legume–Rhizobium community. Despite its wide use, the symbiotic efficiency of this model has been recently questioned and an alternative microsymbiont, S. medicae, has been proposed. However, little is known about the physiological mechanisms behind the higher symbiotic efficiency of S. medicae WSM419. In the present study, we inoculated M. truncatula Jemalong A17 with either S. medicae WSM419 or S. meliloti 2011 and compared plant growth, photosynthesis, N2-fixation rates, and plant nodule carbon and nitrogen metabolic activities in the two systems. M. truncatula plants in symbiosis with S. medicae showed increased biomass and photosynthesis rates per plant. Plants grown in symbiosis with S. medicae WSM419 also showed higher N2-fixation rates, which were correlated with a larger nodule biomass, while nodule number was similar in both systems. In terms of plant nodule metabolism, M. truncatula–S. medicae WSM419 nodules showed increased sucrose-catabolic activity, mostly associated with sucrose synthase, accompanied by a reduced starch content, whereas nitrogen-assimilation activities were comparable to those measured in nodules infected with S. meliloti 2011. Taken together, these results suggest that S. medicae WSM419 is able to enhance plant carbon catabolism in M. truncatula nodules, which allows for the maintaining of high symbiotic N2-fixation rates, better growth and improved general plant performance.
Open Access
Increased ascorbate biosynthesis does not improve nitrogen fixation nor alleviate the effect of drought stress in nodulated Medicago truncatula plants
(Frontiers Media, 2021) Cobos Porras, Inmaculada Libertad; Rubia Galiano, María Isabel; Huertas, Raúl; Kum, David; Dalton, David A.; Udvardi, Michael; Arrese-Igor Sánchez, César; Larrainzar Rodríguez, Estíbaliz; Institute for Multidisciplinary Research in Applied Biology - IMAB; Gobierno de Navarra / Nafarroako Gobernua, PC112-113 LEGUSI
Legume plants are able to establish nitrogen-fixing symbiotic relations with Rhizobium bacteria. This symbiosis is, however, affected by a number of abiotic constraints, particularly drought. One of the consequences of drought stress is the overproduction of reactive oxygen (ROS) and nitrogen species (RNS), leading to cellular damage and, ultimately, cell death. Ascorbic acid (AsA), also known as vitamin C, is one of the antioxidant compounds that plants synthesize to counteract this oxidative damage. One promising strategy for the improvement of plant growth and symbiotic performance under drought stress is the overproduction of AsA via the overexpression of enzymes in the Smirnoff-Wheeler biosynthesis pathway. In the current work, we generated Medicago truncatula plants with increased AsA biosynthesis by overexpressing MtVTC2, a gene coding for GDP-L-galactose phosphorylase. We characterized the growth and physiological responses of symbiotic plants both under well-watered conditions and during a progressive water deficit. Results show that increased AsA availability did not provide an advantage in terms of plant growth or symbiotic performance either under well-watered conditions or in response to drought.
Open Access
A plant gene encoding one-heme and two-heme hemoglobins with extreme reactivities toward diatomic gases and nitrite
(Frontiers Media, 2020) Villar, Irene; Larrainzar Rodríguez, Estíbaliz; Milazzo, Lisa; Pérez Rontomé, Carmen; Rubio, María Carmen; Smulevich, Giulietta; Martínez, Jesús I.; Wilson, Michael T.; Reeder, Brandon; Huertas, Raúl; Abbruzzetti, Stefania; Udvardi, Michael; Becana, Manuel; Ciencias; Zientziak
In plants, symbiotic hemoglobins act as carriers and buffers of O2 in nodules, whereas nonsymbiotic hemoglobins or phytoglobins (Glbs) are ubiquitous in tissues and may perform multiple, but still poorly defined, functions related to O2 and/or nitric oxide (NO). Here, we have identified a Glb gene of the model legume Medicago truncatula with unique properties. The gene, designated MtGlb1-2, generates four alternative splice forms encoding Glbs with one or two heme domains and 215–351 amino acid residues. This is more than double the size of any hemoglobin from plants or other organisms described so far. A combination of molecular, cellular, biochemical, and biophysical methods was used to characterize these novel proteins. RNA-sequencing showed that the four splice variants are expressed in plant tissues. MtGlb1-2 is transcriptionally activated by hypoxia and its expression is further enhanced by an NO source. The gene is preferentially expressed in the meristems and vascular bundles of roots and nodules. Two of the proteins, bearing one or two hemes, were characterized using mutants in the distal histidines of the hemes. The Glbs are extremely reactive toward the physiological ligands O2, NO, and nitrite. They show very high O2 affinities, NO dioxygenase activity (in the presence of O2), and nitrite reductase (NiR) activity (in the absence of O2) compared with the hemoglobins from vertebrates and other plants. We propose that these Glbs act as either NO scavengers or NO producers depending on the O2 tension in the plant tissue, being involved in the fast and fine tuning of NO concentration in the cytosol in response to sudden changes in O2 availability.
Open Access
Split‐root systems applied to the study of the legume‐rhizobial symbiosis: what have we learned?
(Wiley, 2014) Larrainzar Rodríguez, Estíbaliz; Gil Quintana, Erena; Arrese-Igor Sánchez, César; González García, Esther; Marino Bilbao, Daniel; Ciencias del Medio Natural; Natura Ingurunearen Zientziak
Split-root system (SRS) approaches allow the differential treatment of separate and independent root systems, while sharing a common aerial part. As such, SRS is a useful tool for the discrimination of systemic (shoot origin) versus local (root/nodule origin) regulation mechanisms. This type of approach is particularly useful when studying the complex regulatory mechanisms governing the symbiosis established between legumes and Rhizobium bacteria. The current work provides an overview of the main insights gained from the application of SRS approaches to understand how nodule number (nodulation autoregulation) and nitrogen fixation are controlled both under non-stressful conditions and in response to a variety of stresses. Nodule number appears to be mainly controlled at the systemic level through a signal which is produced by nodule/root tissue, translocated to the shoot, and transmitted back to the root system, involving shoot Leu-rich repeat receptor-like kinases. In contrast, both local and systemic mechanisms have been shown to operate for the regulation of nitrogenase activity in nodules. Under drought and heavy metal stress, the regulation is mostly local, whereas the application of exogenous nitrogen seems to exert a regulation of nitrogen fixation both at the local and systemic levels.
Open Access
Drought stress causes a reduction in the biosynthesis of ascorbic acid in soybean plants
(Frontiers Media, 2017) Seminario Huárriz, Amaia; Song, Li; Zulet González, Amaia; Nguyen, Henry T.; González García, Esther; Larrainzar Rodríguez, Estíbaliz; Ciencias del Medio Natural; Natura Ingurunearen Zientziak; Gobierno de Navarra / Nafarroako Gobernua, 2016/PI013; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa, 1287/2011
Drought provokes a number of physiological changes in plants including oxidative damage. Ascorbic acid (AsA), also known as vitamin C, is one of the most abundant water-soluble antioxidant compound present in plant tissues. However, little is known on the regulation of AsA biosynthesis under drought stress conditions. In the current work we analyze the effects of water deficit on the biosynthesis of AsA by measuring its content, in vivo biosynthesis and the expression level of genes in the Smirnoff-Wheeler pathway in one of the major legume crop, soybean (Glycine max L. Merr). Since the pathway has not been described in legumes, we first searched for the putative orthologous genes in the soybean genome. We observed a significant genetic redundancy, with multiple genes encoding each step in the pathway. Based on RNA-seq analysis, expression of the complete pathway was detected not only in leaves but also in root tissue. Putative paralogous genes presented differential expression patterns in response to drought, suggesting the existence of functional specialization mechanisms. We found a correlation between the levels of AsA and GalLDH biosynthetic rates in leaves of drought-stressed soybean plants. However, the levels of GalLDH transcripts did not show significant differences under water deficit conditions. Among the other known regulators of the pathway, only the expression of VTC1 genes correlated with the observed decline in AsA in leaves.
Open Access
Drought stress provokes the down-regulation of methionine and ethylene biosynthesis pathways in Medicago truncatula roots and nodules
(Wiley, 2014) Larrainzar Rodríguez, Estíbaliz; Molenaar, Johanna A.; Wienkoop, Stefanie; Gil Quintana, Erena; Alibert, Bénédicte; Limami, Anis M.; Arrese-Igor Sánchez, César; González García, Esther; Ciencias del Medio Natural; Natura Ingurunearen Zientziak; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa, 735/2008
Symbiotic nitrogen fixation is one of the first physiological processes inhibited in legume plants under water-deficit conditions. Despite the progress made in the last decades, the molecular mechanisms behind this regulation are not fully understood yet. Recent proteomic work carried out in the model legume Medicago truncatula provided the first indications of a possible involvement of nodule methionine (Met) biosynthesis and related pathways in response to waterdeficit conditions. To better understand this involvement, the drought-induced changes in expression and content of enzymes involved in the biosynthesis of Met, S-adenosyl-Lmethionine (SAM) and ethylene in M. truncatula root and nodules were analyzed using targeted approaches. Nitrogenfixing plants were subjected to a progressive water deficit and a subsequent recovery period. Besides the physiological characterization of the plants,the content of total sulphur,sulphate and main S-containing metabolites was measured. Results presented here show that S availability is not a limiting factor in the drought-induced decline of nitrogen fixation rates in M. truncatula plants and provide evidences for a downregulation of the Met and ethylene biosynthesis pathways in roots and nodules in response to water-deficit conditions.
Open Access
A novel Enterococcus-based nanofertilizer promotes seedling growth and vigor in wheat (Triticum aestivum L.)
(MDPI, 2024-10-14) Batool, Salma; Safdar, Maryam; Naseem, Saira; Sami, Abdul; Saleem, Rahman Shah Zaib; Larrainzar Rodríguez, Estíbaliz; Shahid, Izzah; Ciencias; Zientziak; Institute for Multidisciplinary Research in Applied Biology - IMAB
Excessive use of chemical fertilizers poses significant environmental and health concerns. Microbial-based biofertilizers are increasingly being promoted as safe alternatives. However, they have limitations such as gaining farmers¿ trust, the need for technical expertise, and the variable performance of microbes in the field. The development of nanobiofertilizers as agro-stimulants and agro-protective agents for climate-smart and sustainable agriculture could overcome these limitations. In the present study, auxin-producing Enterococcus sp. SR9, based on its plant growth-promoting traits, was selected for the microbe-assisted synthesis of silver nanoparticles (AgNPs). These microbial-nanoparticles SR9AgNPs were characterized using UV/Vis spectrophotometry, scanning electron microscopy, and a size analyzer. To test the efficacy of SR9AgNPs compared to treatment with the SR9 isolate alone, the germination rates of cucumber (Cucumis sativus), tomato (Solanum lycopersicum), and wheat (Triticum aestivum L.) seeds were analyzed. The data revealed that seeds simultaneously treated with SR9AgNPs and SR9 showed better germination rates than untreated control plants. In the case of vigor, wheat showed the most positive response to the nanoparticle treatment, with a higher vigor index than the other crops analyzed. The toxicity assessment of SR9AgNPs demonstrated no apparent toxicity at a concentration of 100 ppm, resulting in the highest germination and biomass gain in wheat seedlings. This work represents the first step in the characterization of microbial-assisted SR9AgNPs and encourages future studies to extend these conclusions to other relevant crops under field conditions.