Legumes grow in temperate and warm climates, being susceptible to unpredictable episodes of water deficit. This study aimed to evaluate (i) morphology and N-compound contents in roots and nodules, (ii) N and C contents in shoots and (iii) crop yield in two peanut cultivars with contrasting drought tolerance, inoculated with a reference N-fixing strain and challenged by water deficit conditions. For that, seeds of two peanut cultivars, Granoleico (sensitive, S) and EC-98 (tolerant, T) were inoculated with Bradyrhizobium sp. SEMIA6144 and 30 days after sowing, plants were separated into the experimental groups: control, drought stress and drought stress and subsequent rehydration. Although the results obtained on root anatomy and histology revealed differential responses between cultivars, they were not associated with tolerance traits in EC-98 (T). In contrast, nodules of EC-98 (T) showed invariable diameter and infection zone upon the exposition to drought stress and rehydration compared to nodules of Granoleico (S) plants exposed to the same treatments. EC-98 (T) showed invariable contents of C in shoots and of nitrates and ureides in roots and nodules of stressed and rehydrated plants, an increase in total amino acids only in nodules of stressed plants and a small reduction in N-content (compared with the sensitive cultivar). The status of these variables related to C- and N-metabolism could be associated with an efficient biological nitrogen fixation. Besides, EC-98 (T) yielded better both in a crop cycle with adequate water supply and in a dry year and the inoculation improved yield in both cultivars. Thus, the inoculation with N-fixing bacteria is recommended for EC-98 (T) in seasons with expected drought stress cycles in crops.

Arsenic (As) has aroused worldwide concern due to its accumulation in the food chain. Inoculated peanut plants with Bradyrhizobium sp. strains showing contrasting tolerance to arsenic (As), were exposed to a low arsenate (As-V) for 30 days in order to decipher the participation of the antioxidant system, mainly related to glutathione (GSH) metabolism, together with the arsenate reductase (AR) activity in roots. Results showed that the Bradyrhizobium sp. strain modulates differentially the AR activity. An increase in the enzymatic activities of superoxide dismutase, glutathione peroxidase/peroxirredoxin and glutathione S-transferase (GST) was observed, while glutathione reductase (GR) and monodehydroascorbate reductase activities were diminished. Particularly, ascorbate peroxidase (APX) activity was reduced when C-145 was inoculated. Gene expression assays reported an increase in the expression of transcripts GR, cAPX and GST in peanut roots inoculated with SEMIA6144. In the system peanut-Bradyrhizobium sp. C-145, the cAPX expression remained unchanged. In both symbiotic interactions, the total glutathione (GSH(T)) and reduced glutathione (GSH(R)) contents diminished, while oxidized glutathione (GSSG) increased leading to a reduction in the GSH(R)/(GSH(R) + GSSG) ratio. We conclude that, irrespectively of the As tolerance that the inoculated strains shows, the antioxidant response is not strain dependent. Thus, glutathione plays a fundamental role not only as an antioxidant metabolite but also as a key molecule to enhance metalloid detoxification in this inoculated crop. Moreover, as the tripeptide participates in the ROS scavenging, acting mainly as a substrate for GST, allow us to describe its activity as a robust biomarker of arsenic contamination in crops.

Arsenic in groundwater constitutes an agronomic problem due to its potential accumulation in the food chain. Among the agro-sustainable tools to reduce metal(oid)s toxicity, the use of plant growth-promoting bacteria (PGPB) becomes important. For that, and based on previous results in which significant differences of As translocation were observed when inoculating maize plants with Az39 or CD Azospirillum strains, we decided to decipher the redox metabolism changes and the antioxidant system response of maize plants inoculated when exposed to a realistic arsenate (AsV ) dose. Results showed that AsV caused morphological changes in the root exodermis. Photosynthetic pigments decreased only in CD inoculated plants, while oxidative stress evidence was detected throughout the plant, regardless of the assayed strain. The antioxidant response was strain-differential since only CD inoculated plants showed an increase in superoxide dismutase, glutathione S-transferase (GST), and glutathione reductase (GR) activities while other enzymes showed the same behavior irrespective of the inoculated strain. Gene expression assays reported that only GST23 transcript level was upregulated by arsenate, regardless of the inoculated strain. AsV diminished the glutathione (GSH) content of roots inoculated with the Az39 strain, and CD inoculated plants showed a decrease of oxidized GSH (GSSG) levels. We suggest a model in which the antioxidant response of the maize-diazotrophs system is modulated by the strain and that GSH plays a central role acting mainly as a substrate for GST. These findings generate knowledge for a suitable PGPB selection, and its scaling to an effective bioinoculant formulation for maize crops exposed to adverse environmental conditions.

The Leguminosae family constitutes the second most important family of crop plants worldwide. Nowadays, legumes provide one-third of the entire amount of protein for human consumption, animal food and edible and industrial oils. Plants are prone to suffer stress episodes such as salinity, drought or the presence of metal(loid)s. On initial exposure to an abiotic stress, plants show alterations in metabolism, ionic balance, osmolarity and membrane stability, among others. An oxidative burst with consequent biomolecules damage aggravates the stress condition. Along the evolution, plants acquired stress-specific cellular sensing mechanisms that help in signal transduction, yielding the activation of transcription factors and genes to counteract the deleterious effects triggered by the stressful condition. Among the contributors to help the plant in re-establishing cellular homeostasis are ion balancing, compatible solutes accumulation, antioxidant defense, hormonal regulation. However, depending on the severity of the stress, plants can retard or cease growth and finally die. Thus, this can conduct to yield loss having a huge impact in agroeconomy.Therefore, the present chapter focuses on the tolerance mechanisms to salinity, drought stress and metal(loid)s and summarizes the human efforts that upraised in an exhaustive tentative for improve stress tolerance in legume crops. This chapter intends to increase the understanding of the tolerance mechanisms evoked by legumes exposed to abiotic stresses, hence avoiding yield loss. The biochemical, molecular and physiological responses triggered by plants to cope with abiotic stresses are presented. Besides, we discuss the last advances in legume improvement through transgenic, breeding or agronomic approaches.

Proline accumulation and metabolism are associated with mechanisms of abiotic stress avoidance in plants. Proline accumulation generally improves osmotic stress tolerance whereas proline metabolism can have varying effects from ATP generation to the formation of reactive oxygen species. To further understand the roles of proline in stress protection, two peanut cultivars with contrasting tolerance to drought were examined by transcriptional and biochemical analyses during water stress. Plants exposed to polyethylene glycol had diminished relative water content and increased proline content; while, only the drought sensitive plants, cultivar Granoleico, showed lipid oxidative damage (measured as thiobarbituric acid reactive substances). The expression of proline biosynthesis genes (P5CS1, P5CS2a, P5CS2b, P5CR) was increased in both cultivars upon exposure to water stress. However, the relative expression of proline catabolism genes (ProDH1, ProDH2) was increased only in the sensitive cultivar during stress. Exogenous addition of proline and the proline analogue thiazolidine-4-carboxylic acid (T4C), both substrates of proline dehydrogenase, was also used to exacerbate and identify plant responses. Pretreatment of plants with T4C induced unique changes in the drought tolerant EC-98 cultivar such as higher mRNA levels of proline biosynthetic and catabolic ProDH genes, even in the absence of water stress. The increased levels of ProDH gene expression, potentially associated with higher T4C conversion to cysteine, may contribute to the tolerant phenotype.

Arsenic (As) can be present naturally in groundwater from peanut fields, constituting a serious problem, as roots can accumulate and mobilize the metalloid to their edible parts. Understanding the redox changes in the legume exposed to As may help to detect potential risks to human health and recognize tolerance mechanisms. Thirty-days old peanut plants inoculated with Bradyrhizobium sp. strains (SEMIA6144 or C-145) were exposed to a realistic arsenate concentration, in order to unravel the redox response and characterize the oxidative stress indexes. Thus, root anatomy, reactive oxygen species detection by fluorescence microscopy and, ROS histochemical staining along with the NADPH oxidase activity were analyzed. Besides, photosynthetic pigments and damage to lipids and proteins were determined as oxidative stress indicators. Results showed that at 3 μM AsV, the cross-section areas of peanut roots were augmented; NADPH oxidase activity was significantly increased and O2˙¯and H2O2 accumulated in leaves and roots. Likewise, an increase in the lipid peroxidation and protein carbonyls was also observed throughout the plant regardless the inoculated strain, while chlorophylls and carotenes were increased only in those inoculated with Bradyrhizobium sp. C-145. Interestingly, the oxidative burst, mainly induced by the NADPH oxidase activity, and the consequent oxidative stress was strain-dependent and organ-differential. Additionally, As modifies the root anatomy, acting as a possibly first defense mechanism against the metalloid entry. All these findings allowed us to conclude that the redox response of peanut is conditioned by the rhizobial strain, which contributes to the importance of effectively formulating bioinoculants for this crop.

>Dear Editor,Arsenic(As) is a harmful metalloid that occurs in soil and water; its concentration varies considerably among geographic regions, with groundwater being the principal source of human contamination(Smedley and Kinniburgh, 2002). Besides the direct contamination effect of drinking water that contains high As concentration, human poisoning may also occur after inges-

Peanut is a widespread legume, with an important agricultural and economic significance. It symbiotically interacts with rhizobia, increasing atmospheric nitrogen assimilation by the biological nitrogen fixation process, therefore improving yield. The presence of the environmental pollutant arsenic and the occurrence of water deficit episodes constitute severe abiotic stresses affecting this symbiosis, being biostimulants a sustainable alternative to increase crop yields. Thus, the objective of this work was to determine the effects of the joint application of a commercial seed non-microbial plant biostimulant (Nutrifer (R) 202) and a microbial plant biostimulant on growth, nodulation and oxidative stress indicator-levels, on peanut plants exposed to arsenic or drought. Biostimulant addition reduced As translocation to leaves and improved plant growth and nodulation in the drought stress condition, in association with proline accumulation, with a protective function on the cellular redox balance. Therefore the application of the biostimulant combination Nutrifer (R) 202 and Bradyrhizobium sp. C-145 is promising for peanut crops growing in regions susceptible to water deficit or arsenic exposure.

Arsenic (As) is a toxic metalloid that has gained special interest in the past years as a global environmental problem. Groundwater in Córdoba province (Argentina) presents high As concentrations which can be absorbed by plants or be used for artificial irrigation. The aim of this research was to elucidate the differential responses of symbiotic interactions established with three bacterial strains and soybean plants to realistic doses of arsenic. The reference strain Bradyrhizobium diazoefficiens USDA110 and the native isolate Bradyrhizobium sp. Per 3.64 were able to grow up to 13 mM As(V) whereas the native strain Bradyrhizobium sp. Per 3.61 grew up to 9.5 mM As(V). Metalloid addition did not modify the soybean plant growth at 6 μM As(V). Nevertheless, it was enough to induce oxidative stress as observed by an increase on lipid peroxidation. The soybean-Bradyrhizobium sp. assay at 6 μM As(V) showed no changes in growth variables (shoot and root dry weight) in plants inoculated with the reference microsymbiont or Bradyrhizobium sp. Per 3.61. Regarding As uptake by plants, metalloid accumulation followed the same distribution pattern among strains. Remarkably, at 6 μM As(V), soybean inoculation with Bradyrhizobium sp. Per 3.61 revealed a significantly lower translocation factor (TF) in comparison to other inoculated strains promoting As phytostabilization. At the highest As(V) concentration tested, only Bradyrhizobium diazoefficiens USDA110 was able to nodulate the legume, however, a significant decrease in the number and dry weight of nodules and nitrogen content was observed. In conclusion, the inoculation of soybean plants with the reference strain Bradyrhizobium diazoefficiens USDA110 exposed to high As(V) concentration represents an effective and promising symbiotic interaction that allows the development of the legume due to the minimal effects on plant growth. However, in low As(V) concentration environments, the native isolate Bradyrhizobium sp. Per 3.61, is shown to be the best inoculant among the tested strains, owing to the limitation of metalloid translocation and accumulation to edible parts of the legume, avoiding fruit contamination and human poisoning.

Groundwater with high arsenic (As) concentration constitutes a serious problem for crops, since roots can accumulate the metalloid acting as the first stage of As distribution in the trophic chain. The aim of this research was to elucidate the impact of a realistic As(V) dose in peanut and maize plants and to determine the contribution of plant growth promoting bacteria (PGPB) to metalloid translocation in both crops. The results obtained revealed that rhizoinoculation of plants exposed to metalloid, contributed not only to improve growth but also to reduce As transport to shoots. Hence, inoculation of peanut and maize with the correct PGPB partner prevents metalloid translocation in plants avoiding possible fruit contamination.

Fil: Bianucci, Eliana Carolina. Universidad Nacional de Rio Cuarto. Facultad de Ciencias Exactas, Fisicoquimicas y Naturales. Departamento de Ciencias Naturales; Argentina. Universidad Autonoma de Madrid; Espana. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Cordoba; Argentina

Fil: Angelini, Jorge Guillermo. Universidad Nacional de Rio Cuarto. Facultad de Ciencias Exactas Fisicoquimicas y Naturales. Instituto de Investigaciones Agrobiotecnologicas - Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Cordoba. Instituto de Investigaciones Agrobiotecnologicas; Argentina

Arsenic (As)-polluted groundwater constitutes a serious problem for peanut plants, as roots can accumulate the metalloid in their edible parts. Characterization of stress responses to As may help to detect potential risks and identify mechanisms of tolerance, being the induction of oxidative stress a key feature. Fifteen-day old peanut plants were treated with arsenate in order to characterize the oxidative stress indexes and antioxidant response of the legume under realistic groundwater doses of the metalloid. Superoxide anion (O-2(center dot-)) and hydrogen peroxide (H2O2 histochemical staining along with the activities of NADPH oxidase, superoxide dismutase (SOD), catalase (CAT) and thiol (glutathione and thioredoxins) metabolism were determined in roots. Results showed that at 20 mu M H2AsO4-, peanut growth was reduced and the root architecture was altered. O-2(center dot-) and H2O2 accumulated at the root epidermis, while lipid peroxidation, NADPH oxidase, SOD, CAT and glutathione S-transferase (GST) activities augmented. These variables increased with increasing As concentration (100 M) while glutathione reductase (GR) and glutathione peroxidase/peroxiredoxin (GPX/PRX) were significantly decreased. These findings demonstrated that the metalloid induced physiological and biochemical alterations, being the NADPH oxidase enzyme implicated in the oxidative burst. Additionally, the strong induction of GST activity, even at the lowest H2AsO4- doses studied, can be exploited as suitable biomarker of As toxicity in peanut plants, which may help to detect risks of As accumulation and select tolerant cultivars. (C) 2017 Elsevier Ltd. All rights reserved.

Legumes belong to the most important crops worldwide. They increase soil fertility due their ability to establish symbiotic associations with soil microorganisms, known as rhizobia, capable of fixing nitrogen from the atmosphere. However, they are frequently exposed to abiotic stress conditions in particular drought. Such adverse conditions impair the biological nitrogen fixation (BNF) and depend largely on the legume. Therefore, two peanut cultivars with contrasting tolerance to drought, namely the more tolerant EC-98 and the sensitive Granoleico, were investigated to elucidate the relative contribution of BNF to the tolerance to drought. The tolerant cultivar EC-98 sustained growth and BNF similar to the control condition despite the reduced water potential and photosynthesis, suggesting the functioning of distinct metabolic pathways that contributed to enhance the tolerance. The biochemical and metabolomics approaches revealed that nodules from the tolerant cultivar accumulated trehalose, proline and gamma-aminobutyric acid (GABA), metabolites with known function in protecting against drought stress. The amide metabolism was severely affected in nodules from the sensitive cultivar Granoleico as revealed by the low content of asparagine and glutamine in the drought stressed plants. The sensitive cultivar upon rehydration was unable to re-establish a metabolism similar to well-watered plants. This was evidenced by the low level of metabolites and, transcripts and specific activities of enzymes from the carbon (sucrose synthase) and nitrogen (glutamine synthetase) metabolism which decreased below the values of control plants. Therefore, the increased content of metabolites with protective functions under drought stress likely is crucial for the full restoration upon rehydration. Smaller changes of drought stress-related metabolites in nodule are another trait that contributes to the effective control of BNF in the tolerant peanut cultivar (EC-98).

Drought stress is one of the most important environmental factors that adversely affect the productivity and quality of crops. Most studies focus on elucidating plant responses to this stress but the reversibility of these effects is less known. The aim of this work was to evaluate whether drought-stressed peanut (Arachis hypogaea L.) plants were capable of recovering their metabolism upon rehydration, with a focus on their antioxidant system. Peanut plants in the flowering phase (30 days after sowing) were exposed to drought stress by withholding irrigation during 14 days and subsequent rehydration during 3 days. Under these conditions, physiological status indicators, reactive oxygen species production and antioxidant system activity were evaluated. Under drought stress, the stomatal conductance, photosynthetic quantum yield and 13C:12C ratio of the peanut plants were negatively affected, and also they accumulated reactive oxygen species. The antioxidant system of peanut plants showed increases in superoxide dismutase-, ascorbate peroxidase- and glutathione reductase-specific activities, as well as the total ascorbate content. All of these responses were reversed upon rehydration at 3 days. The efficient and dynamic regulation of variables related to photosynthesis and the antioxidant system during a drought and rehydration cycle in peanut plants was demonstrated. It is suggested that the activation of the antioxidant system could mediate the signalling of drought stress responses that enable the plant to survive and recover completely within 3 days of rehydration.

Nor Aini ab Shukor M. Z. Abdin Mohammad Reza Abdollahi Malay Adak Tariq Aftab Shinsuke Agehara S. B. Agrawal Ashok Ahuja Oya Akca Sergio Alemano Shafaqat Ali Fernie Alisdair R. Hugo Alonso Pedro Luis Alves Anjali Anand Kalina Ananieva Mats Anderson Diana Andrade Bibi Androniki Adeyemi Aremu Sandeep Arora Idris Arslan Kamal Ram Arya Aleksandr Babosha Peter Bakker Tamara Balakhnina Gabriel Balint Zsófia Bánfalvi Surendra Barpete Raimundo Barros Ponnusamy Baskaran Debabrata Basu Daizy R Batish Helen Belefant-Miller Federico Berli S. R. Bhat Amita Bhattacharya Yurong Bi Eliana Bianucci Zhilong Bie D. J. Bilalis Stefania Biondi A. K. Biswas Michael Blanke Cecilia Blomstedt Patrizia Bogani Marı́a Bompadre Ruth Bonilla Sharmistha Borthakur Jayakumar Bose Renato Botelho Marcia Braga Gloria Burow David Burritt Julieta Cabello Shengguan Cai Birsen Çakir Turgay Cakmak Fangbin Cao Francesco Carimi Esther Carrera Jose Casas Matteo Caser Ana Hortência Castro Stella Castro Supachitra Chadchawan Peter Chandler Yu-Sen Chang Abdelilah Chaoui Qingguo Chen Ruiqiang Chen Zhichang Chen Yongqin Chen Chong-Shun Chen Kunming Chen Xinbo Chen Cheng Cheng Fangmin Cheng D. K. Chooudary C. H. Chou Zhaohui Chu J. D. Cohen Louise Colville Sandra Cordeiro Ashton Cowan Cristina Crosatti Fabiana Csukasi Edvaldo da Silva Fei Dai Huiping Dai