Enhanced adaptability of Sesbania rostrata to Pb/Zn tailings via stem nodulation

Effects of Azorhizobium caulinodans and Piriformospora indica Co-Inoculation on Growth and Fruit Quality of Tomato (Solanum lycopersicum L.) under Salt Stress

Salt stress is a worldwide environmental signal, reducing the growth and yield of crops. To improve crop tolerance to salt, several beneficial microbes are utilized. Here, nitrogen-fixing bacterium Azorhizobium caulinodans and root endophytic fungus Piriformospora indica were used to inoculate tomato (Solanum lycopersicum) under salt stress, and the effects of the co-inoculation were investigated. Results showed that A. caulinodans colonized in the intercellular space in stems and roots of tomato plants, while P. indica colonized in the root cortex. Two weeks following salt treatment, co-inoculated tomato plants grew substantially taller and had larger stem base diameters. Activities of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and reduced and oxidized ascorbate and glutathione (i.e., AsA, DHA, GSH, and GSSG, respectively) concentrations along with the ratios of AsA/(AsA + DHA) and GSH/(GSH + GSSG) increased in the leaves of co-inoculated plants under salt stress. The co-inoculation significantly increased soluble proteins and AsA in fruits; however, concentrations of soluble sugars and proanthocyanins did not show significant changes, compared with NaCl only treatment. Data suggest that A. caulinodans and P. indica co-inoculation boosted tomato growth and improved the quality of tomato fruits under salt stress. O-inoculation of A. caulinodans and P. indica might be employed to enhance tomato plant salt tolerance.

Low Cd-accumulating rice intercropping with Sesbania cannabina L. reduces grain Cd while promoting phytoremediation of Cd-contaminated soil

Paddy field pollution with Cd has become a serious problem and poses threat to public health. Intercropping is new good agricultural practice for phytoremediation in Cd contaminated soil. Field and pot experiments were conducted to examine the effects of intercropping low Cd-accumulating rice with Sesbania cannabina on plant growth, uptake of Cd by the intercropping system, and rhizosphere microecology, and to evaluate the potential remediation of Cd contaminated soil and safety production of rice. The results of in the field experiment show that, in intercropping system, the concentration of Cd in the grain of rice (0.18 mg kg^-1) was below the threshold level permitted by the National Food Safety Standard of China (GB 2762-2017, 0.20 mg kg^-1). Furthermore, the yield per plant of rice in intercropping system significantly (P < 0.05) increased by 19.71%. At the same time, the bio-concentration amount (BCA) of Cd per plant of Sesbania cannabina in intercropping system significantly (P < 0.05) increased by 46.15%. The metal removal equivalent ratio (MRER) of Cd was 1.11, indicating that the intercropping system had advantage in Cd removal. In the pot experiment, the rice intercropped with Sesbania cannabina under no barrier (IN) treatment significantly (P < 0.05) decreased the content of rhizosphere organic acids (oxalic and malic acids), and significantly (P < 0.05) increased the rhizosphere pH value and total iron plaque concentration on the root surface compared to the intercropping with plastic barrier (IN+P) treatment, which could significantly (P < 0.05) decreased the available Cd content in rhizosphere soil and the accumulation of Cd in rice organs. With this study we demonstrated that lower rhizosphere organic acids and higher iron plaque can obstruct and decreased the Cd absorbed by rice in a rice-Sesbania cannabina intercropping system. We conclude that intercropping rice with Sesbania cannabina is a promising and cost-effective agricultural practice for safe crop production and for phytoremediation in Cd-contaminated paddy soil.

Effects of copper oxide nanoparticles on germination of Sesbania virgata (FABACEAE) plants

Nanotechnology is a field that, over the years, has been growing in several research areas, such as medicine, agriculture and cosmetics, among others. As a result, there is a continuous increase in the production, use and disposal of these materials in the environment. The behaviour and (bio) activity of these materials in the atmosphere, water and soil are not fully studied. Therefore, it is necessary to carry out an analysis of the risks of contamination, as well as the possible effects and impacts of nanoparticles (NPs) on the ecosystem. In an attempt to investigate these effects on plants, the present study aimed to investigate the impact of copper oxide nanoparticles (CuO NPs) on the seed germination process of Sesbania virgata. For this, the Sesbania virgata seeds were subjected to different concentration of CuO NPs (0, 100, 200, 300 and 400 mgL-1) and their germination and development were monitored by optical analysis (thermography and chlorophyll a fluorescence). The results show that the CuO NPs induced a reduction on the maximum emission of chlorophyll a, which was concentration-dependent. The data also showed that CuO NPs promoted an increase in the energy dissipated by non-photochemical pathways and the surface temperature of the seeds. Additionally, our findings revealed that CuO NPs caused a root growth inhibition. In summary, the present study demonstrates, for the first time, that CuO NPs can negatively affect the physiological status and development of the S. virgata plant, by altering the efficiency of the functioning of photosystem II in its initial developmental stage, depending on the concentration of CuO NPs.

Enhanced phytoremediation of uranium-contaminated soils by arbuscular mycorrhiza and rhizobium

Uranium phytoextraction is a promising technology, however, facing difficult that limited plant biomass due to nutrient deficiency in the contaminated sites. The aim of this study is to evaluate the potential of a symbiotic associations of a legume Sesbania rostrata, rhizobia and arbuscular mycorrhiza fungi (AMF) for reclamation of uranium contaminated soils. Results showed AMF and rhizobia had a mutual beneficial relations in the triple symbiosis, which significantly increased plant biomass and uranium accumulation in S. rostrata plant. The highest uranium removal rates was observed in plant-AMF-rhizobia treated soils, in which 50.5-73.2% had been extracted, whereas 7.2-23.3% had been extracted in plant-treated soil. Also, the S. rostrata phytochelatin synthase (PCS) genes expression were increased in AMF and rhizobia plants compared with the plants. Meantime, content of malic acid, succinic acid and citric acid were elevated in S. rostrata root exudates of AMF and rhizobia inoculated plants. The facts suggest that the mutual interactions in the triple symbiosis help to improve phytoremediation efficiency of uranium by S. rostrata.

Roles of Extracellular Polysaccharides and Biofilm Formation in Heavy Metal Resistance of Rhizobia

Bacterial surface components and extracellular compounds, particularly flagella, lipopolysaccharides (LPSs), and exopolysaccharides (EPSs), in combination with environmental signals and quorum-sensing signals, play crucial roles in bacterial autoaggregation, biofilm development, survival, and host colonization. The nitrogen-fixing species Sinorhizobium meliloti (S. meliloti) produces two symbiosis-promoting EPSs: succinoglycan (or EPS I) and galactoglucan (or EPS II). Studies of the S.meliloti/alfalfa symbiosis model system have revealed numerous biological functions of EPSs, including host specificity, participation in early stages of host plant infection, signaling molecule during plant development, and (most importantly) protection from environmental stresses. We evaluated functions of EPSs in bacterial resistance to heavy metals and metalloids, which are known to affect various biological processes. Heavy metal resistance, biofilm production, and co-culture were tested in the context of previous studies by our group. A range of mercury (Hg II) and arsenic (As III) concentrations were applied to S. meliloti wild type strain and to mutant strains defective in EPS I and EPS II. The EPS production mutants were generally most sensitive to the metals. Our findings suggest that EPSs are necessary for the protection of bacteria from either Hg (II) or As (III) stress. Previous studies have described a pump in S. meliloti that causes efflux of arsenic from cells to surrounding culture medium, thereby protecting them from this type of chemical stress. The presence of heavy metals or metalloids in culture medium had no apparent effect on formation of biofilm, in contrast to previous reports that biofilm formation helps protect various microorganism species from adverse environmental conditions. In co-culture experiments, EPS-producing heavy metal resistant strains exerted a protective effect on AEPS-non-producing, heavy metal-sensitive strains; a phenomenon termed “rescuing” of the non-resistant strain.

Genomic analyses of metal resistance genes in three plant growth promoting bacteria of legume plants in Northwest mine tailings, China

To better understand the diversity of metal resistance genetic determinant from microbes that survived at metal tailings in northwest of China, a highly elevated level of heavy metal containing region, genomic analyses was conducted using genome sequence of three native metal-resistant plant growth promoting bacteria (PGPB). It shows that: Mesorhizobium amorphae CCNWGS0123 contains metal transporters from P-type ATPase, CDF (Cation Diffusion Facilitator), HupE/UreJ and CHR (chromate ion transporter) family involved in copper, zinc, nickel as well as chromate resistance and homeostasis. Meanwhile, the putative CopA/CueO system is expected to mediate copper resistance in Sinorhizobium meliloti CCNWSX0020 while ZntA transporter, assisted with putative CzcD, determines zinc tolerance in Agrobacterium tumefaciens CCNWGS0286. The greenhouse experiment provides the consistent evidence of the plant growth promoting effects of these microbes on their hosts by nitrogen fixation and/or indoleacetic acid (IAA) secretion, indicating a potential in-site phytoremediation usage in the mining tailing regions of China.