Mechanism and application of Sesbania root-nodulating bacteria: an alternative for chemical fertilizers and sustainable development.

Chemical fertilizers are used in large-scale throughout the globe to satisfy the food and feed requirement of the world. Demanding cropping with the enhanced application of chemical fertilizers, linked with a decline in the recycling of natural or other waste materials, has led to a decrease in the organic carbon levels in soils, impaired soil physical properties and shrinking soil microbial biodiversity. Sustenance and improvement of soil fertility are fundamental for comprehensive food security and ecological sustainability. To feed the large-scale growing population, the role of biofertilizers and their study tends to be an essential aspect globally. In this review, we have emphasized the nitrogen-fixing plants of Sesbania species. It is a plant that is able to accumulate nitrogen-rich biomass and used as a green manure, which help in soil amelioration. Problems of soil infertility due to salinity, alkalinity and waterlogging could be alleviated through the use of biologically fixed nitrogen by Sesbania plants leading to the conversion of futile land into a fertile one. A group of plant growth-promoting rhizobacteria termed as "rhizobia" are able to nodulate a variety of legumes including Sesbania. The host-specific rhizobial strains can be used as potential alternative for nitrogenous fertilizers as they help the host plant in growth and development and enhance their endurance under stressed conditions. The review gives the depth understanding of how the agriculturally important microorganisms can be used for the reduction of broad-scale application of chemical fertilizers with special attention to Sesbania-nodulating rhizobia.

Transcriptome analysis reveals the impact of arbuscular mycorrhizal symbiosis on Sesbania cannabina expose to high salinity.

Arbuscular mycorrhiza can improve the salt-tolerance of host plant. A systematic study of mycorrhizal plant responses to salt stress may provide insights into the acquired salt tolerance. Here, the transcriptional profiles of mycorrhizal Sesbania cannabina shoot and root under saline stress were obtained by RNA-Seq. Using weighted gene coexpression network analysis and pairwise comparisons, we identified coexpressed modules, networks and hub genes in mycorrhizal S. cannabina in response to salt stress. In total, 10,371 DEGs were parsed into five coexpression gene modules. One module was positively correlated with both salt treatment and arbuscular mycorrhizal (AM) inoculation, and associated with photosynthesis and ROS scavenging in both enzymatic and nonenzymatic pathways. The hub genes in the module were mostly transcription factors including WRKY, MYB, ETHYLENE RESPONSE FACTOR, and TCP members involved in the circadian clock and might represent central regulatory components of acquired salinity tolerance in AM S. cannabina. The expression patterns of 12 genes involved in photosynthesis, oxidation-reduction processes, and several transcription factors revealed by qRT-PCR confirmed the RNA-Seq data. This large-scale assessment of Sesbania genomic resources will help in exploring the molecular mechanisms underlying plant-AM fungi interaction in salt stress responses.

Enhanced growth of halophyte plants in biochar-amended coastal soil: roles of nutrient availability and rhizosphere microbial modulation.

Soil health is essential and irreplaceable for plant growth and global food production, which has been threatened by climate change and soil degradation. Degraded coastal soils are urgently required to reclaim using new sustainable technologies. Interest in applying biochar to improve soil health and promote crop yield has rapidly increased because of its multiple benefits. However, effects of biochar addition on the saline-sodic coastal soil health and halophyte growth were poorly understood. Response of two halophytes, Sesbania (Sesbania cannabina) and Seashore mallow (Kosteletzkya virginica), to the individual or co-application of biochar and inorganic fertilizer into a coastal soil was investigated using a 52 d pot experiment. The biochar alone or co-application stimulated the plant growth (germination, root development, and biomass), primarily attributed to the enhanced nutrient availability from the biochar-improved soil health. Additionally, the promoted microbial activities and bacterial community shift towards the beneficial taxa (e.g. Pseudomonas and Bacillus) in the rhizosphere also contributed to the enhanced plant growth and biomass. Our findings showed the promising significance because biochar added at an optimal level (≤5%) could be a feasible option to reclaim the degraded coastal soil, enhance plant growth and production, and increase soil health and food security.

A rhamnose-deficient lipopolysaccharide mutant of Rhizobium sp. IRBG74 is defective in root colonization and beneficial interactions with its flooding-tolerant hosts Sesbania cannabina and wetland rice.

Rhizobium sp. IRBG74 develops a classical nitrogen-fixing symbiosis with the aquatic legume Sesbania cannabina (Retz.). It also promotes the growth of wetland rice (Oryza sativa L.), but little is known about the rhizobial determinants important for these interactions. In this study, we analyzed the colonization of S. cannabina and rice using a strain of Rhizobium sp. IRBG74 dually marked with ß-glucuronidase and the green fluorescent protein. This bacterium colonized S. cannabina by crack entry and through root hair infection under flooded and non-flooded conditions, respectively. Rhizobium sp. IRBG74 colonized the surfaces of wetland rice roots, but also entered them at the base of lateral roots. It became endophytically established within intercellular spaces in the rice cortex, and intracellularly within epidermal and hypodermal cells. A mutant of Rhizobium sp. IRBG74 altered in the synthesis of the rhamnose-containing O-antigen exhibited significant defects, not only in nodulation and symbiotic nitrogen fixation with S. cannabina, but also in rice colonization and plant growth promotion. Supplementation with purified lipopolysaccharides from the wild-type strain, but not from the mutant, restored the beneficial colonization of rice roots, but not fully effective nodulation of S. cannabina Commonalities and differences in the rhizobial colonization of the roots of wetland legume and rice hosts are discussed.

Characterization of cadmium-resistant bacteria for its potential in promoting plant growth and cadmium accumulation in Sesbania bispinosa root.

The cadmium (Cd) resistant bacteria were isolated from soils of Damanganga river, Vapi, and identified 11 potential Cd resistant bacteria based on 16S rDNA sequences. The Cd resistant bacteria belonged to four different genera: Providencia spp., Morganella sp., Stenotrophomonas sp., and Bacillus spp. The assessment of plant growth-promoting (PGP) parameters revealed that the Cd tolerant bacteria showed one or more PGP properties. Further, a pot experiment was conducted to elucidate the effects of Cd resistant bacteria on the plant growth and the uptake of Cd by Sesbania bispinosa. The bacterized seedlings recorded 36.0-74.8% and 21.2-32.9% higher root and shoot lengths, respectively, in Cd amended soil compared with control. The Cd mobilization in the root of S. bispinosa by microbial inoculants ranged from 0.02 ± 0.01 to 1.11 ± 0.06 ppm. The enhanced concentrations of Cd accumulation in S. bispinosa roots correspond to the effect of the bacterial strains on metal mobilization in soil. The present observations showed that the Cd resistant strains protect the plants against the inhibitory effects of Cd, probably due to the production of PGP properties. The present results provided a new insight into the phytoremediation of Cd contaminated soil.

Extraction and characterization of triglycerides from coffeeweed and switchgrass seeds as potential feedstocks for biodiesel production.

BACKGROUND: Although switchgrass has been developed as a biofuel feedstock and its potential for bioethanol and bio-oil from fast pyrolysis reported in the literature, the use of the seeds of switchgrass as a source of triglycerides for biodiesel production has not been reported. Similarly, the potential for extracting triglycerides from coffeeweed (an invasive plant of no current economic value) needs to be investigated to ascertain its potential economic use for biodiesel production. RESULTS: The results show that coffeeweed and switchgrass seeds contain known triglycerides which are 983 and 1000 g kg(-1) respectively of the fatty acids found in edible vegetable oils such as sunflower, corn and soybean oils. In addition, the triglyceride yields of 53-67 g kg(-1) of the seed samples are in the range of commercial oil-producing seeds such as corn (42 g kg(-1) ). CONCLUSION: The results also indicate that the two non-edible oils could be used as substitutes for edible oil for biodiesel production. In addition, the use of seeds of switchgrass for non-edible oil production (as a feedstock for the production of biodiesel) further increases the total biofuel yield when switchgrass is cultivated for use as energy feedstock for pyrolysis oil and biodiesel production. © 2016 Society of Chemical Industry.

[Genetic diversity of the Rhizobia and screening of high-efficient growth-promoting strains isolated from Sesbania cannabina in Rudong County].

OBJECTIVE: To study the genetic diversity and phylogeny of Rhizobia isolated from Sesbania cannabina growing on the tidal flat in Rudong County and screen high-efficient growth-promoting strains as Rhizobia inoculator to S. cannabina. METHODS: Phylogenetic analyses were based on 16S rRNA gene, housekeeping genes (recA, atpD, glnII) and symbiotic genes (nodA, nifH). The growth-promoting efficiency was tested by plant inoculation assay on S. cannabina in greenhouse. RESULTS: The 32 isolates belonged to Ensifer, Neorhizobium, Rhizobium, and most closely related to E. meliloti, N. huautlense, R. pusense. The phylogenies of nodA and nifH were congruent, and most closely related to E. saheli. The 7 representative isolates were resistant to high concentration of NaCl (5%, W/V), and YIC5082 grew well in TY medium with 6% NaCl. In plant inoculation assay, all the 7 representative isolates were effective on symbiotic nitrogen fixation, and 6 out of the 7 isolates significantly enhanced the fresh weight and height of plants. CONCLUSION: Rhizobia isolated from S. cannabina growing on the tidal flat in Rudong County showed rich genetic diversity. N. huautlense and E. meliloti were the dominant species. Most of the isolates showed fine growth-promoting efficiency and salt tolerance. YIC5077 showed the best growth-promoting efficiency, good nodulation and nitrogen fixation abilities, which has promising potential applications as Rhizobia inoculator to S. cannabina.

Effects of green manure cover crops on Spodoptera litura (Lepidoptera: Noctuidae) populations.

Spodoptera litura (F.) is an important pest of numerous agro-economic crops, including green manure cover crops. In Taiwan, sesbania (Sesbanin roxburghii Merr.), sunn hemp (Crotalaria juncea L.), and rapeseed (Brassicae campestris L. variety chinensis) are the most popular green manure crops; sesbania and sunn hemp are commonly planted in warm seasons, whereas rapeseed is grown in the winter. In this study, life-table data for S. litura reared on these three green manures were collected to evaluate their roles as refuges of this pest. The net reproductive rate, intrinsic rate of increase, and finite rate of increase of S. litura were the highest when reared on sesbania (1428.1 offspring, 0.2327 d(-1), 1.2621 d(-1)), followed by sunn hemp (778.4 offspring, 0.2070 d(-1), 1.2300 d(-1)) and rapeseed (737.6 offspring, 0.2040 d(-1), 1.2263 d(-1)). The high growth rates on these green manure crops show that they can serve as potential breeding sites for S. litura. Population projection demonstrated the rapid growth of S. litura on sesbania, sunn hemp, and rapeseed as well. Because most growers have traditionally ignored pest management in green manure fields, the mass emergence of S. litura in these fields may cause unexpected infestations in nearby vegetable, corn, and peanut crops. This study shows that the use of green manures as sources of nutrients should be critically reassessed and an area-wide pest management program should be instituted by taking the population of S. litura in green manure fields into consideration.

Organic C dynamics and its conservation under wheat (Triticum aesetivum) - mint (Mentha arvensis)-Sesbania rostrata cropping in sub-tropical condition of northern Indo-Gangetic plains.

Soil organic carbon (SOC) is accumulated or depleted as a result of cropping and management strategies. It plays a significant role in maintaining soil quality, plant productivity and mitigating greenhouse gas emission. We studied the long-term (20 years) influence of a wheat-mint-Sesbania cropping system on the SOC stock. Estimates of stabilization of SOC in different pools and a tentative C budget were also developed. Twenty years of cultivation caused a decrease in SOC only in control soils, which received no manure and fertilizer. However, it increased with balanced use of NPK inputs. Soil C stock decreased significantly with increased in soil depth 0-15 cm to 15-30 and 30-45 cm. About 6% (-2 to+14) of the C added in crop residues and green manure were stabilized in the soil. On an average 12%, 14%, 59%, 15% of the water stable aggregates were in the >2 mm, 2.0-0.25 mm, 0.25-0.05 mm, and <0-0.5 size fractions, respectively. Significant improvements in structural stability and nitrogen availability were detected in all the treatments compared to the control. The amount of organic C oxidizable by a modified Walkley and Black method, which involves using only half of the amount of sulphuric acid, is a more sensitive indicator of the improvement in soil quality parameters under investigation, namely SOC, and increases in mineralizable N and water stable aggregation than the standard method.

Rhizodegradation of petroleum hydrocarbons by Sesbania cannabina in bioaugmented soil with free and immobilized consortium.

The present study reports the effect of bioaugmentation by free and immobilized bacterial culture on the rhizodegradation of petroleum-polluted soil using Sesbania cannabina plant. Total petroleum hydrocarbon (TPH), hydrocarbon-degrading bacterial counts, microbial activity and root morphology were assessed during 120 days of plant growth. TPH concentration analyzed by GC-MS showed that bioaugmentation did not improve the TPH degradation. TPH concentration decreased from 2541 mg kg(-1) to 673 mg kg(-1) and 867 mg kg(-1) in the rhizosphere of free (FR) and immobilized bacterial inoculated (IR) soil, respectively at the 120th day while in the rhizosphere of uninoculated soil (CR) concentration decreased to 679 mg kg(-1) only at the 90th day, showing higher and rapid rhizodegradation with indigenous bacteria than bioaugmented bacterial cultures. Various predominant bacterial groups responsible for higher TPH degradation in the rhizosphere of S. cannabina were identified by PCR-DGGE analysis. It is concluded that natural plant-microbe interaction in the rhizosphere of S. cannabina was efficient enough to degrade TPH and plant rhizosphere keeps bacterial community in its surrounding therefore immobilized culture had no obvious effect on petroleum degradation.

Absorption and translocation of copper, zinc and chromium by Sesbania virgata.

Heavy metals (HM) incorporated to ecosystems as a mixture could interact and generate contamination, which might be mitigated through phytoremediation. The heavy metal tolerance of native species of Sesbania from the Argentinean Pampas is poorly documented. The objective of this work was to evaluate the effect of interactions between copper, zinc and chromium, in binary form, on Sesbania virgata biomass, absorption and translocation. The HM transfer from a contaminated soil to plants and into plant tissues are discussed in terms of the Bioconcentration Factor (BCF) and the Transfer Factor (TF). In a pot experiment, HM were added either individually or in binary mixture solutions of Cu, Zn and Cr, in low or high doses. In all treatments, the main accumulation of HM appeared in plant roots, and Zn is more removed from soils by S. virgata (BCF average in roots Zn > Cr > Cu). In the binary mixture of Cu and Zn, Sesbania plants absorbed the highest concentrations of these metals. In contrast, Cr was more absorbed in the individual treatments. While the co-presence of metals resulted in a greater reduction in S. virgata biomass than the presence of a single metal, S. virgata tolerated and stabilized high concentrations of Cu, Zn and Cr. In view of this tolerance, S. virgata is excellent specie to be used for heavy metals phytostabilization in contaminated soils.

Interactive effects of lead, copper, nickel and zinc on growth, metal uptake and antioxidative metabolism of Sesbania drummondii.

Sesbania drummondii seedlings were grown in a medium to which lead (Pb), copper (Cu), nickel (Ni) and zinc (Zn) were added singly and in combinations in order to assess the effects of metal interactions on seedling growth, metal accumulation and anti-oxidative system. S. drummondii growth was significantly inhibited with metal treatments. S. drummondii accumulated substantially higher concentrations of metals in the roots than shoots. The uptake of metals followed the order Pb>Cu>Zn>Ni in roots and Pb>Zn>Cu>Ni in shoots. In addition, uptake of a single metal by S. drummondii was affected by the presence of a second metal, suggesting an antagonistic effect or competition between metals at the plant uptake site. A significant increase in both enzymatic [superoxide dismutase (SOD), ascorbate peroxidase (APX), glutathione reductase (GR)] and non-enzymatic (glutathione) antioxidant was observed in the S. drummondii seedlings exposed to different metal treatments. The enhancement in enzyme activities followed the order of Cu>Ni>Pb>Zn. However, compared to the effect of individual metal, metals in combination increased the enzyme activities to varying degrees.

Promising role of plant hormones in translocation of lead in Sesbania drummondii shoots.

Lead (Pb) accumulation in Sesbania drummondii shoots was enhanced by 654 and 415% in the presence of 100 microM IAA and 100 microM NAA, respectively, compared to control plants (Pb alone). However, when IAA or NAA was added along with EDTA, Pb accumulation further increased in shoots by 1349% and 1252%, respectively. Scanning electron microscopic observations revealed that Pb particles in both leaf and stem of Pb+EDTA+IAA and Pb+EDTA+NAA treated plants were concentrated in the region of vascular bundles. In root tissue, Pb particles were present between epidermis to stele region. Plant growth in both treatments (Pb+100 microM IAA and Pb+100 microM NAA) was comparable to control plants; however, it was significantly inhibited in the treatments containing Pb+EDTA and EDTA at concentrations of 10 microM of IAA or NAA. Moreover, the photosynthetic efficiency and strength of the treated plants were not affected in the presence of IAA or NAA and EDTA.

Increase of multi-metal tolerance of three leguminous plants by arbuscular mycorrhizal fungi colonization.

A greenhouse pot experiment was conducted to investigate the effects of the colonization of arbuscular mycorrhizal fungus (AMF) Glomus mosseae on the growth and metal uptake of three leguminous plants (Sesbania rostrata, Sesbania cannabina, Medicago sativa) grown in multi-metal contaminated soil. AMF colonization increased the growth of the legumes, indicating that AMF colonization increased the plant's resistance to heavy metals. It also significantly stimulated the formation of root nodules and increased the N and P uptake of all of the tested leguminous plants, which might be one of the tolerance mechanisms conferred by AMF. Compared with the control, colonization by G. mosseae decreased the concentration of metals, such as Cu, in the shoots of the three legumes, indicating that the decreased heavy metals uptake and growth dilution were induced by AMF treatment, thereby reducing the heavy metal toxicity to the plants. The root/shoot ratios of Cu in the three legumes and Zn in M. sativa were significantly increased (P<0.05) with AMF colonization, indicating that heavy metals were immobilized by the mycorrhiza and the heavy metal translocations to the shoot were decreased.

Accumulation, speciation and cellular localization of copper in Sesbania drummondii.

Growth, accumulation and intracellular speciation and distribution of copper (Cu) in Sesbania drummondii was studied using scanning-electron microscopy (SEM), X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). The growth of seedlings was assessed in terms of biomass accumulation. The growth of the seedling was enhanced by 73.5% at a low Cu concentration (50 mg l-1) compared to the control treatment. Additionally, seedling growth was inhibited by 18% at 300 mg l-1 Cu with respect to the control. Copper concentration in roots and shoots was increased with increasing Cu concentration in the growth solution. The accumulation of Cu was found to be higher in roots than in the shoots. At a concentration of 300 mg l-1 Cu, the roots accumulated 27,440 mg Cu kg-1 dry weight (dw) while shoots accumulated 1282 mg Cu kg-1 dw. Seedlings were assessed for photosynthetic activity by measuring chlorophyll a fluorescence parameters: Fv/Fm and Fv/F0 values. Photosynthetic integrity was not affected by any of the Cu treatments. The X-ray absorption spectroscopic (XAS) studies showed that Cu was predominantly present as Cu(II) in Sesbania tissue. In addition, from the XAS studies it was shown that the Cu exists in a mixture of different coordination states consisting of Cu bound to sugars and small organic acids with some possible precipitated copper oxide. From the EXAFS studies, the coordination of Cu was determined to have four equatorial oxygen(nitrogen) ligands at 1.96 A and two axial oxygen ligands at 2.31 A. Scanning-electron microscopy studies revealed the distribution of Cu within the seedlings tissues, predominantly accumulated in the cortical and vascular (xylem) regions of root tissues. In the stem, most of the Cu was found within the xylem tissue. However, the deposition of Cu within the leaf tissues was in the parenchyma. The present study demonstrates the mechanisms employed by S. drummondii for Cu uptake and its biotransformation.

Solubility and accumulation of metals in Chinese brake fern, vetiver and rostrate sesbania using chelating agents.

Greenhouse experiments were conducted to study the effects of chelating agents on the growth and metal accumulation of Chinese brake fern (Pteris vittata L.), vetiver (Vetiveria zizanioides L.), and rostrate sesbania (Sesbania rostrata L.) in soil contaminated with arsenic (As), Cu, Pb, and Zn. Among the five chelating agents used [ethylenediaminetriacetic acid (EDTA), hydroxyethylenediaminetriacetic acid (HEDTA), nitrilotriacetic acid (NTA), oxalic acid (OA), and phytic acid (PA)], OA was the best to mobilize As, EDTA to mobilize Cu and Pb, and HEDTA to mobilize Zn from soil, respectively. The biomass of vetiver was the highest, followed by rostrate sesbania. All chelating agents inhibited the growth of Chinese brake fern and rostrate sesbania, but HEDTA significantly increased the aboveground biomass of vetiver. Dry weights of both Chinese brake fern and rostrate sesbania decreased with increasing EDTA concentrations amended in the soil, especially in treatments with high EDTA concentrations. EDTA and HEDTA enhanced Cu, Zn, and Pb, but lowered As accumulation in all three plant species, except for As in vetiver, while OA significantly enhanced As accumulation in the aboveground part of vetiver. Concentrations of Cu, Zn, and Pb in the aboveground parts of plants increased significantly with the increase of EDTA concentrations and treatment time. In addition to As, Chinese brake fern also accumulated the highest Cu, Pb, and Zn in its aboveground parts among the three plant species grown in metal-contaminated soil with EDTA/HEDTA treatments. This species, therefore, can be used to simultaneously clean up As, Cu, Pb, and Zn from contaminated soils with the aid of EDTA or HEDTA.

Bioaccumulation and physiological effects of mercury in Sesbania drummondii.

The accumulation of mercury and its effect on growth, photosynthesis and antioxidative responses were studied in Sesbania drummondii seedlings. Mercury concentration in shoots as well as in the roots increased with increasing Hg concentrations in the growth solution. The accumulation of Hg was more in roots than shoots. At 100 mg l-1 Hg concentration, shoots accumulated 998 mg Hg kg -1 dry weight (dw) while roots accumulated 41,403 mg Hg kg-1 dw. Seedlings growth was not significantly affected at lower concentrations of Hg. A concentration of 100 mg l-1 Hg inhibited growth by 36.8%, with respect to control. Photosynthetic activity was assessed by measuring chlorophyll a fluorescence by determination of Fv/Fm and Fv/Fo values. Photosynthetic integrity was not affected up to 50 mg l-1 Hg concentration, however, concentrations higher than 50 mg l-1 affected photosynthetic integrity. Sesbania responded to Hg induced oxidative stress by modulating non-enzymatic antioxidants [glutathione (GSH) and non-protein thiols (NPSH)] and enzymatic antioxidants: superoxide dismutase (SOD), ascorbate peroxidase (APX) and glutathione reductase (GR). Glutathione content and GSH/GSSG ratio increased up to a concentration of 50 mg l-1 while slight down at 100 mg l-1 Hg. The content of NPSH significantly increased with increasing Hg concentrations in the growth medium. The activities of antioxidative enzymes, SOD, APX and GR followed the same trends as antioxidants first increased up to a concentration of 50 mg l-1 Hg and then slight decreased. The results of present study suggest that Sesbania plants were able to accumulate and tolerate Hg induced stress using an effective antioxidative defense mechanisms.

Effects of lead and chelators on growth, photosynthetic activity and Pb uptake in Sesbania drummondii grown in soil.

Effects of lead (Pb) and chelators, such as EDTA, HEDTA, DTPA, NTA and citric acid, were studied to evaluate the growth potential of Sesbania drummondii in soils contaminated with high concentrations of Pb. S. drummondii seedlings were grown in soil containing 7.5 g Pb(NO(3))(2) and 0-10 mmol chelators/kg soil for a period of 2 and 4 weeks and assessed for growth profile (length of root and shoot), chlorophyll a fluorescence kinetics (F(v)/F(m) and F(v)/F(o)) and Pb accumulations in root and shoot. Growth of plants in the presence of Pb+chelators was significantly higher (P<0.05) than the controls grown in the presence of Pb alone. F(v)/F(m) and F(v)/F(o) values of treated seedlings remained unaffected, indicating normal photosynthetic efficiency and strength of plants in the presence of chelators. On application of chelators, while root uptake of Pb increased four-five folds, shoot accumulations increased up to 40-folds as compared to controls (Pb only) depending on the type of chelator used. Shoot accumulations of Pb varied from 0.1 to 0.42% (dry weight) depending on the concentration of chelators used.

Cadmium accumulation and antioxidative responses in the Sesbania drummondii callus.

The effect of cadmium (Cd) on growth, accumulation, and antioxidative response was studied in Sesbania drummondii callus, cultivated on different concentrations of Cd (0-250 microM) for four weeks. Callus growth was comparable to that of the control for concentrations up to 50 microM Cd; however, concentrations higher than 50 microM affected growth. A concentration of 100 microM Cd inhibited growth by 16%, with respect to control. Cd concentration in callus increased with increasing Cd concentrations in the growth medium. Callus accumulated 530 mg Cd kg(-1) of their dry weight at 100 microM Cd concentration. Sesbania callus responded to Cd-induced oxidative stress by modulating antioxidants (glutathione and other non-protein thiols) level and antioxidative enzymes: superoxide dismutase (SOD), ascorbate peroxidase (APX), and glutathione reductase (GR). The content of the glutathione (GSH) and GSH/GSSG ratio first increased up to a concentration of 50 microM Cd and then decreased. The content of other non-protein thiols significantly increased with increasing Cd concentrations in the growth medium. The activities of antioxidative enzymes, SOD, APX, and GR, followed the same trends as antioxidants first increasing up to a concentration of 50 microM Cd and then decreasing. These results suggest that antioxidative defense mechanisms play a significant role in Cd detoxification and accumulation in Sesbania drummondii.

Gibberellins are involved in nodulation of Sesbania rostrata.

Upon submergence, Azorhizobium caulinodans infects the semiaquatic legume Sesbania rostrata via the intercellular crack entry process, resulting in lateral root-based nodules. A gene encoding a gibberellin (GA) 20-oxidase, SrGA20ox1, involved in GA biosynthesis, was transiently up-regulated during lateral root base nodulation. Two SrGA20ox1 expression patterns were identified, one related to intercellular infection and a second observed in nodule meristem descendants. The infection-related expression pattern depended on bacterially produced nodulation (Nod) factors. Pharmacological studies demonstrated that GAs were involved in infection pocket and infection thread formation, two Nod factor-dependent events that initiate lateral root base nodulation, and that they were also needed for nodule primordium development. Moreover, GAs inhibited the root hair curling process. These results show that GAs are Nod factor downstream signals for nodulation in hydroponic growth.