Dynamic role of iron supply in amelioration of cadmium stress by modulating antioxidative pathways and peroxidase enzymes in mungbean

Potassium and melatonin-mediated regulation of fructose-1,6-bisphosphatase (FBPase) and sedoheptulose-1,7- bisphosphatase (SBPase) activity improve photosynthetic efficiency, carbon assimilation and modulate glyoxalase system accompanying tolerance to cadmium stress in tomato seedlings

The mechanism of the combined action of potassium (K) and melatonin (Mel) in modulating tolerance to cadmium (Cd) stress in plants is not well understood. The present study reveals the synergistic role of K and Mel in enhancing physiological and biochemical mechanisms of Cd stress tolerance in tomato seedlings. The present findings reveal that seedlings subjected to Cd toxicity exhibited disturbed nutrients balance [nitrogen (N) and potassium (K)], chlorophyll (Chl) biosynthesis [reduced δ-aminolevulinic acid (δ-ALA) content and δ-aminolevulinic acid dehydratase (δ-ALAD) activity], pathway of carbon fixation [reduced fructose-1,6-bisphosphatase (FBPase) and sedoheptulose-1,7- bisphosphatase (SBPase) activity] and photosynthesis process in tomato seedlings. However, exogenous application of K and Mel alone as well as together improved physiological and biochemical mechanisms in tomato seedlings, but their combined application proved best by efficiently improving nutrient uptake, photosynthetic pigments biosynthesis (increased Chl a and b, and Total Chl), carbon flow in Calvin cycle, activity of Rubisco, carbonic anhydrase activity, and accumulation of total soluble carbohydrates content in seedlings under Cd toxicity. Furthermore, the combined treatment of K and Mel suppressed overproduction of reactive oxygen species (hydrogen peroxide and superoxide), Chl degradation [reduced chlorophyllase (Chlase) activity] and methylglyoxal content in Cd-stressed tomato seedlings by upregulating glyoxalase (increased glyoxalase I and glyoxalase II activity) and antioxidant systems (increased ascorbate-glutathione metabolism). Thus, the present study provides stronger evidence that the co-application of K and Mel exhibited synergistic roles in mitigating the toxic effect of Cd stress by increasing glyoxalase and antioxidant systems and also by improving photosynthetic efficiency in tomato seedlings.

Characterization of plant growth-promoting traits of Enterobacter sp. and its ability to promote cadmium/lead accumulation in Centella asiatica L

In the present study, we characterized the plant growth-promoting traits of Enterobacter sp. FM-1 (FM-1) and investigated its ability to promote growth and increase IAA, P, and Fe concentrations as well as Cd and Pb accumulation in Centella asiatica L. (C. asiatica L.) in upstream area (UA) soil and downstream area (DA) soil that we collected from Siding mine. The results demonstrated that FM-1 secreted IAA, produced siderophores, and had P-solubilization ability even under Cd exposure. IAA secretion reached a maximum of 108.3 ± 1.3 mg L-1 under Cd exposure at 25 mg L-1. Siderophore production reached a maximum of 0.94 ± 0.01 under Cd exposure at 50 mg L-1. Pot experiments indicated that FM-1 successfully colonized the roots of C. asiatica L. In both soils, inoculation with FM-1 decreased the pH in rhizosphere soil and increased the bioavailability of both Cd and Pb. In addition, inoculation with FM-1 increased the IAA, P, and Fe concentrations and simultaneously promoted both Cd and Pb accumulation in C. asiatica L. The Cd and Pb concentrations in leaves increased 1.73- and 1.07-fold in the UA soil and 1.25- and 1.11-fold in the DA soil, respectively. Thus, the Cd-resistant strain FM-1 presented excellent PGP traits and could facilitate Cd and Pb phytoremediation by C. asiatica L.

Target-Based Physiological Modulations and Chloroplast Proteome Reveals a Drought Resilient Rootstock in Okra (Abelmoschus esculentus) Genotypes

As climate changes increase, drought stress is becoming a problem for all major horticultural crops; among them is okra (Abelmoschus esculentus). Despite its superior resilience to heat stress and high nutritional content, it is still underutilized in contrast to other vegetable crops. Moreover, the drought-resistant and drought-sensitive genotypes of okra are also not well known and require further exploration to improve their productivity. To investigate this in more detail, we performed comparative physiological and large-scale chloroplast proteomics on drought-stressed genotypes of okra. We evaluated four major genotypes of okra, viz., NS7774, NS7772, Green Gold, and OH3312 for drought resilient rootstock. The physiological modulations demonstrated a significant change by 50-76% in biomass, net-photosynthetic machinery, water transport, and absorption both in early and late stages of drought stress compared to well-watered crops in all genotypes. Maximum oxidative damage due to drought stress was observed for the genotypes NS7772, Green Gold and OH3312 as depicted by H2O2 and O2- determination. Greater oxidative stress was correlated to lesser antioxidant activity and expression of antioxidant enzymes, such as catalase and ascorbate peroxidase under stress in okra genotypes. The overall photosynthetic pigments, such as total chlorophyll, and total carotenoid content, were also decreased, and stomatal guard cells were disrupted and appeared closed compared to the control for the above three mentioned genotypes, except NS7774. A subsequent tissue-specific proteome analysis of chloroplasts and thylakoids analyzed by BN-PAGE (blue native polyacrylamide gel electrophoresis) revealed either over or under expression of specific proteins, such as ATPase, PSI, PSII core dimer, PSII monomer and ATP synthase. The expression of multiprotein complex proteins, including PSII-core dimer and PSII-core monomer, was slightly higher for the genotype NS7774 when compared to three other genotypes for both 5 and 10 days of drought stress. Further identification of specific proteins obtained in second dimension BN-PAGE provided descriptive detail of seven proteins involved in drought resistance across all genotypes. The identified proteins are majorly involved in photosynthesis under drought stress, suggesting NS7774 as a drought tolerant genotype. Further, the proteomic results were confirmed using Immunoblot by selecting specific protein such as PsaA. Overall, from our physiological modulations and chloroplast proteomics in all genotypes, we summarized NS7774 as a resilient rootstock and the other three genotypes (NS7772, OH3312, and Green Gold) as sensitive ones.

Role of hepcidin in oxidative stress and cell death of cultured mouse renal collecting duct cells: protection against iron and sensitization to cadmium

The liver hormone hepcidin regulates systemic iron homeostasis. Hepcidin is also expressed by the kidney, but exclusively in distal nephron segments. Several studies suggest hepcidin protects against kidney damage involving Fe2+ overload. The nephrotoxic non-essential metal ion Cd2+ can displace Fe2+ from cellular biomolecules, causing oxidative stress and cell death. The role of hepcidin in Fe2+ and Cd2+ toxicity was assessed in mouse renal cortical [mCCD(cl.1)] and inner medullary [mIMCD3] collecting duct cell lines. Cells were exposed to equipotent Cd2+ (0.5-5 μmol/l) and/or Fe2+ (50-100 μmol/l) for 4-24 h. Hepcidin (Hamp1) was transiently silenced by RNAi or overexpressed by plasmid transfection. Hepcidin or catalase expression were evaluated by RT-PCR, qPCR, immunoblotting or immunofluorescence microscopy, and cell fate by MTT, apoptosis and necrosis assays. Reactive oxygen species (ROS) were detected using CellROX™ Green and catalase activity by fluorometry. Hepcidin upregulation protected against Fe2+-induced mIMCD3 cell death by increasing catalase activity and reducing ROS, but exacerbated Cd2+-induced catalase dysfunction, increasing ROS and cell death. Opposite effects were observed with Hamp1 siRNA. Similar to Hamp1 silencing, increased intracellular Fe2+ prevented Cd2+ damage, ROS formation and catalase disruption whereas chelation of intracellular Fe2+ with desferrioxamine augmented Cd2+ damage, corresponding to hepcidin upregulation. Comparable effects were observed in mCCD(cl.1) cells, indicating equivalent functions of renal hepcidin in different collecting duct segments. In conclusion, hepcidin likely binds Fe2+, but not Cd2+. Because Fe2+ and Cd2+ compete for functional binding sites in proteins, hepcidin affects their free metal ion pools and differentially impacts downstream processes and cell fate.

Growth and Antioxidant Responses in Iron-Biofortified Lentil under Cadmium Stress

Cadmium (Cd) is a hazardous heavy metal, toxic to our ecosystem even at low concentrations. Cd stress negatively affects plant growth and development by triggering oxidative stress. Limited information is available on the role of iron (Fe) in ameliorating Cd stress tolerance in legumes. This study assessed the effect of Cd stress in two lentil (Lens culinaris Medik.) varieties differing in seed Fe concentration (L4717 (Fe-biofortified) and JL3) under controlled conditions. Six biochemical traits, five growth parameters, and Cd uptake were recorded at the seedling stage (21 days after sowing) in the studied genotypes grown under controlled conditions at two levels (100 μM and 200 μM) of cadmium chloride (CdCl₂). The studied traits revealed significant genotype, treatment, and genotype × treatment interactions. Cd-induced oxidative damage led to the accumulation of hydrogen peroxide (H₂O₂) and malondialdehyde in both genotypes. JL3 accumulated 77.1% more H₂O₂ and 75% more lipid peroxidation products than L4717 at the high Cd level. Antioxidant enzyme activities increased in response to Cd stress, with significant genotype, treatment, and genotype × treatment interactions (p < 0.01). L4717 had remarkably higher catalase (40.5%), peroxidase (43.9%), superoxide dismutase (31.7%), and glutathione reductase (47.3%) activities than JL3 under high Cd conditions. In addition, L4717 sustained better growth in terms of fresh weight and dry weight than JL3 under stress. JL3 exhibited high Cd uptake (14.87 mg g⁻¹ fresh weight) compared to L4717 (7.32 mg g⁻¹ fresh weight). The study concluded that the Fe-biofortified lentil genotype L4717 exhibited Cd tolerance by inciting an efficient antioxidative response to Cd toxicity. Further studies are required to elucidate the possibility of seed Fe content as a surrogacy trait for Cd tolerance.

Comparative physiological and proteomic analysis deciphering tolerance and homeostatic signaling pathways in chrysanthemum under drought stress

Drought is increasing prevalently, mostly due to global warming, and harmful effects associated with drought stress include a reduction in the developmental phases of the plant life cycle. Drought stress affects vital metabolic processes in plants such as transpiration, photosynthesis and respiration. The other physiological and cellular processes like protein denaturation and aggregation are also affected by drought. Drought stress severely affects the floral industry by reducing the yield of flowers and among them is chrysanthemum (Dendranthema grandiflorum). In this study, we determined the critical signaling pathways, tolerance mechanism and homeostatic maintenance to drought stress in chrysanthemum. We compared the proteome of chrysanthemum leaves under drought stress. Among 250 proteins on 2DE gels, 30 protein spots were differentially expressed. These proteins were involved in major signaling pathways including, stress response, flower development and other secondary metabolism like physiological transport, circadian rhythm, gene regulation, DNA synthesis and protein ubiquitination. A reduction in a biomass, flower development, photosynthesis, transpiration, stomatal conductance, PSII yield and stomatal index was also observed in our results. Moreover, the stress markers and leaf water potential were also analyzed to depict the level of stress tolerance in chrysanthemum. Our data suggested that chrysanthemum plants developed reactive oxygen species and revealed signaling pathways to cope with drought stress. These results, thus, provide crucial information about how chrysanthemum plants respond to drought stress to maintain homeostasis.

Differential lead-fluoride and nickel-fluoride uptake in co-polluted soil variably affects the overall physiome in an aromatic rice cultivar

The present study aimed to show that nickel and fluoride exhibited synchronized co-inhibited uptake in the aromatic rice cultivar, Gobindobhog, since bioaccumulation of the two elements was lower than that during individual stress, so that overall growth under combined stress was similar to control seedlings. On the contrary, lead and fluoride stimulated their co-uptake which triggered oxidative damages, NADPH oxidase activity, methylglyoxal accumulation, photosynthetic inhibition, membrane-protein damages, necrosis and genomic template degradation. Accumulation of proline, anthocyanins, non-protein thiols and phytochelatins was stimulated for systemic protection against reactive oxygen species (ROS) and xenobiotic-mediated injuries during lead-fluoride toxicity. ROS accumulation during nickel-fluoride stress was insignificant due to which enhanced accumulation of most antioxidants was not required. Glutathione depletion during combined lead-fluoride toxicity was due to its utilization in the glyoxalase cycle and also inhibition of glutathione reductase. However, the nickel-fluoride-treated sets maintained glutathione reserves and glyoxalase activity similar to those in control. Presence of fluoride 'safeguarded' the glutathione-utilizing enzymes like glutathione reductase, glutathione peroxidase and glutathione-S-transferase during dual lead-fluoride stress. This was because these enzymes showed higher activity compared to that under lead toxicity alone. Enzymatic antioxidants like superoxide dismutase, ascorbate peroxidase and guaiacol peroxidase were activated during lead-fluoride toxicity due to altered iron and copper homeostasis. Catalase activity was strongly inhibited, resulting in the inability to scavenge H₂O₂ and suppression of the fluoride-adaptable phenotype. However, none of the enzymatic antioxidants were inhibited during nickel-fluoride stress, which cumulatively allowed the seedlings to maintain normal physiology. Overall our findings holistically reveal the physiological plasticity of Gobindobhog in response to two different heavy metals under the influence of fluoride.

Nano-scale zero valent iron modulates Fe/Cd transporters and immobilizes soil Cd for production of Cd free rice

In recent decades, nanoscale zero valent iron (nZVI) has been found to be a promising approach for heavy metal remediation. This study is the first report highlighting the role of nZVI to ameliorate Cadmium (Cd) stress in rice along with its effects in expressions of transporter genes, agronomic parameters and grain nutrient status. Initially, 3 concentration of Cd (10, 50, 250 μM) and nZVI (50, 100, 200 mg L^-1) were selected. PCA analysis based on growth parameters, photosynthetic pigment contents and lipid peroxidation rate confirmed that 100 mg L^-1 nZVI was most suitable for remediation of 10 μM Cd. It was evident that, nZVI can alleviate Cd-induced toxic effects by enhancing antioxidant defense mechanisms and other physiological processes in plants. nZVI treated rice seedlings also showed upregulation of phytochelatins which aided in Cd chelation within vacuoles. Study of root morphology with scanning electron microscopy and ROS imaging with confocal microscopy confirmed that nZVI could alleviate oxidative stress due to Cd uptake. In nZVI treated rice seedlings, gene expressions of iron (Fe) transporters (like, IRT1,IRT2,YSL2,YSL15) which are responsible for both Fe and Cd uptake were significantly down-regulated whereas, OsVIT1 and OsCAX4 genes were over expressed which lead to sequestration of Cd in vacuoles. Cd localization assay with leadmium proved that Cd translocation was reduced with nZVI treatment. To further validate our findings a pot experiment was carried out where it was found that nZVI could immobilize Cd in soil prevented accumulation of Cd in rice grains in addition to improving yield.