Effect of vanadium on Lactuca sativa L. growth and associated health risk for human due to consumption of the vegetable

The induction of polyamines metabolism pathway and membrane stability with silicon alleviate the vanadium toxicity in pepper plants

The vanadium (V) toxicity predominantly is the primary limitation in restraining pepper growth. The silicon (Si) in pepper plants induced the transcript level of the polyamines metabolism pathway genes, including the arginase (CbARG), ornithine decarboxylase (CbODC), arginine decarboxylase (CbADC), N-carbamoylputrescine amidase (CbNCA), Spermidine synthase (CbSPDS), copper binding diamine oxidase (CbCuAO) to overcome the V toxicity. The polyamines, including the Spm, Spd, and Put, induced with Si about 41.37 %, 33.12 %, and 27.90 %, respectively, in V stress. Moreover, the Si application decline in the leaf and root V contents, which was around 49.5 % and 40.74 %, respectively, then the V stress plants. The soluble protein, proline, and Si level in root/leaf with Si treatment significantly induced around 55.55/50.22 %, 42.85/55.35 %, and 49.92/85.29 %, respectively, as compared to the V stress. Si also heightened the nitrate reductase (NR), phosphoenolpyruvate carboxylase (PEPC), and malate dehydrogenase (MDH) levels. Our study revealed that Si maintained the PSII integrity and induced PSII efficiency genes. Si preserves the membrane stability, as evidenced by less accumulation in EL, H2O2, and MDA levels. The Si also induces the AsA-GSH to eliminate the reactive oxygen species (ROS) in the pepper plants. In summary, our research elucidated that Si addition improved pepper plants' tolerance to V toxicity.

Fe(III) reduction mediates vanadium release and reduction in vanadium contaminated paddy soil under different organic amendments

Vanadium(V) contaminated soil is abundant in iron(Fe) oxides due to co-occurrence of V and Fe bearing minerals. However, biogeochemical transformation of redox-active V and Fe in soil, and the bacteria involved, has remained less investigated. This study explored the extent to which microbial mediated organic decomposition coupled to Fe(III) reduction contributed to V(V) release/reduction in V-contaminated paddy soil under different organic amendments. Soil flooding decreased toxic reducible V while increased less toxic oxidizable V. Glucose and straw promoted V(V) release with temporarily increasing V(V) concentration by 73.59-106.34 mg/kg compared to the control treatment and subsequently promoted V(V) reduction with decreasing V(V) to concentrations eventually similar to the control treatment. Biochar incorporation under glucose and straw amendments moderately alleviated V(V) release. The significantly positive correlation between Fe(II) and V(V) concentrations during the V solubilization process indicated a temporal coupling of Fe(III) reduction and V(V) release. Clostridium and Massilia mediated Fe(III) reductive dissolution and V(V) release, while Anaeromyxobacter, Sphingomonas, Bryobacter, Acidobacteriaceae and Anaerolineaceae contributed to V(V) reduction. This study provides a deeper understanding of V biotransformation coupled to Fe and C cycling and suggests a remediation strategy for V-contaminated soils via regulating Fe(III) reduction to weaken V(V) release or to promote V(V) reduction.

Citric Acid and Poly-glutamic Acid Promote the Phytoextraction of Cadmium and Lead in Solanum nigrum L. Grown in Compound Cd-Pb Contaminated Soils

Phytoextraction is an efficient strategy for remediating heavy metal-contaminated soil. Chelators can improve the bioavailability of heavy metals and increase phytoextraction efficiency. However, traditional chelators have gradually been replaced due to secondary pollution. In this study, a typical organic acid (citric acid, CA) and a novel biodegradable chelator (poly-glutamic acid, PGA), were investigated using pot experiments to compare the phytoextraction efficiency of Solanum nigrum L. (a Cd (hyper)accumulator) for cadmium (Cd) and lead (Pb) in contaminated soil. The results showed CA and PGA significantly improved plant growth, and total Cd and Pb amounts of S. nigrum, both CA and PGA significantly increased the shoot Cd and Pb concentrations. However, only PGA significantly increased the root Pb concentration. CA and PGA application promoted the bioavailability of Cd and Pb in rhizosphere soils and their translocations from roots to shoots in S. nigrum. Both CA and PGA increased the phytoextraction efficiency of Cd and Pb in S. nigrum plants, and the PGA for Cd and Pb phytoextraction was more effective than CA. Our findings demonstrate that the biodegradable chelator PGA has great potential for enhancing phytoextraction from compound Cd-Pb contaminated soils, suggesting that biodegradable chelator-assisted phytoextraction with (hyper)accumulator is strongly recommended in severely contaminated sites.

Reduction mechanisms of V5+ by vanadium-reducing bacteria in aqueous environments: Role of different molecular weight fractionated extracellular polymeric substances

Extracellular polymeric substances (EPS) are high-molecular polymers secreted by microbes and play essential roles in metallic biogeochemical cycling. Previous studies demonstrated the reducing capacity of the functional groups on EPS for metal reduction. However, the roles of different EPS components in vanadium speciation and their responsible reducing substances for vanadium reduction are still unknown. In this study, the EPS of Bacillus sp. PFYN01 was fractionated via ultrafiltration into six components with different kDa (EPS_>100, EPS_100-50, EPS_50-30, EPS_30-10, EPS_10-3, and EPS_<3). Batch reduction experiments of the intact cells, EPS-free cells, the pristine and fractionated EPS with V⁵⁺ were conducted and characterized. The results demonstrated that the extracellular reduction of V⁵⁺ into V⁴⁺ by EPS was the major reduction process. Among the functional groups in EPS, C=O/C-N of amide in protein/polypeptide and CO of carboxyl in fulvic acid-like substances might act as the reductants for V⁵⁺, while CO in polysaccharide molecules and PO in phosphodiester played a key role in the adsorption process. The intracellular reduction was via translocating V⁵⁺ into the cells and releasing V⁴⁺ by the intracellular reductases. The reducing capacity of the fractionated EPS followed a sequence of EPS_<3 > EPS_10-3 > EPS_50-30 > EPS_100-50 > EPS_30-10 > EPS_>100. The small molecules of fulvic acid-like substances and amino acids were responsible for the high reducing capacity of EPS_<3. EPS_>100 had the lowest reducing capacity due to its macromolecular structure decreasing the exposure of the reactive sites. In addition to reduction, those intermediate EPS components may also have supporting functions, such as connecting protein skeletons and increasing the specific surface area of EPS. Therefore, the diverse effects of the EPS components cannot be neglected in vanadium biogeochemical cycling.

Vanadium Stress Alters Sweet Potato (Ipomoea batatas L.) Growth, ROS Accumulation, Antioxidant Defense System, Stomatal Traits, and Vanadium Uptake

Vanadium (V) is a heavy metal found in trace amounts in many plants and widely distributed in the soil. This study investigated the effects of vanadium concentrations on sweet potato growth, biomass, root morphology, photosynthesis, photosynthetic assimilation, antioxidant defense system, stomatal traits, and V accumulation. Sweet potato plants were grown hydroponically and treated with five levels of V (0, 10, 25, 50, and 75 mg L^-1). After 7 days of treatment, V content at low concentration (10 mg L^-1) enhanced the plant growth and biomass; in contrast, drastic effects were observed at 25, 50, and 75 mg L^-1. Higher V concentrations negatively affect the relative water content, photosynthetic assimilation, photosynthesis, and root growth and reduce tolerance indices. The stomatal traits of sweet potato, such as stomatal length, width, pore length, and pore width, were also decreased under higher V application. Furthermore, V concentration and uptake in the roots were higher than in the shoots. In the same way, reactive oxygen species (ROS) production (hydrogen peroxide), lipid peroxidation (malondialdehyde), osmolytes, glutathione, and enzymes (catalase and superoxide dismutase) activities were increased significantly under V stress. In conclusion, V at a low level (10 mg L^-1) enhanced sweet potato growth, and a higher level of V treatment (25, 50, and 75 mg L^-1) had a deleterious impact on the growth, physiology, and biochemical mechanisms, as well as stomatal traits of sweet potato.