Recent Advances in Minimizing Cadmium Accumulation in Wheat

Associations between plasma metabolites and heavy metal exposure in residents of environmentally polluted areas

Heavy metals are commonly released into the environment through industrial processes such as mining and refining. The rapid industrialization that occurred in South Korea during the 1960s and 1970s contributed significantly to the economy of the country; however, the associated mining and refining led to considerable environmental pollution, and although mining is now in decline in South Korea, the detrimental effects on residents inhabiting the surrounding areas remain. The bioaccumulation of toxic heavy metals leads to metabolic alterations in human homeostasis, with disruptions in this balance leading to various health issues. This study used metabolomics to explore metabolomic alterations in the plasma samples of residents living in mining and refining areas. The results showed significant increases in metabolites involved in glycolysis and the surrounding metabolic pathways, such as glucose-6-phosphate, phosphoenolpyruvate, lactate, and inosine monophosphate, in those inhabiting polluted areas. An investigation of the associations between metabolites and blood clinical parameters through meet-in-the-middle analysis indicated that female residents were more affected by heavy metal exposure, resulting in more metabolomic alterations. For women, inhabiting the abandoned mine area, metabolites in the glycolysis and pentose phosphate pathways, such as ribose-5-phosphate and 3-phosphoglycerate, have shown a negative correlation with albumin and calcium. Finally, Mendelian randomization(MR) was used to determine the causal effects of these heavy metal exposure-related metabolites on heavy metal exposure-related clinical parameters. Metabolite biomarkers could provide insights into altered metabolic pathways related to exposure to toxic heavy metals and improve our understanding of the molecular mechanisms underlying the health effects of toxic heavy metal exposure.

Endophytic Plant Growth-Promoting Bacterium Bacillus subtilis Reduces the Toxic Effect of Cadmium on Wheat Plants

Heavy metal ions, in particular cadmium (Cd), have a negative impact on the growth and productivity of major crops, including wheat. The use of environmentally friendly approaches, in particular, bacteria that have a growth-stimulating and protective effect, can increase the resistance of plants. The effects of the pre-sowing seed treatment with the plant growth-promoting endophyte Bacillus subtilis 10-4 (BS) on cadmium acetate (Cd)-stressed Triticum aestivum L. (wheat) growth, photosynthetic pigments, oxidative stress parameters, roots' lignin content, and Cd ions accumulation in plants were analyzed. The results showed that the tested Cd-tolerant BS improved the ability of wheat seeds to germinate in the presence of different Cd concentrations (0, 0.1, 0.5, and 1 mM). In addition, the bacterial treatment significantly decreased the damaging effects of Cd stress (1 mM) on seedlings' linear dimensions (lengths of roots and shoots), biomass, as well as on the integrity and permeability of the cell walls (i.e., lipid peroxidation and electrolyte leakage) and resulted in reduced H₂O₂ generation. The pretreatment with BS prevented the Cd-induced degradation of the leaf photosynthetic pigments chlorophyll (Chl) a, Chl b, and carotenoids. Moreover, the bacterial treatment intensified the lignin deposition in the roots under normal and, especially, Cd stress conditions, thereby enhancing the barrier properties of the cell wall. This manifested in a reduced Cd ions accumulation in the roots and in the restriction of its translocation to the aboveground parts (shoots) of the bacterized plants under Cd stress in comparison with non-bacterized controls. Thus, the pre-sowing seed treatment with the endophyte BS may serve as an eco-friendly approach to improve wheat production in Cd-contaminated areas.

Agronomic and ionomics indicators of high-yield, mineral-dense, and low-Cd grains of wheat (Triticum aestivum L.) cultivars

The accumulation of toxic and essential nutrient elements in wheat grain influences wheat yield, grain nutritional quality, and human health. Here, we assessed the potential for breeding wheat cultivars to combine high yield with low cadmium and high iron and/or zinc concentrations in grains, and we screened appropriate cultivars. A pot experiment was conducted to explore differences in grain cadmium, iron, and zinc concentrations among 68 wheat cultivars, as well as their relationships with other nutrient elements and agronomic characters. The results showed 2.04-, 1.71-, and 1.64-fold differences in grain cadmium, iron, and zinc concentrations, respectively, among the 68 cultivars. Grain cadmium concentration was positively correlated with grain zinc, iron, magnesium, phosphorus, and manganese concentrations. Grain copper concentration was positively correlated with grain zinc and iron concentrations, but not with grain cadmium concentration. Therefore, copper has a potential role in regulating grain iron and zinc accumulation without influencing cadmium concentration in wheat grain. There were no significant relationships between grain cadmium concentration and four important wheat agronomic characters (i.e., grain yield, straw yield, thousand kernel weight, and plant height), indicating that the breeding of low-cadmium-accumulating cultivars with dwarfism and high yield characteristics is possible. On cluster analysis, four cultivars (Ningmai11, Xumai35, Baomai6, and Aikang58) exhibited low-cadmium and high-yield characteristics. Among them, Aikang58 contained moderate iron and zinc concentrations, while Ningmai11 had relatively high iron but low zinc concentrations in the grain. These results imply that it is feasible to breed high-yield dwarf wheat with low cadmium and moderate iron and zinc concentrations in the grain.

Remediation effects and mechanisms of typical minerals combined with inorganic amendment on cadmium-contaminated soil: a field study in wheat

The remediation of cadmium (Cd)-contaminated soil has gained much attention recently because Cd in soil threatens human health through the food chain. Although tremendous progress has been made in the remediation of Cd-contaminated soil in rice acid soil system, the mechanism and effects of Cd-contaminated soil remediation under these amendments in wheat weak alkaline soil are still limited. In this study, the remediation effect and related mechanism of Cd in weakly alkaline soil were carried out using zeolite, diatomite, and sodium bentonite as the main remediation components, supplemented by calcium dihydrogen phosphate and fulvic acid. The results of field experiments showed that the concentration of Cd reduced by 27.3 ~ 31.2% in rhizosphere soil and 34.3 ~ 54.2% in non-rhizosphere soil, and the maximum reduction rate of Cd concentration in wheat grain was 25.5%. The main factors affecting the concentration of Cd in wheat grains include the change in exchangeable Cd, the absorption capacity of wheat root, and the inhibitory effect on Cd transport from stem to grain in this paper. In general, this work provides a new potential management feasible pathway to alleviate the Cd toxicity of weakly alkaline soil and wheat grain.

Wheat Selenium-binding protein TaSBP-A enhances cadmium tolerance by decreasing free Cd2+ and alleviating the oxidative damage and photosynthesis impairment

Cadmium, one of the toxic heavy metals, robustly impact crop growth and development and food safety. In this study, the mechanisms of wheat (Triticum aestivum L.) selenium-binding protein-A (TaSBP-A) involved in response to Cd stress was fully investigated by overexpression in Arabidopsis and wheat. As a cytoplasm protein, TaSBP-A showed a high expression in plant roots and its expression levels were highly induced by Cd treatment. The overexpression of TaSBP-A enhanced Cd-toleration in yeast, Arabidopsis and wheat. Meanwhile, transgenic Arabidopsis under Cd stress showed a lower H2O2 and malondialdehyde content and a higher photochemical efficiency in the leaf and a reduction of free Cd2+ in the root. Transgenic wheat seedlings of TaSBP exhibited an increment of Cd content in the root, and a reduction Cd content in the leaf under Cd2+ stress. Cd2+ binding assay combined with a thermodynamics survey and secondary structure analysis indicated that the unique CXXC motif in TaSBP was a major Cd-binding site participating in the Cd detoxification. These results suggested that TaSBP-A can enhance the sequestration of free Cd2+ in root and inhibit the Cd transfer from root to leaf, ultimately conferring plant Cd-tolerance via alleviating the oxidative stress and photosynthesis impairment triggered by Cd stress.

Deciphering soil amendments and actinomycetes for remediation of cadmium (Cd) contaminated farmland

Soil heavy metal pollution is one of the most serious environmental problems in China, especially cadmium (Cd), which has the most extensive contaminated soil coverage. Therefore, more economical and efficient remediation methods and measures are needed to control soil Cd contamination. In this study, different amendments (biochar (B), organic fertilizer (F), lime (L)) and actinomycetes (A) inoculants were applied to Cd contaminated farmland to explore their effects on wheat growth. Compared with Control, all treatments except A treatment were able to significantly increase the underground parts dry mass of wheat, with the highest increase of 57.19 %. The results showed that the B treatment significantly increased the plant height of wheat by 3.45 %. All treatments increased wheat SOD activity and chlorophyll content and reduced the MDA, which contributes to wheat stress resistance under Cd contamination. F, L and AF treatments can significantly reduce the Cd content in wheat above- and underground parts by up to 56.39 %. Soil amendments can modify the physical and chemical properties of the soil, which in turn affects the absorption of Cd by wheat. Moreover, the addition of soil amendments significantly affects the composition and structure of the rhizospheric soil bacterial community at the wheat jointing stage. The application of organic fertilizer increases the richness and diversity of the bacterial community, while lime makes it significantly decreases it. T-test and microbiome co-occurrence networks show that actinomycetes could not only effectively colonize in local soil, but also effectively enhance the complexity and stability of the rhizosphere microbial community. Considering the practical impact of different treatments on wheat, soil microorganisms, economic benefits and restoration of soil Cd contamination, the application of organic fertilizer and actinomycetes in Cd contaminated soil is a more ideal remediation strategy. This conclusion can be further verified by studying larger repair regions and longer consecutive repair cycles to gain insight into the repair mechanism.

Multi-Omics Uncover the Mechanism of Wheat under Heavy Metal Stress

Environmental pollution of heavy metals has received growing attention in recent years. Heavy metals such as cadmium, lead and mercury can cause physiological and morphological disturbances which adversely affect the growth and quality of crops. Wheat (Triticum aestivum L.) can accumulate high contents of heavy metals in its edible parts. Understanding wheat response to heavy metal stress and its management in decreasing heavy metal uptake and accumulation may help to improve its growth and grain quality. Very recently, emerging advances in heavy metal toxicity and phytoremediation methods to reduce heavy metal pollution have been made in wheat. Especially, the molecular mechanisms of wheat under heavy metal stress are increasingly being recognized. In this review, we focus on the recently described epigenomics, transcriptomics, proteomics, metabolomics, ionomics and multi-omics combination, as well as functional genes uncovering heavy metal stress in wheat. The findings in this review provide some insights into challenges and future recommendations for wheat under heavy metal stress.

Effects of Rhizobium leguminosarum Thy2 on the Growth and Tolerance to Cadmium Stress of Wheat Plants

Cadmium (Cd) stress is an obstacle for crop production, quality crops, and sustainable agriculture. An important role is played by the application of eco-friendly approaches to improve plant growth and stress tolerance. In the current study, a pre-sowing seed treatment with Rhizobium leguminosarum strains, isolated from the leguminous plants Phaseolus vulgaris (strain Pvu5), Vicia sylvatica (strain VSy12), Trifolium hybridium (strain Thy2), and T. pratense (strain TPr4), demonstrated different effects on wheat (Triticum aestivum L.) plant growth under normal conditions. Among all tested strains, Thy2 significantly increased seed germination, seedling length, fresh and dry biomass, and leaf chlorophyll (Chl) content. Further analysis showed that Thy2 was capable of producing indole-3-acetic acid and siderophores and fixing nitrogen. Under Cd stress, Thy2 reduced the negative effect of Cd on wheat growth and photosynthesis and had a protective effect on the antioxidant system. This was expressed in the additional accumulation of glutathione and proline and the activation of glutathione reductase. In addition, Thy2 led to a significant reduction in oxidative stress, which was evidenced by the data on the stabilization of the ascorbate content and the activity of ascorbate peroxidase. In addition, Thy2 markedly reduced Cd-induced membrane lipid peroxidation and electrolyte leakage in the plants. Thus, the findings demonstrated the ability of the R. leguminosarum strain Thy2, isolated from T. hybridium nodules, to exert a growth-promoting and anti-stress effect on wheat plants. These results suggest that the Thy2 strain may enhance wheat plant growth by mitigating Cd stress, particularly through improving photosynthesis and antioxidant capacity and reducing the severity of oxidative damage. This may provide a basic and biological approach to use the Thy2 strain as a promising, eco-friendly candidate to combat Cd stress in wheat production.