A critical review on effects, tolerance mechanisms and management of cadmium in vegetables

Combined application of silicon and nitric oxide jointly alleviated cadmium accumulation and toxicity in maize

Co-application of biochar and plant growth regulators improves maize growth and decreases Cd accumulation in cadmium-contaminated soil

Cadmium minimization in wheat: A critical review

Integration of Transcriptome and Metabolome Analyses Reveals the Mechanistic Basis for Cadmium Accumulation in Maize.

Substation of vermicompost mitigates Cd toxicity, improves rice yields and restores bacterial community in a Cd-contaminated soil in Southern China

It is well established that low levels of selenium (Se) are protective against low levels of cadmium (Cd) toxicity and can significantly reduce Cd uptake in plants. However, our previous study reported that the addition of Se hampered the growth of paddy rice exposed to high levels of Cd and enhanced Cd uptake. The relevant mechanisms underlying the dual effects of Se on Cd uptake and toxicity are unclear. This study attempted to illustrate the potential mechanisms of the effect of selenite on Cd toxicity and uptake in paddy rice using hydroponic culture, mainly focusing on the changes in root morphology and the responses of antioxidative enzymes to low and high levels of Se and Cd. A root image analysis system equipped with WinRHIZO image analysis software was used to analyze the root morphology. When no Cd was added, a level of Se as low as 0.2 mg L−1 decreased the shoot malondialdehyde (MDA) content and enhanced the growth of paddy rice; however, Se levels of up to 0.8 mg L−1 inhibited the growth and increased the MDA content of shoots, demonstrating the dual effect of Se on plants. Superoxide dismutase (SOD) appeared to be activated, especially in the roots, when Se was added to solutions containing a high concentration of Cd; however, single addition of Se or Cd inhibited SOD activity. The addition of Se to a solution containing Cd stimulated only root ascorbate peroxidase (APX) activity. Peroxidase (POD) and catalase (CAT) enzymes appeared to have limited roles in detoxifying Cd when increasing amounts of Se were added. When Se was absent from the solution, Cd levels as low as 1 mg L−1 had beneficial effects on root growth but not on shoot growth; however, these beneficial effects were accompanied by a significant increase in shoot MDA content. Cd levels higher than 4 mg L−1 inhibited the growth of shoots and roots, suggesting that Cd toxicity had occurred in the paddy rice. The addition of Se to the treatments containing Cd significantly reduced the proportion of fine roots and tended to increase the proportion of coarse roots, which might explain the decreases in Cd uptake in this study and the decreases in the uptake of other minerals observed in other studies. The addition of Se could mitigate the toxicity of Cd; however, these protective effects are likely dependent on the doses of Se and Cd. Several Se-mediated mechanisms for the mitigation of Cd toxicity were proposed, including (1) an increase in the proportion of coarse roots to reduce Cd uptake and (2) the activation of certain antioxidative enzymes. When 12 mg L−1 Cd was added to the solution, the addition of Se inhibited plant growth instead of mitigating the toxicity of Cd; this finding was thought to be related to the increased permeability of the root cells to Cd due to the damaged cell membranes produced by Se supplementation.

Cadmium (Cd) toxicity is highly detrimental for the human and largely originated from faulty industrial and agricultural practices. Cadmium toxicity can be observed in minute concentration and highly mobile in the soil–plant system and availability in soil is mainly governed by various physio-chemical properties of the soil. Cereals and vegetables cultivated in peri-urban areas, former mining and industrial areas accumulate Cd in toxic limit as they receive Cd from multiple ways. In general, when the total cadmium (Cd) concentration in soil exceeds 8 mg kg−1, or the bioavailable Cd concentration becomes >0.001 mg kg−1, or the Cd concentration in plant tissue reaches 3–30 mg kg−1 most plants exhibit visible Cd toxicity symptoms. The impacts of Cd toxicity are seed germination, growth, photosynthesis, stomata conductance, enzyme activities and alteration in mineral nutrition. The major source of Cd in human is food chain cycle and causes disorders like “itai-itai” disease, cancer, and nephrotoxicity. Cadmium harms kidney, liver, bone and reproductive body parts and may be fatal in serious condition. WHO recommended the tolerable monthly Cd intake are 25 μg kg−1 body weights and in drinking water Cd concentration should not exceed 3 μg L−1. It is hard to remove these potent and hazardous metals from the environment as they have long mean residence time but, can be converted into less toxic form through bioremediation. This chapter focuses on the effect of Cd toxicity in soil–plant-human continuum and its bioremediation techniques to mitigate the Cd- toxicity.

Cadmium (Cd) is a potentially hazardous element with significant biological toxicity, negatively affecting plant growth and physio-biochemical metabolism. Thus, it is necessary to examine practical and eco-friendly approaches to reduce Cd toxicity. Titanium dioxide nanoparticles (TiO2-NPs) are growth regulators that help in nutrient uptake and improve plant defense systems against abiotic and biological stress. A pot experiment was performed in the late rice-growing season (July—November) 2022 to explore the role of TiO2-NPs in relieving Cd toxicity on leaf physiological activity, biochemical attributes, and plant antioxidant defense systems of two different fragrant rice cultivars, i.e., Xiangyaxiangzhan (XGZ) and Meixiangzhan-2 (MXZ-2). Both cultivars were cultivated under normal and Cd-stress conditions. Different doses of TiO2-NPs with and without Cd-stress conditions were studied. The treatment combinations were: Cd−, 0 mg/kg CdCl2·2.5 H2O; Cd+, 50 mg/kg CdCl2·2.5 H2O; Cd + NP1, 50 mg/kg Cd + 50 TiO2-NPs mg/L; Cd + NP2, 50 mg/kg Cd + 100 TiO2-NPs mg/L; Cd + NP3, 50 mg/kg Cd + 200 TiO2-NPs mg/L; Cd + NP4, 50 mg/kg Cd + 400 TiO2-NPs mg/L. Our results showed that the Cd stress significantly (p < 0.05) decreased leaf photosynthetic efficiency, stomatal traits, antioxidant enzyme activities, and the expression of their encoding genes and protein content. Moreover, Cd toxicity destabilized plant metabolism owing to greater accretion of hydrogen peroxide (H2O2) and malondialdehyde (MDA) levels at vegetative and reproductive stages. However, TiO2-NPs application improved leaf photosynthetic efficacy, stomatal traits, and protein and antioxidant enzyme activities under Cd toxicity. Application of TiO2-NPs decreased the uptake and accumulation of Cd in plants and levels of H2O2 and MDA, thereby helping to relieve Cd-induced peroxidation damage of leaf membrane lipids by enhancing the activities of different enzymes like ascorbate peroxidase (APX), catalase (CAT), peroxidase (POS), and superoxide dismutase (SOD). Average increases in SOD, APX, CAT, and POS activities of 120.5 and 110.4%, 116.2 and 123.4%, 41.4 and 43.8%, and 36.6 and 34.2% in MXZ-2 and XGZ, respectively, were noted in Cd + NP3 treatment across the growth stages as compared with Cd-stressed plants without NPs. Moreover, the correlation analysis revealed that the leaf net photosynthetic rate is strongly associated with leaf proline and soluble protein content, suggesting that a higher net photosynthetic rate results in higher leaf proline and soluble protein content. Of the treatments, the Cd + NP3 (50 mg/kg Cd + 200 mg/L TiO2-NPs) performed the best for both fragrant rice cultivars under Cd toxicity. Our results showed that TiO2-NPs strengthened rice metabolism through an enhanced antioxidant defense system across the growth stages, thereby improving plant physiological activity and biochemical characteristics under Cd toxicity.

Among heavy metals, cadmium (Cd) is highly toxic to plants and it is even considered as one of the most toxic elements released into environments at very low concentrations. The development of industry and agriculture have led to the increase of Cd content in soil environment. Cd is released into the soil through application of phosphate fertilizer, animal manures, waste water etc. Cadmium is a non-essential element for plant nutrition but because of its strong toxicity can seriously affects crop growth and development. Due to the high mobility of Cd in soil, the concentration of this element above the critical level can strongly inhibit the growth of plants as well as damage cell structure by interfering with different biochemical and physiological processes. Accumulation of Cd to phytotoxic levels may cause significant growth and yield decrease. If plants are grown in soil contaminated with Cd, they produce products containing this heavy metal, and such plant products are the main source of Cd entering the human body through the trophic chains. Thus, Cd may be an element with high residue, difficult to degrade and easy to accumulate, which may seriously threaten the health of human beings and animals. Cereals such as wheat, rice and maize are the main food crops in the world. Among them, wheat is the source of staple food for more than half of the world's population. Compared with other heavy metals, cadmium is more easily absorbed and accumulated by wheat. This poses a serious threat to human health. Wheat products are the main source of Cd intake by human. Wheat mainly uptakes Cd through the root system, and then it migrates to the above-ground part, and finally accumulates in the wheat grain. Agronomic management practices have been used to reduce Cd uptake and toxicity in wheat. However, these measures could pose some problems, such as large investment, high energy consumption, difficult operation and easy to produce secondary pollution. Low-Cd wheat varieties are the most effective and economic way to reduce the risk of cadmium to human health associated with food consumption. In the traditional breeding process, the selection of Cd-tolerant wheat samples is carried out on the basis of morphological, physiological or biochemical characteristics associated with Cd stress. It is of great significance to study the molecular mechanism of Cd absorption, transport of wheat and the creation of wheat varieties with low Cd accumulation for ensuring food security and food safety. Using molecular breeding technology and their successful integration with traditional breeding methods to select crop varieties with low accumulation of Cd will have a potential impact on the development of low Cd wheat germplasm and important practical significance for ensuring safe agricultural production of Cd contaminated soil. The objective of the present review is to discuss the Cd impact on wheat growth and development, Cd toxicity and tolerance mechanisms and some possible breeding strategies to alleviate Cd toxicity in wheat. The paper reviewed the effects of cadmium on the growth and development of wheat, the absorption, transport and distribution of cadmium in wheat, the tolerance mechanism and the molecular biological level of cadmium in wheat plant. To provide strategies and possible schemes for breeding wheat varieties with low cadmium accumulation

Cadmium (Cd) stress in agricultural soils poses a significant threat to wheat production, food safety, and human health. Wheat productivity is severely hampered by Cd toxicity; however, to overcome this problem silicon (Si) fertilization has emerged as a promising strategy to mitigate heavy metal toxicity in plants; in this study, we compare the efficacy of natural and synthetic Si fertilization sources in modulating wheat growth, Cd accumulation, and antioxidant responses under Cd-contaminated soil. The Si was used as Ca silicate at 75 kg ha-1 (synthetic Si source), and the rice husk at 150 kg ha-1 (natural Si source) with and without humic acid (10 mg kg-1 of soil) in comparison to control (Cd stress). Both Si sources were found to significantly boost the growth and yield attributes of wheat, while Cd stress significantly increased the electrolyte leakage that triggered oxidative stress. However, both Si sources decrease the oxidative stress and increase the superoxide dismutase and peroxidase activities. Si fertilization also inhibited the uptake of Cd from roots and its translocation to shoots and grains of wheat plant. In comparison, the synthetic Si fertilization was more effective than natural Si fertilization as it produced highest increase in plant height (21.40%), grain yield (25.21%), and reduced Cd concentration in root (42.60%) and shoot (59.71%) than control (Cd stress). Conclusively, Si fertilization (preferably Ca silicate at 75 kg ha-1) alleviates the opposing impact of Cd on wheat growth by strengthening the antioxidant defense system, decreasing the Cd uptake and its translocation to humans.

Cadmium (Cd) toxicity not only affects plant growth and development, but also affects human health through the food chain. Several studies have demonstrated that Selenium (Se) alleviates Cd stress in plants; however, whether and how Se-alleviated Cd stress by regulating the structure of soil microbial community remain largely unclear. Here, we investigated the alleviating effects of exogenous applied Se (foliar spraying or root application) on plant growth under Cd stress in perilla (Perilla frutescens L.) by measuring the biomass, photosynthetic fluorescence parameters, root cell wall components and soil microbial community structure and diversity. Under Cd stress, perilla seedlings supplemented with Se increased chlorophyll content. Foliar spraying Se increased the levels of relative chlorophyll content (ΦII), photosynthetic system II (ΦPSII) and electron transport rate (ETR) in perilla leaves under Cd stress; while, root application of Se increased the levels of photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), water use efficiency (WUE) and stomatal limitation value (Ls) under Cd stress. Compared with Cd toxicity alone, root application of Se increased the contents of hemicellulosic 1 and hemicellulosic 2 in the cell wall of perilla roots. Cd toxicity or root application of Se did not affect soil bacterial community diversity. Root application of Se increased the relative abundance of Proteobacteria, Bacteroidetes, Fibrobacteres, Sphingomonas and Nitrosospira in Cd-contaminated soil, and thereby improving soil microbial community structure, finally promoting the growth of perilla seedlings.

Silicon (Si) alleviates cadmium (Cd) toxicity and accumulation in a number of plant species, but the exact molecular mechanisms responsible for this effect are still poorly understood. Here, we investigated the effect of Si on Cd toxicity and accumulation in rice (Oryza sativa) by using two mutants (lsi1 and lsi2) defective in Si uptake and their wild types (WTs). Root elongation was decreased with increasing external Cd concentrations in both WTs and mutants, but Si did not show an alleviative effect on Cd toxicity in all lines. By contrast, the Cd concentration in both the shoots and roots was decreased by Si in the WTs, but not in the mutants. Furthermore, Si supply resulted in a decreased Cd concentration in the root cell sap and xylem sap in the WTs, but not in the mutants. Pre-treatment with Si also decreased Cd accumulation in the WTs, but not in the mutants. Silicon slightly decreased Cd accumulation in the cell wall of the roots. The expression level of OsNramp5 and OsHMA2 was down-regulated by Si in the WTs, but not in the mutants. These results indicate that the Si-decreased Cd accumulation was caused by down-regulating transporter genes involved in Cd uptake and translocation in rice.

Auxins play crucial regulatory roles in plants coping with cadmium (Cd) stress. However, the regulatory mechanism by which auxins alleviate Cd toxicity in tomato seedlings remains unclear. Here, we demonstrate that exposure to Cd stress leads to dynamic changes in the auxin response in tomato roots, characterized by an initial increase followed by a subsequent weakening. Under Cd stress, tomato seedlings show primary root- and hypocotyl-growth inhibition, accompanied by the accumulation of Cd and reactive oxygen species (ROS) in the roots. The exogenous application of 1-naphthylacetic acid (NAA) does not mitigate the inhibitory effect of Cd toxicity on primary root growth, but it does significantly enhance lateral root development under Cd stress. Auxin transport inhibitors, such as 1-N-naphthylphthalamic acid (NPA) and 2,3,5-triiodobenoic acid (TIBA), aggravate the growth inhibition of primary roots caused by Cd stress. Additionally, lateral root development was inhibited by NPA. However, applying auxin synthesis inhibitors L-kynurenine (kyn) and yucasin alleviated the tomato root growth inhibition caused by Cd stress; between them, the effect of yucasin was more pronounced. Yucasin mitigates Cd toxicity in tomato seedlings by reducing Cd2+ absorption and auxin accumulation, strengthening ROS scavenging, and reducing cell death in roots. These observations suggest that yucasin potentially mitigates Cd toxicity and improves the tolerance of tomato seedlings to Cd stress.

Silicon (Si) application could significantly alleviate the toxic effects of cadmium (Cd) on the growth and development of rice. Here, we examined the regulatory effects of Si on Cd accumulation and stress response in rice seedlings through a hydroponic root separation test. The results showed that the biomass of rice seedlings decreased significantly under Cd stress, while the addition of Si could alleviate such negative effect. The uptake, transfer, and accumulation of Cd in rice seedling were significantly affected by Si addition under Cd stress. Si application under the unilateral Cd stress (Si-Cd+Si, Si-Cd) increased Cd-retention coefficient of root by 83.3%-83.6%, which restricted the transfer of Cd from root to aboveground. However, the treatment with Si added to the non-stressed side (Si-Cd) elevated the uptake and accumulation of Cd in rice seedling, with the accumulation in root being increased by 48.2% when compared to the treatment under the unilateral Cd stress without the addition of Si (CK-Cd). The treatment with Si added in two sides (Si-Cd+Si) decreased the uptake of Cd both in root and aboveground parts by 36.7% and 54.9%, respectively. The addition of Si under bilateral Cd stress (Cd-Cd+Si) significantly reduced the Cd uptake of both the root and aboveground parts by 57.8% and 46.5%, respectively, compared to the treatment of bilateral Cd stress (Cd-Cd). Higher Si concentration in rice seedling was found under the Cd stress. More Si was accumulated in rice seedling to resist the Cd stress when Si was added. The addition of Si affected the absorption of other metal elements in rice seedlings, including calcium (Ca), magnesium (Mg) and manganese (Mn). The concentrations of Ca and Mg in root and aboveground parts were significantly increased by Si addition under bilateral Cd-stress (Cd-Cd+Si), but Mn concentration was changed with the stress degree of Cd. The activities of superoxide dismutase (SOD) and peroxidase (POD) in root were affected by Si under Cd stress, especially for the Si-Cd treatment. The activity of POD in the root of the Cd-stress side and that of SOD in non-stress side were significantly increased, which benefit to scavenging the free radicals induced by Cd stress. In conclusion, Si could regulate the growth of rice seedlings, the uptake of elements such as Cd and Si, and the antioxidant reaction of the root system under the Cd stress. High Si concentration in plant is conducive to enhancing Cd tolerance.

Cadmium (Cd) is a highly toxic metal that poses a threat to human health and animals through food chain as well as impacts on plants even at low concentrations. It is a global environmental issue due to its widely distributed and has natural source and increasing anthropogenic activities such as metal industries, sewage sludges, mining, wastewater, chemical incidents, combustion emissions, and phosphate fertilizers increase the Cd concentration in the environment. In this review, we have discussed the source of Cd in the environment, the impacts of soil physiochemical properties on Cd, dynamics of Cd uptake mechanism, translocation, distribution, and toxic effects of Cd in plants. In crops, Cd toxicity reduces the uptake and translocation of essential nutrients and water and disrupts crucial physiological, biochemical, and molecular processes including photosynthesis, ROS homeostasis, activity of enzymes, cell death, leading to inhibits plant growth, resulting in yield losses. Additionally, potential remediation strategies and defense mechanisms are also highlighted. Although, plants have a complex defense mechanism against Cd toxicity but these mechanisms are often insufficient to address high concentrations of Cd. In addition, selenium (Se) is an important trace element for human, animals, and plants, and has shown remarkable potential to mitigate Cd toxicity in plants. Supplementation with Se minimize the detrimental effects of Cd by enhancing physiological, biochemical, and molecular functions, while also promoting Cd immobilization, co-precipitations, and compartmentalization. However, supplementation and mechanisms of Se and its other forms on plant performance in Cd-contaminated soils remain largely unclear. Thus, focuses on the promising role of Se supplementation and its underlying mechanism under Cd stress in plants, how Se can protect against Cd toxicity to plants by using different application methods, and increasing sequestration of Cd in cell walls by reducing the bio-availability of Cd in soil. Additionally, we also discussed research gaps and future research of Se to alleviate Cd induced toxicity. Taken together, low supplementations of Se and Se-NPs mitigate the human health risk associated with Cd toxicity in plants, especially in lightly contaminated soil. Overall, findings of this review will help to improve our understanding role of Se and its different forms such as Se-NPs to mitigate Cd toxicity and will offer deep knowledge for developing promising strategies to address the environmental challenges threatened by Cd toxicity in crops and improve agricultural productivity in Cd contaminated soils.