Ca2SiO4 chemigation reduces cadmium localization in the subcellular leaf fractions of spinach (Spinacia oleracea L.) under cadmium stress

Efficacy of malic and tartaric acid in mitigation of cadmium stress in Spinacia oleracea L. via modulations in physiological and biochemical attributes

The increasing level of cadmium (Cd) contamination in soil due to anthropogenic actions is a significant problem. This problem not only harms the natural environment, but it also causes major harm to human health via the food chain. The use of chelating agent is a useful strategy to avoid heavy metal uptake and accumulation in plants. In this study, randomized design pot experiment was conducted to evaluate potential role of malic acid (MA) and tartaric acid (TA) foliar spray to mitigate Cd stress in Spinacia oleracea L plants. For Cd stress, S. oleracea plants were treated with CdCl2 solution (100 µM). For control, plants were given distilled water. One week after Cd stress, MA and TA foliar spray was employed at concentration of 100 and 150 µM for both. The results of this study revealed that Cd stress (100 µM) significantly reduced growth attributes, photosynthetic pigments and related parameters and gas exchange attributes. Cadmium stress also stimulated antioxidant defense mechanism in S. oleracea. Cd stressed plants had elevated levels of Cd metal ions in root and consumable parts (i.e. leaves) and caused severe oxidative damages in the form of increased lipid peroxidation and electrolytic leakage. MA and TA supplements at both low and high levels (100 and 150 µM) effectively reversed the devastating effects of Cd stress and improved growth, photosynthesis and defense related attributes of S. oleracea plants. These supplements also prevented excessive accumulation of Cd metal ions as indicated by lowered Cd metal contents in MA and TA treated plants. These findings demonstrated that MA and TA treatments can potentially reduce Cdl induced phytotoxicity in plants by reducing its uptake and enhancing photosynthesis and defense related parameters.

Exogenous salicylic acid reduces cadmium content in spinach (Spinacia oleracea L.) shoots under cadmium stress

BACKGROUND

Consumption of leafy vegetables is a primary route of cadmium (Cd) exposure in the human body. Salicylic acid (SA) is a major stress signaling molecule that alleviates Cd toxicity in various plants. Our study aimed to investigate the effects of different SA concentrations on spinach growth, cadmium accumulation, and stress resistance physiology under cadmium stress (50 µmol/L).

RESULTS

Cd stress significantly markedly decreased spinach growth and biomass, reduced its photosynthetic efficiency, increased activities of antioxidative enzymes, and upregulated the relative expression of several genes involved in cadmium absorption and transport compared to the control. The exogenous application of SA mitigated the harmful effects of Cd in spinach. 0.8 and 1.6 mmol/L SA significantly increased spinach root length, plant height, and biomass and decreased the Cd content in shoots by 30.03 and 17.35% compared to the Cd-treated group. Moreover, SA alleviated the yellowing of leaves caused by Cd stress. Exogenous SA ameliorated Cd toxicity in spinach by reducing reactive oxygen species, malondialdehyde, proline, and soluble protein levels. Exogenous SA application reduced Cd absorption in spinach leaves by downregulating the expression of genes involved in Cd transport, such as SoHMA4-like, SoNramp3.1-like, SoNramp6-like, and SoNramp7.2-like. Principal component analysis and correlation analysis showed that exogenous SA application under Cd stress was correlated with plant Cd content, photosynthetic pigment content, and relative expression of Cd absorption and transportation-related genes.

CONCLUSIONS

To summarize, these findings indicate that SA mitigates Cd toxicity in spinach by reversing the adverse effects of Cd stress on plant growth and reducing Cd accumulation in the shoots.

Cadmium toxicity promotes hormonal imbalance and induces the expression of genes involved in systemic resistances in barley

Cadmium (Cd) is a widely distributed pollutant that adversely affects plants' metabolism and productivity. Phytohormones play a vital role in the acclimation of plants to metal stress. On the other hand, phytohormones trigger systemic resistances, including systemic acquired resistance (SAR) and induced systemic resistance (ISR), in plants in response to biotic interactions. The present study aimed to investigate the possible induction of SAR and ISR pathways in relation to the hormonal alteration of barley seedlings in response to Cd stress. Barley seedlings were exposed to 1.5 mg g-1 Cd in the soil for three days. The nutrient content, oxidative status, phytohormones profile, and expression of genes involved in SAR and ISR pathways of barley seedlings were examined. Cd accumulation resulted in a reduction in the nutrient content of barley seedlings. The specific activity of superoxide dismutase and the hydrogen peroxide content significantly increased in response to Cd toxicity. Abscisic acid, jasmonic acid, and ethylene content increased under Cd exposure. Cd treatment resulted in the upregulation of NPR1, PR3, and PR13 genes in SAR pathways. The transcripts of PAL1 and LOX2.2 genes in the ISR pathway were also significantly increased in response to Cd treatment. These findings suggest that hormonal-activated systemic resistances are involved in the response of barley to Cd stress.

Insights into the antagonistic effects of calcium on cadmium accumulation in peanuts (Arachis hypogaea L.)

Peanut (Arachis hypogaea L.) plant has a high requirement for calcium (Ca) during its growth and development, and possesses the ability to accumulate cadmium (Cd) from soil. However, the precise mechanisms underlying the antagonistic effects between Ca and Cd remain unclear. This study aimed to explore the dynamic changes in Cd accumulation in peanut seedlings by varying the Ca-to-Cd concentration ratio (CRCa/Cd) from 250 to 3500. Additionally, the influence of ion channel competition and cell wall fixation in the root on Cd accumulation in peanuts was explored by analyzing Cd chemical forms, subcellular distribution, pectin content, and Cd2+ fluxes using a non-invasive micro-test technique (NMT). The findings revealed that Cd accumulation in peanut seedlings was significantly lower when the CRCa/Cd was higher than 2000. In the Ca-pretreated seedlings (cell wall fixation treatment), Cd content in the shoots and roots decreased by 18.9% and 25.0%, respectively, compared with the simultaneous exposure to Ca and Cd (ion channel competition treatment). Cd2+ influx in peanut roots decreased by 55.8% in the Ca-pretreated group. However, increasing the competitive strength of Ca2+ and Cd2+ did not affect Cd2+ influx under normal Ca conditions (>2 mM Ca). Meanwhile, Ca pretreatment significantly increased Cd distribution in the root cell wall, pectate, and protein-binding forms, while significantly reducing Cd distribution in root soluble components and inorganic Cd forms. The pectin content in the roots increased by 128% and 226% in the Ca and Cd simultaneous exposure treatment and Ca pretreatment, respectively. These results suggest that Ca pretreatment enhanced Cd retention in the root cell wall. Overall, exogenous Ca effectively mitigated Cd accumulation in peanut plants when the CRCa/Cd was below 2000, and Ca2+ channels partially facilitate the entry of Cd2+ into peanut roots. Under normal Ca supply conditions, exogenous Ca reduced Cd accumulation in peanuts primarily through root cell wall fixation rather than ion channel competition. Our findings provide insights into the mechanism by which Ca alleviates the uptake and transfer of Cd in peanuts.

Low apoplastic Na+ and intracellular ionic homeostasis confer salinity tolerance upon Ca2SiO4 chemigation in Zea mays L. under salt stress

Salinity is known to have a greater impact on shoot growth than root growth. Na+ buildup in plant tissue under salt stress has been proposed as one of the main issues that causes growth inhibition in crops via ionic imbalances, osmotic stress and pH disturbances. However, the evidence for apoplastic Na+ buildup and the role of silicon in Na+ accumulation at the subcellular level is still enigmatic. The current study focuses on the accumulation of Na+ in the apoplast and symplast of younger and older leaves of two maize varieties (Iqbal as salt-tolerant and Jalal as salt-sensitive) using hydroponic culture along with silicon supplementation under short-term salinity stress. Subcellular ion analysis indicated that silicon nutrition decreased Na+ concentration in both apoplastic washing fluid and symplastic fluid of maize under salt stress. The addition of silicon under NaCl treatment resulted in considerable improvement in fresh biomass, relative water content, chlorophyll content, and concentration of important subcellular ions (i.e., Ca2+, Mg2+, and K+). Knowledge of subcellular ion analysis is essential for solving the mechanisms underlying vital cellular functions e.g. in the current study, the soluble Na+ concentration in the apoplast of older leaves was found to be significantly greater (36.1 mM) in the salt-sensitive variety under NaCl treatment, which was 42.4% higher when compared to the Na+ concentration in the salt-tolerant variety under the same treatment which can influence permeability of cell membrane, signal transduction pathways and provides insights into how ion compartmentalization can contributes to salt tolerance. Calcium silicate enrichment can contribute to increased growth and improved ionic homeostasis by minimizing leaf electrolyte leakage, improving mechanical functions of cell wall and reducing water loss, and improved photosynthetic function. In current investigation, increased water content and intracellular ionic homeostasis along with reduced concentration of Na+ in the maize leaf apoplast suggest that calcium silicate can be used to ameliorate the adverse effects of salt stress and obtain yield using marginal saline lands.

Foliar application of salicylic acid inhibits the cadmium uptake and accumulation in lettuce (Lactuca sativa L.)

Introduction

Salicylic acid (SA) is a multi-functional endogenous phytohormone implicated in the growth, development, and metabolism of many plant species.

Methods

This study evaluated the effects of different concentrations of SA (0, 25, 100, 200, and 500 mg/L) on the growth and cadmium (Cd) content of lettuce (Lactuca sativa L.) under Cd stress. The different concentrations of SA treatments were administered through foliar application.

Results

Our results showed that 100-200 mg/L SA significantly increased the plant height and biomass of lettuce under Cd stress. When SA concentration was 200 mg/L, the plant height and root length of lettuce increased by 19.42% and 22.77%, respectively, compared with Cd treatment alone. Moreover, 200 mg/L and 500mg/L SA concentrations could reduce peroxidase (POD) and superoxide dismutase (SOD) activities caused by Cd stress. When the concentration of exogenous SA was 500 mg/L, the POD and SOD activities of lettuce leaves decreased by 15.51% and 19.91%, respectively, compared with Cd treatment. A certain concentration of SA reduced the uptake of Cd by the lettuce root system and the transport of Cd from the lettuce root system to shoots by down-regulating the expression of Nramp5, HMA4, and SAMT, thus reducing the Cd content of lettuce shoots. When the concentration of SA was 100 mg/L, 200 mg/L, and 500 mg/L, the Cd contents of lettuce shoots were 11.28%, 22.70%, and 18.16%, respectively, lower than that of Cd treatment alone. Furthermore, principal component and correlation analyses showed that the Cd content of lettuce shoots was correlated with plant height, root length, biomass, antioxidant enzymes, and the expression level of genes related to Cd uptake.

Discussion

In general, these results provide a reference for the mechanism by which SA reduces the Cd accumulation in vegetables and a theoretical basis for developing heavy metal blockers with SA components.

Foliar application of flavonoids (rutin) regulates phytoremediation efficiency of Amaranthus hypochondriacus L. by altering the permeability of cell membranes and immobilizing excess Cd in the cell wall

The gap between the current serious soil heavy metal (HM) contamination and the low efficiency of soil remediation threatens human health. The aim of this study was to propose a method to improve the efficiency of phytoremediation by exogenous rutin application and explain the potential mechanism. A series of rutin treatments were designed to evaluate the biomass, cadmium (Cd) accumulation and physiological and biochemical responses of Amaranthus hypochondriacus under different Cd stresses. The results showed a decline in cell membrane damage with rutin application, and more Cd ions were immobilized in the cell wall than in the vacuole, resulting in an increase in Cd tolerance in plants. The addition of rutin caused significant effects on the synthesis of glutathione (GSH), including the advancement of the conversion of GSH to phytochelatins (PCs). Among them, PC₂ and PC₃ in the leaves contributed the most to the high accumulation of Cd. Overall, the phytoremediation efficiency and phytoextraction amount of Amaranthus hypochondriacus with rutin application were improved maximumly by 219.48% and 260.00%, respectively. This study provides a constructive approach for improving the efficiency of phytoremediation by foliar application of flavonoids and contributes to the further development of soil remediation in Cd-contaminated fields.

Theoretical insights into the adsorption mechanism of Cd(II) on the basal surfaces of kaolinite

Retardation of Cd(II) migration is an ongoing concern for environmental remediation, but a prevalent obstacle of the procedure originates from the lack of an atomic-scale description of the inherent mechanism for Cd(II) adsorption at mineral-water interfaces. Herein, we performed first-principles calculations and ab initio molecular dynamics (AIMD) simulations to explore the adsorption mechanism of Cd(II) on the basal surfaces of kaolinite. Representative monodentate and bidentate Cd(II) complexes were constructed on the Kln-Al(001) and Kln-Si(001̅) surfaces. The results showed that bidentate coordination of Cd(II) on the Kln-Al(001) surface was superior to all other studied models due to the favorable formation energy and better agreement with EXAFS data. The calculated electron density difference revealed the charge transfer from surface oxygen (O_s) to Cd(II) upon adsorption. In particular, partial density of states (PDOS) analysis indicated that the Cd-O_s bond exhibited covalent characteristics, attributed to the overlaps of Cd-5p and O_s-2p orbitals in the valence band. Furthermore, radial distribution functions supported by AIMD simulations were employed to confirm the structural features of Cd(II) coordination shell at kaolinite-water interfaces. This theoretical study provides insightful guidance for future Cd(II) research to improve current assessments of contaminant remediation.