Nodes play a major role in cadmium (Cd) storage and redistribution in low-Cd-accumulating rice (Oryza sativa L.) cultivars

Foliar spraying of Zn/Si affects Cd accumulation in paddy grains by regulating the remobilization and transport of Cd in vegetative organs

The reduction of cadmium (Cd) accumulation in rice grains through biofortification of essential nutrients like zinc (Zn) and silicon (Si) is an area of study that has gained significant attention. However, there is limited understanding of the mechanism of Zn/Si interaction on Cd accumulation and remobilization in rice plants. This work used a pot experiment to examine the effects of Zn and Si applied singly or in combination on the physiological metabolism of Cd in different rice organs under Cd stress. The results revealed that: Zn/Si application led to a significant decrease in root Cd concentration and reduce the value of Tf Soil-Root in filling stage. The content of phytochelatin (PCs, particularly PC2) and glutathione (GSH) in roots, top and basal nodes were increased with Zn/Si treatment application. Furthermore, Zn/Si treatment promoted the distribution of Cd in cell wall during Cd stress. These findings suggest that Zn/Si application facilitates the compartmentalization of Cd within subcellular structures and enhances PCs production in vegetative organs, thereby reducing Cd remobilization. Zn/Si treatment upregulated the metabolism of amino acid components involved in osmotic regulation, secondary metabolite synthesis, and plant chelating peptide synthesis in vegetative organs. Additionally, it significantly decreased the accumulation of Cd in globulin, albumin, and glutelin, resulting in an average reduction of 50.87% in Cd concentration in milled rice. These results indicate that Zn/Si nutrition plays a crucial role in mitigating heavy metal stress and improving the nutritional quality of rice by regulating protein composition and coordinating amino acid metabolism balance.

New insights into the key role of node I in thallium accumulation in seed of coix (Coix lacryma-jobi L.)

The mechanisms underlying the distribution of many toxic metal(loid)s in shoots and metal(loid) transport to grains have been well documented in the quest for food safety but there remains a lack of knowledge on thallium (Tl) accumulation in food crops. Here, field investigations combined with a glasshouse pot experiment were conducted to investigate the characteristics of Tl distribution and accumulation in coix, a major food crop in south Guizhou province, China, and the role of node I in restricting Tl transport to the seed. Fourteen percent of coix seed samples collected from the Lanmuchang Tl-As-Hg mine contained higher Tl concentrations than the recommended limit for foods and feedstuffs in Germany (0.5 mg kg-1), with the highest exceedance rate of the metal(loid)s determined, when grown in soils surrounding the mine with a very high Tl concentration of 0.07-89.5 mg kg-1 and a general low pH of 4.19-6.48. Thallium concentrations were higher in coix nodes than in internodes, followed by roots and grains. The Tl translocation factors from node I to grains were 0.01-0.21 and were the lowest of any translocation factors between different tissues. Node I is therefore the key tissue restricting Tl transport to coix grains. Thallium was localized mainly in the diffuse vascular bundles (DVBs) in node I. The co-localization of Tl and sulfur in the DVBs and Tl contamination-induced phytochelatin (PC) accumulation indicate that Tl storage in the DVBs involving complexation with PCs in node I is an important process in Tl accumulation in coix grains. Moreover, the area of DVBs in node I increased with increasing soil Tl pollution level, providing more channels for Tl transport to the panicles and grains and thereby acting as a key factor restricting Tl transport to the grains. These results provide new insights into the key role of node I in Tl accumulation in coix grains and indicate key points to minimize Tl accumulation in grains for food safety.

Genotypic variation in grain cadmium concentration in wheat: Insights into soil pollution, agronomic characteristics, and rhizosphere microbial communities

Soil cadmium (Cd) pollution poses a serious threat to both the productivity and quality of wheat. This study aimed to investigate the genotypic variation in grain Cd concentration in wheat through field and pot experiments. Among 273 wheat genotypes, a significant genotypic difference was found in grain Cd concentration, ranging from 0.01 to 0.14 mg kg-1. Two contrasting genotypes, X321 (a low grain Cd accumulator) and X128 (a high grain Cd accumulator), were selected for pot experiments. X321 exhibited a 17.9% greater reduction in yield and a 10.2% lower shoot-to-grain Cd translocation rate than X128 under Cd treatment. Grain Cd content showed a positive correlation with soil available Cd content and a negative correlation with Cu content. Soil catalase activity significantly decreased in X128 under Cd stress, whereas no difference was found in X321. The grains of X321 exhibited a more compact spatial distribution of starch grains and protein matrix than those of X128. Moreover, the size of A-type starch in X128 was larger than in X321. Meanwhile, X128 contained much B-type starch, with some surface pits observed on A-type granules under Cd stress. Cd treatment increased the abundance of rhizosphere microorganism communities, with Ellin6067 and Ramlibacter being enriched in X128 under Cd treatment, which might facilitate Cd uptake. The accumulation of Cd in grains demonstrated a strong positive correlation with the rhizosphere bacterial diversity (correlation coefficient = 0.78). These findings provide new insights into the basis of grain Cd accumulation in wheat and have potential implications for developing new verities with low Cd accumulation to ensure food safety and minimize human exposure.

Stable Isotope Ratios Trace the Rice Uptake of Cadmium from Atmospheric Deposition via Leaves and Roots

Cadmium (Cd) stable isotopes provide a novel technique to investigate the fate of Cd in the environment, but challenges exist for tracing the sources in the plants. We performed individual rice leaf and root exposures to dry and wet deposition using customized open-top chambers (OTCs) in the greenhouse and in the field next to a smelter, respectively. The field experiment also included a control without Cd deposition and a "full" treatment. The exposure experiments and isotope signatures showed that leaves can directly take up atmospheric Cd and then translocate within rice plants to other tissues, contributing 52-70% of Cd in grains, which exceeded the contribution (30-48%) by root exposure. The Cd isotopes in leaves, nodes, internodes, and grains demonstrate that roots preferentially take up Cd from wet deposition, but leaves favor uptake of Cd from dry deposition. The Cd uptake by leaves is redistributed via nodes, allowing for upward transport to the grains but preventing downward transport to the roots. Leaves favor uptake of heavy isotopes from atmospheric deposition (ΔCd114/110Leaf-Dust: 0.10 ± 0.02‰) but retain light isotopes and transport heavy isotopes to the nodes and further to grains. These findings highlight the contribution of atmospheric deposition to rice and Cd isotopes as a useful tracer for quantifying sources in plants when different isotopic compositions are in sources.

Effect of polylactic acid microplastics and lead on the growth and physiological characteristics of buckwheat

Microplastics (MPs) and heavy metals are common, often co-existing pollutants, that threaten crop growth and productivity worldwide. We analysed the adsorption of lead ions (Pb2+) to polylactic acid MPs (PLA-MPs) and their single factor and combined effects on tartary buckwheat (Fagopyrum tataricum L. Gaertn.) in hydroponics by measuring changes in the growth characteristics, antioxidant enzyme activities and Pb2+ uptake of buckwheat in response to PLA-MPs and Pb2+. PLA-MPs adsorbed Pb2+, and the better fitting second-order adsorption model implied that Pb2+ was adsorbed by chemisorption. However, the similar Pb2+ contents in the plants treated with Pb2+ only and those treated with the combined PLA-MPs-Pb2+ suggested that the adsorption played no role in the uptake of Pb2+. Low concentrations of PLA-MPs promoted shoot length. At high concentrations of both PLA-MPs and Pb2+, buckwheat growth was inhibited, and leaf peroxidase (POD), superoxide dismutase (SOD) and catalase (CAT) activities and malondialdehyde (MDA) contents were higher than in the control. No significant differences were observed in seedling growth between exposure to Pb2+ only and combined exposure to PLA-MPs with Pb2+, implying that PLA-MPs did not increase the toxicity of Pb2+ at macroscopic level. POD activity was higher and chlorophyll content was lower with PLA-MPs in the low Pb2+ dose treatments, suggesting that PLA-MPs may increase the toxicity of naturally occurring Pb2+. However, the conclusions must be verified in controlled experiments in natural soil conditions over the whole cultivation period of buckwheat.

Mitigation strategies for excessive cadmium in rice

Cadmium (Cd)-contaminated rice is a human food safety problem that lacks a clear solution. A large amount of rice having an excessive Cd content is processed yearly, but it cannot be discarded and placed in landfills because it will cause secondary pollution. How do we best cope with this toxic rice? From the perspectives of food safety, food waste prevention, and human hunger eradication, the use of contemporary physical, chemical, and biological techniques to lower the Cd content in postharvest Cd-contaminated rice so that it can be used safely is the best course of action. In this review, the contamination, chemical speciation, and distribution of Cd in rice are analyzed and discussed, as are the methods of Cd removal from rice, including a comparison of the advantages and disadvantages of various techniques. Owing to the limitations of current technology, research and technological development recommendations for removing Cd from rice grain are presented. The chemical and biological methods produce higher Cd-removal rates than physical methods. However, they are limited to small-scale laboratory applications and cannot be applied on a large industrial scale. For the efficient safe removal of Cd from food, mixed fermentation with lactic acid bacteria and yeast has good application prospects. However, limited strains having high Cd-removal rates have been screened. In addition, modern biotechnology has rarely been applied to reduce rice Cd levels. Therefore, applying genetic engineering techniques to rapidly obtain microorganisms with high Cd-removal rates in rice should be the focus of future research.