Myung-Sook Kim

Arsenic (As) contamination poses a serious threat to rice production and food safety. Although sulfur (S) nutrition is known to alleviate As toxicity through thiol-based detoxification, the mechanisms underlying the relationship between S-induced As accumulation and tolerance remain poorly understood. We investigated the effects of contrasting S levels (0, 1, and 4 mM) on As accumulation, translocation, oxidative stress responses, thiol metabolite pools, and mineral nutrient profiles in hydroponically grown rice seedlings exposed to 15 µM As for 15 days. S supplementation alleviated As-induced growth inhibition in a dose-dependent manner despite increasing total As accumulation in both roots and shoots, demonstrating that S-mediated tolerance is independent of reduced As accumulation. Elevated S supply reduced oxidative stress markers (O₂^•–, H₂O₂, and MDA), while markedly enlarged the pools of γ-glutamylcysteine (γ-EC), glutathione, and phytochelatins (PCs), particularly in roots. S supplementation also improved the uptake of major essential nutrients, including nitrogen and potassium in shoots, while selectively modulating micronutrient distributions under As stress. Correlation analysis showed that root As content was strongly and positively correlated with γ-EC and PC2–PC4, and principal component analysis separated the treatments along the S gradient in both roots and shoots. Collectively, these results suggest that S enhances As tolerance in rice seedlings through thiol-dependent detoxification, thereby decoupling As tolerance from As accumulation rather than by restricting As accumulation.

Cadmium (Cd) is a potentially toxic element that impairs plant growth and threatens food safety and human health. This study aimed to investigate the effects of sulfur (S) supplementation on Cd uptake and tolerance in rice under hydroponic conditions. Rice seedlings were exposed to Cd stress and treated with S at different concentrations. Physiological traits, oxidative damage markers, thiol compounds, and ionomic profiles in rice plants were assessed. S supplementation reduced Cd-induced growth inhibition, restoring plant biomass. Although Cd accumulation increased with S treatment, it was accompanied by enhanced antioxidant responses, scavenging reactive oxygen species (ROS) and malondialdehyde. S application increased the production of thiol-containing compounds, including γ-glutamylcysteine, glutathione, and phytochelatins, which helped chelate Cd and sequester it in vacuoles, particularly in roots. Additionally, S supplementation altered the essential nutrient composition in rice tissues, particularly the uptake of N, P, and K, while influencing levels of Ca, Mg, and other essential elements. S supplementation enhanced rice tolerance to Cd stress by reestablishing ROS balance, activating thiol-based detoxification pathways, and regulating mineral nutrient balance. Furthermore, sulfur (S) exhibited a dual effect in plants, enhancing cadmium (Cd) uptake while also promoting its detoxification, underscoring its role in improving crop resilience in contaminated soils.

Potentially toxic elements (PTE), such as cadmium (Cd), lead (Pb), and arsenic (As), threaten rice (Oryza sativa L.) crop productivity and pose significant risks to human health when they are present in soil. This review summarizes the current understanding of soil and rice contamination with As, Cd, and Pb to provide an in-depth understanding of the dynamics of these contaminants and the mechanisms regulating their flow from soil to plants. It focuses on the following aspects: (1) these metals’ geochemical distribution and speciation in soil–rice systems; (2) factors influencing the transformation, bioavailability, and uptake of these metals in paddy soils; (3) metal uptake, transport, translocation, and accumulation mechanisms in rice grains; and (4) the roles of transporters involved in metal uptake, transport, and accumulation in rice plants. Moreover, this review contributes to a clearer understanding of the environmental risks associated with these toxic metals in soil–rice ecosystems. Furthermore, it highlights the challenges in simultaneously managing the risks of As, Cd, and Pb contamination in rice. The study findings may help inspire innovative methods, biotechnological applications, and sustainable management strategies to mitigate the accumulation of As, Cd, and Pb in rice grains while effectively addressing multi-metal contamination in paddy soils.