Cadmium accumulation, sub-cellular distribution and chemical forms in rice seedling in the presence of sulfur

• Cd accumulation in rice roots was more than in shoots.
• Cd mainly existed in cell wall and soluble fraction in rice.
• Cd contents in cell wall abided by the order: no S > moderate S > high S.
• Inorganic form of Cd contents followed the rule: no S > moderate S > high S.
• Cd contents in soluble fraction or Cd with pectate and protein showed contrary trend.

Changes in cadmium (Cd) accumulation, distribution, and chemical form in rice seedling in the joint presence of different concentrations of sulfur (S) remain almost unknown. Therefore, the indoor experiments were performed to determine the accumulation, sub-cellular distribution and chemical forms of Cd under three S levels in rice seedling for the first time. The result showed that Cd accumulation in rice roots was more than in shoots. Sub-cellular distribution of Cd in rice roots and shoots indicated that the largest proportion of Cd accumulated in cell walls and soluble fractions. As S supply increased, the proportion of Cd in cell walls reduced, while it increased in the soluble fractions. The majority of Cd existed in inorganic form, and then gradually changed to organic forms that included pectates and proteins with increased S supply. The results showed that S supply significantly influenced Cd accumulation, distribution, and chemical forms, suggesting that S might provide the material for the synthesis of sulfhydryl protein and thereby affect Cd stress on plants. These observations provided a basic understanding of potential ecotoxicological effects of joint Cd and S exposure in the environment.