ABSTRACT
Millions of people around the world rely on rice (Oryza sativa) for a significant portion of daily calories, but rice is a relatively poor source of essential micronutrients like iron and zinc. Rice has been shown to accumulate alarmingly high concentrations of toxic elements, such as cadmium. Cadmium in foods can lead to renal failure, bone mineral density loss, cancer, and significant neurotoxicological effects. Several strategies to limit cadmium and increase micronutrient density in staple food crops like rice have been explored, but even when cadmium concentrations are reduced by a management strategy, total cadmium levels in rice grain are an unreliable means of estimating human health risk because only a fraction of the minerals in grains are bioaccessible. The goal of this work was to assess the influence of cadmium and zinc supplied to plant roots on the bioaccessibility of cadmium and essential minerals from grains of three rice lines (GSOR 310546/low grain Cd, GSOR 311667/medium grain Cd, and GSOR 310428/high grain Cd) that differed in grain cadmium accumulation. Treatments consisted of 0 µM Cd + 2 µM Zn (c0z2), 1 µM Cd + 2 µM Zn (c1z2), or 1 µM Cd + 10 µM Zn (c1z10). Our results revealed that an increased grain cadmium concentration does not always correlate with increased cadmium bioaccessibility. Among the three rice lines tested, Cd bioaccessibility increased from 2.5% in grains from the c1z2 treatment to 17.7% in grains from the c1z10 treatment. Furthermore, Cd bioccessibility in the low-Cd-accumulating line was significantly higher than the high line in c1z10 treatment. Zinc bioaccessibility increased in the high-cadmium-accumulating line when cadmium was elevated in grains, and in the low-cadmium line when both cadmium and zinc were increased in the rice grains. Our results showed that both exogenous cadmium and elevated zinc treatments increased the bioaccessibility of other minerals from grains of the low- or high-grain cadmium lines of rice. Differences in mineral bioaccessibility were dependent on rice line. Calculations also showed that increased cadmium bioaccessibility correlated with increased risk of dietary exposure to consumers. Furthermore, our results suggest that zinc fertilization increased dietary exposure to cadmium in both high and low lines. This information can inform future experiments to analyze genotypic effects of mineral bioavailability from rice, with the goal of reducing cadmium absorption while simultaneously increasing zinc absorption from rice grains.
ABSTRACT
Plants can readily accumulate cadmium (Cd), transferring this element to edible leaves, fruits, and seeds. Rice and wheat are among the top crop sources of Cd. Toxic heavy metals like Cd have chemical properties similar to essential micronutrients such as zinc (Zn) and are generally transported in plants by the same transporters as those essential micronutrients. Unfortunately our knowledge of Cd translocation and accumulation in seeds is still unclear. We conducted a partitioning study to assess both the whole plant Cd distribution and accumulation and potential source-sink remobilization during grain filling period in two near-isogenic lines of durum wheat that differ in root to shoot translocation and grain Cd content. We also assessed the role of Zn fertilization in Cd translocation and accumulation in the grains. There was no remobilization of Cd in both lines during grain filling. Although majority of Cd partitioned to the roots in both lines, root to shoot translocation of Cd differed in both lines. In contrast, there were no significant differences in Zn partitioning between the lines and remobilization was observed in different tissues. Although there was some remobilization of Zn, the main source of Cd and Zn is continued uptake and translocation to sources during grain fill.
