Uptake and Partitioning of Cd and Zn by Two Non-hybrid Rice Cultivars in Different Growth Stages: Effect of Cultivars, Soil Type and Cd Spike

Soil-food crop-diet transfer has been considered as the dominant pathway of human exposure to Cd and the potential health risk. Rice(Oryza sativa L.),in particular, has been concerned as a food crop that significantly accumulates Cd in grains. A pot experiment of Cd and Zn uptake and portioning in plant organs during the whole growing period was conducted using consistently submerged condition. Two cultivars of non-hybrid rice, Suxiangjing 1(high Cd affinity cultivars)and 99-22(low Cd affinity cultivars),were grown in two paddy soils with contrasting chemical properties and soil total Cd and Zn contents. Cd was spiked at 0mg·kg-1 of soil(as the control)and 2mg·kg-1, respectively. Rice plants were harvested in different growth stages and the biomass and Cd and Zn contents, of different organs were determined. The results obtained were as follows:1)Uptake of Cd and Zn by the rice were affected by soil type, cultivars, and Cd spike, of which under a positive mutual interaction(high Cd affinity cultivars on the soil of high Cd availability)very high grain Cd and Cd/Zn ratio was observed due to strong uptake and high grain partitioning of Cd; 2)Cd uptake and organ partitioning by rice plant varied with the different growing stages. Significant uptake of Cd was observed in the tillering and ripening stages while that of Zn was in tillering, spiking and filling stages; Zn depletion with enhanced Cd uptake was aparent in the whole life period, especially under spiked Cd treatments;3)There existed significant differences in Cd and Zn partitioning in plant organs both between the growth stages of a single cultivars and between the cultivars in a single stage. Total Cd amount was in the order: roots grains shoots, and the total Zn was in an order: shoots roots and grains. An intense translocation of plant Cd to grains happened even the ripening stage of both cultivars. Stronger Cd but weaker Zn transfer to grains by the high Cd affinity cultivars than the low one could be considered as a major plant factor controlling high Cd uptake and accumulation, and the high Cd/Zn ratio in rice grains.