Differences among soybean cultivars with regard to the cadmium-accumulation patterns in various organs
Soybean cultivars show significant differences in seed cadmium (Cd) concentrations, primarily because of genetic rather than environmental, factors. Through grafting experiments, we demonstrate that the shoot Cd concentration is determined by the Cd-accumulation capacity of the roots: in cultivars with a low capacity for Cd-accumulation in the roots, Cd is translocated to and accumulates in the shoots. However, cultivars differ in the seed Cd content. Next, we investigated how Cd translocated from the root to the shoot is distributed to and accumulates in each shoot organ during soybean development.
Compared to cultivars with low seed concentrations of Cd, those with high concentrations had higher Cd concentrations in all the shoot organs during development. The leaves (including petioles and fallen leaves) had the highest Cd concentration and the seeds the lowest. In Suzuyutaka, which had high Cd concentration in the seeds, the concentration of Cd distributed from the shoots to the leaves was 67% and that distributed from the shoots to the seeds was 13%. In Kantou 100, which had low Cd concentration in the seeds, 57% Cd was distributed from the shoots to the leaves and 21% from the shoots to the seeds. These results suggest that cultivars that have a low capacity for Cd accumulation in the roots have a mechanism that prevents Cd accumulation in the seeds by promoting its accumulation in the leaves.