Genotypic differences in cadmium uptake and distribution in soybeans

In order to investigate the genetic differences in uptake and distribution of cadmium in soybeans, 17 varieties of soybean were grown first in soil and then four or five varieties of soybean were grown in nutrient solution with different levels of cadmium. Significant genotypic differences in seed cadmium levels were found. The seed cadmium concentration was lowest for the En-b0-1-2 soybean variety, and highest for Harosoy, in both field and pot experiments. The seed cadmium levels of Tohoku 128, a cross between Enrei and Suzuyutaka, were intermediate between those of the parents. For four soil types, containing from 0.2 to 6.5 mg kg(-1) extractable cadmium, the ranking of soybean genotypes based on seed cadmium level was similar, indicating that there is a genetic factor involved in the varietal differences in cadmium concentration. Among the four soybean varieties tested in one experiment in the present study, the cadmium concentrations in leaves, stems and pods as well as the total cadmium uptake were lowest for En-b0-1-2. These results suggest that cadmium uptake and/or translocation from root to shoot are low in En-b0-1-2. In solution culture containing 100 mug L-1 cadmium, the cadmium concentrations in seeds, stems and pods at the seed maturation stage were also the lowest for En-b0-1-2. In a second experiment, the cadmium concentrations in the leaves, stem and petiole were lower at both 7 and 15 days after the addition of cadmium to the nutrient solution for En-b0-1-2 and Enrei than for Tohoku 128, Suzuyutaka and Harosoy; however, the cadmium concentrations of roots for En-b0-1-2 and Enrei were higher than for the other varieties. We propose that the lower levels of cadmium found in the seeds of certain varieties of soybean result from the combination of lower initial uptake and retention of higher levels of cadmium in the roots, thus limiting its translocation to the shoot.