Differences in Cadmium Accumulation and Root Morphology in Seedlings of Japanese Wheat Varieties with Distinctive Grain Cadmium Concentration

A low cadmium (Cd) concentration in wheat grain is desirable because of Cd toxicity to humans. Grain Cd concentrations in Japanese wheat differed among the varieties in previous study. In this study, we hypothesized that the varieties with a low concentration of Cd in grain have (1) low Cd uptake from the soil through the roots during early growth and/or (2) low Cd translocation from the roots to shoots, and also, that (3) Cd uptake from soil is affected by root morphology. These hypotheses were verified by investigating the concentration and quantity of Cd in root, shoot and leaf tissues, and examining the root morphology of young seedlings of wheat varieties with high and low grain Cd concentrations. Seedlings of 'Kitahonami' and 'Nanbukomugi' which had low grain Cd concentration (low Cd/G varieties) had a lower Cd quantity in whole plant tissues than 'Nishikazekomugi' and 'Kitakamikomugi' which had high grain Cd concentration (high Cd/G varieties) during early growth. Low Cd/G varieties also showed lower root to shoot (aerial parts) translocation of Cd than high Cd/G varieties. Seedlings of low Cd/G varieties showed less root branching than high Cd/G varieties. Root frequency showed a significant positive correlation with Cd quantity in whole plant tissues. These results suggest that low Cd/G varieties used in this study have low Cd uptake and translocation from the roots to shoots during early growth, and furthermore, that low Cd uptake at the seedling stage may relate to slow and/or limited development of branching roots.