The variation of rice cultivars in Cd toxicity and distribution of the seedlings and their root histochemical examination

Rice cultivars showing low Cd transportation into the aboveground parts of a plant can be selected to reduce Cd contamination in grains. In this study, eight rice cultivars, TY3, TK9, TNG71, KH145, TKW1, TKW3, TCS10, and TCS17, which are commonly grown in Taiwan, were used. The seedlings of each cultivar were transplanted with 0, 5, 10, 50, 100, and 250 mu M CdCl2 solutions, respectively, for a 7-day treatment in hydroponics. The Cd treatment resulted in significant reductions in the root elongation and the shoot extension of rice seedlings for each cultivar. According to the Cd distributions in the root and shoot for the used cultivars, the Cd absorption by rice plants was predominantly accumulated in the root rather than transferred to the shoot. The Cd treatment induced lignification in the sclerenchyma tissue and in the endodermis and metaxylem cell walls of the rice root specimens. The lignification of the cell walls enhancing the Cd sequestration by the root would be related to the tolerance to Cd toxicity and to the Cd transfer into the aboveground parts of a rice plant. Much higher Cd concentrations in the shoot were found for the TY3 and TK9 plants. By contrast, the translocations of Cd in TNG71, KH145, TKW1, and TKW3 plants were relatively low. Thus, TNG71, KH145, TKW1, and TKW3 would be the candidates for cultivation to reduce Cd transported into the aboveground parts of a rice plant. TCS10 and TCS17 cultivars also showed low translocation of Cd from the root to the shoot, but their Cd absorption rates in the plant were much higher than the other cultivars.