Subcellular and Molecular Distribution of Cadmium in Two Rice Genotypes With Different Levels of Cadmium Accumulation

The chemical form and subcellular and molecular distribution of cadmium (Cd) in the roots and leaves was investigated in two rice genotypes: the low Cd-accumulating ‘‘Guangyuanzhan No. 3’, and the high Cd-accumulating ‘‘Zhenguiai.’’ Elevated Cd level in the medium caused a significant increase in Cd concentration in all parts of the roots and leaves. The soluble fractions in leaves and roots of ‘Zhenguiai’ contained a higher proportion of the Cd than those in ‘Guangyuanzhan No. 3’. Furthermore, ‘Zhenguiai’ had a higher proportion of de-ionized water and 80% ethanol-extractable Cd, which is the most mobile Cd among its various chemical forms. Following gel filtration of the soluble fraction of leaf and root extracts of both genotypes, a compound with a molecular weight of ∼3 kDa, probably comprising phytochelatins (PCs), was the major Cd-binding component. The Cd concentrations in the fractions from the roots of ‘Zhenguiai’ were noticeably higher than those of ‘Guangyuanzhan No. 3’, which possibly resulted in the latter cultivar having a lower Cd mobility in the roots and less Cd translocation from the roots to the aboveground parts.