Tissue Fractions of Cadmium in Two Hyperaccumulating Jerusalem Artichoke Genotypes

In order to investigate the mechanisms in two Jerusalem artichoke (Helianthus tuberosus L.) genotypes that hyperaccumulate Cd, a sand-culture experiment was carried out to characterize fractionation of Cd in tissue of Cd-hyperaccumulating genotypes NY(2) and NY(5). The sequential extractants were: 80% v/v ethanol (F(E)), deionized water (F(W)), 1 M NaCl (F(NaCl)), 2% v/v acetic acid (F(Acet)), and 0.6 M HCl (F(HCl)). After 20 days of treatments, NY(5) had greater plant biomass and greater Cd accumulation in tissues than NY(2). In both genotypes the F(NaCl) fraction was the highest in roots and stems, whereas the F(Acet) and F(HCl) fractions were the highest in leaves. With an increase in Cd concentration in the culture solution, the content of every Cd fraction also increased. The F(W) and F(NaCl) ratios in roots were lower in NY(5) than in NY(2), while the amount of other Cd forms was higher. It implied that, in high accumulator, namely, NY(5), the complex of insoluble phosphate tends to be shaped more easily which was much better for Cd accumulation. Besides, translocation from plasma to vacuole after combination with protein may be one of the main mechanisms in Cd-accumulator Jerusalem artichoke genotypes.