Responses to cadmium stress in two tomato genotypes differing in heavy metal accumulation

Our previous research defined two tomato (Solanum lycopersicum) genotypes: high cadmium (Cd) accumulator YSL189 and low Cd accumulator HZ903. Further hydroponics experiments investigated the different tolerance mechanisms to Cd stress between YSL189 and HZ903 at the seedling stage. When Cd concentration was >20 mu M in the growing medium, the uptake rate of Cd was significantly higher in roots of YSL189 than it was in roots of HZ903. When plants were supplied with 50 and 100 mu M Cd in the growing medium, there were higher Cd concentration, higher biomass and plant height, shorter roots, and higher expression levels of transporter genes natural resistance associated macrophage proteins (Nramp) 2, Nramp3, and zinc and iron regulated transporter (ZIP) in roots of YSL 189 compared to HZ903. We infer that the high Cd accumulation in YSL189 was partly due to the higher Cd uptake rate and higher expression levels of Nramp2, Nramp3, and ZIP in its roots. At the same time, the degree of cell injury indicated by thiobarbituric acid reactive substance showed no significant differences in roots and stems between the two genotypes. We attribute this to the higher activities of superoxide dismutase, peroxidase, and catalase in roots and stems of YSL189 compared to HZ903.