Subcellular Cd distribution and its correlation with antioxidant enzymatic activities in wheat (Triticum aestivum) roots

The subcellular partitioning of Cd in wheat root was obtained by differential centrifugation of root homogenates to quantify the amounts of Cd associated with five operationally defined subcellular fractions, namely Cd-rich granule (MRG), cellular debris, organelles, heat-denatured protein (HDP), and heat-stable protein (HSP). Their correlations were investigated with the changes in antioxidant enzymatic activities under Cd stress (0.01-9.68 μM) for 72 h. The results showed that the relative Cd distribution in detoxified fractions (MRG+HSP) was decreased with increasing [Cd], but in metal-sensitive fractions (HDP+organelles) was increased. Consequently, the content of superoxide dismutase (SOD) and catalase (CAT) was decreased. Additionally, an increase of the total antioxidant capacity (A-TOC) and a slight decrease of malondialdehyde (MDA) were also observed. Interestingly, the relative root elongation (RRL) and CAT were significantly correlated with the Cd-sensitive fractions. These results suggest that the Cd toxicity to wheat roots strongly depends on the subcellular Cd distribution.