Physiological and Biochemical Mechanisms Preventing Cd Toxicity in the New Hyperaccumulator Abelmoschus manihot

Abelmoschus manihot, an ornamental plant, was examined for phytoremediation purposes in accordance with the ability to accumulate cadmium and physiological mechanisms of cadmium tolerance. A net photosynthetic rate (A (N)) glasshouse experiment for 60 days was conducted to investigate the influence of different cadmium amounts (0-100 mg kg(-1)) on the growth, biomass, photosynthetic performance, reactive oxygen species (ROS) production, antioxidative enzyme activities, Cd uptake and accumulation of A. manihot. Exposure to cadmium enhanced plant growth even at 100 mg kg(-1), without showing symptoms of visible damage. The cadmium concentration of shoots (stems or leaves) and roots was more than the critical value of 100 mg kg(-1) and reached 126.17, 185.26 and 210.24 mg kg(-1), respectively. BCF values of A. manihot plants exceeded the reference value 1.0 for all the Cd treatments, and TF values were greater than 1 at 15-60 mg kg(-1) Cd treatment. The results also showed that cadmium concentrations of 60 mg kg(-1) or less induced a significant enhancement in plant net photosynthetic rate (A (N)), stomatal conductance (G (s)), transpiration rate (T (r)), photosynthetic pigments and F (v)/F (m). These parameters were slightly decreased at the higher concentration (100 mg kg(-1)). The ROS production (O-2 (-), H2O2) and antioxidative response including SOD, CAT and POD were significantly enhanced by increasing cadmium. These results suggest that A. manihot can be considered as a Cd-hyperaccumulator and the hormetic effects may be taken into consideration in remediation of Cd contamination soil.