Plant growth, antioxidative enzyme, and cadmium tolerance responses to cadmium stress in Canna orchioides

The cadmium tolerance capacity of Canna orchioides was evaluated using glasshouse experiment to lay a theoretical foundation to broad applications of this species in cadmium (Cd) polluted areas. The plant growth, Cd absorption, and antioxidative enzyme activities of canna plants treated with different Cd concentrations (0, 100, and 200 mg · kg−1 per dry soil) for 30 days were investigated. The results indicated that the growth of roots, leaves and stems was restricted following Cd addition. The bio-concentration factor was the highest in the roots, followed by the leaves, rhizomes, and stems. Compared with the control, the translocation factor decreased sharply after 100 mg · kg−1 or 200 mg · kg−1 Cd treatment, whereas the tolerance index decreased significantly under 200 mg · kg−1 Cd exposure. The Cd accumulation rate and total Cd accumulation significantly increased under 200 mg · kg−1 Cd treatment than the control. The malondialdehyde content remained unchanged at different Cd concentrations, while the relative electrical conductivity of the root increased significantly following 200 mg · kg−1 Cd treatment. Cd stress increased significantly the activity of superoxide dismutase (SOD), peroxidase (POD), and ascorbate peroxidase (APX) in the leaves, whereas only SOD was raised in the roots. The catalase (CAT) and POD activity in the roots did not differ significantly at different Cd concentrations. Conversely, APX in the roots decreased significantly under Cd stress, which suggests that the protective mechanisms in the leaves differ from those in the roots. These results indicated that C. orchioides has a high tolerance for Cd. Furthermore, the reactive oxygen species caused by Cd stress could be effectively scavenged by the antioxidative system. The present study proved that C. orchioides constitutes a promising ornamental plant for use in the restoration of areas contaminated with Cd.