Photosynthetic response, antioxidase activity, and cadmium uptake and translocation in Monochoria korsakowii with cadmium exposure

Abstract

To identify the tolerance mechanisms of wetland plants exposed to heavy metal, a hydroponic experiment was used to investigate variations in photosynthetically physiological parameters and antioxidant enzyme activities in leaves of Monochoria korsakowii exposed to 0.05, 0.15, 0.30, and 0.45 mM Cd2+ for 7 d. The Cd2+ concentrations in the plant roots, stems, and leaves were also investigated. Cd2+ exposure significantly decreased the total chlorophyll content, net photosynthetic rate, intercellular carbon dioxide concentration, and stomatal conductance, while stomatal limitation value had the opposite trend (P, 0.05). During Cd2+ stress, ascorbate peroxidase activity significantly increased (P, 0.05). The translocation factor for Cd2+ was significantly lower than that of the control, and both were less than 1 (P, 0.05). Cd2+ stress damaged the photosynthetic apparatus in the leaves. During Cd2+ stress, M. korsakowii alleviated oxidative stress by increasing the activities of antioxidant enzymes, such as APX. Under 0.45 mM Cd2+ stress, increased heat dissipation was responsible for alleviating the photooxidative damage to photosynthetic organs in the leaves. Meanwhile, the majority of Cd2+ was immobilized in the roots, thus alleviating excessive Cd2+ phytotoxicity in the aboveground parts. Generally, M. korsakowii has potential application in the phytoremediation of low-cadmium-polluted water.