Photosynthetic Performance and Anti-oxidative Response of Cornus Controversa Seedlings under Cadmium and Lead Stress

The photosynthetic efficiency of Cornus controversa leaves was decreased significantly under Cd treatment while it was not affected by Pb exposure. Cd decreased while Pb treatment increased the chlorophyll contents of Cornus controversa leaves. Furthermore, the peroxidase (GPX) activities were decreased after Cd treatment while elevated by Pb exposure in Cornus controvera seedlings. In addition, both Cd and Pb exposures increased the malondialdehyde (MDA) and proline contents and elevated the superoxide dismutase (SOD) activities of Cornus controvera seedlings. Collectively, these results indicated that Cornus controversa may be more tolerant to Pb than Cd toxicity. This finding will contribute to the evaluation of planting Cornus controversa in heavy metal polluted soil conditions. Introduction Environmental heavy metal contamination is becoming a worldwide problem that has attracted a great deal of attention. The release of heavy metals into the environment is mainly caused by various anthropogenic activities associated with agricultural practices, mineral exploration, industrial processes and solid waste management (Alumaa et al. 2002). Heavy metal pollution causes serious physiological damage to the plants. Exposure to high levels of heavy metals induces inhibition of nutrient uptake, hindering the activity of photosynthetic apparatus, inhibiting the activation of antioxidant enzymes (Sandalio et al. 2001), and displacing the essential elements in plants. Heavy metals also damage the plant cellular components, such as membranes, nucleic acids, chloroplast pigments, and peroxidizing lipid. Among the heavy metal pollutants, cadmium (Cd) and lead (Pb) are considered as the most toxic element. The plants subjected to heavy metal contaminations display various morphological, physiological, and biochemical changes, and these changes are usually considered to be the indicators of the degree of heavy metal injury. Photosynthesis is one the most fundamental and intricate physiological processes in higher plants. The mechanism of photosynthesis involves various components, including photosynthetic pigments and photosystems, the electron transport system, and CO2 reduction pathways, any damage caused by a stress may reduce the overall photosynthetic capacity of a green plant (Ashraf and Harris 2013). Heavy metal pollutions such as Cd, copper (Cu), and chromium (Cr) can inhibit the photosynthetic performance of plants by affecting the fluorescence emission kinetic characteristics and photosynthetic pigments of plants (Huseynova et al. 2009, Nagajyoti et al. 2010). Furthermore, the responses of plant natural *Author for correspondence: . Key Laboratory of Plant Resources Conservation and Sustainable Utilization, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou 510650, China.