Effects of polycyclic aromatic hydrocarbons exposure on antioxidant system activities and proline content in Kandelia candel

The antioxidant system effects of Kandelia candel were investigated under four different levels of PAH stress. The activities of antioxidant enzymes including superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD), the responses to the change of malondialdehyde (MDA) contents and the accumulation of proline in K. candel were determined. Our results suggested that the activities of SOD, CAT, POD increased significantly in leaves and roots of K. candel (p≤0.05) with the increase of the external PAH concentrations, while in stems, the activities of these antioxidant enzymes were all significantly inhibited (p≤0.01). We also observed an increase of MDA in leaves, stems and roots, and an obvious correlation between MDA content and PAH concentrations in three locations, which showed that the change of MDA content could be used as a biomarker of K. candel under PAH stress. The proline content was found remarkably enhanced in leaves, stems and roots. However, a significant inverse correlation was observed between the proline content and SOD (r=-0.99, p≤0.01), POD (r=-0.95, p≤0.05) activities in stems. This study suggested that the antioxidative system of K. candel has an obvious organ-dependent feature when exposed to PAH contamination as revealed by discriminant analysis (DA).