Ecological aspects of antioxidant enzymes and Glutathione-S-transferases in Three Papilio Species

Phototoxins are compounds capable of absorbing light to form an excited state molecule, which can itself react with macromolecules to cause toxicity or react with molecular oxygen to form toxic oxygen species such as singlet oxygen, superoxide anion, and other oxyradicals. Aerobic organisms possess a suite of antioxidant enzymes to protect against reactive oxygen damage. Significant differences in activities of antioxidant enzymes as well as glutathione-S-transferases were found in larvae of three species of Papilio (Lepidoptera: Papilionidae). Levels of catalase, glutathione reductase, glutathione peroxidase, and glutathione transferase were high in P. polyxenes, intermediate in P. cresphontes, and low in P. glaucus glaucus. Levels of superoxide dismutase were similar in P. polyxenes and P. cresphontes and significantly higher than in P. glaucus glaucus. The overall hierarchy of antioxidant enzyme activity level in these species is consistent with the phytochemical composition of their host plants: P. polyxenes and P. cresphontes feed almost exclusively on plants (in the Apiaceae and Rutaceae, respectively) that contain phototoxic compounds; P. glaucus glaucus feeds almost exclusively on plants that lack phototoxins. The presence of considerable antioxidant enyme activity in the integument of P. polyxenes and P. cresphontes suggests that these enzymes may protect cuticle, which is not only exposed to sunlight but also to toxic oxyradicals generated from phototoxins at the leaf surface.