Quantitative Changes of PR Proteins and Antioxidative Enzymes in Response to Glomus intraradices and Phytophthora capsici in Pepper (Capsicum annuum L.) Plants

To investigate protective activity in pepper plants, which were pre-inoculated with arbuscular mycorrhizal (AM) fungi Glomus intra radices (Gi), against pathogenic strain Phytophthora capsici (Pc), pathogenesis-related (PR) proteins and antioxidant enzymes were examined. The growth of root and shoot was the highest in peppers inoculated with G. intraradices, compared with non-inoculated control plants and those challenged by the pathogen with and without mycorrhizae after nine days of infection. Mycorrhizal colonization rate was reduced by about 10% in pathogen-challenged plants, but disease pressure was reduced. The activities of PR proteins, $\beta$-1- 3-glucanase and chitinase, were increased in Pc-treated plants compared to Gi+Pc-treated plants in leaves, but those in roots were suppressed. Superoxide dismutase activity and $H_2O_2${/TEX> content in Gi+Pc and Pc-treated plants were gradually increased in leaves. However, those in roots continuously increased up to 5 days, and then decreased dramatically. Peroxidase activity in leaves and roots increased after P. capsici infection both in plants inoculated with or without G. intraradices. These results suggest that AM fungi, G. intra radices, potentially act as one of the protective agents against plant pathogens. Changes of PR proteins and antioxidative enzymes in mycorrhizae-inoculated pepper appear to be regulated differently in leaves and roots by pathogen infection.