Response of antioxidative enzymes of Abies firma seedlings under chronic acid fog exposure and/or drought treatment.

To understand the oxidative stress conditions of momi fir (Abies firma Sieb. et Zucc.) seedlings under acid fog exposure and/or drought stress, we assayed the activities of antioxidative enzymes, such as superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX), in the seedlings. We found that SOD and APX activities were not affected by the stress conditions, but drought stress stimulated CAT activity irrespective of acid fog exposure. This suggests the production of a large amount of hydrogen peroxide, which is one of the substances involved in the signal transduction pathway for stomatal closure. However, we previously observed sufficient stomatal closure under drought stress and insufficient stomatal closure under combined acid fog exposure and drought stress. This inconsistency indicates that acid fog exposure affects the signal transduction pathway from the production of hydrogen peroxide to stomatal closure in momi fir seedlings.