CHANGES IN ACTIVITIES OF ASCORBATE PEROXIDASE AND ASCORBATE OXIDASE IN N-(2-CHLOROPYRIDYL)-N'-PHENYLUREA(CPPU)-INDUCED PARTHENOCARPIC FRUITS OF LAGENARIA LEUCANTHA

Lagenaria leucantha is an important vegetable crop and a potential model for the study of fruit development. We previously demonstrated that CPPU, a synthetic cytokinin, effectively induced parthenocarpic growth and cell division and expansion in Lagenaria leucantha. In this study we investigated the changes in activities of antioxidant enzymes, including ascorbate peroxidase (APX), guaiacol peroxidase (GPX), superoxide dismutase (SOD) and catalase (CAT), and ascorbate oxidase (AOX) during fruit development of Lagenaria leucantha, which have been only occasionally studied in fruit development. CPPU increased the activities of SOD, APX and AOX, which rapidly increased after anthesis and reached their maximum values 1 day after anthesis (DAA) and then declined. In unpollinated ovaries, however, the activity of SOD declined slightly after anthesis, and then showed a peak at 8 DAA, and APX and AOX activities dramatically decreased after anthesis. In comparison, the activity of GPX in unpollinated ovaries increased and maintained a high level after anthesis. In CPPU-induced parthenocarpic fruit, however, the activity of GPX declined gradually during fruit development. There was no difference between CAT activities in CPPU-induced parthenocarpic fruits and unpollinated ovaries. These results suggest that the two enzymes of APX and GPX may be under different regulatory mechanisms and APX may be more important in fruit development of Lagenaria leucantha than GPX. CPPU induced parthenocarpic fruit growth and development partly by increasing activities of APX, which was involved in the regulation of H₂O₂ metabolism to allow proper cell-wall reconstitution, and of AOX, which may be involved in cell division.