Formation of Ascorbate Oxidase in Cultured Pumpkin Cells

Abstract

Ascorbate oxidase activity rapidly increased during callus formation from pumpkin fruit tissue. The activity reached a maximum at 5 days after transfer and then declined. In callus which had been subcultured at about 4-week intervals for more than one year, the activity also increased after transfer to fresh medium and reached a maximum in the early logarithmic phase of growth. Light had little effect on the appearance of ascorbate oxidase activity in pumpkin callus. In the callus grown in the presence of 10μM CuSO4, the activity was about 10 times that in the presence of 0.1 μM CuSO4, suggesting that the formaton of ascorbate oxidase in pumpkin callus is stimulated by copper, a prosthetic metal of the enzyme. From 45 to 75% of the total ascorbate oxidase activity in pumpkin cell suspension cultures was found in the medium. Ascorbate oxidase activity in the medium, as well as that in the cells, increased soon after transfer to fresh medium, and reached a maximum at about 5 days.