Immunochemical evidence for phytochrome regulation of the specific activity of ascorbate oxidase in mustard seedlings.

A monospecific antiserum to a Cucurbita ascorbate oxidase was shown to cross-react with the mustard enzyme. Purified antiserum was used in rocket immunoelectrophoresis plates to measure the amount of ascorbate oxidase protein in mustard cotyledon and hypocotyl extracts. On transfer from darkness to far-red light and activity of the enzyme in expanding cotyledons increased but the amount of enzyme protein remained the same. Unimbibed mustard seeds were shown to contain the same amount of antigenic protein as expanding cotyledons although in the seeds the enzyme was inactive. In hypocotyls continuous far-red light treatment also led to an increase in ascorbate oxidase activity; in this case there was also an increase in enzyme protein although this was relatively small. The results are discussed in relation to the mechanism by which phytochrome may control the activity of this enzyme.