Root and leaf specific ACC oxidase activity in corn and sunflower seedlings

Ethylene production by roots and leaves of sunflower and corn with exposure to varying CO, concentrations was studied. CO2 strongly promoted ethylene production by the leaves of both species, but did not promote ethylene production by roots; in vivo analysis of ACC oxidase activity with and without 5% CO2 showed that CO2 promoted activity in leaves while it had little or no effect on ACC oxidase activity in roots. In vitro analysis of ACC oxidase extracted from roots and leaves of the two species revealed that substrate K(m)s, K-CO2 and response to pH were different for enzyme extracted from the two organs. These differences were consistent between the two species, indicating that this may be a general phenomenon. ACC and ascorbate levels measured in the different organs corresponded with the differences observed in the K-ACC and K-ascorbate. The data suggest that ACC oxidase may exist as organ specific isoenzymes which are tailored to the environmental and physiological status of each organ. (C) 1997 Elsevier Science Ltd. All rights reserved.