Increase of indoleacetic acid oxidase isoenzymes by gibberellic acid in tobacco callus cultures

Indoleacetic acid (IAA) oxidase in tobacco callus tissues (Nicotiana tabacum L., cultivar White Gold) grown on a medium supplemented with gibberellic acid (GA3), IAA, and kinetin was resolved into seven isoenzymes by polyacrylamide gel electrophoresis. Gibberellic acid promoted the development of three fast-migrating IAA oxidase isoenzymes which were 7- to 10-fold more active than those of the control. Gibberellic acid was effective at 2 × 10−9 M and its activity increased with increasing concentration up to 2 × 10−7 M. Actinomycin D and cycloheximide inhibited the development of these isoenzymes, suggesting a requirement for both RNA and protein synthesis. The GA3-promoted IAA oxidase isoenzymes increased with time and were positively associated with the GA3-induced characteristic type of growth.The expression of the GA3 effect on IAA oxidase isoenzymes and growth was dependent on IAA and kinetin. In the presence of appropriate concentrations of kinetin, the combined effect of GA3 and IAA was more than additive. A possible interpretation of the GA3–IAA interaction is discussed.