Regulation of cytokinin oxidase activity in callus tissues of Phaseolus vulgaris L. cv Great Northern

• Published in: Plant physiology (Bethesda) 1986-02, Vol.80 (2), p.493-499
• Main Authors: Chatfield, J.M, Armstrong, D.J
• Format: Article
• Language: English
• Subjects: ACTIVIDAD ENZIMATICA; ACTIVITE ENZYMATIQUE; Agronomy. Soil science and plant productions; Biological and medical sciences; Callus; CITOCININAS; CYTOKININE; CYTOKININS; Economic plant physiology; Enzyme activity; Enzymes; ENZYMIC ACTIVITY; Ethanol; Fundamental and applied biological sciences. Psychology; Gene expression regulation; Growth and development; Growth regulators; Imidazoles; Isomers; Oxidases; OXIDOREDUCTASES; OXIDORREDUCTASAS; OXYDOREDUCTASE; PHASEOLUS VULGARIS; Plant physiology and development; Plant tissues; Tissue cultures, protoplasts
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.80.2.493

The regulation of cytokinin oxidase activity in callus tissues of Phaseolus vulgaris L. cv Great Northern has been examined using an assay based on the oxidation of $\text{N}^{6}$-(Δ 2-isopentenyl)adenine-8-14C ($\text{i}^{6}\text{Ade}$-8-14C) to adenine. Solutions of exogenous cytokinins applied directly to the surface of the callus tissues induced relatively rapid increases in cytokinin oxidase activity. The increase in activity was detectable after 1 hour and continued for about 8 hours, reaching values two- to three-fold higher than the controls. The cytokinin-induced increase in cytokinin oxidase activity was inhibited in tissues pretreated with cordycepin or cycloheximide, suggesting that RNA and protein synthesis may be required for the response. Rifampicin and chloramphenicol, at concentrations that inhibited the growth of Great Northern callus tissues, were ineffective in inhibiting the increase in activity. All cytokinin-active compounds tested, including both substrates and nonsubstrates of cytokinin oxidase, were effective in inducing elevated levels of the enzyme in Great Northern callus tissue. The cytokinin-active urea derivative, Thidiazuron, was as effective as any adenine derivative in inducing this response. The addition of Thidiazuron to the reaction volumes used to assay cytokinin oxidase activity resulted in a marked inhibition of the degradation of the labeled $\text{i}^{6}\text{Ade}$-8-14C substrate. On the basis of this result, it is possible that Thidiazuron may serve as a substrate for cytokinin oxidase, but other mechanisms of inhibition have not yet been excluded.