Degradation of cytokinins by maize cytokinin dehydrogenase is mediated by free radicals generated by enzymatic oxidation of natural benzoxazinones.
Hydroxamic acid 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-one (DIMBOA) was isolated from maize phloem sap as a compound enhancing the degradation of isopentenyl adenine by maize cytokinin dehydrogenase (CKX), after oxidative conversion by either laccase or peroxidase. Laccase and peroxidase catalyze oxidative cleavage of DIMBOA to 4-nitrosoresorcinol-1-monomethyl ether (coniferron), which serves as a weak electron acceptor of CKX. The oxidation of DIMBOA and coniferron generates transitional free radicals that are used by CKX as effective electron acceptors. The function of free radicals in the CKX-catalyzed reaction was also verified with a stable free radical of 2,2'-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid. Application of exogenous cytokinin to maize seedlings resulted in an enhanced benzoxazinoid content in maize phloem sap. The results indicate a new function for DIMBOA in the metabolism of the cytokinin group of plant hormones.
Frébortová
Jitka
J
Laboratory of Growth Regulators, Faculty of Science, Palacký University/Institute of Experimental Botany of the Academy of Science, Slechtitelů 11, 783 71 Olomouc, Czech Republic. jitka.frebortova@upol.cz
Novák
Ondrej
O
Frébort
Ivo
I
Jorda
Radek
R
D048588:Benzoxazines / Q000737:chemistry / Q000378:metabolism*; D055162:Biocatalysis; D003583:Cytokinins / Q000378:metabolism*; D005609:Free Radicals / Q000378:metabolism; D042845:Laccase / Q000378:metabolism; D015394:Molecular Structure; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000378:metabolism*; D009195:Peroxidase / Q000378:metabolism; D052585:Phloem / Q000201:enzymology; D003313:Zea mays / Q000201:enzymology*
D048588:Benzoxazines; D003583:Cytokinins; D005609:Free Radicals; D010088:Oxidoreductases; D042845:Laccase; D009195:Peroxidase; C019984:cytokinin oxidase