Tissue localization of cytokinin dehydrogenase in maize [Zea mays]: Possible involvement of quinone species generated from plant phenolics by other enzymatic systems in the catalytic reaction

• Published in: Plant and cell physiology Vol. 46; no. 5; pp. 716 - 728
• Main Authors: Galuszka, P.(Palacky Univ., Olomouc (Czech)), Frebortova, J, Luhova, L, Bilyeu, K.D, English, J.T, Frebort, I
• Format: Journal Article
• Language: English
• Published: Japan Oxford University Press 01-05-2005; Oxford Publishing Limited (England)
• Subjects: 3-dimethoxy-5-methyl-1; 4-benzoquinone; 6-dichlorophenol indophenol; ACTIVIDAD CATALITICA; ACTIVITE CATALYTIQUE; biochemical pathways; biosynthesis; bovine serum albumin; BSA; Catalysis; CATALYTIC ACTIVITY; CITOQUININAS; CKX; COMPOSE PHENOLIQUE; COMPUESTOS FENOLICOS; corn; Cytokinin; Cytokinin dehydrogenase; cytokinin dehydrogenase (EC 1.5.99.12); CYTOKININE; CYTOKININS; Cytokinins - metabolism; DCPIP; dimethylsulfoxide; DMSO; encoded by the gene Zmckx1 (GenBank AF044603); Energy Metabolism - physiology; enzyme activity; EST; expressed sequence tag; flavoproteins; gene expression regulation; grain crops; Immunohistochemistry; iPR; Laccase; Laccase - metabolism; Maize; Microscopy, Confocal; Molecular Sequence Data; N6-(2-isopentenyl)adenine; N6-(2-isopentenyl)adenosine; OXIDOREDUCTASES; Oxidoreductases - metabolism; OXIDORREDUCTASAS; OXYDOREDUCTASE; PBS; PHENOLIC COMPOUNDS; Phenols - metabolism; phosphate-buffered saline; plant biochemistry; plant exudates; Plant phenolics; plant physiology; plant proteins; Plant Proteins - metabolism; Plant Shoots - enzymology; QUINONAS; QUINONE; QUINONES; Quinones - metabolism; reverse transcription–polymerase chain reaction; RT–PCR; seeds; Seeds - enzymology; the CKX enzyme from maize; tissue distribution; ZEA MAYS; Zea mays - enzymology; ZmCKX1
• ISSN: 0032-0781; 1471-9053
• DOI: 10.1093/pcp/pci074

The degradation of cytokinins in plants is controlled by the flavoprotein cytokinin dehydrogenase (EC 1.5.99.12). Cytokinin dehydrogenase from maize showed the ability to use oxidation products of guaiacol, 4-methylcatechol, acetosyringone and several other compounds as electron acceptors. These results led us to explore the cability for indirect production of suitable electron acceptors by different quinone-generating enzymes. The results reported here revealed that the electron acceptors may be generated in vivo from plant phenolics by other enzymatic systems such as peroxidase and tyrosinase/laccase/catechol oxidase. Histochemical localization of cytokinin dehydrogenase by activity staining and immunochemistry using optical and confocal microscopy showed that cytokinin dehydrogenase is most abundant in the aleurone layer of maize kernels and in phloem cells of the seedling shoots. Cytokinin dehydrogenase was confirmed to be present in the apoplast of cells. Co-staining of enzyme activity for laccase, an enzyme poised to function on the cell wall in the apoplast, in those tissues suggests a possible cooperation of the enzymes in cytokinin degradation. Additionally, the presence of precursors for electron acceptors of cytokinin dehydrogenase was detected in phloem exudates collected from maize seedlings, suggestive of an enzymatic capacity to control cytokinin flux through the vasculature. A putative metabolic connection between cytokinin degradation and conversion of plant phenolics by oxidases was proposed.