Tissue Localization of Cytokinin Dehydrogenase in Maize: Possible Involvement of Quinone Species Generated from Plant Phenolics by Other Enzymatic Systems in the Catalytic Reaction

Abstract

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.

An Intracellular Laccase is Responsible for the Epicatechin Mediated Anthocyanin Degradation in Litchi Fruit Pericarp

“…In plants, laccases participate in lignin biosynthesis, carrying out the oxidative polymerization of monolignols (Sterjiades et al, 1992(Sterjiades et al, , 1993Ranocha et al, 1999;Schuetz et al, 2014). These enzymes were also found to be involved in additional physiological processes, such as cytokinin homeostasis (Galuszka et al, 2005), resistance to phenolic pollutants (Wang et al, 2004), flavonoid polymerization in seed coats (Pourcel et al, 2005), and iron metabolism (Hoopes and Dean, 2004). To our knowledge, this is the first report of a plant laccase involved in anthocyanin degradation.…”

Cytokinins - recent news and views of evolutionally old molecules

“…The finding that CKX can effectively use a variety of artificial electron acceptors under anaerobic conditions (Galuszka et al 2001;Frébort et al 2002) led to the reclassification of the enzyme as CK dehydrogenase (EC 1.5.99.12). Biochemical studies on the ZmCKX1 reaction mechanism suggested the preference of quinones as electron acceptors (Frébortová et al 2004) generated from plant phenolics by peroxidise, and either tyrosine, laccase or catechol oxidase (Galuszka et al 2005). Recently, free radicals generated by enzymatic oxidation of natural benzoxazinones were shown to be the most efficient electron acceptors of CKX .…”

Current potential and limitations of immunolabeling in cereal grain research

“…Maize (Galuszka et al, 2005) Aleurone Arabinoxylan Wheat (Beaugrand et al, 2005;Beaugrand, Reis, et al, 2004;Guillon et al, 2004;Lovegrove et al, 2013;Philippe et al, 2006;Philippe et al, 2007;Robert et al, 2011;Suliman et al, 2013); oat, rye ; barley Xylan Wheat (Lovegrove et al, 2013) Xyloglucan Barley (13),(14)--D-glucan Wheat Philippe et al, 2006;Robert et al, 2011;; barley Callose Wheat (Philippe et al, 2006); barley (Wilson et al, 2012) Mannan Barley Ferulic acid Wheat (Philippe et al, 2007;Robert et al, 2011) p-Coumaric acid Wheat Tranquet et al, 2009) Xylanase Wheat (Beaugrand, Cronier, et al, 2004;Beaugrand et al, 2005;Beaugrand, Reis, et al, 2004) Glycosyltransferase Wheat (Suliman et al, 2013) Oxalate oxidase Wheat ( Wheat (Van Herpen et al, 2008;Wiley et al, 2007) Oleosin / Caleosin Rice (Chen et al, 2012); oat (Heneen et al, 2008) Puroindolines Wheat (Capparelli et al, 2005) Transfer cells Arabinoxylan Wheat Lovegrove et al, 2013;Robert et al, 2011); oat, rye, barley …”

“…The flavoprotein cytokinin dehydrogenase controls the degradation of cytokinins, which are plant hormones that contribute to the regulation of numerous developmental processes. Histochemical localization of cytokinin dehydrogenase by activity staining and immunochemistry using optical and confocal microscopy have shown that cytokinin dehydrogenase is most abundant in the aleurone layer of maize kernels and in phloem cells of seedling shoots (Galuszka, et al, 2005).…”

“…2a), in the light microscope (Van Herpen, et al, 2008) (Fig. 2b) or by confocal laser scanning microscopy (CLSM) (Galuszka, et al, 2005). Silver enhancement is also necessary when the gold particles bound to the secondary antibody are too small to be detected even by TEM (Lesage, et al, 2011).…”