1. Laboratoř růstových regulátorů, PřF UP Olomouc a ÚEB AV ČR Laboratory of Growth Regulators, Faculty of Science, Palacký University in Olomouc and Institute of Experimental Botany ASCR, Czech Republic Xanthine dehydrogenase and cytokinin metabolism Jitka Frébortová Cytokinin meeting, Olomouc, September 8, 2011

2. Xanthine oxidoreductase HypoxanthineXanthineUric acid XO/XDH Werner and Witte (2011) Trends Plant Sci. 16, 381-387.

3. Interaction of cytokinins with bovine milk xanthine oxidase max = 269 nm max = 275 nm max = 306 nm (pH 7, iP, tZ) Chen et al. (1975) Biochemistry 14, 3088-3093.  Cytokinins described also as inhibitors of bovine milk XO  Conversion of cytokinins to 8-hydroxyderivatives confirmed also in rhizobacterium Serratia protemaculans XO Sheu et al. (1996) Anticancer Res. 16, 3571-3576. Sheu et al. (1997) Anticancer Res. 17, 1043-1050. Taylor et al. (2006) Phytochemistry 67, 1887-1894.

4. Plant xanthine dehydrogenase and cytokinin metabolism Is AtXDH1 converting cytokinins? Are cytokinins substrates or inhibitors of XORs? Are the relevant metabolites present in plants? Biological activity of 8-OH and 2,8-OH cytokinins

5. Cytokinin free bases are substrates of AtXDH1 and milk XO Kinetic constants for the oxidation of cytokinins and xanthine by AtXDH1 and milk XO Chromatographic analysis of t-zeatin oxidation by AtXDH1 275 nm 310 nm N9-ribosides, ribotides and glucosides are not oxidized

6. N9-substituted cytokinins do not interact with AtXDH1 and milk XO Effect of N9–substituted cytokinins on xanthine oxidation by AtXDH1 and milk XO a Data taken from Sauer et al. (2002) Plant Physiol. Biochem. 40, 393-400.

7. Cytokinins may interfere with normal purine metabolism Inhibition of uric acid formation by AtXDH1 using cytokinins as inhibitors

8. Plant xanthine dehydrogenase and cytokinin metabolism Is AtXDH1 converting cytokinins? Are cytokinins substrates or inhibitors of XORs? Are the relevant metabolites present in plants? Is there any physiological function for interaction of cytokinins with XDH? Biological activity of 8-OH and 2,8-OH cytokinins

9. Acknowledgements Laboratory of Growth Regulators Lukáš Spíchal Palacký University/ Institute of Experimental Botany Technische Universität Braunschweig Florian Bittner Palacký University Department of Biochemistry Petr Tarkowski Pavel Jaworek Institut für Pflanzenbiologie