title: Comparison of endogenous cytokinins and cytokinin oxidase/dehydrogenase activity in germinating and thermoinhibited Tagetes minuta achenes.
abstract: Tagetes minuta L. achenes are thermoinhibited at temperatures above 35°C and have accelerated radicle emergence (germination) when subsequently transferred to an optimal temperature (25°C). Endogenous cytokinins and cytokinin oxidase/dehydrogenase (CKX) activity were compared in normally germinating (25°C) and thermoinhibited (72h at 36°C then transferred to 25°C) T. minuta achenes. Following imbibition, endogenous cytokinin concentrations changed in normally germinating T. minuta achenes, with a gradual decrease in dihydrozeatin-type (DHZ) cytokinins, a large increase in cis-zeatin-type (cZ) cytokinins, a smaller increase in N⁶-(2-isopentenyl)adenine-type (iP) cytokinins and a peak of trans-zeatin-type (tZ) cytokinins at 13 h. These changes in the isoprenoid cytokinin profile were similar in the thermoinhibited achenes imbibed at 36°C, despite the thermal block preventing radicle emergence. The exception was the iP-type cytokinins that only increased when transferred to 25°C. Profiles of the physiologically active free bases showed an increase in tZ prior to radical emergence in both normally germinating (13 h) and thermoinhibited achenes. A large transient peak in aromatic cytokinins [N⁶-benzyladenine-type (BA)] occurred during early seedling establishment in normally germinating achenes (40 h) while a transient maximum in BA-type cytokinins was found prior to radicle emergence in the thermoinhibited achenes (24 h). The CKX activity was enhanced in normally germinating achenes as the cytokinin concentration increased following imbibition. In thermoinhibited achenes, an elevated temperature negatively affected the CKX activity that only increased when the achenes were transferred to 25°C, corresponding to an increase in iP-type cytokinins. However, the favored cytokinin deactivation pathway in T. minuta appears to be 9-glycosylation, as 9-glucosides accounted for over 50% of the total cytokinin pool in both normal and thermoinhibited achenes.
authors.affiliation: Research Centre for Plant Growth and Development, School of Life Sciences, University of KwaZulu-Natal Pietermaritzburg, P/Bag X01, Scottsville 3209, South Africa. stirk@ukzn.ac.za
authors.forename: Wendy A
authors.initials: WA
authors.lastname: Stirk
authors.forename: Ondřej
authors.initials: O
authors.lastname: Novák
authors.forename: Eva
authors.initials: E
authors.lastname: Zižková
authors.forename: Vaclav
authors.initials: V
authors.lastname: Motyka
authors.forename: Miroslav
authors.initials: M
authors.lastname: Strnad
authors.forename: Johannes
authors.initials: J
authors.lastname: van Staden
mesh_terms: D003583:Cytokinins / Q000378:metabolism*; D018525:Germination; D006358:Hot Temperature / Q000009:adverse effects; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000378:metabolism*; D010937:Plant Growth Regulators / Q000378:metabolism*; D018517:Plant Roots / Q000737:chemistry / Q000201:enzymology / Q000502:physiology; D036226:Seedlings / Q000737:chemistry / Q000201:enzymology / Q000502:physiology; D031686:Tagetes / Q000737:chemistry / Q000201:enzymology* / Q000502:physiology
chemical_list: D003583:Cytokinins; D010937:Plant Growth Regulators; D010088:Oxidoreductases; C019984:cytokinin oxidase