Stirk W.A., Novák O., Žižková E., Motyka V., Strnad M., van Staden J.
JOURNAL OF PLANT PHYSIOLOGY
169:
696-703,
2012
Klíčová slova:
Cytokinin biosynthesis, Cytokinin oxidase/dehydrogenase, Deactivation, Germination, Thermoinhibition
Abstrakt:
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 (72 h 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 transzeatin-
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.
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Autoři z ÚEB: Václav Motyka,
Ondřej Novák,
Miroslav Strnad,
Eva Žižková
Čeština
English