Stirk W.A., Václavíková K., Novák O., Gajdošová S., Kotland O., Motyka V., Strnad M., van Staden J.
JOURNAL OF PLANT GROWTH REGULATION
31:
392-405,
2012
Keywords:
cis-Zeatin, cytokinin oxidase/dehydrogenase, dihydrozeatin, lucerne, maize, oats, tRNA degradation
Abstract:
The aims of this study were to monitor
endogenous cytokinin levels during germination and early
seedling establishment in oats, maize, and lucerne to
determine which cytokinin forms are involved in these
processes; to quantify the transfer ribonucleic acid (tRNA)-bound cytokinins; and to measure cytokinin oxidase/dehydrogenase (CKX) activity. Cytokinins were identified
using UPLC-MS/MS. The predominant free cytokinins
present in the dry seeds were dihydrozeatin-type (DHZ) in
lucerne and maize and cZ-type (cis-zeatin) in oats. Upon
imbibition, there was a large increase in cZ-type cytokinins
in lucerne although the cZ-type cytokinins remained at
high levels in oats. In maize, the high concentrations of
DHZ-type cytokinins decreased prior to radicle emergence. Four tRNA-bound cytokinins [cis-zeatin riboside
(cZR) > N6-(2-isopentenyl)adenosine (iPR), dihydrozeatin
riboside (DHZR), trans-zeatin riboside (tZR)] were detected in low concentrations in all three species investigated.
CKX activity was measured using an in vitro radioisotope
assay. The order of substrate preference was N6-(2-isopentenyl)adenine (iP) > trans-zeatin (tZ) > cZ in all three
species, with activity fluctuating as germination proceeded.
There was a negative correlation between CKX activity
and iP concentrations and a positive correlation between
CKX activity and O-glucoside levels. As O-glucosides are
less resistant to CKX degradation, they may provide a
readily available source of cytokinins that can be converted
to physiologically active cytokinins required during germination. Aromatic cytokinins made a very small contribution to the total cytokinin pool and increased only
slightly during seedling establishment, suggesting that they do not play a major role in germination.
Fulltext: contact IEB authors
IEB authors: Václav Motyka,
Ondřej Novák,
Miroslav Strnad
Čeština
English