Yevdakova NA, Motyka V, Malbeck J, Trávníčková A, Novák O, Strnad M, von Schwartzenberg K
JOURNAL OF PLANT GROWTH REGULATION
27:
271-281,
2008
Klíčová slova:
Physcomitrella, ove mutant, cytokinin biosynthesis, tRNA-isopentenyltransferase, tRNA-bound cytokinins
Abstrakt:
To study cytokinin biosynthesis, we characterized
a temperature-sensitive cytokinin-overproducing
mutant, oveST25, of the moss Physcomitrella patens with
respect to changes in cytokinin content during thermal
induction in comparison to wild type. Our findings, based
on combined liquid chromatography-mass spectrometry
(LC-MS) analyses, show that thermoinduction caused a
strong increase of extracellular N6-(D2-isopentenyl)adenine
(iP), N6-(D2-isopentenyl)adenosine (iPR), cis-zeatin (cZ),
cis-zeatin riboside (cZR) and its O-glucoside cZROG in
oveST25. In contrast, no significant changes were measured
in the wild type. To investigate the relevance of
tRNA for cytokinin production in Physcomitrella, we
determined cytokinins in tissue and culture medium as well
as in tRNA hydrolysates. The analysis of cytokinins from
whole-culture extracts of wild type revealed 56% of
iP-type, 32% of cZ-type, and 11% of trans-zeatin (tZ)-type
forms. In tRNA, 90% of cytokinins were represented by
cZ-type and 8% by iP-type forms; tZ-type cytokinins were
found only in trace amounts. The finding that the major
free cytokinins are, albeit with altered proportions, also
major forms in tRNA is compatible with the hypothesis of
a strong tRNA-mediated biogenesis of cytokinins in this
plant. Our RT-PCR-based studies on the expression of the
tRNA-IPT gene, PpIPT1, revealed enhanced transcription
levels in the cytokinin-overproducing oveST25 mutant at
the inducing temperature of 25C, but not at noninducing
conditions (15C). A wild-type transgenic line with cytokinin
deficiency due to heterologous cytokinin oxidase/
dehydrogenase overexpression (AtCKX2) also exhibited
enhanced PpIPT1 expression levels, indicating that cytokinin
deficiency might upregulate tRNA-mediated
cytokinin biosynthesis. The evidence that the tRNA-mediated
pathway might be mainly responsible for biosynthesis
of isoprenoid cytokinins in Physcomitrella is strongly
supported by the recent release of the Physcomitrella
genomic sequence where only tRNA-IPTs but no adenylate-
IPTs are present.
Fulltext: kontaktujte autory z ÚEB
Autoři z ÚEB: Jiří Malbeck,
Václav Motyka,
Ondřej Novák,
Miroslav Strnad,
Alena Trávníčková
Čeština
English