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(Last modification: 17.
Feb. 2008)
Psilotum nudum
Es gibt Information über diese Pflanze in Wikipedia:
English: Psilotum
Deutsch:
Gabelblattgewächse
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Zitat aus Wikipedia
(englische Version):
Psilotum (whisk fern) is a genus of fern-like
vascular plants, one of two genera in the family Psilotaceae, order Psilotales,
and division Psilotophyta (the other being Tmesipteris).
They have traditionally been thought not to be
true ferns, but rather, odd "primitive" vascular plants that reproduce solely by
spores, without seeds. In addition, they lack true leaves and roots (like the
Bryophytes), and thus represent the simplest of vascular plants, albeit whose
"simple" features are the apparent reduction from more complex evolutionary
predecessor. Indeed, recent molecular genetic evidence (Qiu
and Palmer 1999) has suggested that they may in fact be ferns (Phylum
Pterophyta) that have lost a number of pteridophytic characteristics, but their
status is still uncertain.
Das
Psilotinin in dieser Pflanze ist
ein interessantes
Naturprodukt, und eine Typ III PKS
ist vermutlich das Schlüsselenzym der Biosynthese:
Mehr...
Psilotum nudum ist offensichtlich in vieler Weise eine ungewöhnliche
Pflanze, Mehrere
Typ III Polyketidsynthasen wurden aus ihr kloniert
(Yamazaki et
al., 2001), und die funktionelle
Analyse mit rekombinanten Enzymen zeigte Proteine mit folgenden Eigenschaften:
Chalconsynthase
(CHS),
Stilbensynthase (STS), und
Valerophenonsynthase (VPS). CHS scheint okay (Flavonoid-Biosynthese), aber die Bedeutung der
STS und VPS Aktivitäten bleibt obskur: So weit bekannt, enthält die Pflanze
keine Naturstoffe, die über solche Reaktionen abgeleitet werden können.
Zitate
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Yamazaki, Y., Suh, D.-Y., Sitthithaworn, W.,
Ishiguro, K., Kobayashi, Y., Shibuya, M., Ebizuka, Y., Sankawa, U., 2001.
Diverse chalcone synthase superfamily enzymes from the most primitive
vascular plant, Psilotum nudum.
Planta 214, 75-84.
Psilotum nudum Griseb is a
pteridophyte and
belongs to the single family (Psilotaceae) of the division, Psilophyta.
Being the only living species of a once populated division, P. nudum
is the most primitive vascular plant. Chalcone synthase (CHS; EC
2.3.1.74) superfamily enzymes are responsible for biosyntheses of
diverse secondary metabolites, including flavonoids and stilbenes. Using
a reverse transcription-polymerase chain reaction strategy, four
CHS-superfamily enzymes (PnJ, PnI, PnL and PnP) were cloned from P.
nudum, and heterologously expressed in Escherichia coli.
These four enzymes of 396-406 amino acids showed sequence identity of
>50% among themselves and to other higher-plant CHS-superfamily enzymes.
PnJ and PnP preferred p-coumaroyl-CoA and isovaleryl-CoA,
respectively, as starter CoA and catalyzed CHS-type ring formation,
indicating that they are CHS and phloriso valerophenone synthase,
respectively. On the other hand, PnI and PnL preferred cinnamoyl-CoA as
starter CoA and catalyzed stilbene synthase-type cyclization and thus
were determined to be pinosylvin synthases (EC 2.3.1.146). In addition,
PnE, which uniquely contains a glutamine in place of otherwise strictly
conserved histidine, had no apparent in vitro catalytic
activity. Phylogenetic analysis indicated that these P. nudum
clones form a separate cluster together with Equisetum arvense
CHS. This cluster of pteridophytes is located next to the cluster formed
by pine (gymnosperm) enzymes, in agreement with their evolutionary
relationships. Psilotum nudum represents a plant with the most
diverse CHS-superfamily enzymes and this ability to diverge may have
provided a survival edge during evolution.
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Qiu, Y.-L. and Palmer, J.D. (1999) Phylogeny of early land plants: insights from genes and genomes. Trends in
Plant Science 4, 26-30.
A large
body of evidence from molecular systematic studies has confirmed the
charophytic origin of land plants, and clarified monophyly of many
lineages in charophytes and land plants. These studies have also
identified liverworts as the earliest land plants, and the lycopods as
the extant sister group to all other vascular plants, Two traditionally
defined groups - bryophytes and pteridophytes - are now recognized as
early grades of land plant evolution. However, several problems that
complicate the use of sequence data in reconstructing plant phylogeny
have become apparent; reconstruction of an accurate land plant phylogeny
will require analysis of sequences of multiple genes and genomic
structural characters of all three genomes.
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