Agriculture Reference
In-Depth Information
Phenylalanine
Shikimic acid
Shikimate pathway
PAL
C4H
SDH
Stilbenes
Dehydroshikimate
4CL
R OM T
Pterostilbene
SDH
ST S
4-Coumaroyl-CoA
Resveratrol
Glc T
Gallic acid
Piceid
CHS
GlcT (e.f.e.)
L acca se?
Oligomers
CHI
β
-Glucogallin
Peroxidase?
AT?
F3H
Gallotannin
(F3 H/F3 5 H)
Dihydroflavonol
DFR
F LS
GTs
MT
Flavonols
Laccase
Ellagitannin
LAR
Leucoanthocyanidin
(+)-Catechin
Hydrolysable
tannins
AT?
PA s
ANS/LDOX
Polymerization?
ANR
Anthocyanidin
(-)-Epicatechin
Galloylated
PA s
UFGT
Flavan-3-ols
Glucosylated anthocyanin
GTs
MT
AT
Decorated anthocyanin
Anthocyanins
Fig. 9.3. Schematic representation of the biosynthesis pathways of phenolic compounds. Enzyme names
are shown in bold. PAL, phenylalanine ammonia lyase; C4H, cinnamate 4-hydroxylase; 4CL, 4-coumarate
CoA ligase; CHS, chalcone synthase; CHI, chalcone isomerase; F3H, fl avonone 3-hydroxylase; F3 c H,
fl avonoid 3 c -hydroxylase; F3 c 5 c H, fl avonoid 3 c ,5 c -hydroxylase; FLS, fl avonol synthase; DFR, dihydrofl avonol
4-reductase; ANS, anthocyanidin synthase; LDOX, leucoanthocyanidin dioxygenase; LAR,
leucoanthocyanidin reductase; ANR, anthocyanidin reductase; UFGT, UDP-glucose:fl avonoid 3- O -glucosyl
transferase; AT, acyltransferase; MT, methyltransferase; GTs, glycosyltransferase; ROMT, resveratrol- O -
methyltransferase; GlcT, glucosyltransferase; e.f.e., ester-forming enzyme; SDH, shikimate dehydrogenase.
substitutions. The dihydrofl avonol is then
oxidized to fl avonol via fl avonol synthase
(FLS) or reduced by dihydrofl avonol
reductase to leucoanthocyanidin and then
to anthocyanidin, by leucoanthocyanidin
dioxygenase (also called anthocyanidin
synthase). Further reactions such as
glycosylation, methylation and acylation
lead to fl avonol derivatives and antho-
cyanins. In particular 3- O -glycosylation of
the anthocyanidin (e.g. glucosylation,
catalysed by UDP-glucose:fl avonoid 3- O -
glucosyltransferase (UFGT)), stabilizing
anthocyanidins, is the fi rst step in
anthocyanin biosynthesis (Harborne and
Williams, 2000). Glycosylation is specifi c
both for the sugar and for the substitution
position. The sequence of methylation,
glycosylations and acylations is variable. In
contrast to the well-conserved main
pathway, these steps are family, species
and even variety dependent, and are
believed to provide fl avonoids with unique
properties.
Concerning the PA pathway, antho-
cyanidin reductase (ANR), fi rst described
in Arabidopsis , catalyses the formation of
epicatechin from anthocyanidin (Xie et al. ,
2003), whereas leucoanthocyanidin re-
ductase, fi rst identifi ed in Lotus , catalyses
 
 
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