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a
b
Fig. 10.3.
Effect of the melatonin synthesis inhibitor
p
-chlorophenylalanine on morphogen-
esis in St. John's wort:
a
control explant,
b
explant cultured on medium supplemented with
p
-chlorophenylalanine. Quantification of indoleamines in St. John's wort tissues exposed to
p
-chlorophenylalanine demonstrated the complete inhibition of melatonin synthesis and
elevated concentrations of serotonin
N
NH
2
OH
H
2
CH
C
O
tryptophan
N
N
N
NH2
OH
OH
H
2
C
HO
H2
C
N
H
2
H2
CH
C
H
2
O
Indole-3-acetic acid
O
tryptamine
5-hydroxytryptophan
H
N
O
C
H
3
H
2
C
HO
H
N
C
H2
C
N-acetylserotonin
N
N
H
C
CH
3
O
H
N
H
3
C
H
C
H
2
C
HO
H
2
NH
2
O
melatonin
serotonin
14
C-tryptophan was recovered as
14
C-indoleacetic acid,
14
C-
Fig. 10.4.
Radiolabel from
tryptamine,
14
C-serotonin and
14
C-melatonin. (Adapted from Murch et al. 2000, 2002)
attenuate auxin-generated growth. A high ratio of auxin to cytokinin will
encourage the regeneration of long, thin tissues such as adventitious roots,
whereas a low auxin-to-cytokinin ratio ensures the regeneration of the
thicker, more isodiametric tissue forms that are associated with shoots.
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