References

10 Neurotransmitters, Neuroregulators and Neurotoxins in Plants 141
a b
Fig.10.3. Effect of the melatonin synthesis inhibitor p-chlorophenylalanine on morphogenesis
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
H
N
C
H 2
C
OH
Indole-3-acetic acid
O
H 3C
O
H
N
NH 2
C CH C
H2 tryptophan
H
N
H
N
C
H 2
melatonin
C
H 2
tryptamine
H 2
C
H
N
C
O
CH 3
OH
O
H 2
C NH 2
HO
HO
HO
H
N
NH 2
C CH C
H2 5-hydroxytryptophan
H
N
C
H 2
H 2
C
H
N
N-acetylserotonin
H
N
C
H 2
serotonin
C
OH
O
O
H 2
C NH 2
Fig.10.4. Radiolabel from 14 C-tryptophan was recovered as 14 C-indoleacetic acid, 14 Ctryptamine,
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.
CH 3