Serotonin has a similar effect like auxin inhibitor
Serotonin (5-hydroxytryptamine, SER) is a well-known
indoleamine neurotransmitter that regulates mood, sleep and anxiety in
mammals (Murch, & Saxena, 2002). It was initially identified as a
vasoconstrictor substance in blood serum, named as 5-hydroxytryptamine
(5-HT). It appears to play a role to cope with neuropsychiatric
disorders in neuropharmacology (Weele, Anderson, & Cook, 2000). Plants
can synthesize SER themselves, which is abundant in companion and xylem
cells. SER may become a central role in maintaining the cellular
integrity for facilitating efficient nutrient recycling from senescing
leaves to sink tissues (Ramakrishna, Giridhar, & Ravishankar, 2011).
Plants are capable of taking up exogenous serotonin, which coincided
with stimulated root development as a natural auxin inhibitor
(Pelagio-Flores et al., 2011). It is essential for signaling and stress
mitigating molecules in plant growth (Erland, Shukla, Singh, Murch, &
Saxena, 2018; Erland, Murch, Reiter, & Saxena, 2015). There has been
found a crosstalk between 5-HT (0.01-0.03 mM) and phytohormones such as
SA, ABA, and zeatin (Erland, Shukla, Singh, Murch, & Saxena, 2018).
Moreover, previous research showed that serotonin could regulate growth
process including root and shoot organogenesis (Erland, Shukla, Singh,
Murch, & Saxena, 2018), light mediated responses (Leclercq et al.,
2002; Erland, Turi, & Saxena, 2016), maintenance of plant tissues
(Erland, Turi, & Saxena, 2016), and delay of senescence (Erland, Murch,
Reiter, & Saxena, 2015).
In addition, SER acts as an antioxidant to protect plants (Kang, Kim,
Park, & Back, 2009; Kang et al., 2007) and responses to biotic and
abiotic stresses such as cold and salt stress (Mukherjee, David, Yadav,
Baluška & Bhatla, 2014). Previous research demonstrated a high level of
serotonin accumulated in senescing leaves and roots as the plants aged.
Also, pathogenic infection can lead to accumulated serotonin against
pathogens by strengthening of the cell wall (Ramakrishna, Giridhar, &
Ravishankar, 2011; Kang, Kim, Park, & Back, 2009). Absence of serotonin
is suggestive of a relatively lesser sensitivity of plant tissues to
environmental stress.
Furthermore, there have been interactions between serotonin and other
small-molecular regulators, such as melatonin. A balance of the
endogenous serotonin and melatonin may modulate plant morphogenesis in
vitro (Murch, & Saxena, 2001). Thus, serotonin is implicated in several
physiological roles in plants such as flowering, morphogenesis, and
adaptation to environmental changes. However, these physiological
functions provide new avenues to consider health effects of plant SER in
human.