The antioxidant regulation of dopamine
Dopamine is a critical neurotransmitter in animals. It has multiple
phenolic hydroxyl groups and an amino group which make it antioxidative
(Glód, Stanczak, & Wozniak, 2005). Dopamine acts as a signal in the
body to regulate the nervous system and affects the immune function of T
cells in the body (Levite, 2016). The content of dopamine in the body is
linked to serious human disease like Parkinson’s disease, depression.
Individual plants can synthesize dopamine themselves. As early in 1984,
scientists found that the leaves of opium poppy, capsule and peduncle
have the biosynthetic activity of dopamine for early stage (Kamo &
Mahlberg, 1984). Banana pulp and peel contain a large amount of
dopamine. For instance, dopamine levels in peel is between 80-560 mg/100
g. In pulp ranging from 2.5-10 mg/100g (Kanazawa,& Sakakibara, 2000).
The antioxidant activity of dopamine is as even same as the strongest
antioxidants gallocatechin gallate and ascorbic acid. This also proves
that bananas are antioxidant fruits in some degrees (Kanazawa,&
Sakakibara, 2000).
Moreover, dopamine plays a critical role in response to environmental
stimuli including alkali, salt, and drought (Li et al., 2015; Gao et
al., 2020; Jiao et al., 2019; Lan, Jiao, Wang, Sun, & Sun, 2020). These
resistances to environmental stress are likely due to its antioxidant
capacity. Previous results suggested that dopamine could be used as an
exogenous antioxidant to increase the absorption efficiency of nutrients
in begonia, to alleviate the stress response caused by the lack of
nutrients in begonia. Also, in Rosaceae family, recent research
has found that exogenous dopamine could regulate apple’s drought
resistance and salt tolerance by stomatal behavior (Li et al., 2015; Gao
et al., 2020), as well as alleviate the drought-induced damages,
replenishing of K, N, P, S, Cu and other trace elements (Li et al.,
2015; Gao et al., 2020). Research about soybean even demonstrated that
dopamine can affect the activity of antioxidant enzymes and the content
of reactive oxygen species (ROS) in roots, thus enhancing the
antioxidant activity in plants (Gomes et al., 2014).
In addition, dopamine can regulate expression of five SOS pathway genes,
which increases the levels of
H2O2-scavenging enzymes in leaf. The SOD
activity has the same tendency (Li et al., 2015). To some extent, this
is also an indirect way for dopamine to improve the resistance of plants
to adversity. Although previous research and experiments on dopamine
have been discovered and carried out, there are many questions which
remain unanswered about the role of dopamine in plants.