Melatonin regulates plant stress resistance and immune system
Melatonin (N-acetyl-5-methoxytryptamine) is a kind of hydrophilic and
lipophilic hormone with various regulation of circadian rhythm (Behram,
Aydin, & Gorgisen, 2017), which regulates sleep and circadian functions
in animals (Radogna, Diederich, & Ghibelli, 2010). Melatonin also plays
crucial role as an anti-oxidant, anti-inflammatory, immune-modulatory
effects on human tissues (Nayak et al., 2019).
Notably, endogenous melatonin has also been found in plants as an
effective antioxidant and free radical scavenger (Kang, Lee, Park,
Byeon, & Back, 2013; Murch, Alan, Cao, & Saxena, 2009). Studies have
shown that melatonin can modify the structure of plant hormone carriers
and the development pattern of stems and leaves (Arnao, &
Hernández-Ruiz, 2015). Physiological processes including seed and root
growth (Arnao, & Hernández-Ruiz, 2014; Sarropoulou, Dimassi-Theriou,
Therios, & Koukourikou-Petridou,2012; Byeon, & Back, 2014; Park, Le,
Byeon, Kim, & Back, 2013), flowering (Huang et al., 2017; Kolář,
Johnson, & Macháčková, 2003), photosynthetic system (Zhao et al., 2015;
Arnao, & Hernández‐Ruiz, 2009) and reproductive system could be
regulated by melatonin. As antioxidant in plant, previous research has
found that melatonin decreased significantly free radicals in barley
tissues, which protect chlorophyll from aging (Arnao & Hernández‐Ruiz,
2009; Wang et al., 2013). Furthermore, melatonin can keep leaf from
senescence by regulating the activity of antioxidant enzymes (Zhao et
al., 2017). It improves photosynthesis, CO2 uptake and
biomass. Accordingly, it can be used to protect plants exposed to strong
light from burns and enhance the resistance to strong light (Zhao et
al., 2017). Additionally, exogenous melatonin can influence the early
stages of flower induction and development.
In addition, melatonin can resist biotic and abiotic stress (Fu et al.,
2017; Lee, Byeon, & Back, 2014; Weeda et al., 2014) and regulate plant
physiological ion balance against stress (Wei et al., 2015; Zeng et al.,
2018) Plant damage caused by environmental stress including cold,
drought, UV irradiation, and chemical stressors (Arnao, &
Hernández-Ruiz, 2015; Weeda et al., 2014; Mandal, Suren, Ward,
Boroujerdi, & Kousik, 2018) can be mitigated by melatonin. Under
bacterial pathogen infection, increased endogenous can induce the
transcription of stress-related genes, such as CBF/DREB1s inArabidopsis thaliana (Shi, Qian, Tan, Reiter, & He, 2015).
Moreover, the rise of soluble sugar caused by melatonin is also
responsible for its biological resistance (Yang et al., 2010; Qian, Tan,
Reiter, & Shi, 2015). The overexpression of melatonin andCBF/DREB1s results in the increase of transcription levels of
multiple stress response genes, and the accumulation of soluble sugars,
such as sucrose (Qian, Tan, Reiter, & Shi, 2015). It has great
potential for melatonin to regulate plant against biotic and abiotic
stress. Ideas about melatonin as new plant growth regulator could
provide insights into the solution for food security issues (Lee, Byeon,
& Back, 2014).
Furthermore, melatonin can interact with the endogenous plant hormones.
Previous research showed that melatonin can stimulate plant to produce
ABA and ethylene, which lead to berry ripening (Fu et al., 2017; Qian,
Tan, Reiter, & Shi, 2015). In addition, it could regulate nitrogen
oxides and salicylic acid levels by activating plant defense-related
genes to relieve the biological pressure (Yin et al., 2013; Li et al.,
2018). The effects of melatonin on plants can be used as a plant
regulator with potential applications in crop improvement and protection
(Arnao, & Hernández-Ruiz, 2015).