Melatonin and its potential biological functions in the fruits of sweet cherry

Abstract

Melatonin is a well-known molecule which possesses many beneficial effects on human health. Many agriculture products provide natural melatonin in the diet. Cherry is one such fruit as they are rich in melatonin. In order to understand the biological roles of melatonin in cherry fruit, melatonin synthesis and its changes over 24 hr period were systematically monitored both during their development and in the ripe cherries in two cultivars, 'Hongdeng' (Prunus avium L. cv. Hongdeng) and 'Rainier' (Prunus avium L. cv. Rainier). It was found that both darkness and oxidative stress induced melatonin synthesis, which led to dual melatonin synthetic peaks during a 24 hr period. The high levels of malondialdehyde induced by high temperature and high intensity light exposure were directly related to up-regulated melatonin production. A primary function of melatonin in cherry fruits is speculated to be as an antioxidant to protect the cherry from the oxidative stress. Importantly, plant tryptophan decaboxylase gene (PaTDC) was identified in cherry fruits. Our data shows that PaTDC expression is positively related to the melatonin production in the cherry. This provides additional information to suggest that tryptophan decaboxylase is a rate-limiting enzyme of melatonin synthesis in plants.

The levels of melatonin and its metabolites in conditioned corn (Zea mays L.) and cucumber (Cucumis sativus L.) seeds during storage

“…(Tal et al 2011) and also in higher plants: Chenopodium rubrum L. (Kolar et al 1995(Kolar et al , 1997Wolf et al 2001), Eichhornia crassipes (hyacinth) (Tan et al 2007), Vitis vinifera (Boccalandro et al 2011), and Prunus sp. (Zhao et al 2013), pointing to its possible role as a regulator of light/dark-mediated rhythms. The changes mentioned above were associated with the external factor-photoperiod.…”

“…This implies the role of the described indoleamine also in combat against biotic stresses. The importance of melatonin in stress effects/injuries limitation during different developmental stages including flowering, fruiting, and senescence was discussed (Kolar et al 2003;Arnao and Hernández-Ruiz 2009a;Zhao et al 2013;. An increase in melatonin level in sunflower seeds during sprouting was also observed (Cho et al 2008).…”

Determining diurnal and seasonal changes in melatonin andtryptophan contents of eggplant (Solanum melongena L.)

“…Two peaks of melatonin production in plants are not rare and have previously been documented. For example, Zhao et al (2013) reported dual peaks of melatonin production during a 24-h period in cherry fruits grown under natural environment (i.e. plants exposed to daily changing light and temperature conditions).…”

“…Additionally, several studies demonstrated dual melatonin peaks in the circadian cycle of some plants. For example, two peaks of melatonin production, just before sunrise and late in the afternoon when peak temperatures occurred, have been reported in sweet cherry fruits (Zhao et al, 2013) and in apple leaves (Zuo et al, 2014) during a 24-h period. Similar results were also found in the leaves and roots of lupin and barley plants (Arnao and Hernández-Ruiz, 2015a).…”

“…Starting with the amino acid precursor tryptophan, melatonin is synthesized in four successive steps, the intermediate molecules being tryptamine (5-hydroxytryptophan in animals), serotonin, and N-acetylserotonin (Reiter et al, 2015). In plants, the conversion of tryptophan to tryptamine catalyzed by the enzyme tryptophan decarboxylase is known to be the rate-limiting step (Zhao et al, 2013). On the other hand, Kang et al (2013) presented new evidence that the last step in the pathway (conversion of N-acetylserotonin to melatonin), regulated by the enzyme N-acetyl serotonin methyltransferase, determines melatonin production in plants.…”