Profiling the melatonin content in organs of the pepper plant during different growth stages

• Melatonin contents of pepper plant organs during different growth stages were profiled.
• Seedlings at cotyledon stage had the highest melatonin content.
• Melatonin content in leaves was at the lowest level at flowering stage.
• Fruit and seed melatonin content increased as the fruits reached red mature stage.
• Variations in melatonin content depending on the developmental stage suggested that melatonin controls these developmental processes.

Melatonin (N-acetyl-5-methoxytryptamine), a well-known animal hormone, was first isolated from bovine pineal gland and, since then, it was discovered in evolutionary distant organisms including bacteria, algae, invertebrates, and finally in higher plants. Although the presence of melatonin in plants seems to be a universal phenomenon, there is still an absence of information on its occurrence in important plant species, one of which is pepper (Capsicum annuum L.). Our objective was to determine the presence of melatonin in different organs (leaves, roots, fruits and seeds) of two pepper cultivars and its variation during various growth stages (germination, seedling, flowering, and harvest) using HPLC–FD. We found very high concentration of melatonin in seedlings at the cotyledon stage (108.6–111.6 ng g−1 FW) with a progressive decline as the plants matured. Melatonin was also found to accumulate highly in mature seeds, and to varying concentrations in fruits, leaves, and roots depending on the developmental stage, strongly suggesting that melatonin controls these developmental processes.