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

The objective of this study was to simultaneously determine changes in tryptophan and melatonin contents of eggplant seedlings at two different growth stages during a 24-h period. Variations in tryptophan and melatonin levels in different organs (roots, leaves, fruits, and seeds) and the distribution and accumulation of these molecules in these organs during various growth stages were also investigated. In eggplant seedlings, melatonin showed a strong peak at the beginning of the dark period, while tryptophan levels were at the lowest. Melatonin was also high in the middle of the light period and an inverse relationship was observed between melatonin and tryptophan levels. These results indicated that melatonin fluctuations in eggplant seedlings are likely the result of the combined effects of endogenous and environmental factors. Melatonin was found in high quantities in seedlings and mature seeds, and its concentration in leaves and roots decreased dramatically as the growth stages progressed. On the other hand, tryptophan content in leaves and roots increased markedly as the growth season progressed, and the highest tryptophan levels were detected in roots of older plants, flowers, and fruits at mature seed stage. Significant seasonal variations in melatonin levels suggest that melatonin may play a key role in eggplant developmental processes.