South African Journal of Botany, vol.156, pp.79-90, 2023 (SCI-Expanded)
Since the discovery of the melatonin, comprehensive research has been conducted to reveal the physiological role of melatonin and changes in melatonin contents in different plant species. Although variations in melatonin content of a plant within a day and roles of melatonin in tolerance to abiotic and biotic stressors were well-documented, there is not much information about fluctuations in seed melatonin and its pre-cursor-tryptophan contents and their potential effects on seed viability or ageing process. This study was conducted to unveil the changes in melatonin and tryptophan contents of tomato seeds stored for 28 months and to determine potential effects of pre-storage melatonin and tryptophan treatments on seed viability or ageing process. Tomato seeds were treated with melatonin and tryptophan (0 μM or 250 μM) for one day before storage and then stored at room temperature (25 °C) for up to 28 months. Effects of pre-storage melatonin and tryptophan treatments on seed quality and ageing were investigated through various tests and analyses. Seed melatonin contents changed significantly during the storage, reached the highest level at 12th and 24th months of storage, which corresponds to August 2018 and August 2019 while tryptophan levels exhibited an opposite trend during the months when melatonin peaked strongly. These results indicated that higher seed melatonin content in August is a strategy that tomato seeds have in order to ensure their life after leaving the mother plant and to establish their next generation. Pre-storage treatments reduced the ageing-induced damage significantly by lowering the seed MDA and H2O2 contents and improved germination performance especially at low temperature. Thus, melatonin and tryptophan treatments could be used as an effective tool to preserve seed viability, minimize storage losses and slow down the ageing process, which could have practical implications especially for long-term storage of seeds of endangered species or valuable breeding materials.