Effects of melatonin and tryptophan applications on viability and germination performance of tomato seeds during and after artificial aging

Although the diurnal fluctuations of melatonin (Mel) content in plants and its role in abiotic and biotic stress tolerance are well-documented, little is known about its changes within seeds and its potential effects on seed viability or the aging process. This study aimed to determine how artificial aging, induced by a controlled deterioration test, affects the Mel and tryptophan (Trp) content and seed viability. Furthermore, the study evaluated the effects of Mel and Trp applications on mitigating the impacts of aging in artificially aged seeds. Tomato seeds treated with 250 µM Mel and Trp were artificially aged for up to 8 days through controlled deterioration test after which Mel and Trp changes during ageing and the effect of treatments on seed viability and germination performance was determined. Seeds were also treated with Mel and Trp following artificial ageing in order to determine the effects of Mel and Trp on aged seeds. The positive effects of Mel and Trp applications on seed viability and vigor were particularly evident during and after artificial aging, compared to control seeds. It was observed that in control seeds subjected to controlled deterioration test, Mel and Trp contents exhibited an opposite trend. Applications of Mel and its precursor Trp, before and after artificial aging, significantly slowed down the aging process or alleviated the adverse effects of aging by protecting membrane structures against peroxidation and the accumulation of malondialdehyde (MDA) and H2O2. Moreover, indicators of seed deterioration such as electrical conductivity, MDA, and H2O2 contents were significantly reduced compared to untreated seeds, while the activities of antioxidant enzymes were boosted. In conclusion, the importance of Mel and Trp applications in preserving seed viability, minimizing storage losses, and slowing seed aging has been demonstrated, suggesting practical applications, particularly in preserving seeds of endangered species or valuable breeding materials.