FLUCTUATIONS IN MELATONIN CONTENT AND ITS EFFECTS ON THE AGEING PROCESS OF LETTUCE SEEDS DURING STORAGE

This research was carried out to determine the changes in melatonin and tryptophan contents and the possible effects of melatonin on the ageing process of lettuce seeds stored for two years. For this purpose, seeds were treated with melatonin (0 or 250 mu M) for one day after which they were stored for up to two years at two temperature (4 degrees C or 25 degrees C) regimes. The results showed that seed melatonin content varied significantly during storage reaching its peaks in October-December and lowest levels in August while tryptophan levels displayed an opposite trend with a strong peak in August and low levels in October. Similar seasonal changes were observed in seeds stored under both temperature conditions suggesting that endogenous melatonin could play a crucial role in seasonal rhythms independent of environmental conditions. Lettuce seed quality deteriorated fast when stored at 25 degrees C but pre-treatment with melatonin reduced seed deterioration significantly by increasing the activities of antioxidant enzymes and restoring membrane properties indicating that melatonin could be used to slow the ageing process in seeds.