ABSTRACT
ABSTRACT Seed development involves highly coordinated signaling pathways associated with desiccation phase, accumulation and mechanisms of scavenging of reactive oxygen species (ROS), and differential activity of a variety of growth regulators. Seed germination and seedling establishment involves mobilization of reserves accompanied with long-distance signaling of biomolecules from roots to cotyledons. Serotonin and melatonin, two major indoleamines in plants, exhibit a crucial role in the plethora of events involved in these biological processes. The serotonin and auxin biosynthetic pathway is regulated by tryptophan metabolism in developing seeds, thus affecting serotonin accumulation in seedlings. Various pharmacological treatments have demonstrated a concentration-dependent regulation of seedling growth by exogenous application of serotonin and melatonin. Abiotic stress acclimatization in seedlings has been observed to be modulated by endogenous and exogenous levels of these indoleamines. Melatonin structurally consists of free radical scavenging sites and regulates metabolomic changes associated with hormones and antioxidant enzymes during seedling growth. Abiotic stress-induced modulation of melatonin accumulation by hydroxyindole-O-methyltrasferase (HIMOT) activity during seedling growth is likely to be effective in providing stress tolerance in various plant systems. Oilseed crops are unique model systems to decipher lipolytic events associated with seed germination and seedling growth. Such events, under the impact of various environmental cues, are positively modulated by these indoleamines, thus imparting abiotic stress tolerance and longevity to young seedlings. Genetic manipulation of indoleamine biosynthetic pathway is likely to provide new information on the mechanisms of stress management in oilseed crops. Biotechnological implications of these indoleamines have been suggested with reference to crop management in response to adverse effects of biotic and abiotic stress.
