Latest on enzymology of serotonin biosynthesis in walnut seeds.

Serotonin (5-HT) accumulation in walnut cotyledons is seen as a detoxification mechanism protecting the sensitive plant tissues of seeds from highly toxic ammonia concentrations following seed desiccation. Different metabolic pathways and cell compartments are involved in biosynthesis and storage of 5-HT. Ammonia fixation and incorporation into the indole moiety of tryptophan is followed by 5-HT biosynthesis via tryptamine in a two-step pathway with the adaptive tryptophan decarboxylase and the constitutive tryptamine 5-hydroxylase.