ABSTRACT
ABSTRACT For many decades, melatonin (MEL) has been considered as a typically animal hormone, but its wide occurrence in the plant kingdom has now been well recognized. Its content in plants varies not only between species but also between organs of the same plant. Although the mechanism of MEL action is not precisely elucidated in plants, its role seems to be very important. In this chapter we (1) describe the history of MEL discovery, (2) indicate its presence especially in phototrophic organisms, and (3) gather the available knowledge on its biosynthetic pathways and localization in plants. Although plants and animals share a common scheme of MEL biosynthetic pathways, recently collected data revealed some plant-specic steps. Additionally, the site of MEL biosynthesis in plant cells (mitochondria and chloroplasts), as well as the availability of a MEL precursor-tryptophan-–may account for the much higher level of this indoleamine in plants than in animals.
