Morfoanatomia e histoquímica de nectários florais de Parkia (Leguminosae: Mimosoideae) e suas relações com os sistemas de polinização no gênero

Abstract

Parkia R. Br. is a genus with a pantropical distribution, with approximately 35 described species divided in three taxonomic sections based on the number of specialized flowers in the capitulum. In two sections of the group (Parkia and Platyparkia), the species have nectariferous flowers which are responsible for the nectar secretion, while in section Sphaeroparkia, the flowers are only fertile and there is no nectar production. The nectar has a fundamental role in the animal/plant interaction in the Angiosperms and seems be an important factor in system, shifts of pollination within groups of plants, since such factors could promote the specialization of particular pollinators. However, few studies have related changes in nectar production with changes in the pollinators. This issue has been approached in Parkia, that has floral characters and nectar prodution on different groups of pollinators, like bees and bats. In this research, the morfoanatomy of the floral nectaries has been observed by using optical and scanning electronic microscopy, comparing the different sections of the genus and relating this to the pollination system (bees/bats) and the characteristics of the nectaries/nectar. Our results show that Parkia floral nectary is located in the ring formed by the fusion of the stames at the base of the ovary. The species of sections Parkia and Platyparkia haven similar histological compositions, with changes only in the shape of the epidermal cells. When comparing the pollination systems it is possible to see striking differences between the species: in flowers pollinizated by bats, the tissue is filled with substances which give positive reactions to histochemical exams for lipids, proteins and phenolic compounds, while in the entomophilous species these reactions are restricted to scattered idioblasts on stamenal discs. Ontogenic studies are necessary to verify the production sites of nectary at cellular level which could enhance the comprehension of mecanisms in the nectary secretion.