Morphoanatomy, ontogeny and histochemistry of internal mucilage-secreting structures in the bracts and flowers of three genera of Bromeliaceae

Abstract

The presence of mucilaginous secretion in peduncles and inflorescences has been associated with certain species in the tribe Vrieseeae, within the genera Alcantarea, Vriesea, and Werauhia. Given the diversity of secretory structures and their ecological and functional significance, our objective was to describe the structures responsible for the secretions found in flowers and bracts of 16 species from the tribe Vrieseeae distributed across the three genera mentioned above, and to address questions regarding the type of structures and the chemical nature of the secretion, as well as their functional role. Samples of bracts, floral buds, and open flowers were analyzed at various developmental stages through anatomical and histochemical analyses using light microscopy and scanning electron microscopy. We documented and described two types of internal secretory structures that produce hydrophilic and mucilaginous secretions: secretory ducts in flowers and mucilage-secreting tissue in bracts. The presence of secretory structures varied in different regions depending on the species, being found in flowers (receptacle base and sepals) and floral and peduncle bracts. The mucilaginous secretion could play a protective role against desiccation, pathogens, and insects, similar to the function of colleter secretions. Furthermore, the mucilage stored in flowers may act as a polysaccharide reserve, aiding in the survival of these species under environmental stress, for example. The results obtained are relevant for expanding our understanding of secretory structures in Bromeliaceae, as well as for the conservation of the family in nature.