Estruturas secretoras em uma espécie de Salicaceae típica de áreas alagáveis da Amazônia

Abstract

The diversity of secretory structures in Salicaceae is frequently reported in the literature and is an important source of data for taxonomic studies. Descriptions that address the structure and secretion of these glands are essential for their recognition, classification and understanding of their functionality. The present study aims to characterize the anatomy and histochemistry of the internal and external secretory structures of Laetia corymbulosa Spruce ex Benth.. The species was collected in flooded areas of the Amazon region and processed according to methods used for anatomical and histochemical studies. Standard colleters were recorded at the apex of the teeth on the leaf margin, being the first record of such structures outside the genus Casearia. The secretory cavities distributed in the leaves were described for the first time in Laetia, varying in relation to the distribution in the mesophyll and the circular or elongated shape of the lumen. This study describes for the first time the cavities in reproductive structures in the group. Additionally, characteristics suggesting a probable secretory activity were observed in the floral stigma. The results of the histochemical tests on the colleter revealed a mixed secretion composed of polysaccharides, pectins, proteins, and essential oils, an unprecedented record for the family. The detection of phenolic compounds was common in colleters at an advanced stage of development. The cavities of the leaves and flower buds showed secretions of an equivalent nature, composed of traces of polysaccharides, proteins, and mainly essential oils. The secretory structures identified here are related to protection against pathogens and in combating herbivory, and the secretion of the colleter also acts in the protection of the meristems. Furthermore, the data gathered in this work reinforce the similarities shared between Laetia and Casearia, which may contribute to taxonomic and evolutionary studies of the family.