Estruturas secretoras em espécies de leguminosas da subtribo Cassiinae (Fabaceae, Caesalpinioideae, Cassieae)

Abstract

Fabaceae (Leguminosae) is considered one of the three major families of Angiospermae, containing 730 genera and 19,500 species of cosmopolitan distribution, being in Brazil, found about 190 genera and 2,100 native species. Several legumes groups have been amended over time, for instance subtribe Cassiinae, which features three genera resulting from dividing Cassia lato sensu rating: Cassia stricto sensu, Senna and Chamaecrista. External and internal secretory structures are widely distributed in Caesalpinioideae, being cited, extrafloral nectaries, mucilage cells, secretory cavities and ducts. The relevance of secretory structures in Cassiinae becomes evident when we see that in phylogenetic analysis: two clades are distinct in Senna based on the presence or absence of extrafloral nectaries. Thus, the present work has the general objective to investigate the occurrence of secretory structures in fruits, seeds and seedlings of Senna and and flowers of Cassia, Chamaecrista and Senna (Fabaceae, Caesalpinioideae). The aim is also to identify the type of secretory structure and infer the presence of these in adaptation of plants to the environment as well as the fruits and seeds protection, providing information that may be useful for the phylogenetic analysis of the group. The receptaculares colleters of Senna macranthera are located at the base of the floral receptacle and present early development and are fully developed and in secretory activity in the final stages of pre-anthesis. Colleters present structure and cellular dynamics compatible with the acidic polysaccharides synthesis of, dictyosomes as producing large amount of vesicles, flaked appearance secretion accumulation in the periplasmic and subcuticular space. At anthesis, the secretory activity ceases and there is early senescence colleters. The pericarpiais colleters of Senna occidentalis match trichomes that are located in the region corresponding to the median of the fruit valves depression; are functional during the period between anthesis and early fruit ripening, when they become senescent. Colleter secretion accumulates in the periplasmatic and subcuticular spaces; subcuticular space secretion overflows to the outside through fissures in the cuticle. Colleters are present in embryos and seedlings of various Senna species are located in the axils of the cotyledons, lateral to the plumule, in the apex of the embryo axis and seedling. Colleters are present in the embryo of the seed prior to dehydration, in the seedling during germination and seedling up to seven days, when they become senescent. The secretion has pectic nature and form a film covering the region of the apex and sides of the embryo and seedling. Floral colleters were observed in all genera of Cassiinae, highlighting their presence in Chamaecrista, in sections Apoucouita, Caliciopses, Chamaecrista and Xerocalyx, and Senna, which were observed in all species, presenting a unique distribution in the subtribe Cassiinae: scattered throughout the floral receptacle. The extrafloral nectaries study of Senna species deserves enphasys to the EFN amount for taxonomy, phylogenetic inferences and especially for his role in the genus Senna dispersal and adaptation to diverse habitats. The presence of colleters has proved to great importance in the genus Senna, is acting in protection against flowers and fruits desiccation in development, or in facilitating seed germination and seedling establishment for several genus species. The presence of this structure in several secretory organs and species of Senna should be explored in future phylogenetic analyzes, with the studies expansion to Cassia and Chamaecrista genera, as was done for the floral colleters, so that these data can contribute to understanding of relationships in subribo Cassiinae.