Desenvolvimento de anteras em espécies de clados basais de Malpighiaceae

Abstract

Malpighiaceae comprises about 1,300 tropical species, distributed in 78 genera. The family is proven monophyletic. However, many of its intrafamilial relationships have not been elucidated, so its lineages are treated as informal clades. Embryological data, especially on the development of anthers in the family, are available in the literature for only six species. Of these, only Stigmaphyllon bonariense (Hook. & Arn.) C.E. Anderson and S. jatrophifolium A. Juss. have detailed descriptions of anther development, but both belong to derived lineages of Malpighiaceae. Embryological data are taxonomically promising when examined from a phylogenetic perspective and could, for example, assist in circumscribing genera and subfamilies in Malpighiaceae. In this context, the objective was to describe the development of anthers, as well as the microsporogenesis and microgametogenesis of species of basal lineages of Malpighiaceae and, by comparing them to the data available in the literature for Malpighiaceae and other phylogenetically close families, to raise possible plesiomorphic embryological characters for the family. For this, we selected floral buds at different stages of the development of Galphimia gracilis Bartl. and Verrucularia glaucophylla Juss. (galphimioid clade), Byrsonima dealbata Griseb. and Byrsonima intermedia A.Juss. (byrsonimoid clade) and Pterandra pyroidea A.Juss. (acmantheroid clade). The samples were usually processed for light microscopy, and histochemical tests were performed. The anthers of the five species showed very similar developmental patterns, fitting into the basic type of development. However, the number of medium layers was variable: three in P. pyroidea and two in the other species. The five species share the secretory tapetum with binucleated cells, the simultaneous cytokinesis of microsporocytes; microspore tetrahedral tetrads; pollen grains dispersed in bicellular form. In species of derived lineages, the basic type of anther development is also observed. However, in Stigmaphyllon, the tapetum cells are multinucleated, and the tissue can be secretory type in S. jatrophifolium, non-syncytial invasive in S. bonariense and syncytial invasive in S. periplocaefolium f. intermediate Nied. The anthers of the species analyzed in this work still share, with other families of Malpighiales, the basic type of development, the secretory tapetum with binucleated cells, and the bicellular pollen grains at the time of dispersal. Based on this data, it is possible to infer that the basic anther developmental type, the secretory tapetum with binucleated cells, and the dispersed grains with two cells are plesiomorphic states in Malpighiaceae. However, knowledge about the development of Malpighiaceae anthers should be expanded, and more species should be studied to corroborate the observed trends.