Ontogênese da antera, microsporogênese e microgametogênese de Dyckia strehliana H. Büneker & R. Pontes (bromeliaceae)

Abstract

Many species of angiosperms are considered rheophytes, that is, they develop in the banks of streams and fast-flowing rivers and are subject to the action of frequent floods, as is the case of Dyckia strehliana H. Büneker & R. Pontes (Bromeliaceae). Also considered saxicolous, its development occurs on basaltic rocky banks of the Toropi River, in the municipality of Quevedos, RS. It is an endemic species in this region, an area at risk of environmental degradation due to the construction of hydroelectric plants, appearing as a threat to extinction. Thus, this study aimed to anatomically analyze and describe the development of the anther of D. strehliana, in addition to characterizing the embryological processes, microsporogenesis and microgametogenesis, and the dynamics of starch during these stages. In order to carry out the study, inflorescences were collected at different stages of development and processed in the Structural Botany Laboratory. The emergence of stem primordia in the floral meristem of D. strehliana occurs through layer II divisions. The formation of the sporangium is of the basic type, the epidermis persists throughout development, and its cells acquire a rounded shape during anther maturation. The endothelium acquires U- and O-shaped thickening, the middle layer may divide again in some places in the sporangium, degenerating into anther maturation. The mat is an invasive secretor, starts a process of changing its chemical composition at the onset of meiosis in archesporial cells and later has a tendency to invade the anther loculus. Meiosis is successive, forming tetrads of isobilateral and decussed arrangement. Microspore mitosis is asymmetric and pollen grains have a grooved opening. The sporoderm is composed of lipid and protein exine, and pectic, protein and cellulosic intin. The connective has fibrous thickenings. Raphids are common in the connective and regions close to the locules. Pollen grains have a cycle of amylogenesis – amylolysis, with a peak of starch accumulation during the phase in which the generative cell is moved to the central position of the vegetative cell. Sporangium and connective showed small amounts of starch grains during anther development, and in the mat they were observed during degeneration. The general embryological results found are in agreement with those described for Bromeliaceae and Dyckia, however, details related to the tapetum and starch dynamics contrast D. strehliana from other species of the genus. Such data are added to studies already carried out and contribute to future studies. Thus, it will contribute to the characterization of the reproduction process, phylogenetic relationships and will help for its conservation and preservation.