Ontogênese e anatomia do androceu de Cassia grandis L.f. (Fabaceae)

Abstract

The androecium of Cassia, Senna and Chamaecrista shows considerable evolutionary importance in the delimitation of these genera. However, gaps remain in understanding stamen development and function within these genera. To expand knowledge of floral form and function in Cassieae, floral buds and flowers of Cassia grandis L.f. at various developmental stages were collected in Uberlândia, Minas Gerais, Brazil. Specimens were fixed and processed using standard techniques for light microscopy, scanning electron microscopy and X-ray microtomography. The androecium of C. grandis comprises ten stamens arranged in two cycles. The antesepalous cycle comprises three long abaxial stamens and two short adaxial stamens, both with dorsifixed anthers. The abaxial filaments are sigmoid, while the adaxial ones are slightly curved. The antepetalous cycle comprises five medium-sized stamens with slightly curved filaments and dorsifixed anthers. All anthers are pilose, bithecate, and tetrasporangiate. The development of the wall of all anthers is of the Basic type, and they have a persistent epidermis, a persistent fibrous endothecium, a varying number of middle layers depending on the position of the stamen, a secretory tapetum, the formation of tetrads of tetrahedral microspores by simultaneous cytokinesis, and bicellular pollen. In the antesepalous cycle, the long stamens have nine middle layers, and the short stamens have two. In the antepetalous cycle, all the stamens have five middle layers. The pollen grains development, morphology, and chemical composition also vary between the antesepalous and antepetalous stamens. The anthers of the antesepalous stamens develop before those of the antepetalous stamens. The main morphological differences in the pollen grains are related to size, shape, and ornamentation between the anthers of each cycle. Additionally, the thickness of the exine varies between each type of anther, with the pollen grains from the larger anthers having a thinner exine than those from the medium and smaller anthers. In the antesepalous cycle, the pollen grains from the abaxial anthers contain proteins, while those from the adaxial anthers contain both carbohydrates and proteins. In the antepetal cycle, the anthers are composed of carbohydrates and proteins. The observed differences in anther wall development, and pollen morphology and chemical composition suggest functional diversification within the androecium.