Cytological aspects of pollen germination in Mauritia flexuosa (Arecaceae).

Little is known about the dynamics of pollen germination in palms. Mauritia flexuosa (buriti) is native to the Amazon but also occurs in wetland areas (veredas) within the Cerrado. The species is dioecious and, in this environment, exhibits supra-annual flowering, which underscores the importance of post-pollination events for its reproductive success. The aim of this study was to define the stages of buriti pollen germination, to describe the mobilization of reserve compounds, and to examine subcellular changes during pollen tube development. Cytochemical tests and ultrastructural analyses were performed throughout the germination process and the in vitro development of the pollen tube. The pollen of M. flexuosa is sphero-oblate and monoporate. The exine is thick and impregnated with structural phenolic compounds, with pointed spicules and pollenkitt. The intine is thin, becoming thicker in the pore region, where it exhibits a mixed composition. The protoplast of the vegetative cell is rich in reserve compounds. Germination occurs in four phases. In the pore region, the pectin-rich intine ensures effective rehydration. The mobilization of starch and lipids, in coordinated stages, provides energy for pollen tube elongation, accompanied by continuous wall synthesis. Protoplast reorganization supports pollen tube growth, with proliferation of dictyosomes, endoplasmic reticulum, mitochondria, and ribosomes. The second mitosis takes place shortly after pollen tube emergence, contributing to rapid fertilization. The structural features of the pollen and the dynamics of germination favor the reproductive success of M. flexuosa, particularly in semiarid environments.