Male gametogenesis in the red algae Gracilaria and Gracilariopsis (Rhodophyta, Gracilariales)

Abstract

Male gametogenesis in Gracilaria caudata J. Agardh, G. mammillaris (Montagne) Howe and Gracilariopsis tenuifrons (Bird et Oliveira) Fredericq et Hommersand, with respectively, “ verrucosa”, “ textori” and “ chorda” types of spermatangial arrangement, were compared using light and electron microscopy. Although the development of spermatangia among the three species is clearly distinctive when viewed with light microscopy, there are only minor differences in spermatial subcellular structure. In the three species studied, spermatangial mother cells (SMC) differ from surrounding vegetative cells by having poorly developed chloroplasts and numerous plastoglobuli. Endoplasmic reticulum is concentrated at the cell periphery, contributing to the formation of the spermatangial vesicle (SV). The spermatangial nucleus is pushed to the upper end of the cell due to an expansion of the large SV and chloroplasts and starch grains are lacking. In the process of maturation, small cytoplasmic vesicles fuse with the cell membrane to form a mucilaginous envelope around each spermatium. Before being released, the SV releases its contents to the outside, breaking the pit connection with the SMC. Spermatangia have a cell wall with two layers, but spermatia are naked when released.