Eyespot Behavior during the Fertilization of Gametes in Ulvalean Alga Enteromorpha compressa (Linnaeus) Nees Revealed by Field Emission Scanning Electron Microscopy

Abstract

Fate of the eyespots during the fertilization of ulvalean alga Enteromorpha compressa was studied using field emission scanning electron microscopy (FE-SEM). FE-SEM enabled the visualization of the eyespot of biflagellate male and female gamete. The smaller male gamete has 1 protruded smaller eyespot and the larger female gamete has larger one on a posterior position of the cell. The cell membrane over the eyespot region is relatively smooth compared to other part of the cell body and exhibits hexagonal arranged lipid globules. Since the size of cell body and the eyespot is slightly different between male and female gamete, the author could follow the fate of the eyespots during the fertilization. In most of the mating pairs, larger female gamete has always fused along the same side as the eyespot, while smaller male gamete along the side away from its eyespot. As fusion proceeds, the gamete pair is transformed into the quadriflagellate planozygote, in which the eyespots are positioned side by side on the region of cell fusion. These observations indicated that the opposite positioning of the eyespot relative to the cell fusion site in male and female gametes is important for the proper arrangement of the eyespots in the planozygote.