Behavior of Flagella and Eyespot during Fertilization of Anisogametes in Caulerpa racemosa (Forsskal) J. Agardh var. laetevirens (Montagne) (Ulvophyceae, Chlorophyta) Revealed by Field Emission Scanning Electron Microscopy

Abstract

Respective fates of male and female flagella and the eyespot during fertilization of ulvophycean alga Caulerpa racemosa (Forsskal) J. Agardh var. laetevirens (Montagne) were studied using field emission scanning electron microscopy (FE-SEM). FE-SEM allowed visualization of the eyespot of the biflagellate gamete. The female gamete has one eyespot on a posterior position of the cell body; the male gamete does not. The female gamete eyespot was oriented to the direction of the plane of the flagellar beat. The female gamete is larger than the male one and has the only eyespot. For those reasons, the author followed the fate of the flagella and eyespot during fertilization. When both gametes were mixed, the initial cytoplasmic contact and cell fusion between them usually took place at the anterior end slightly below the flagellar base. In most mating pairs, the female gamete fuses at the left side of the eyespot and male gamete at a cell surface that is perpendicular to the plane of the flagellar beat. As fusion proceeds, the gamete pair is transformed into a quadriflagellate planozygote in which two flagella each from the male and female gametes point in nearly the same direction. In particular, the no. 2 flagellum of the female gamete and one male flagellum were directed to the eyespot. These observations indicated that cell fusion at the particular area of the gamete is important for proper arrangement of the flagella and eyespot in the planozygote.