Flagellar structure of the gametes of Ectocarpus siliculosus (Phaeophyta) as revealed by negative staining

Abstract

From light microscopic observations of the mating reaction in the marine brown alga Ectocarpus siliculosus it can be deduced that the foremost part of the front flagellum of the male gamete plays an important role in establishing initial sexual contact. The flagellar apparatus of both male and female isogametes of this organism has been studied electron microscopically using negative staining technique, with special attention focused onto the whiplash tips (“acronema”). The fine structure of this terminal flagellar appendage, which is very long (about 10 μm) and extremely sensitive to mechanical stress, is identical in structure in both, the tinsel and the smooth (hind) flagellum. It is characterized by a continuation of only the two central microtubules of the flagellar shaft which appear cross-bridged to each other and are ensheathed by the plasma membrane. Although the two types of gametes are different in their functions, differences in the fine structure of their flagellar apparatus were not detected.