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A survey of zoospore and sperm ultrastructure in the Laminariales (Phaeophyceae) Henry, Eric Charles


Zoospores of 17 species in 14 genera and sperm of 13 species in 11 genera of Laminariales were studied by electron microscopy. The zoospores are unique in the brown algae in lacking both an eyespot in the single chloroplast and an associated swelling at the base of the shorter, posterior flagellum. Spores of all species possess a distal whiplash on the longer, mastigoneme-bearing anterior flagellum; although it is only seldom preserved for electron microscopy, this appendage may sometimes be as long as the mastigoneme-bearing portion of the flagellum. A microtubular cytoskeleton with connections to the flagellar basal bodies is responsible for maintaining the shape of the zoospore. The sperm are also unique in the brown algae. They are elongate and possess two to three plastids and several mitochondria, but lack an eyespot. Their most distinctive feature is the long posterior flagellum which tapers distaliy as the doublet microtubules of the axoneme are transformed into singlets and then decrease in number. The sperm also bear a distal whiplash on the mastigoneme-bearing anterior flagellum. These laminarialean zoospores and sperm are ultrastructurally distinct from those known in other orders of brown algae, and from Chorda of the Laminariales, which confirms that Chorda is primitive. The longer posterior flageilum of the sperm recalls similar modifications in sperm of other oogamous brown algae, and suggests a common functional significance.

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