PARASITIC INTERACTIONS AND VEGETATIVE ULTRASTRUCTURE OF CHOREOAEMA THURETII (CORALLINALES, RHODOPHYTA)¹

Abstract

The monotypic coralline red alga, Choreonema thuretii (Bornet) Schmitz (Choreonematoideae), grows endophytically within three geniculate genera of the Corallinoideae. Although the thallus of Choreonema is reduced, lacks diJkentiated plastids, and is endophytic except for its conceptacks, its status as a parasite has been questioned because cellular connections to the host had not been o b served. Transmission electron microscofi, however, disclosed a previously undesm'bed lype of parasitic interaction in which Choreonema interacts with its host through specialized cells known as knticular cells. These small, lens-shaped cells are produced from the single file of hostpenetrating vegetative cells. Pit plug morphology between uegetatiue and 1entiLdar cells is polarized. Plug caps facing the vegetative cell have nonnal coralline moqhology, while those Jizcing the lenticular cell are composed of three layers. Regions of lenticular cells near host cells protrude toward the host cell; upon encountering the host cell wall, the prolrusion produces numerous finger-like jmbriate procesm that make cellular connections with the host cell. Lenticular cells m.ay extend several protrusions toward a hmt cell or penetrate more than one host cell; two or more lenticular cells may also penetrate the same host cell. The lack of secondary pit connections, cell fusims, and passage of parasitic nucki suggest that this parasitic relationship may be evolutionari(y older than previously rqorted cases of parasitism in red algae.

CONCEPTACLE STRUCTURE OF THE PARASITIC CORALLINE RED ALGA CHOREONEMA THURETII (CORALLINALES) AND ITS TAXONOMIC IMPLICATIONS1

“…The thallus was divided into a parenchymatous mat of cells supporting the conceptacle and a single parasitic filament extending for a short distance into the host (Fig. 1, B–D) (see Broadwater and LaPointe 1997 for further details). Tetrasporangia and carposporangial initials were confined to the floor of the conceptacle (Fig.…”

“…11 and 13) and examination of unpublished material indicated the presence of lenticular cells in this alga. Because lenticular cells in C. thuretii were shown to be directly involved in parasitizing cells of the host Jania tenella (Broadwater and LaPointe 1997), the presence of comparable cells in A. intumescens suggested that a similar type of parasitism might be operative.…”

“…Both subfamilies Choreonematoideae and Austrolithoideae were created without the presumption of parasitism among endophytic members. However, Broadwater and LaPointe (1997) described a new type of parasitic interaction by C. thuretii that is observable only at the ultrastructural level. This evidence of parasitism brought into question the value of some taxonomic characters used to define the genus and subfamily: lack of cell fusions or secondary pit connections, lack of epithallial cells, and presence of conceptacle roofs comprised of only one cell layer.…”

Molecular phylogenetics supports a clade of red algal parasites retaining native plastids: taxonomy and terminology revised

“…The abundance of successful independent evolutions of parasitism within the Florideophyceae seems in large part due to their ability to form direct cell‐to‐cell fusions between adjacent, non‐daughter cells (Wetherbee and Quirk , Goff and Coleman ). With few exceptions (e.g., Choreonema thuretii ; Broadwater and LaPointe ), red algal parasites use their ability to form cell fusions as a means of infecting their host (Goff and Coleman , Zuccarello et al. ).…”

Epulo multipedes gen. et sp. nov. (Corallinaceae, Rhodophyta), a coralline parasite from Australia

“…Morcom & Woelkerling (2000, p. 6) define a parasite as a living organism that adversely affects another (the host) as a consequence of obtaining nutrients (from the host). The presence of parasitic taxa within the coralline algae has been assumed (Goff 1982), then questioned (Woelkerling & Ducker 1987;Woelkerling 1988;Harvey & Woelkerling 1995) and finally observed at an ultrastructural level, to the extent that it is now accepted that in at least one coralline species, Choreonema thuretii (Bornet) Schmitz, a truly para sitic association exists with its host (Broadwater & Lapointe 1997 Chamberlain 1999). All but one of the coralline parasites and endophytes described in the literature (Goff 1982;Chamberlain 1999) infest other coralline algae.…”