Ultrastructural study of the brown algaPetroderma maculiforme(Phaeophyceae) in the free-living state and in lichen symbiosis with the intertidal marine fungusVerrucaria tavaresiae(Ascomycotina)

Abstract

A comparative TEM study was carried out on the phaeophyte Petroderma maculiforme, collected from San Francisco Bay both as free-living thalli and as phycobiont of the lichen fungus Verrucaria tavaresiae. The free-living alga usually had thicker cell walls and substantially greater reserves in storage bodies than the lichenized form. Cell division patterns were altered in symbiosis, and formation of zoosporangia was not observed on the lichenized filaments. Both free-living and lichenized Petroderma showed an abundance of densely osmiophilic deposits associated with vesicles, which were interpreted as physodes; Golgi and ER appeared to be involved in the elaboration of their contents. Plastids of both free-living and lichenized forms possessed a large pyrenoid deeply penetrated by tubular invaginations of the plastidial membranes. This pyrenoid was often enfolded by lobes of the plastid as previously reported, but also commonly occurred as a broad-based protrusion from the surface of the plastid. Smaller, exserted pyrenoids with a very narrow base and no tubular invaginations were sometimes also observed on plastids of the lichenized alga, but were not seen on those of free-living thalli. The significance of this variation in pyrenoid type was not clear. The considerable variation in pyrenoid position and form in P. maculiforme suggests that the protruding, enfolded, and stellate pyrenoid positions known in brown algae are not profoundly different from each other developmentally.

Composition of Intracellular and Cell Wall-Bound Phlorotannin Fractions in Fucoid Algae Indicates Specific Functions of These Metabolites Dependent on the Chemical Structure

“…Polyphenols are known to be involved in the interactions between vascular plants and symbiotic fungi; in particular, mycorrhizal infection leads to changes in polyphenolic profiles [ 55 , 56 ]. Sanders et al [ 57 ] showed that the brown alga Petroderma maculiforme , occurring in both free-living and lichenized state, continued producing high abundance of physodes under the nutritional burden of supporting a fungal symbiont. Together with our results, this data suggests that certain phlorotannins (presumably, dhE/C series) may contribute to alga–fungus interactions.…”

Asymmetric Co-evolution in the Lichen Symbiosis Caused by a Limited Capacity for Adaptation in the Photobiont

“…Although photobionts belong to very diverse groups of organisms, the only major groups of algae represented those that include multicellular species i.e. not only the green algae (Chlorophycae) but now also the red algae (Phaeospora lemaneae and a species of red alga probably Lemanea sp., Rhodophycae; Hawksworth, 1987Hawksworth, , 1988Hill, 1992a) and the brown algae (Petroderma maculiforme, Phaeophycae; Sanders et al, 2005). All these groups capable of multicellular organisation have physiological features in common (e.g.…”

Lichen algae: the photosynthetic partners in lichen symbioses

“…2D) but not readily visible with light microscopy. The pyrenoids are traversed by branching tubules arising from invagination of the plastidial boundary membranes (rather than thylakoids, as in Trebouxia and Heveochlorella); the position of the pyrenoid may be laminar, protruding to exserted, or enfolded by chloroplast lobes (Sanders et al 2005). The alga was first brought to the attention of lichenologists by a footnote in a phycology dissertation (Wynne 1969) that reported it in symbiosis with a Verrucaria species on intertidal rocks in northern California.…”