Cytological aspects of the mycobiont-phycobiont contact were investigated in the lichen species Peltigera aphthosa, Cladonia macrophylla, Cladonia caespiticia and Parmelia tiliacea by means of freeze-etch and thin sectioning techniques, and by replication of isolated fragments of myco- and phycobiont cell walls.

In the symbiotic state of the mycobionts investigated a thin outermost wall layer with a distinct pattern was observed mainly in the hyphae contacting phycobiont cells and in the upper medullary layer. No comparable structures were noted on the hyphal surface of the cultured mycobionts of the Cladonia and Parmelia species investigated. A distinct rodlet layer was found on the hyphal surface of the mycobiont of Peltigera aphthosa, while mycobionts of Cladonia macrophylla, C. caespiticia and Parmelia tiliacea had a mosaic of small, irregular ridges, each corresponding in its size to a bundle of rodlets on the outermost wall layer. Comparable surface layers have been described in aerial hyphae of a great number of non-lichenized fungi.

The rodlet layer of the mycobiont wall surface of Peltigera aphthosa adheres tightly to the outermost layer of the sporopollenin-containing cell wall of the Coccomyxa phycobiont. Mature trebouxioid phycobiont cells of the Cladonia and Parmelia species investigated in the symbiotic state had an outermost wall layer which was structurally indistinguishable from the tessellated surface layer of the mycobiont cells. A rodlet pattern was detected in the outermost wall layer of Trebouxia autospores still surrounded by the cellulosic mother cell wall. In mature Trebouxia cells the bundles of rodlets became increasingly covered by a homogeneous material, and thus attained the same tessellated pattern which was observed on the mycobiont wall surface. No comparable structures were found on the wall surface after culturing the Trebouxia phycobionts axenically in liquid media. Confluence of the tessellated surface layers of fungal and algal origin was noted at the contact sites of growing hyphal tips and young Trebouxia cells.

The possible correlations between these cytological features and published immunological data on the cell surface of cultured and symbiotic lichen myco- and phycobionts are discussed.

The cell wall composition of several species of the lichen phycobionts Trebouxia and Pseudotrebouxia has been investigated using gas chromatography, thin layer chromatography and infrared absorption spectrophotometry. In addition cell wall components (cellulose, non-cellulosic polysaccharides, sporopollenin, protein) were localized with cytochemical methods at the EM- level. The cell walls of Trebouxia and Pseudotrebouxia consist of several layers. In Trebouxia the inner layer (Si) consists mainly of cellulose, then followed by a non-cellulosic polysaccharide layer (S2), a sporopollenin-layer (S3) and an outer layer consisting again of a non-cellulosic polysaccharide (S4). In addition Trebouxia is surrounded by a sheath (a polysaccharide with species-specific terminal residues). In Pseudotrebouxia the cell wall is similarly constructed compared to Trebouxia, however, the sheath is lacking and the S4 layer contains a polysaccharide with species-specific terminal sugar residues. The role of the different cell wall constituents for the recognition mechanism between the lichen symbionts is discussed.

The photosynthetic capacity changes that have previously been documented in lichens are reviewed together with the mechanisms of photosynthetic capacity change in free-living algae recently proposed by Prezelin and co-workers. Examination of seasonal capacity changes in Peltigera praetextata, P. rufescens, Cladonia rangiferina, C. stellaris, and Caloplaca trachyphylla using photosynthetic-illumination curves, provisionally establishes that synthesis of additional photosynthetic units, seasonal interruption of energy transduction, as well as enzymatic rate changes in the Calvin cycle, are all involved in these capacity changes.

Heavy metal uptake by lichens is briefly reviewed in terms of the trapping of paniculate material and the uptake of soluble cations. The kinetics of uptake to extracellular sites and intracellular carrier-mediated incorporation into cells are compared and the effects of competing cations and the energetics of the processes considered. The influence of heavy metals on lichen growth, morphology and physiology are reviewed emphasizing recent reports showing the greater sensitivity of cyanobacterial compared with chlorophycean lichens, the induction of heavy metal tolerance in the field and laboratory in Peltigera species, and alterations in intracellular cadmium uptake kinetics by some, but not all, tolerant Peltigera populations.

Peltularia crassa P. M. Jørg. & D. Galloway, a new, umbilicate lichen in the family Coccocarpiaceae is described from Campbell Island south of New Zealand. It occurs also on Macquarie Island. Its taxonomic and phytogeographical relationships are discussed.

Investigation of two sites in the Caledonian allochthon of the central part of the Scandinavian peninsula has shown that several copper tolerant lichens occur on cupriferous substrates. Analysis of the thalli of two of these species, Acarospora rugulosa and Lecidea theiodes, using atomic absorption spectroscopy, X-ray diffraction, infrared spectroscopy and electron probe microanalysis has revealed that copper occurs at high concentrations (5% Cu dry weight) principally as crystals of copper oxalate (1–5 μm diam) encrusting the fungal hyphae within the medulla.