Phycobionts

Weare, N. M., Azam, F., et al. (1974). Microautographic studies of the marine phycobionts Rhizoso-lolenia and Richelia. J. Phycol. 10, 369—371. 

Most lichens grow very slowly. Lichens in which the phycobiont is a blue-green bacterium have the ability to fix nitrogen gas into ammonia. Some lichens can commonly reach ages of many centuries, especially... 

Among the few known examples of secondary metabolites synthesized by the phycobiont are the nostoclides (e.g., 90), " hepatotoxic microcystins (e.g., [ADMAdda ]microcystin-LR, 91), and the cytotoxic cryptophy-cins " from cyanobacteria. The cryptophycin analogue cryptophycin 52 (92) reached clinical trials for cancer chemotherapy but was later abandoned. " ... 

Tschermak-Woess, E. (1978). Myrmecia reticulata as a phycobiont and free-living - free-living Treouxia - problem of Stenocybe septata. Lichenologist 10, 69-79. 

In a second set of experiments, chlorophyll fluorescence characteristics were compared between lichen thalli with green or blue-green algal phycobionts. Green algae are known to possess the xanthophyll cycle, whereas blue-green algae lack the xanthophyll cycle, i.e. they lack the epoxide forms violaxanthin (di-epoxide) and antheraxanthin (mono-epoxide) which are the... 

Included are, firstly, the two partners of a Pseudocyphellaria phycosymbiodeme, in which lobes with green algae and those with blue-green algal phycobionts grow together in one organism. 

Lichen substances affect the permeability of the cell walls of the phycobionts, and could play an important role in symbiotic equilibrium (FoUmann and Villagran 1965 Kinrade... 

StL Nostoc phycobiont from Peltigera canina (L.) WiUd. 

Lenton JR, Goad LJ, Goodwin TW (1973a) Sterols of the mycobiont and phycobiont isolated from the lichen Xanthoria parietina. Phytochemistry 12 2249-2253 Lenton JR, Goad LJ, Goodwin TW (1973b) Sterols of Xanthoria parietina evidence for two sterol pools and the identification of a novel Qs triene, ergosta-5,8,22-trien-3-P-ol. Phytochemistry 12 1135-1140 Letcher RM (1968) Chemistry of lichen constituents VII mass spectra of some pulvic acid derivatives. Org Mass Spectrom 1 805-817... 

The mobile carbohydrates produced by photosynthesis in lichens have been studied and this work has been reviewed by Richardson (272). Hill and Ahmadjian (7(57) have shown that four genera of lichen algae isolated in pure culture were able to produce the polyol which is known to move from alga to fungus in lichens containing these algae. Similar results were obtained by Komiya and Shibata (2J3) by working with cultured phycobionts and mycobionts. 

Takahashi, Takeda, and Shibata (322) have made a comparative study of the water-soluble polysaccharides isolated from laboratory cultures of lichen phycobionts and mycobionts. Those of the mycobionts were closely related to those of the parent lichen so that it is likely that the water-soluble lichen polysaccharides are produced by the mycobiont like the lichen metabolites of lower molecular weight. 

Evidence for two sterol pools in lichens has been presented (228,229). The first pool, associated with the mycobiont, is readily extracted from the lichen and consists mainly of C28 sterols while the second pool is tightly bound and can only be extracted after hydroxide digestion of the lichen. This second group consists largely of C29 sterols which are dominant in the phycobiont. 

Sterols of the Mycobiont and Phycobiont Isolated from the Lichen Xanthoria... 

The habit of hairlike lichens, with their threadlike thalli, resembles that of fruticose lichens. These lichens, however, are much smaller and usually not more than a few millimeters high. In contrast to most lichens, the habit is principally determined by the phycobiont. Filamentous algae, belonging to the Chlorophyceae or the Cyanophyceae, are more or less closely ensheathed by hyphae of the mycobionts (Figs. 23-25). 

Some lichens not only consist of one mycobiont and one phycobiont, but of one mycobiont associated with two different algae. The main algal partner always belongs to the Chlorophyceae, the second to the Cyanophyceae. The importance of the latter for the mycobiont lies in the fact that the additional blue-green alga is able to fix atmospheric nitrogen and has been shown to pass this to the mycobiont in the main part of the thallus (see Chapter 9). 

Ben-Shaul, Y., Paran, N., and Galun, M. (1969). The ultrastructure of the association between phycobiont and mycobiont in three ecotypes of the lichen Caloplacaaurantiavar.aurantia. J. Microsc. Paris) 8, 415-422. 

Scott (1959) found with Peltigera praetextata that an aqueous extract of the phycobiont must be present for successful germination. 

This chapter summarizes the submicroscopical investigations on lichens. The substructure of phycobionts and mycobionts and their symbiotic relationships are considered as well as changes in substructure due to different ecological conditions. Thallus surface structures are illustrated with the scanning electron microscope. 

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