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Thallus ultrastructure and the localization of proteins involved in photosynthesis, N2 fixation and ammonia assimilation was studied in the Lichina confinis (O. F. Müll) C. Ag.-Calothrix symbiosis. The lichen thallus showed profuse branching. Within this, the cyanobiont was located in the cortical zone. Haustoria were frequently observed in contact with vegetative cells of the cyanobiont but not with heterocysts. An extensive mucilage layer containing numerous vesicles occurred around cyanobiont cells. Immunolabelling showed nitrogenase to be exclusively located in heterocysts of the cyanobiont and the free-living Calothrix sp. Glutamine synthetase (GS) levels in the cyanobiont were found to be drastically decreased compared to the levels in free-living (cultured) Calothrix sp. Such a decrease was more prominent in mature parts of the thallus than in the apical region. Rubisco was mostly located in carboxysomes of the vegetative cells of the cyanobiont. There were relatively low levels of Rubisco in the cytoplasm of vegetative cells, while heterocysts showed negligible levels. In free-living (cultured) Calothrix sp., phycoerythrin (PE) was found to be located along the thylakoid membranes both in vegetative cells and heterocysts. Cyanobiont cells showed a similar pattern but the levels were relatively lower. [ABSTRACT FROM AUTHOR]

Acetylene reduction (nitrogenase activity) by excised cephalodia of Peltigera aphthosa Willd, slowly declined on transfer of the cephalodia from light to darkness. The decline was more rapid in the absence of CO2 or when phosphoenolpyruvate carboxylase activity was inhibited by adding maleic acid or malonic acid. When glutamine synthetase (GS) activity was totally inhibited by adding L-methionine-DL- sulphoximine (MSX) the decline in nitrogenase activity in the absence of CO2 still occurred, However, this loss of activity did not occur when the mycobiont was disrupted using digitonin (0.01% wlv) and the fixed NH4+ was released into the medium. The data suggest that dark CO2 fixation by the fungus supplies carbon skeletons which remove newly fixed NH4+ produced by the cyanobacterium. When such carbon skeletons are not available NH4+ accumulates and inhibits nitrogenase activity even in the absence of GS activity. It is probable that NH4+ and a product of GS exert independent inhibitory effects on nitrogenase activity. [ABSTRACT FROM AUTHOR]

The qualitative distribution and quantitative estimates of nitrogenase (EC 1.7.99.2), glutamine synthetase (EC 6.3.1.2), phycoerythrin and ribulose 1,5-bisphosphate carboxylase/oxygenase (EC 4.1.1.39) were studied in the cyanobacterium Nostoc residing in internal cephalodia of the tripartite lichen Nephroma arcticum L. Polyclonal antisera, raised in rabbit against the proteins, and goat anti-rabbit IgG conjugated to 10 nm gold were used as probes to detect the antigens by transmission electron microscopy. Western blot analyses demonstrated the monospecificity of the antisera. Nitrogenase was localized in heterocysts, with vegetative cells showing a label intensity comparable to the background. Distribution of the antigen within the heterocysts was uniform. Glutamine synthetase labelling was very low, but appeared to be distributed in both cell types. An intense phycoerythrin labelling was associated with the thylakoid region of the vegetative cells, whereas a much lower labelling was observed in the heterocyst. No significant differences were found between cyanobionts in younger and older cephalodia except for the nitrogenase labelling, which was higher in heterocysts of the cyanobiont in younger cephalodia. Most of the ribulose 1.5-bisphosphate carboxylase/oxygenase (Rubisco) label was present in vegetative cells. The Rubisco label was pronounced in the carboxysomes, whereas the label in the cytoplasm, on a unit area basis, was much lower. Heterocysts showed a label intensity similar to that of the vegetative cell cytoplasm. In Nostoc of the bipartite lichen Peltigera canina L., the Rubisco protein showed a comparable distribution pattern, but the average number of carboxysomes per vegetative cell was about 4 times higher. [ABSTRACT FROM AUTHOR]