QUANTITATIVE APPROACH TO THE FINE-STRUCTURE OF BOTH SYMBIONTS OF 9 UMBILICARIA SPECIES

The ultrastructure of the photobiont and mycobiont of nine Umbilicaria species has been studied. The stereological parameter Vv (volume density) has been estimated for the most important organelles and cellular structures in order to quantify their volumetric contribution to the cells of both symbionts and to assess their inter- and intraspecific variability. The relationship between the symbionts is analyzed with respect to the absence of intracellular haustoria in the material together with the nutritional aspects linked to the storage bodies (lipids and starch). The fine structure of the algal pyrenoid is reconsidered in the light of the various arrangements of pyreno-globuli in the ''impressa'' type of pyrenoid, the only one present in the samples studied. On only a few occasions could the species-specific ultrastructural features be related to their autoecology or physiology.