Localisation cellulaire du calcium chez le champignon Ascomycète Sphaerostilbe repens par analyse directe à la microsonde électronique

In the Ascomycete Sphaerostilbe repens, where calcium is necessary for the differentiation of aggregated organs, microlocalization of calcium was determined both in undifferentiated mycelium and in rhizomorphs. In every case cell walls contained high calcium concentrations. Mucilaginous compounds around cells also contain this cation but at a lower level.In the vegetative mycelium, Woronin bodies and particularily mitochondria accumulated calcium. In the vacuoles of rhizomorph cells, calcium concentration was low.Calcium location in cell walls suggests that this element could play a role in cell-to-cell adhesion.

Influence of calcium on the differentiation and growth of aggregated organs in Sphaerostilbe repens

In the ascomycete Sphaerostilbe repens the vegetative mycelium aggregated into structures composed of aerial coremia and rhizomorphs immersed in the culture medium. The morphology and growth of the cultures were examined on a defined medium with and without calcium supplementation.Initiation and growth of aggregated organs occurred only if calcium was present continuously in the culture medium. On calcium-deficient media the fungus produced only vegetative mycelium which retained its ability to aggregate in the presence of the cation. Small concentrations of calcium (less than 1 ppm) stimulated aggregation of the mycelium, but higher concentrations (about 200 ppm) were necessary to obtain optimum development of the aggregated organs. Strontium partially replaced calcium, but lithium did not, as a stimulator of aggregation.