[Release of "Saccharomyces cerevisiae" protoplasts: scanning electron microscope study (author's transl)].

In a previous study we described the minimal methodology used to obtain protoplasts from ascomycetous yeasts. Using a reducing agent associated with 1,3-beta-glucanase at 26 degrees C, protoplasts were invariably obtained. In the present study we localized the disruption spots of the cell wall using the two same reagents. The observations were made with the scanning electron microscope. The disruption site was always in the subterminal region, and this very simple structure (proteins with disulphide bridges and 1,3-beta-glucans) was opposite the birth-scar. The dissociation of the two reagents showed that a small part of the yeast population was able to release protoplasts with only glucanase. We believe these very sensitive yeasts (2 to 10% population) to be very young cells. These disruption sites seemed very different from budding-sites. They might be identical with elongation-sites, or with the opening in the ascus-wall during germinating ascospore release.