Préservation de L'Ultrastructure du Sclérote de Sclerotinia tuberosa (Champignon Discomycète); un Modèle pour la Préparation des Echantillons Imperméables et Hétérogènes

Abstract

Preservation of Fine Structure in the Sclerotium of Sclerotinia tuberosa, a Discomycete Fungus; a Model for Preparing Infiltration Resistant and Heterogeneous Specimens
The sclerotium of Sclerotinia tuberosa is difficult to prepare for electron microscopy, on account of its resistance to infiltration and its heterogeneity. In this work, several preparative methods have been investigated. The effects of varying composition, concentration and pH of the fixative mixture, fixation time (from 2 to 24 hours), embedding medium have been discussed. This kind of sample re-quires a formaldehyde-glutaraldehyde mixture rather than glutaraldehyde only. The nature of buffer plays an important role in preserving the fine structure. It appears that buffers are to be valued for their capacity to restrict ionic leakage and protein extraction. From this point of view the citrate-phosphate buffer allows the best overall pictures to be obtained. However a long fixation time limits the characteristic effects of the buffer and should be preferred to a shorter time, as far as topographic research is concerned. It is also necessary to increase the post-fixation time in order to obtain a good contrast although this may be less important if the aldehyde fixation is sufficiently long. In conclusion a satisfactory fixation and embedding technique for the sclerotium of Sclerotinia tuberosa is herewith suggested, which can be applied to other samples with the same technical problems.