Caractéristiques ultrastructurales de Ceratocystis ulmi en milieux naturel et artificiel

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Abstract
The ultrastructure of Ceratocystis ulmi (Buism.) C. Moreau was studied in both synthetic and natural media (infected tissues of elm). In fungal cells located at the cultures' margin and therefore considered young, a primitive ultrastructure with the following characteristics was observed. (1) The relatively voluminous nuclear area has irregular contours and appears to be devoid of an enclosing membrane; structures identified as developing mitochondria are contiguous to the nuclear area; endoplasmic reticulum is not evident. (2) As aging and septation of cells occur, the cytoplasm becomes less dense and organelles appear to be better delimited. Use of the goniometer has permitted the confirmation in many cases of the absence of membranes, and in others, their presence. Radioautographic studies of material labeled with [6-3H]thymidine showed that incorporation was greater in younger cells than older ones. Labeling in the latter occurred in association with fibrillar material within the nuclear areas, developing mitochondria, and other unidentified fibrillar masses. The importance of these observations is discussed. A mimeographed English version of results and discussion parts is available from the junior author.