versity of Michigan. Ann Arbor.)~Within the limits of the light microscope the sequence of events occurring during conjugation in Tetrahymena pyriformis is well known (2, 4, 5).However, certain questions regarding the finer morphological details can be resolved only with the electron microscope. One such question is concerned with the interchange of cytoplasmic particulates between mates during conjugation. Silver-line studies of single vegetative cells show no pellicular modifications in the preoral region that would indicate the presence of a special attachment organelle (1). Light microscope studies of conjugating cells give no hint of pellicular differentiation in the region of contact, between the mates. It, therefore, came as somewhat of a surprise to find a well defined region of differentiated pellicle which may serve the function of permitting a flow of some cytoplasmic particulates from one cell to the other during conjugation. The purpose of this report is to describe this observation.
Materials and MethodsThe strains of T. pyrlformls used in this investigation were the following: strains WH 6 and WH 14, mating types I and II respectively of variety t; strains TC 110 and TC 89, mating types I and V respectively of variety 9. Representatives of two varieties were employed for comparative purposes.The cells were grown in 500 ml. flasks in stock 2 per cent proteose-peptone-tryptone media at pH 7.2. Toward the end of logarithmic growth, they were washed twice by centrifugafion in double-glass-distilled water and stored for 12 hours. The cells were then mated in equal numbers in standard ten depression slides and incubated at 25°C. Pairs accumulating at the bottom of the depression were removed with a micropipette at specified time intervals and transferred to centrifuge tubes in which they were fixed, dehydrated, and embedded in plastic.To one part of a concentrated suspension of T.pyriformis were added, in succession, one part of McIlvaine buffer pH 7.4 (0.9 ml. of 0.1 M citric acid and 9.1 ml. of 0.2 M Na2 HPO4) and two parts of 2 per cent * This investigation was supported by a research grant (PHS E1416) from the National Institutes of Health, Public Health Service, and the Horace H. Rackham School for Graduate Studies, University of Michigan.Received for publication, June 9, 1958. OsO4. The final concentration of OsO4 was therefore 1 per cent. The period of fixation was 1 hour at room temperature. Dehydration at 15 minute intervals through changes of ethanol was carried out in centrifuge tubes. Infiltration was accomplished by three changes of a mixture of 40 per cent ethyl methacrylate and 60 per cent n-butyl methacrylate. The pellets were then embedded in No. 00 gelatin capsules containing the above methacrylate mixture plus 1 per cent luperco CDB. Polymerization was accomplished by heating at 60°C. for 24 hours.Sections were cut with glass knives on a PorterBlum microtome set to cut at 1/40/z. The sections were then floated on 20 per cent ethyl alcohol from which they were mounted on formvar-cov...
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