Clonal aging in Paramecium tetraurelia. Absence of evidence for a cytoplasmic factor.

Cells of Paramecium tetraurelia show clonal aging with characteristics comparable to the aging seen in tissue culture cell lines. An investigation is underway to determine the relative contributions, if any, of the cytoplasm and the macronucleus to the onset of senescence. Using a microinjection protocol, the importance of the cytoplasm to aging was tested. Cytoplasm was transferred from young cells into old cells to see if the mean age of death of the injected cell lines could be increased, compared with uninjected controls and sham injected controls. Cytoplasm from old cells was transferred into young cells to see if the mean age of death of the injected cell lines could be decreased, compared with sham injected and uninjected controls. In neither case was there any statistically significant change in mean ages of death. Furthermore, no changes can be demonstrated even with a protocol which transplanted 3 times the normal cytoplasmic volume. Thus, a cytoplasmic effect upon vegetative aging in P. tetraurelia cannot be demonstrated. Tests of a macronuclear influence are now underway.