Main Content

The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Ref ID : 7598

Stephen F. NG and Mikami Kazuyuki; Morphogenetic Role of the Germ Nucleus in Paramecium tetraurelia. Protistologica XVII(4):497-509, 1981

Reprint

In File

Notes

The morphogenetic role of the germ nucleus (micronucleus) in Paramecium tetraurelia was investigated. 18 young amicronucleate cell lines were generated by removal of the micronuclei with a micropipette. Within 20 fissions after their initiation, the cell lines were in a state of depression characterized by abnormal oral apparatus, slow feeding rate, slow growth and small cell size. The oral abnormalities included reduction in the length of the buccal cavity, reduction and disruption of the regular pattern of the oral membranelles, and in extreme cases the loss of the entire buccal cavity resulting in nonfeeding thin cells. Subsequently, the cell lines contained more and more partially-normal progeny: gross oral abnormalities were rare; feeding rate, growth rate and cell size all increased. Nevertheless, the cell lines remained subnormal before clonal aging. These observations demonstrated a definite, but not indispensable role of the micronucleus in stomatogenesis during asexual reproduction. On the other hand, during autogamy amicronucleates resorbed the preexisting oral apparatus, but failed to produce a new one. Formation of the new oral apparatus did not proceed beyond the initial proliferation of basal bodies on the right of the vestibule; thereafter no buccal cavity or oral membranelles were formed. Such failures cannot be accounted for by the absence of the macronuclear anlagen since the anlagen normally only appear after the initiation of these morphogenetic events. Postautogamous amicronucleates could not feed and ultimately died of starvation, except under rare circumstances when the preexisting oral apparatus persisted. The present observations thus demonstrated the indispensability of the micronucleus in oral replacement, in addition to its germinal role, during sexual reproduction.