Stomatogenic function of the micronucleus in Paramecium jenningsi

The stomatogenic function of the micronucleus in Paramecium jenningsi is documented in the present report. Amicronucleate cell lines were generated by removal of the micronuclei with a microinjection needle. Such cell lines exhibited a temporary state of growth depression marked by the development of abnormal oral apparatuses, and they gradually recovered to nearnormal. During sexual reproduction, the amicronucleates failed to develop an oral apparatus but resorbed the pre-existing oral apparatus, resulting in astomy. The types of stomatogenic abnormalities exhibited during asexual and sexual reproduction, apart from some unique features, were largely similar to those observed in P. tetraurelia. Reimplantation of the micronucleus into amicronucleates during the depression period likewise promoted stomatogenic recovery, both in speed and in extent. These similarities between the two species indicate that the control of oral development by the micronucleus in them have much in common, suggesting that the stomatogenic function of the micronucleus is a characteristic of the genus Paramecium. Some of the cells in the renucleated cell lines lost the micronuclei during asexual propagation. Some preliminary observations indicated that such amicronucleates arising in the renucleated cell lines were not as abnormal as those amicronucleates derived by enucleation in the early phase of depression, but were comparable to the latter after the latter had recovered. This suggested that such amicronucleates had suffered only a "minor depression". The genetic implications of this was discussed in the context of the mechanism of stomatogenic recovery in amicronucleates.