Protoplasmic Streaming and Nuclear Differentiation during Conjugation of Paramecium caudatum

Abstract

It is known in Paramecium that the fate of the micronucleus is determined by the intracellular localization of the nucleus and that protoplasmic streaming named cyclosis is very active during vegetative phase. The active streaming, if it occurs during conjugation, may interfere with the correct positioning of micronuclei and/or cytoplasmic determinants in a cell. In the present work, the velocity of protoplasmic streaming was measured during conjugation of P. caudatum. The results showed that the velocity changed remarkably at 3 stages. (1) It increased with the expansion of its active area 3 to 5 minutes after the mating reaction and then decreased again to the ordinary speed within 3 hours. The results of micro- or macronuclear removal showed that the increase in the velocity was not mediated either by the micronucleus or by the macro-nucleus. Moreover, injection of the anti-α-tubulin antibody at the mating reaction did not suppress the protoplasmic streaming effectively, although a role of microtubules on the protoplasmic streaming is not ruled out completely. (2) At the stages of disintegration of meiotic products and the exchange of gametic nuclei, the cytoplasm ceased streaming and then resumed it soon after synkaryon formation. (3) The streaming ceased again at the critical stage of macro-and micronuclear differentiation after the separation of mating pair, although the streaming was very active before and after this stage. Both cessations of (2) and (3) were not influenced by removal of the micronucleus during conjugation. The velocity of protoplasmic streaming during conjugation does not directly correlated with the micronuclear behavior. The cessation seems to be very convenient for intracellular positioning of the cytoplasmic determinants and/or of the micronuclei for the nuclear differentiation.