伍氏游仆虫接合过程中老大核后碎块的去向

在伍氏游仆虫(Euplotes woodruffi)接合后体发育过程中,已呈退化状态的老大核后碎块,在细胞第二次形态发生时,逐渐恢复其正常形态结构。T形新大核原基向后延伸而与恢复正常形态的老大核后碎块紧密靠拢。此时在光镜下观察,很容易误认为二者已融合为一。但在接合后体分裂之前,老大核后碎块再次瓦解,T形大核原基缩短成棒状而与老大核后碎块分开,此时二者界限分明。细胞分裂后,残存的老大核后碎块停留于后子虫中,最后被吸收。几个关键时期大核原基和老大核后碎块DNA含量的测定,也证明新老大核不融合。本文还讨论了老大核后碎块在有性过程中的功能。

THE FATE OF POSTERIOR FRAGMENTS OF OLD MACRONUCLEUS DURING CONJUGATION IN EUPLOTES WOODRUFFI

After conjugation,the anterior fragments of the old degenerating macronucleus became pycnotic and disappeared soon, while the posterior fragments remained until the exconjugant divided once or twice. The first sign of degeneration of the posterior fragments was the appearance of Feulgen-negative vacuoles. EM photographs also showed chromatin-surrounded electron-light spaces. At the time of second cortex morphogenesis of the exconjugants, the posterior fragments began to regenerate: Feulgen-negative vacuoles disappeared, and densely stained chromatin granules became evenly scattered throughout. The "T"-shaped macronuclear anlage extended posteriorly and ended very closely to the regenerated posterior fragments which stained as intensely as the macronuclear anlage. This condition, which lasted at least five days if no food was supplied, gave a look as if the macronuclear anlage and the posterior fragments had fused to form the new macronucleus, but actually it was not so. When the "T"-shaped macronucleus shortened to rod-shape to prepare for division, it was clearly de- marcated from the posterior fragments. The latter began to shrink, and after cell division, became pycnotic and were finally absorbed in the opisthe.Measurement of DNA content of the macronuclear anlage also showed that the posterior fragments did not fuse with the anlage.