棘尾虫接合生殖期间核对形态发生的影响

THE NUCLEAR EFFECT ON MORPHOGENESIS DURING CONJUGATION IN STYLONYCHIA MYTILUS

本文完成了四项实验,即1.促成棘尾虫无小核系与有小核系接合;2.诱导无小核系自系接合;3.在正常接合对上摘除全部大核或一个接合体的大核及小核;4.在正常接合后体上对老大核碎块和新大核胚基进行损伤实验。以改进过的黑色素法显示这些实验的结果,发现第一次接合形态发生和小核的有性过程都主要是由大核支持的,小核在第一次形态发生中也起重要作用。这些核产物可从一个有核接合体穿过细胞质桥去支持另一无核接合体的发育。本文还发现接合第二次形态发生由新大核胚基控制。损伤染色体和多线染色体时期的大核胚基,第二次形态发生消失或不正带。越过第二次形态发生的大核胚基显著增强耐受损伤的能力,这些结果符合Prescott等(1973)对棘尾虫大核遗传装置的设想。

Four experiments were carried out and the results are reported in the present paper. In experiment 1, amicronucleate Stylonychia mytilus obtained naturally were allowed to conjugate with micronucleate of its opposite mating type. The 1st conjugational morphogenesis in both conjugants progressed normally through the whole course except the oral primordium in amicronucleate conjugant was smaller in initial stage than that of the micronucleate. In experiment 2, conjugation was induced between two amicronucleates in the same clone. The 1st conjugational morphogenesis in the amicronucleate selfing pair could also progress through the whole course, but the cirral and oral primordia manifested abnormalities in many respects, and exconju-gant didn't undergo the 2nd morphogenesis and ended in death. In the experiment 3, the macro-or both macro- and micronuclei were removed from one or both conjugants of a normal micronucleate mating pair. In the mating pair from which the macronuclei of both sides were removed, the 1st conjugational morphogenesis didn't occur and the micronuclear development was arrested at the stage at which the macronuclei were removed. In the mating pair from which only one side's macronucleus was removed, the 1st conjugational morphogenesis and micronuclear development in both sides progressed normally, but more slowly. IB the conjugant with both micro- and macronuclei removed, morphogenesis progressed normally too, but no micronuclear events,happened. In the 4th experiment, the macronuclear anlage in each developmental stage was subjected to stabbing or cutting, it was found that the anlage in chromosomal or polytene chromosomal stage was most sensitive to injury. Once it was reduced in size by stabbing, the exconjugant didn't undergo 2nd morphogenesis any longer and eventually perished, while the anlage in rod-shaped stage with replication band emerging was most insusceptible to injury. These results lead the authors to conclude that the 1st conjugational morphogenesis is controlled by the macronucleus and effected partially by the micronuclei, and the nuclear products supporting morphogenesis may be transmitted through the cytoplasmic bridge from one conjugant to the other, and that the 2nd conjugational morphogenesis is controlled by the macronuclear anlage, and it has nothing to do with the macronuclear fragments.