冠突伪尾柱虫(Pseudourostyla cristata)接合生殖的研究 Ⅰ.核器演化

STUDIES ON CONJUGATION IN PSEUDOUROSTYLA CRIST ATAⅠ.NUCLEOGENESIS

在25℃条件下,冠突伪尾柱虫接合生殖全程历时10天左右。接合生殖过程中的核器演化包括:①数十枚老的大核逐步瓦解。电镜观察表明,老的大核是以一种类似于食物泡消化的方式被吸收的,并在此过程中伴有大量溶酶体出现。②仅8枚左右小核中的一枚参与新核器的发生。首先,位于胞口后部的一枚小核膨大并进行一次预备分裂,接着发生三次成熟分裂。每一接合体内形成一枚雄原核和一枚雌原核。雄原核互向对方迁移并与其雌原核融合成为合子核。合子核分裂两次,四枚子核之一发育为大核原基,另一枚发育为小核原基,其余两枚退化。预备分裂和前两次成熟分裂各自产生的两枚子核中,仅一枚进入下一次分裂,另一枚解体消失。在第一次成熟分裂前期,“降落伞”的形成和发展经历着复杂的结构变化,持续一小时以上。③大核原基经过长时间的发育,伴有多线染色体的形成和解体等一系列变化,方达成熟状态。成熟的大核原基以伸长断裂、分叉断裂和哑铃形缢缩三种方式进行分裂,小核原基亦随之分裂,逐步形成具60枚左右大核、8枚左右小核的正常营养体。其后,大核融合,开始配后第一次无性分裂。值得注意的是,大核原基发育到将成熟时,最初的迹象是染色质向大核原基中央集结成团,染色质团与核膜之间充满着匀质的核液。

During conjugation of Pseudourostyla cristata,only one of about 8 mi-cronuclei undergoes a preliminary division in each conjugant,then followed by three successive maturation divisions.The third division produces two pronu-clei.Following the male pronuclei exchange and fertilization,synkaryon divides twice.One of the four products develops into a macronuclear anlage,another into a micronuclear anlage,and the remaining two degenerate.In the pro-phase of the first maturation division,it was found that the development of parachute stage undergoes very complex changes that lasting at least for one hour.The macronuclear anlage develops for about 5 days and undergoes a series of complex changes including formation and disintegration of polytene chromosomes.As the macronuclear anlagen are on the point of maturing,the chromotin aggregates and forms a piece of chromotin in the centre of anlagen.The place between the piece and the nuclear membrane is full of homogeneous nuclear fluid.When the chromotin piece lengthens in anlagen,we have found that a large lump of nuclear material(about 1/2 of the centre chromotin piece)was removed from the anlagen,and its nature has not been known.Subsequently,the mature anlagen start to divide in three ways.During the development of new nuclei,the old macronuclei gradually disintegrate in such a way as in digestion and absorption of food vacuoles,and a lot of lysosomes are produced in the meantime.