贻贝棘尾虫(原生动物,纤毛门)镜像骈体自身各部移接的实验

Experiment of transposition between different regions in mirror-image doublets of Stylonychia mytilus (Protozoa:Ciliophora:Hypotrichida)

棘尾虫是细胞表面具有特殊纤毛结构排列方式的复杂下毛类纤毛虫。其镜像骈体的两列纤毛结构几乎完全是左右对称排列 ,一个是正常方式排列的 ,另一个是相反方式排列。本文包括两项移接实验 :1)将棘尾虫口对镜像骈体一侧细胞的后半部分倒转 180°与另一侧细胞的前半部分对接 ;2 )将此种骈体一侧后半部分调转90°与另一侧细胞的前半部分对接。接后定时分期固定接块 ,以蛋白银染色法 ,观察其发育过程及结果。实验 1的发育结果为有的仍形成口对镜像骈体 ;有的成为末端对末端的镜像骈体。实验 2的发育结果为全部成为口对镜像骈体。两项实验结果均可用位置值假说解释 ,实验 1属于位置值插入的结果 ;实验 2为位置值添加的结果。为何实验Ⅰ有的发育成口对镜像骈体有的发育成末端对末端的镜像骈体 ,而实验 2却全部发育成口对镜像骈体呢 ?这是接块发育中是否发生对折的结果。Shietal.(1991)认为与预存的缘棘毛和是否具有完整表膜的面积大小有关系。接块在发育中是否发生对折与接块的伤口一侧面积大小和具完整表膜有关系。接块具完整表膜和缘棘毛的一侧由于新缘棘毛和口围带的发育生长 ,造成该侧的伸张 ,产生前后两接块向伤口一侧对折的压力 ,从而接块发生对折形成口对镜像骈体。我们认为还应有其它因素 :(1)与细胞?

Styonychia mytilus is a well-known hypotrichous ciliate with compound ciliary structures arranged in a specific manner on the cell surface. In mirror-image doublets (MID below) of this ciliate, two nearly complete sets of ciliary structures are arrayed side-by side, one in a normal, and another in a reversed arrangement. This paper includes two kinds of transposing experiments:1)Transposing the posterior half on one side to the anterior half on the other side with 180° rotation, and 2)transposing the posterior half on one side to the anterior half on the other side with 90°rotation.Then we use the modified protargol technique to observe the whole process and results of pattern formation. The first experiment showed that some masses regenerate into side-by-side MID whereas others turn into end-to-end MID. The results of these two experiment can be explained by the hypothesis of positional values. The results of the first experiment correspond to the descriptions of the inserting positional value, whereas the second phenomena can be explained by the adding mode hypothesis. Regarding the results that both side-by-side MID and end-to-end MID were generated in the second experiment, the following data or reasons are possible, based on the present studies. Shi et al.(1991) think that it is related to pre-existing marginal cirri and the integrity of the original pellicle.The development of a new adoral zone of membranelles (AZM) and marginal cirri that near the original pellicle and marginal cirri produce tension on this side. This tension forces the two transposing masses to fold together. So they would regenerate into mirror-image doublets MID. We think there are additional factors:(1) the surface tension of cytoplasm plays an important role. The cytoskeleton keeps the shape of the MID fixing. If it is destroyed, the surface tension promotes the two masses to fold together. The side-by-side MID are produced;(2) the polarity and orientation are important factors. According to the principle of vector addition, if the polarities of the two half masses are inverse exactly, the regeneration will produce end-to-end MID. And if there exists an angle between the two regeneration orientation of the two half masses, the result will be a side-by-side MID .