蓝氏贾第虫核被膜缺口的电镜观寨

ELECTRON- MICROSCOPICAL OBSERVATIONS ON THE NUCLEAR ENVELOPE OPENINGS OF Ciardia lamblia

双滴虫类是迄今所知的现存最原始的真核生物类群。以蓝氏贾第虫作为双滴虫类的代表，对其细胞核进行了电镜观察。除了未见有核仁外，还发现其核被膜的横切面上存在有缺口。在缺口的边缘处，核内膜与校外膜是相互连接着的，表明并非切片时所造成的假象。核被膜缺口处常有一核纤层样的薄层分隔核质与细胞质。用高锰酸钾固定细胞以求只保存膜结构时，核被膜缺口仍然可见，上述的薄层即未见到。核被膜缺口的发现证实了李靖炎（１９７９）的核被膜起源假说所作出的推断。

There are evidences showing that diplomonads would be the most primitive eukaryotesamong all present- existing organisms. Therefore, the informations about diplomonads nucle us are very important for investigating the origin and early evolution of cell nucleus. However, they are very seldom in literature. The nucleus of Glardia lamblla was Investigated as a representative of dlplomonad nucleus with electron- microscopy. The perlnuclear space within the nuclear envelope of Giardia is very prominent and on this background we found that there were openings on the nuclear envelope, which were very much larger than the nuclear pores.The sixe of the opening varied in different nuclei.At the margin of the opening.the nuclear inner membrane is continuous with the nuclear outer mem brane(Figs.1, 4). Therefore, the opening can not be theartefact due to sectioning. Usually,at the opening,there is a nuclear lamina-like thin layer separating nucleoplasm from cytoplasm(Fig.2). The layer seems not membranous, because when Giardia cells were fixed with KMnO4 to preserve only membranous structures, this layer were absent(Fig.4). Thelayer might perhaps be a part of the nuclear lamina of Giardia.Although after a series of specific extractions to demonstrate Giardia nuclear matrix;nuclear lamina could not be found (Dai et al.,1996), it might still be exist butonly so primitive that could not bear the routine extratlons. Nuclear envelope must have originated from the primitive endoplasmic reticulum in the elosest prokaryotic ancestor of eukaryotic cells(Li, 1979). Those parts of the primitive endoplasmic reticulum, which were directly neighboring to the'nuclear region'oftheprokaryotic ancestor evolved into nuclear envelope(Li, 1996). According to this hypothesis,at the earlier stage of this evolutionary process, the newly formed primitive nuclear envelope could not enclose the whole nuclear region and there must have remained many openings.The discovery of nuclear envelope openings in Giardia nucleus has confirmed this deduction.