杜仲次生木质部导管分子分化中的程序性死亡

PROGRAMMED CELL DEATH DURING THE VESSEL ELE MENT DIFFERENTIATION OF THE SECONDARY XYLEM IN EUCOMMIA ULMOIDES SHOOTS 

运用原位末端标记法，证明了杜仲（ＥｕｃｏｍｍｉａｕｌｍｏｉｄｅｓＯｌｉｖ．）次生木质部的导管分子分化过程是程序性死亡（ｐｒｏｇｒａｍｍｅｄｃｅｌｄｅａｔｈ，ＰＣＤ）过程。它包括一系列的物质合成和细胞结构的解体和自溶：细胞核逐步变得极不规则，染色质高度凝集，有些细胞核的核周腔膨大，核周腔内存在着包裹有核物质的内膜凸起，最后，核膜消失，核解体。细胞核是ＰＣＤ中最后消失的细胞器之一。线粒体有两种解体方式，一种为线粒体内部结构紊乱，嵴极不清晰，线粒体皱缩变形；另一种为线粒体出现一些电子密度低的透明区，进而裂开。内质网囊泡化，相邻的内质网槽库之间互相连接，形成分隔。内质网和液泡共同行使溶酶体功能，吞噬各种细胞器残体。解体后的物质可能有两种去向，一是通过纹孔运输到邻近的细胞中。

The result from in situ end labelling of fragmented DNA indicated that the vessel element differentiation of the secondary xylem in Eucommia ulmoides Oliv. was a typical programmed cell death (PCD) which involved a series of events, viz. synthesis of components essential for the secondary wall formation and a well organized succession of protoplast degeneration and autolysis in the tracheary cells. The nuclei gradually became irregular with highly condensed chromatin. In some nuclei, the cisterna of the nuclear envelope became unevenly dilated within which some inner membrane protrusion enclosed with nuclear materials were present. The nuclear envelope underwent disruption and the nucleus eventually degenerated. However, as the nucleus was one of the most stable components in the cell, it was among the last organelles disappeared during the autolytic process. In the process, there were two forms of degeneration in the mitochondria (Mit). In one form the Mit shrank and became disorganized; in the other, part of the matrix in the Mit became electron lucent with breakage of the membrane nearby. The cytoplasmic component residues were phagocitized and sequestered by the dilated rough endoplasmic reticulum (RER) cisternae. The RER and vacuoles did play a vital role in the further degeneration of other organelles just similar to the lysosomes acting in the animal cells. The autolyzed debri might be utilized in situ by taking part in the formation of secondary wall or be transported to the adjacent cells through the pits.