洋葱根尖淹水诱发细胞衰老过程的超微结构研究

洋葱根尖在水中培养一段时间后,一些根尖细胞开始衰老。细胞染色加深,分辨度下降,细胞结构不清楚。进而核糖体减少,细胞器出现解体。与此同时,细胞壁变厚,染色变深胞间连丝增多,胞间隙加大。一些细胞质、小泡,甚至衰老的线粒体常常通过胞间连丝进入相邻细胞。最后细胞彻底瓦解。

ULTRASTRUCTURAL STUDY ON SENESCENT PROCESS OF ONION (A. CEPA L. )ROOT-TIP CELLS

It is well known that onion is a kind of vegetable used for cytological study . In this paper we used it to study cell senescence, when onion roots grew about 5cm high in water there were often some senescing cells which were variable in number among the root-tip cells. Their senescent sequence was systematically studied by transmission electron microscopy. Our results showed that the senescing cells differed from the normal developing roottip cells in ultrastructure and electrondensity, and were relative to cell senescent degree. As the cells initially senesced, the conspicuous changes were that their cytoplasm became darker in electron densityand their resolving power declined, and cellular structures appeared unclear. Then their cytoplasm was deereased, organelles degraded vacuolation in the cells obviously increased. Finally, thd cells hardly contained any ribo-somes, only some degrading endoplasmic reticulum, dictyosomes and mitochondria. At the same time, the cells lost their nomal structual features. In addition to above-described ultrastructural changes, onion root tip cells during senescence possessed other features: their cell walls became thicker in width, darker in electron density ( plasmodesmata were distinctly increased in number ;intercellular spaces enlarged in volume,in which there was often some fibrillar-shaped or cotton-shaped material which was electron-dense; there were some irregular spaces between cell wall and plasma, membrane, but some vesiclaar-shaped, tubular-shaped and membranousshaped material was various in number.With the cell senescent progress, the spaces continuously enlarged and the material in the spaces was getting more and more in number . Also the cell contents, for example , cytoplasm, vesicles, even some senescing mitochondria often enter into one or few neighbouring cells through the plasmodesmata in their cell walls, carrying out frequent material translocation .