Abstract:

Since nuclear extrusion was rediscovered in young Allium scale by S.H.WU in the years of 1950’s systematic investigations on this phenomenon were carried outwith various kinds of microscopic techniques and plant materials to collect more effective evidence to clarify the debate about whether the nuclear extrusion is an artifact or normal event. In the cooperative research of S. H. WU and C. H. LOU the normality of the occurrence of nuclear extrusion either in growing part of plant or in senescent tissue has been confirmed. This event is intimately associated with the physiological state of the tissues/cells and may play an important role in redistribution and reutilization of cell contents. Based on the results obtained a hypothesis of intercellular movement of protoplasm as a means of translocation of organic material in plants was suggested. Chromatin extrusion was also discovered in the pollen mother cells (cytomixis) of certain angiosperms by G. C. ZHENG and his team. Intercellular migration of chromatin appears most frequently at the stage of synizesis. Cytomixis has been studied in relation to variation and evolution. Chromosome aberration has been considered to be closely associated with chromatin extrusion. By vital microscopic observations of the live tissues of garlic ( Allium sativum L.) bud and wheat(Triticum aestivum L.) ovule combined with cinemicroscopy and video recording it has been uncovered that, not only the nuclear material but also the cytoplasm could traverse the intercellular channels by vigorous contraction and expansion, and they may simultaneously extrude out of a cell but often asynchronously migrate from one cell to another. The involvement of cytoplasmic constituents in intercellular migration was also detected in pollen mother cells with electron microscopy. Regarding the mechanism of intercellular movement a series of experiments provide convincing evidence showing that this kind of movement is an active metabolic process closely coupled with energy metabolism, and the motive power for driving the extrusion may be supplied by the contractile proteins in protoplasm.

高等植物中原生质细胞间运动研究的进展
张伟成
（中国科学院上海植物生理生态研究所，上海200032）

摘要： 20世纪初已在植物营养组织和生殖体中观察到细胞核或染色质在细胞间的穿壁迁移。但多年来涉及这一研究的学者大多倾向于将它看做是人为赝象而未予深究。50 年代中期，自吴素萱在葱（ Allium L.）、蒜（Allium sativum L）等植物中重新发现了核穿壁运动现象以来，我国植物细胞与生理学家随之进行了系统与广泛的探讨。穿壁运动的研究及进展主要包括两个方面。一方面是营养组织中原生质的细胞间运动，由吴素萱、娄成后合作主持的有关研究项目着重与营养组织中有机物的运输、分配与再利用生理过程相联系。多年来积累的成果表明：1）核物质的穿壁运动是广泛存在于植物营养组织中的固有正常现象，是一定生理状态下有机物在细胞间运输与细胞内含物再分配的一种方式；2）通过对蒜芽鞘、小麦（Triticum aestovum L.）珠心、胚乳等组织的显微活体观察与亚显微结构分析，揭示与记录了原生质在细胞间运动的全过程与动态细节，发现参与穿壁过程的不限于核，核和胞质各组分可同时、亦可分别借自身的主动伸缩穿壁迁移；呈现穿壁运动的组织中，壁上部分胞间连丝结构剧烈变更，胞间通道明显扩大，可100-300nm，核或胞质可经此开放通道迁移而不致有损通道外沿质膜的完整；2.原生质穿壁运动的动力来自细胞的能量代谢，与微丝活动密切有关，穿壁的原生质组分呈现活跃的ATP酶活性。近期的研究表明，小麦胚乳细胞中作活跃伸缩运动的胞质纤索是由F肌动蛋白集束组成，肌动蛋白纤丝可跨胞分布而存在于常态胞间连丝中，从而使相邻细胞的胞质骨架得以实现胞间连续。另一方面是生殖体中染色质的穿壁运动研究，主要在郑国锠主持下开展，着重探讨花粉母细胞间染色质穿壁现象的普遍性及其与遗传、变异和进化的关系；对多种植物的系统观察证明，染色质穿壁出现在减数分裂前期I的凝线期，染色质通过胞质通道在一系列细胞间依次迁移；由电镜观察可见，参与穿壁运动的还包括胞质的多种成员；穿壁运动的动力被认为由原生质的收缩蛋白提供。郑国锠等的研究成果表明，染色质穿壁运动可导致染色体数目、结构的改变，由此产生的部分有活力的配子体经受精后有可能导致新一代个体出现多倍体或非整倍体，引起遗传性状的变异。
关键词： 核穿壁；胞间连丝

Key words: nuclear extrusion, plasmodesma