杨树筛管/伴胞复合体细胞程序性死亡的超微结构分析

利用电镜技术研究美洲黑杨次生韧皮部筛管和伴胞发育过程中细胞超微结构的动态变化,观察到筛管和伴胞由同一个次生韧皮部衍生细胞分裂分化形成.筛管的发育历经未成熟期、成熟期和衰退期的变化.未成熟期筛管分子表现为细胞的径向扩展、壁的增厚、筛管质体和P-蛋白质的产生;成熟期筛管分子细胞组分发生选择性自溶,细胞核核质弥散状,核膜不清晰,或核膜清晰而核物质降解,最后细胞核完全解体转化为P-蛋白质类的物质;衰退期筛管分子细胞质完全解体消失,失去功能.在筛管成熟期间,伴胞的细胞质较浓,内含丰富的核糖核蛋白体、线粒体等细胞器,与筛管相连的细胞壁上具有胞间连丝.随着筛管功能的衰退,伴胞表现出典型的细胞程序性死亡特征,细胞质内质网库槽膨大,细胞核核周腔出现,染色质凝聚边缘化,最后细胞完全解体消失.总之,美洲黑杨次生韧皮部筛管发育首先经历了细胞去核化的过程,在维持一段时间的生理功能后细胞质逐渐解体消失,与此同时伴胞细胞核、细胞质降解.笔者推测筛管与伴胞一起作为功能复合体共同完成各自的细胞程序性死亡过程.

Ultrastructural Analyses on Programmed Cell Death on Sieve Element/Companion Cell Complex in Poplar

The ultrastructural changes during the development of sieve element(SE)/companion cell(CC) complex(SE/CC complex)in Populus deltoides were investigated using electronic microscopy.The result showed that SE and CC come from the same secondary phloem mother cell.The development of sieve element went through three stages,i.e.immature,mature,and degenerate stage.In immature stage,the sieve element presented radial expansion,cell wall thickening,and production of sieve plastid and P-protein.The cytoplasma selectivly autolysed in mature stage.At the same time,karyoplasm was dispersed,and nuclear envelope was not clear,or karyoplasm was disorgnized,and nuclear envelope was clear.The karyopalsm finally turned into P-protein.In degenerate stage,the cytoplasm completely disappeared,and the function was lost.There was lots of organelle,such as ribsomes,mitochondria in companion cell during the mature stage of SE.Also the plasmodesmata appeared in cell wall between SE and CC.With decline of function in SE,the CC presented on a typical characteristic of programmed cell death.The endoplasm reticulum cisterna was enlarged,and so did perinuclear space.Synchronously,the chromatin condensed and aggregated towards the nuclear envelope.At last,the CC was disappeared completely.In conclusion,the development of secondary phloem SE underwent denucleation firstly.And the cytoplasm degenerated gradually after carrying out some physiological function.Simultaneously,the nuclear and cytoplasm of CC degenerated.We presume that SE and CC took the same programmed cell death procedure an intact function complex.