荔枝(Litchi chinensis Sonn.) 花芽分化过程的细胞超微结构观察

应用透射电镜对荔枝茎类生长锥由营养生长转变为生殖生长过程的细胞超微结构进行观察。结果表明，荔枝圆锥花序发育期细胞排列紧密,细胞质浓，液泡小，细胞核大并占据着细胞大部分位置；细胞质内有丰富的线粒体和膜状系统，整个膜状系统内连细胞核，细胞内囊泡大量形成、融合与迁移。这些均显示出细胞内结构物质在此期经历着活跃的周转和合成代谢，细胞内部在基因 的控制下有序地表达，为发育过程质的转变积累足够的信息和物质。生长锥由尖长变为宽平的花序原基时，其组织细胞结构也发生了相应的变化，最显著的特征是在此过程中，有一些细胞发生了程序性死亡。正在凋亡的细胞核染色质固缩、趋边、核膜破裂或皱缩、细胞质囊泡化并将降解的物质运转到周围细胞，从而保证了其他细胞正常发育以及生长的细胞对物质和能量的需求。

Observation on Cell Ultrastructure of Flower Bud Differentiation in Litchi (Litchi chinensis Sonn.)

Cell ultrastructure of litchi meristem of stem apex transformed in the process of devel- opment from vegetative growth to reproductive growth have been observed by transmission electron microscope. Cells before paniculiform development arrange tightly without cell gap,cytoplasm is thick,vacuole issmall,and mostroom of cell is occupied by big and round nucleus.There existsome transparentelectron regions in the middle of nucleus with scattering particles and microfibrils.There are abundant mitochondria and many membranaceous structures in the cytoplasm. The whole mem- branceous system connects nucleus and plasmodesmata.A lotof vesicles form,fuse and migrate.The results show thatstructure substances of cells are ongoing actively synthetic metabolism and change, and genes in cells express regularly to accumulate enough information and substances for radical changes in the process of development.When the cone of growth is from sharp and long to thin and flatduring paniculiform development,changes take placein cellularstructure to fitforthe differentia- tion of floral primodia. The most obvious characteristics is that programmed cell death ( PCD) oc- curred in some cells.In the PCD,condensation of nucleus,marginalization of chromatin,nuclear membrane shrinkage and destruction definitely occur.There are many vesicles in the cytoplasm, which may be related to the degradation of cell substances.The degradation productwas transfered to nearby cells in the form of vesicles through plasmodesmata.Thereby,the need of other normal cell development for substances and energy is guaranteed.