甜菊组织培养物中叶绿体的超微结构与脱分代

含有叶绿体的甜菊（Ｓｔｅｖｉａｒｅｂａｕｄｉａｎａ）愈伤组织细胞转移至新鲜培养基后，导致光合片层的逐渐减少或消失，最后叶绿体脱分化形成原质体样的结构。超微结构观察表明，光合片层的减少或消失与降解及叶绿体分裂特别是不均等缢缩分裂而致基质组分和类囊体膜稀释有关。这一过程并不完全同步，一些质体含有少量正常的片展而另一些质体含有退化的片层甚至片展结构完全消失。细胞的一个明显特点是细胞器大多聚集在细胞核附近，细胞质增加并向细胞中央伸出细胞质丝。同时可观察到原质体。培养７ｄ后，许多细胞呈分生状态，细胞质富含细胞器，充满了细胞的大部分空间。此时细胞中的质体大多呈原质体状态。在细胞生长的稳定期，质体内膜组织成基质基粒片层，同时质体核糖体增加。文中讨论了高度液泡化细胞脱分化与细胞中叶绿体脱分化的关系。

CHLOROPLAST ULTRASTRUCTURE AND DEDIFFERENTIATION IN TISSUE CULTURES OF STAEVIA REBAUDIANA BERTONI

Cells of Stevia rebaudiana callus tissue contain chloroplasts when cultured in a liquid medium in the light. Transfer of the callus into the fresh culture medium results in the gradual decrease or disappearance of photosynthetic lamellae and the eventual dedifferentiation of chloroplasts to form proplastid-like structures. This decrease or disappearance of photosynthetic lamellae is found to be correlated with the degradation of internal membranes, coupled With the diluting out of stroma constituents and thylakoid membranes due to chloroplast divisions, especially unequal constriction. The process is not completely synchronized so that some plastids still retain a few intact lamellae while other plastids contain degenerating lamellae or have lost the lamellae completely. In addition, some plastids observed at this stage contain one to several starch grains although starch is very rarely found in the inocula. A stricking feature at this stage is the apparent grouping of organells in the vicinity of the nudeus. The cytoplasm has increared in quantity and crosses the cell in bridge-like extensions partially filling in the cell center. At this stage, well defined proplastids are recognized. After 7 days of continuous culture, many Cells appear meristematic in that the cytoplasm, rich in organelles, fills most of the cell. The majority of the plastids found in the cell at this stage are proplastids. They may be ptesent as budded dividing forms or as oval spheroids. Their internal structure consists of randomly positioned single thylakoids resembling those of proplastids in intact development leaves. During the stationary phase of cell growth, the internal membranes of plastids are organized into stacked grana interconnected by stroma thylakoids, and at the same time the plastid ribosomes increase. A correlation was discussed between the dedifferentiation of the highly vacuolate cells induced by the subculturing process and a dedifferentiation of the chloroplasts with the cells.