The fine structure of the embryogenic callus of Ranunculus sceleratus L.
The fine structure of the embryogenic callus of Ranunculus sceleratus L.
复制标题
毛茛胚性愈伤组织的精细结构。
作者：
E. Thomas;R. Konar;H. Street
毛茛愈伤组织切片显示其组织为细胞聚集体，其表面细胞具有高细胞质，而内部细胞较大，细胞质密度较低且具有更高的空泡化。一些内部细胞的扩张和最终死亡导致细胞分离和聚集体分解。许多表面细胞参与愈伤组织中胚状体的起始，并且它们在结构上与幼苗茎表皮的胚发生细胞相对应。在存在 2,4-二氯苯氧基乙酸 (2,4-D) 的情况下，胚状体的发育会受到延迟，而当培养物转移到不含 2,4-D 的培养基中时，胚状体的发育会变得更快且更多产。愈伤组织培养物的胚胎发生细胞与幼苗茎表皮的胚胎发生细胞之间的相似性延伸到细胞大小、核大小、空泡化程度、核糖体和线粒体的丰度、淀粉体的存在和球体的突出。描述了球体的各种形式并讨论了它们可能的功能。在更高级的胚状体中观察到分化成叶绿体的淀粉体。有证据表明胚状体可以由单细胞产生，但不确定是否所有胚状体都是单细胞起源的。当胚胎发生细胞开始胚胎发生时，它们与周围细胞保持原生质连续性。一些表面细胞也明显地进行着活跃的分裂，但其结构却相当不同。典型地，它们的细胞核显示出高度的染色质浓缩，并且它们的细胞质包含纤维材料束。这表明这些细胞在胚胎发生中不直接发挥作用。聚集体的内部细胞具有低密度的核糖体和很少的内质网图谱或正常线粒体。在这些细胞中观察到沿着细胞核轮廓的极其细长的线粒体结构。在似乎发生细胞质解体的细胞中经常观察到未识别的结构。
Sections of callus of Ranunculus sceleratus reveal its organization into cellular aggregates, the superficial cells of which are highly cytoplasmic and the inner cells of which are larger, have less-dense cytoplasm and are more highly vacuolated. Expansion and ultimate death of some of the internal cells leads to cell separation and break up of the aggregates. Many of the superficial cells are involved in the initiation of embryoids in the callus and they correspond in structure with the embryogenic cells of the seedling stem epidermis. The embryoids are retarded in their development in presence of 2,4-dichlorophenoxyacetic acid (2,4-D) and embryoid development becomes more rapid and more prolific when cultures are transferred to a medium without 2,4-D. The similarity between the embryogenic cells of the callus cultures and those of the seedling stem epidermis extends to cell size, nuclear size, degree of vacuolation, abundance of ribosomes and mitochondria, presence of amyloplasts and prominence of spherosomes. The various forms of spherosome are described and their possible function discussed. Amyloplasts differentiating into chloroplasts are observed in the more advanced embryoids. There is evidence that embryoids can arise from single cells but it is uncertain whether all are of single-cell origin. The embryogenic cells are in protoplasmic continuity with surrounding cells when they embark upon embryogenesis. Some of the superficial cells, also clearly undergoing active division, are of rather different structure; characteristically their nuclei show a high degree of chromatin condensation and their cytoplasm contains bundles of fibrous material. It is suggested that these cells do not function directly in embryogenesis. The internal cells of the aggregates have a low density of ribosomes and very few ER profiles or normal mitochondria. Extremely elongated mitochondrial structures following the outline of the nucleus are observed in these cells. An unidentified structure is frequently observed in cells in which cytoplasmic disorganization appears to be occurring.