Department of Biology, University of California, Santa Barbara.
Planta. 1966 Mar;72(1):78-90. doi: 10.1007/BF00388147.
Sterile pith cultures of Nicotiana tabacum have been induced to form localized regions of differentiating tracheids. These localized regions have been examined by phase, fluorescence, and electron microscopy, and polarization optics. Fixation for electron microscopy was with glutaraldehyde-osmium. The differentiating tracheids develop characteristic thick cell walls which are eventually lignified. The lignifications appear to be uniform throughout the secondary wall and little or no lignin appears to be deposited in the primary walls or intercellular layer. At all stages of secondary wall deposition, the peripheral cytoplasm contains a system of microtubules which form a pattern similar to that of the developing thickenings. Within this system the microtubules are oriented, the direction of orientation mirroring that of the fibrils in the most recently deposited parts of the wall. The observations support the view that the microtubules are somehow involved in microfibril orientation. The microtubules appear to be attached to the plasma membrane which has a triple layered structure. The two electron dense layers of the plasma membrane have a particulate structure. In the differentiating tracheids at regions where secondary wall thickening has not yet been deposited numerous invaginations of the plasma membrane are observed which contain loosely organized fibrillar material. It is suggested that these are areas of localized activity of the plasma membrane and that the enzymes concerned with the final organization of the cellulose microfibrils are situated at the surface of the plasma membrane. Dictyosomes in the differentiation cells give rise to vesicles which contain fibrous material and the contents are incorporated into the cell wall. Numerous profiles characteristic of plasmodesmata are evident in sections of the secondary thickenings.
烟草无菌髓组织培养物诱导形成局部分化的导管区域。通过相差、荧光和电子显微镜以及偏振光对这些局部区域进行了检查。电子显微镜固定剂为戊二醛-锇。分化的导管形成具有特征性的厚细胞壁，最终木质化。木质素似乎在次生壁中均匀分布，在初生壁或细胞间隙层中几乎没有或没有木质素沉积。在次生壁沉积的所有阶段，周围细胞质都含有微管系统，其形成类似于正在发育中的加厚物的图案。在这个系统中，微管定向，定向的方向反映了壁中最近沉积部分的原纤的方向。这些观察结果支持微管以某种方式参与微纤丝取向的观点。微管似乎附着在具有三层结构的质膜上。质膜的两个电子致密层具有颗粒状结构。在尚未沉积次生壁加厚的分化导管中，观察到质膜的许多内陷，其中含有松散组织的原纤维物质。有人认为这些是质膜局部活性的区域，与纤维素微纤丝最终组织有关的酶位于质膜的表面。分化细胞中的高尔基器产生含有纤维状物质的小泡，其内容物被纳入细胞壁。次生加厚的切片中明显存在许多特征性的胞间连丝轮廓。
