Tilney L G, Cooke T J, Connelly P S, Tilney M S
Department of Biology, University of Pennsylvania, Philadelphia 19104.
J Cell Biol. 1991 Feb;112(4):739-47. doi: 10.1083/jcb.112.4.739.
Plasmodesmata or intercellular bridges that connect plant cells are cylindrical channels approximately 40 nm in diameter. Running through the center of each is a dense rod, the desmotubule, that is connected to the endoplasmic reticulum of adjacent cells. Fern, Onoclea sensibilis, gametophytes were cut in half and the cut surfaces exposed to the detergent, Triton X 100, then fixed. Although the plasma membrane limiting the plasmodesma is solubilized partially or completely, the desmotubule remains intact. Alternatively, if the cut surface is exposed to papain, then fixed, the desmotubule disappears, but the plasma membrane limiting the plasmodesmata remains intact albeit swollen and irregular in profile. Gametophytes were plasmolyzed, and then fixed. As the cells retract from their cell walls they leave behind the plasmodesmata still inserted in the cell wall. They can break cleanly when the cell proper retracts or can pull away portions of the plasma membrane of the cell with them. Where the desmotubule remains intact, the plasmodesma retains its shape. These images and the results with detergents and proteases indicate that the desmotubule provides a cytoskeletal element for each plasmodesma, an element that not only stabilizes the whole structure, but also limits its size and porosity. It is likely to be composed in large part of protein. Suggestions are made as to why this structure has been selected for in evolution.
连接植物细胞的胞间连丝或细胞间桥是直径约40纳米的圆柱形通道。每个通道的中心贯穿一根致密的杆状物，即连丝微管，它与相邻细胞的内质网相连。将敏感鳞毛蕨的配子体切成两半，把切面暴露于去污剂Triton X 100中，然后进行固定。尽管限制胞间连丝的质膜部分或完全溶解，但连丝微管仍保持完整。或者，如果将切面暴露于木瓜蛋白酶中，然后固定，连丝微管会消失，但限制胞间连丝的质膜尽管肿胀且轮廓不规则，但仍保持完整。对配子体进行质壁分离处理，然后固定。当细胞从细胞壁缩回时，它们留下仍插入细胞壁中的胞间连丝。当细胞本体缩回时，它们可以干净地断裂，或者可以连同细胞膜的部分一起拉走。在连丝微管保持完整的地方，胞间连丝保持其形状。这些图像以及使用去污剂和蛋白酶的结果表明，连丝微管为每个胞间连丝提供了一种细胞骨架成分，这种成分不仅能稳定整个结构，还能限制其大小和孔隙率。它很可能在很大程度上由蛋白质组成。文中还对这种结构在进化中被选择的原因提出了一些建议。
