Am J Bot. 1997 Sep;84(9):1169.
We have used transmission electron microscopy to examine plasmodesmata of the charophycean green alga Chara zeylanica, and of the putatively early divergent bryophytes Monoclea gottschei (liverwort), Notothylas orbicularis (hornwort), and Sphagnum fimbriatum (moss), in an attempt to learn when seed plant plasmodesmata may have originated. The three bryophytes examined have desmotubules. In addition, Monoclea was found to have branched plasmodesmata, and plasmodesmata of Sphagnum displayed densely staining regions around the neck region, as well as ring-like wall specializations. In Chara, longitudinal sections revealed endoplasmic reticulum (ER) that sometimes appeared to be associated with plasmodesmata, but this was rare, despite abundant ER at the cell periphery. Across all three fixation methods, cross-sectional views showed an internal central structure, which in some cases appeared to be connected to the plasma membrane via spoke-like structures. Plasmodesmata were present even in the incompletely formed reticulum of forming cell plates, from which we conclude that primary plasmodesmata are formed at cytokinesis in Chara zeylanica. Based on these results it appears that plasmodesmata of Chara may be less specialized than those of seed plants, and that complex plasmodesmata probably evolved in the ancestor of land plants before extant lineages of bryophytes diverged.
我们利用透射电子显微镜观察了石莼目绿藻石莼（Chara zeylanica）、可能早期分化的苔藓植物Monoclea gottschei（地钱）、Notothylas orbicularis（角苔）和 Sphagnum fimbriatum（泥炭藓）的胞间连丝，试图了解植物的胞间连丝可能起源于何时。我们观察的三种苔藓植物都有胞间小管。此外，Monoclea 还被发现具有分枝的胞间连丝，并且 Sphagnum 的胞间连丝在颈部区域周围显示出染色密集的区域，以及环状的细胞壁特化。在石莼中，纵切显示内质网（ER）有时似乎与胞间连丝有关，但这种情况很少见，尽管细胞周围有丰富的 ER。在所有三种固定方法中，横切视图都显示了一个内部中央结构，在某些情况下，该结构似乎通过辐状结构与质膜相连。胞间连丝甚至存在于正在形成的细胞板的不完全形成的网状物中，我们由此得出结论，在石莼的有丝分裂过程中形成了初级胞间连丝。基于这些结果，石莼的胞间连丝似乎不如种子植物的胞间连丝专业化，并且复杂的胞间连丝可能在现存苔藓植物谱系分化之前就在陆地植物的祖先中进化而来。
