Tilney L G, Cooke T J, Connelly P S, Tilney M S
Marine Biological Laboratory, Woods Hole, MA 02543.
Development. 1990 Dec;110(4):1209-21. doi: 10.1242/dev.110.4.1209.
Fern (Onoclea sensibilis) gametophytes when grown in the dark form a linear file of cells (one-dimensional) called a protonema. In the light two-dimensional growth occurs which results in a heart-shaped prothallus one cell thick. The objective of this paper is to relate the most common pattern of cell division observed in developing gametophytes to the formation of the plasmodesmatal network. Since the prothalli are only two dimensional, we can easily determine from thin sections the total number and the density (number per unit surface area) of plasmodesmata at each developmental stage. As the prothallus grows the number of plasmodesmata increases 50-fold in the apical or meristematic cell. This number eventually reaches a plateau even though the density continues to increase with each new cell division. What is particularly striking is that both the number and density of plasmodesmata between adjacent cells is precisely determined. Furthermore, the pattern of plasmodesmata distribution is predictable so that (1) we can identify the apical meristematic cells by their plasmodesmata number, or density, as well as by their size, shape and location, (2) we can predict, again from plasmodesmata number, the location of a future wall of the apical cell prior to its actual formation, (3) we can show that the density of plasmodesmata in the triangular apical cell of the prothallus (14 plasmodesmata microns-2) is comparable to those reported for secretory glands which are known to have high rates of plasmodesmatal transport and (4) we can show that once the plasmodesmata have been formed during division, no subsequent change in the number of plasmodesmata occurs following cell plate formation.
蕨类植物（敏感鳞毛蕨）的配子体在黑暗中生长时会形成一列呈线性排列的细胞（一维结构），称为原丝体。在光照条件下，会发生二维生长，从而形成一个单细胞厚度的心形原叶体。本文的目的是将发育中的配子体中观察到的最常见细胞分裂模式与胞间连丝网络的形成联系起来。由于原叶体仅为二维结构，我们可以通过薄片轻松确定每个发育阶段胞间连丝的总数和密度（每单位表面积的数量）。随着原叶体的生长，顶端或分生细胞中的胞间连丝数量增加了50倍。尽管随着每一次新的细胞分裂密度持续增加，但这个数量最终会达到一个稳定水平。特别引人注目的是，相邻细胞之间胞间连丝的数量和密度都是精确确定的。此外，胞间连丝的分布模式是可预测的，因此（1）我们可以通过胞间连丝的数量、密度以及大小、形状和位置来识别顶端分生细胞，（2）我们可以再次根据胞间连丝的数量预测顶端细胞未来细胞壁实际形成之前的位置，（3）我们可以表明原叶体三角形顶端细胞中的胞间连丝密度（14个胞间连丝/平方微米）与已知具有高胞间连丝运输速率的分泌腺所报道的密度相当，（4）我们可以表明一旦在细胞分裂过程中形成了胞间连丝，在细胞板形成后胞间连丝的数量不会发生后续变化。
