Department of Biology, University of North Dakota, Grand Forks, North Dakota 58202 USA.
Am J Bot. 2001 Jul;88(7):1326-30.
Angiosperms and Gnetales (Ephedra, Gnetum, Welwitschia) represent the only seed plants that regularly produce bisexual cones. Unfortunately, the fertility and function of ovules formed on bisexual cones of Gnetales have remained unclear. Some reports indicate that the ovules are sterile while others indicate that they may develop into seeds. This study demonstrates three different developmental patterns of ovules formed on bisexual cones of Gnetum gnemon. Type I ovules did not develop at all after pollination and represented the majority of ovules on each cone. Type II ovules enlarged slightly after pollination due to the enlargement of nucellar tissue. Type III ovules were typically found on the terminal whorl and developed into seed-like structures. The enlargement was due to proliferation of megagametophyte tissue. Sectioned material revealed that megagametophytes show altered development compared to those found in functional female ovules. None of the ovules studied contained embryos, and thus all were sterile. Densitometry of 4',6-diamidino-2-phenylindole (DAPI)- stained sections revealed that megagametophyte nuclei formed in the sterile ovules are unreduced (diploid) and thus do not form viable female gametes.
被子植物和买麻藤植物（麻黄、买麻藤、百岁兰）是唯一定期产生两性球果的种子植物。不幸的是，买麻藤植物两性球果上形成的胚珠的育性和功能仍不清楚。一些报道表明胚珠是不育的，而另一些报道则表明它们可能发育成种子。本研究表明买麻藤植物两性球果上形成的胚珠有三种不同的发育模式。授粉后，I 型胚珠根本没有发育，占每个球果上胚珠的大多数。授粉后，由于珠心组织的增大，II 型胚珠略有增大。III 型胚珠通常出现在末端轮生，发育成类似种子的结构。增大是由于大配子体组织的增殖。切片材料显示，与功能正常的雌性胚珠相比，大配子体的发育发生了改变。研究的胚珠都没有胚胎，因此都是不育的。4'，6-二脒基-2-苯基吲哚（DAPI）染色切片的密度测量显示，不育胚珠中的大配子体核是未减数的（二倍体），因此不能形成有活力的雌性配子。
