Institute of Systematic Botany, University of Zurich, Zollikerstrasse 107, 8008 Zurich, Switzerland.
Ann Bot. 2011 Jun;107(9):1465-89. doi: 10.1093/aob/mcr120. Epub 2011 May 23.
Ovules as developmental precursors of seeds are organs of central importance in angiosperm flowers and can be traced back in evolution to the earliest seed plants. Angiosperm ovules are diverse in their position in the ovary, nucellus thickness, number and thickness of integuments, degree and direction of curvature, and histological differentiations. There is a large body of literature on this diversity, and various views on its evolution have been proposed over the course of time. Most recently evo-devo studies have been concentrated on molecular developmental genetics in ovules of model plants.
The present review provides a synthetic treatment of several aspects of the sporophytic part of ovule diversity, development and evolution, based on extensive research on the vast original literature and on experience from my own comparative studies in a broad range of angiosperm clades.
In angiosperms the presence of an outer integument appears to be instrumental for ovule curvature, as indicated from studies on ovule diversity through the major clades of angiosperms, molecular developmental genetics in model species, abnormal ovules in a broad range of angiosperms, and comparison with gymnosperms with curved ovules. Lobation of integuments is not an atavism indicating evolution from telomes, but simply a morphogenetic constraint from the necessity of closure of the micropyle. Ovule shape is partly dependent on locule architecture, which is especially indicated by the occurrence of orthotropous ovules. Some ovule features are even more conservative than earlier assumed and thus of special interest in angiosperm macrosystematics.
胚珠作为种子的发育前体，是被子植物花中至关重要的器官，可以追溯到最早的种子植物。被子植物胚珠在其在子房中的位置、珠心厚度、珠被的数量和厚度、弯曲的程度和方向以及组织分化方面存在多样性。关于这种多样性有大量的文献，并且随着时间的推移提出了各种关于其进化的观点。最近，演化发育研究集中在模式植物胚珠的分子发育遗传学上。
本综述基于对大量原始文献的广泛研究以及我自己在广泛的被子植物类群中的比较研究经验，对胚珠多样性、发育和进化的孢子体部分的几个方面进行了综合处理。
在被子植物中，外珠被的存在似乎对胚珠的弯曲起作用，这可以从通过被子植物主要类群的胚珠多样性研究、模式物种的分子发育遗传学、广泛的被子植物中异常胚珠以及与具弯曲胚珠的裸子植物的比较研究中得到证明。珠被的裂片不是从端细胞进化而来的返祖现象，而只是由珠孔封闭的必要性引起的形态发生限制。胚珠形状部分取决于心皮室的结构，这在直生胚珠的发生中尤为明显。有些胚珠特征甚至比以前假设的更为保守，因此在被子植物宏观系统学中特别有趣。
