Department of Marine Biology, Texas A & M University, Galveston, Texas 77551 USA.
Am J Bot. 2010 Jan;97(1):1-14. doi: 10.3732/ajb.0800423. Epub 2009 Dec 18.
The evolution of female gametophyte development provides an example of how minor ontogenetic modifications can impact the functional biology of seeds. Mature Peperomia-type female gametophytes are normally depicted as 16-nucleate, nine-celled structures. However, recent ultrastructural data have demonstrated that many previous reports were incorrect, suggesting that our understanding of the Peperomia-type ontogeny is incomplete. In this investigation, female gametophyte and early seed development is described in Peperomia dolabriformis, P. jamesoniana, and P. hispidula. Nuclear positioning, nuclear division, and vacuole morphology are documented during the syncytial stages of development, and two mature female gametophyte cellular configurations are described. Endosperm ploidy is measured in each species using microspectrofluorometry. We conclude that a 10-celled construction is likely the most common cellular configuration in Peperomia and that a three-celled female gametophyte exists in P. hispidula. We also describe how developmental modifications of wall formation could produce the diverse cellular configurations observed throughout Peperomia. Interestingly, the onset of female gametophyte diversification within Piperales correlates with the origin of the perisperm in the common ancestor of Piperaceae + Saururaceae. We posit that the origin of the perisperm may have relaxed selection on endosperm genetic constructs, thereby promoting diversification of female gametophyte ontogeny.
雌性配子体发育的演化提供了一个例证，说明微小的个体发育改变如何影响种子的功能生物学。成熟的胡椒型雌性配子体通常被描述为 16 核、9 细胞结构。然而，最近的超微结构数据表明，许多先前的报告是不正确的，这表明我们对胡椒型个体发生的理解是不完整的。在这项研究中，描述了 Peperomia dolabriformis、P. jamesoniana 和 P. hispidula 中的雌性配子体和早期种子发育。在发育的合胞体阶段记录核定位、核分裂和液泡形态，描述了两种成熟的雌性配子体细胞结构。使用微分光荧光光度计测量每种物种的胚乳倍性。我们得出结论，10 细胞结构可能是胡椒属中最常见的细胞结构，而在 P. hispidula 中存在 3 细胞雌性配子体。我们还描述了细胞壁形成的发育修饰如何产生在整个胡椒属中观察到的不同细胞结构。有趣的是，胡椒目中雌性配子体多样化的开始与 Piperaceae + Saururaceae 共同祖先中胚乳的起源相关。我们假设，胚乳的起源可能放松了对胚乳遗传结构的选择，从而促进了雌性配子体个体发生的多样化。
