Mayer Juliana Lischka Sampaio, Scopece Giovanni, Barone Lumaga Maria Rosaria, Coiro Mario, Pinheiro Fabio, Cozzolino Salvatore
Department of Plant Biology, Institute of Biology, State University of Campinas - UNICAMP - 13083-862, Campinas, SP, Brazil.
Department of Biology, University of Naples Federico II, Naples, Italy.
Am J Bot. 2021 Dec;108(12):2405-2415. doi: 10.1002/ajb2.1770. Epub 2021 Dec 5.
Unlike most flowering plants, orchid flowers have under-developed ovules that complete development only after pollination. Classical studies reported variation in the stage in which ovule development is arrested, but the extent of this variation and its evolutionary and ecological significance are unclear.
Here, we used light microscopy to observe ovule development at anthesis for 39 species not previously studied and surveyed the literature gaining information on 94 orchid species. Tropical and temperate members of all five orchid subfamilies as well as species with contrasting pollination strategies (rewarding versus deceptive) and life forms (epiphytic versus terrestrial) were represented. We analyzed the data using statistical comparisons and a phylogenetic generalized least square (PGLS) analysis.
Apostasioideae, the sister to the rest of the orchids, have mature ovules similar to other Asparagales, while under-differentiated ovules are present in the other subfamilies. Ovule developmental stages showed high variation even among closely related groups. Ovules were more developed in terrestrial than in epiphytic, in temperate than in tropical, and in rewarding than in deceptive pollination orchid species. This latter comparison was also significant in the PGLS analysis.
These results suggest that ovule developmental stage in orchids can be shaped by ecological factors, such as seasonality and pollination strategy, and can be selected for optimizing female reproductive investment.
与大多数开花植物不同，兰花的胚珠发育不完全，只有在授粉后才会完成发育。经典研究报道了胚珠发育停滞阶段的差异，但这种差异的程度及其进化和生态意义尚不清楚。
在这里，我们使用光学显微镜观察了39种此前未研究过的兰花在花期时的胚珠发育情况，并查阅文献获取了94种兰花的相关信息。所有五个兰花亚科的热带和温带成员以及具有不同授粉策略（有报酬授粉与欺骗性授粉）和生活型（附生型与地生型）的物种均有涉及。我们使用统计比较和系统发育广义最小二乘法（PGLS）分析对数据进行了分析。
与其他兰花的其余部分为姐妹群的拟兰亚科具有与其他天门冬目植物相似的成熟胚珠，而其他亚科则存在发育不完全的胚珠。即使在亲缘关系密切的类群中，胚珠发育阶段也表现出高度差异。地生兰花的胚珠比附生兰花的更发达，温带兰花的胚珠比热带兰花的更发达，有报酬授粉的兰花的胚珠比欺骗性授粉的兰花的更发达。在PGLS分析中，后一种比较也具有显著性。
这些结果表明，兰花的胚珠发育阶段可能受到季节性和授粉策略等生态因素的影响，并且可以通过选择来优化雌性功能投资。
