Department of Biology, Complesso Universitario MSA, University of Naples Federico II, via Cinthia, I-80126, Naples, Italy.
Protoplasma. 2020 Mar;257(2):613-618. doi: 10.1007/s00709-019-01464-1. Epub 2019 Dec 12.
Orchids, differently from most flowering plants, have under-differentiated ovules at anthesis that require pollination to complete differentiation. This ovule developmental stage has been often observed in tropical species in which the absence of an evident seasonality may allow plants to extend their phenology beneficiating of a long time for post-pollination events. Here, we used scanning electron microscopy (SEM) to detect ovule integument developmental stages in 21 species of Mediterranean Orchidoideae and Epidendroideae and in 11 tropical Epidendroideae with the aim of understanding whether species with a seasonal constraint and shorter time for post-pollination ovule maturation are characterized by different stages of ovule development at anthesis. We found that Mediterranean orchids (both Orchidoideae and Epidendroideae) have more developed ovule integuments than tropical orchids. Most species show partially to fully developed ovules at anthesis with the exception of Cephalanthera where ovules are arrested in a very early developmental stage. Despite the phylogenetic signal, anthetic ovule integument development differs between related species (with different pollination strategies or blooming times), suggesting the presence of some ecological constraints. The synchronization between ovule integuments and megagametophyte development, as found in tropical orchids, is also confirmed in Mediterranean orchids. Our data show that Mediterranean and tropical orchids clearly differ in anthetic ovule developmental stages, likely depending on seasonality.
兰花与大多数开花植物不同，在开花时其胚珠分化程度较低，需要授粉才能完成分化。这种胚珠发育阶段在热带物种中经常观察到，在这些物种中，由于缺乏明显的季节性，植物可以延长其物候期，从而为授粉后事件提供更长的时间。在这里，我们使用扫描电子显微镜（SEM）来检测 21 种地中海兰科和 Epidendroideae 以及 11 种热带 Epidendroideae 的胚珠内种皮发育阶段，目的是了解是否具有季节性限制和授粉后胚珠成熟时间较短的物种在开花时具有不同的胚珠发育阶段。我们发现地中海兰花（Orchidoideae 和 Epidendroideae）的胚珠内种皮比热带兰花更为发达。大多数物种在开花时具有部分到完全发育的胚珠，但 Cephalanthera 的胚珠处于非常早期的发育阶段。尽管存在系统发育信号，但相关物种（具有不同的授粉策略或开花时间）之间的开花期胚珠内种皮发育不同，这表明存在一些生态限制。在热带兰花中发现的胚珠内种皮和大配子体发育之间的同步性也在地中海兰花中得到了证实。我们的数据表明，地中海兰花和热带兰花在开花期胚珠发育阶段明显不同，这可能取决于季节性。
