Department of Plant Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EA, UK.
Am J Bot. 2009 Dec;96(12):2184-96. doi: 10.3732/ajb.0900079. Epub 2009 Nov 10.
Angiosperms possess a variety of complex floral traits that attract animal pollinators. Dark petal spots have evolved independently many times across the angiosperm phylogeny and have been shown to attract insect pollinators from several lineages. Here we present new data on the ontogeny and morphological complexity of the elaborate insect-mimicking petal spots of the South African daisy species, Gorteria diffusa (Asteraceae), commonly known as the beetle daisy, although it is fly-pollinated. Using light and scanning electron microscopy and histology, we identified three distinct specialized cell types of the petal epidermis that compose the petal spot. Sophisticated patterning of pigments, cuticular elaborations, and multicellular papillate trichomes make the G. diffusa petal spot a uniquely complex three-dimensional floral ornament. Examination of young inflorescence meristems revealed that G. diffusa ray florets develop (and probably also initiate) basipetally, in the opposite direction to the disc florets-a developmental phenomenon that has been found in some other daisies, but which contradicts conventional theories of daisy inflorescence architecture. Using these ontogenetic and morphological data, we have identified the mechanism by which G. diffusa patterns its insect-mimicking petal spots, and we propose a testable model for the genetic regulation of petal spot identity.
被子植物具有多种复杂的花部特征，这些特征能够吸引动物传粉者。深色花瓣斑在被子植物的系统发育中独立进化了多次，并且已经证明它们能够吸引来自几个谱系的昆虫传粉者。在这里，我们提供了南非雏菊属（菊科）物种——Gorteria diffusa 的精致昆虫模拟花瓣斑的发生和形态复杂性的新数据，这种雏菊通常被称为甲虫雏菊，尽管它是蝇类传粉的。我们使用光学显微镜、扫描电子显微镜和组织学技术，鉴定了组成花瓣斑的花瓣表皮的三种不同的特化细胞类型。色素的复杂图案、表皮的特化和多细胞乳突状毛状体使 G. diffusa 的花瓣斑成为一种独特的复杂三维花饰。对幼嫩花序分生组织的研究表明，G. diffusa 的辐射状花瓣（可能也起始于）是向基发育的，与盘状花瓣的发育方向相反——这种发育现象在一些其他雏菊中已经发现，但与雏菊花序结构的传统理论相矛盾。利用这些个体发生和形态学数据，我们确定了 G. diffusa 模式化其昆虫模拟花瓣斑的机制，并提出了一个可测试的花瓣斑身份遗传调控模型。
