Raguso R A, Roy B A
Department of Biology, University of Michigan, Ann Arbor 48109-1048, USA.
Mol Ecol. 1998 Sep;7(9):1127-36. doi: 10.1046/j.1365-294x.1998.00426.x.
Crucifers (Brassicaceae) in 11 genera are often infected by rust fungi in the Puccinia monoica complex. Infection causes a 'pseudoflower' to form that is important for attracting insect visitors that sexually outcross the fungus. 'Pollinator' attraction is accomplished through visual floral mimicry, the presence of a nectar reward and floral fragrances. Here we used gas chromatography and mass spectrometry to identify and quantify fragrance production by these rust fungi on several Arabis hosts, and by co-occurring true flowers that share insect visitors. Fungal pseudoflowers produced distinctive floral fragrances composed primarily of aromatic alcohols, aldehydes and esters. Pseudoflower fragrances were chemically similar to noctuid-moth-pollinated flowers, such as Cestrum nocturnum and Abelia grandiflora, but were very different from host flowers, host vegetation and the flowers of coblooming, nonhost angiosperms. There was variation in the quantity and composition of fragrance profiles from different fungal species as well as within and among hosts. The evolution of scent chemistry is relatively conservative in these fungi and can be most parsimoniously explained in three steps by combining chemical data with a previously determined rDNA ITS sequence-based phylogeny. Pseudoflower scent does not appear to represent a simple modification of host floral or vegetative emissions, nor does it mimic the scent of coblooming flowers. Instead, we suspect that the unique fragrances, beyond their function as pollinator attractants, may be important in reducing gamete loss by reinforcing constancy among foraging insects.
十字花科（Brassicaceae）11个属的植物常被单花柄锈菌复合体（Puccinia monoica complex）中的锈菌感染。感染会导致形成一种“假花”，这种假花对于吸引昆虫访客至关重要，这些昆虫会帮助锈菌进行有性异花授粉。“传粉者”的吸引是通过视觉上的花模拟、花蜜奖励的存在以及花香来实现的。在这里，我们使用气相色谱和质谱法来鉴定和量化这些锈菌在几种阿拉比亚属（Arabis）寄主上以及与共享昆虫访客的同时开放的真正花朵所产生的香气。真菌假花产生独特的花香，主要由芳香醇、醛和酯组成。假花的香气在化学上与夜蛾授粉的花朵相似，如夜香树（Cestrum nocturnum）和大花六道木（Abelia grandiflora），但与寄主花朵、寄主植物以及同时开花的非寄主被子植物的花朵有很大不同。不同真菌物种以及寄主内部和之间的香气成分在数量和组成上存在差异。这些真菌中气味化学的进化相对保守，通过将化学数据与先前确定的基于rDNA ITS序列的系统发育相结合，可以用三个步骤最简洁地解释。假花的气味似乎既不代表寄主花或植物排放物的简单修饰，也不模仿同时开花花朵的气味。相反，我们怀疑这些独特的香气，除了作为传粉者引诱剂的功能外，可能通过增强觅食昆虫之间的专一性在减少配子损失方面很重要。
