College of Life Sciences, Wuhan University, Wuhan, 430072, PR China.
Ann Bot. 2011 Jul;108(1):65-71. doi: 10.1093/aob/mcr105. Epub 2011 May 5.
Why are sterile anthers and carpels retained in some flowering plants, given their likely costs? To address this question, a cryptically dioecious species, Petasites tricholobus, in which male and female plants each have two floret types that appear pistillate and hermaphroditic, was studied. The aim was to understand the function of sterile hermaphroditic florets in females. In addition, the first examination of functions of sterile female structures in male plants was conducted in the hermaphroditic florets on males of this species. These female structures are exceptionally large in this species despite being sterile.
Differences in floret morphology between the sex morphs were documented and the possible functions of sterile sex organs investigated using manipulative experiments. Tests were carried out to find out if sterile female structures in male florets attract pollinators and if they aid in pollen dispersal, also to find out if the presence and quantity of sterile hermaphroditic florets in females increase pollinator attraction and reproductive success. To investigate what floret types provide nectar, all types of florets were examined under a scanning electron microscope to search for nectaries.
The sterile female structures in male florets did not increase pollinator visits but were essential to secondary pollen presentation, which significantly enhanced pollen dispersal. Sterile pistillate florets on male plants did not contribute to floral display and disappeared in nearly half of the male plants. The sterile hermaphroditic florets on female plants attracted pollinators by producing nectar and enhanced seed production.
The presence of female structures in male florets and hermaphroditic florets on female plants is adaptive despite being sterile, and may be evolutionarily stable. However, the pistillate florets on male plants appear non-adaptive and are presumably in decline. Differential fates of the sterile sex organs in the species are determined by both the historical constraints and the ecological functions.
为什么有些开花植物会保留无菌的花药和心皮，尽管它们可能有代价？为了解决这个问题，我们研究了一种隐雌雄同株的植物——岩菖蒲，其中雄性和雌性植物各有两种看起来是雌性和两性花的小花类型。我们的目的是了解雌性无菌两性小花的功能。此外，我们首次在该物种的两性小花的雄性中，研究了无菌雌性结构在雄性植物中的功能。尽管这些雌性结构是无菌的，但在该物种中它们异常大。
记录了性形态之间小花形态的差异，并通过操纵实验研究了无菌性器官的可能功能。我们进行了测试，以确定雄性小花中的无菌雌性结构是否吸引传粉者，以及它们是否有助于花粉传播，还确定了雌性中无菌两性小花的存在和数量是否增加了传粉者的吸引力和繁殖成功率。为了研究哪种小花类型提供花蜜，我们用扫描电子显微镜检查了所有类型的小花，以寻找蜜腺。
雄性小花中的无菌雌性结构并没有增加传粉者的访问次数，但对于二次花粉展示是必不可少的，这显著增强了花粉的传播。雄性植物上的无菌雌性小花对花的展示没有贡献，而且在近一半的雄性植物中消失了。雌性植物上的无菌两性小花通过产生花蜜吸引传粉者，并提高种子产量。
尽管无菌，雄性小花中的雌性结构和雌性植物上的两性小花的存在是适应性的，并且可能是进化稳定的。然而，雄性植物上的雌性小花似乎是不适应的，并且可能在减少。该物种中无菌性器官的不同命运是由历史约束和生态功能决定的。
