Current Biology:植物利用花粉爆炸授粉

厄瓜多尔和哥斯达黎加的山间隐藏着一种不同寻常的花——Axinaea。当研究人员爬上陡峭的山坡，将摄像机安装在这种花生长的树上时，他们发现这种植物会为来访的鸟儿提供糖衣包裹的酬劳。

这些酬劳就是球形的、色彩明亮的植物附器，其中含有高浓度糖分和柠檬酸。它们主要附着在这种植物的雄蕊上。但是，一旦鸟嘴压下来，这种“弹簧”器官会将其海绵状组织中的空气压入雄蕊内部的贮粉室。

于是，花粉会向外“爆炸”，喷到不知情的鸟的嘴部或前额上。当鸟儿掠过另一棵树时，它们会将花粉传授到其他花朵的雌蕊上。这是科学家首次发现开花植物用生殖器官为授粉者提供食物奖励。

研究人员近日将相关成果在线发表于《当代生物学》期刊。该研究小组推测，这种植物在进化出“弹簧”功能之前，其球形器官看上去就十分像植物果实，从而愚弄鸟儿去吃它。

原文摘要：

A Specialized Bird Pollination System with a Bellows Mechanism for Pollen Transfer and Staminal Food Body Rewards

Agnes S. Dellinger, Darin S. Penneys, Yannick M. Staedler, Lena Fragner, Wolfram Weckwerth, Jürg Schönenberger

Bird pollination has evolved repeatedly among flowering plants but is almost exclusively characterized by passive transfer of pollen onto the bird and by nectar as primary reward. Food body rewards are exceedingly rare among eudicot flowering plants and are only known to occur on sterile floral organs. In this study, we report an alternative bird pollination mechanism involving bulbous stamen appendages in the Neotropical genus Axinaea (Melastomataceae). We studied the pollination process by combining pollination experiments, video monitoring, and detailed analyses of stamen structure and metabolomic composition. We show that the bulbous stamen appendages, which are consumed by various species of passerines (Thraupidae, Fringillidae), are bifunctional during the pollination process. First, the appendages work as bellows organs in a unique pollen expulsion mechanism activated by the passerines. As the birds seize an appendage with their beaks in order to remove it from the flower for consumption, air contained in the appendage’s aerenchymatous tissue is pressed into the hollow anther. The resulting air flow causes the expulsion of a pollen jet and the deposition of pollen on the bird’s head and beak. Second, the stamen appendages provide a hexose-rich, highly nutritious (15,100 J/g) food body reward for the pollinating passerines. This discovery expands our knowledge of flowering plant pollination systems and provides the first report of highly specialized bellows organs for active pollen transfer in flowering plants. In addition, this is the only known case of a food body reward associated with reproductive structures in the eudicot clade of flowering plants.

作者：砂之时光