Kobayashi Sawa, Asai Teigo, Fujimoto Yoshinori, Kohshima Shiro
Department of Bioscience and Biotechnology, Tokyo Institute of Technology, Meguro, Tokyo 152-8551, Japan.
Ann Bot. 2008 May;101(7):1035-47. doi: 10.1093/aob/mcn033. Epub 2008 Mar 15.
Recent studies have shown that small structures on plant surfaces serve ecological functions such as resistance against herbivores. The morphology, distribution, chemical composition and changes during shoot and leaf development of such small structures were examined on Paulownia tomentosa.
The morphology and distribution of the structures were studied under light microscopy, and their chemical composition was analysed using thin-layer chromatography and high-performance liquid chromatography. To further investigate the function of these structures, several simple field experiments and observations were also conducted.
Three types of small structures on P. tomentosa were investigated: bowl-shaped organs, glandular hairs and dendritic trichomes. The bowl-shaped organs were densely aggregated on the leaves near flower buds and were determined to be extrafloral nectarines (EFNs) that secrete sugar and attract ants. Nectar production of these organs was increased by artificial damage to the leaves, suggesting an anti-herbivore function through symbiosis with ants. Glandular hairs were found on the surfaces of young and/or reproductive organs. Glandular hairs on leaves, stems and flowers secreted mucilage containing glycerides and trapped small insects. Secretions from glandular hairs on flowers and immature fruits contained flavonoids, which may provide protection against some herbivores. Yellow dendritic trichomes on the adaxial side of leaves also contained flavonoids identical to those secreted by the glandular hairs on fruits and flowers. Three special types of leaves, which differed from the standard leaves in shape, size and identity of small structures, developed near young shoot tips or young flower buds. The density of small structures on these leaf types was higher than on standard leaves, suggesting that these leaf types may be specialized to protect young leaves or reproductive organs. Changes in the small structures during leaf development suggested that leaves of P. tomentosa are primarily protected by glandular hairs and dendritic trichomes at young stages and by the EFNs at mature stages.
The results indicate that P. tomentosa protects young and/or reproductive organs from herbivores through the distribution and allocation of small structures, the nature of which depends on the developmental stage of leaves and shoots.
近期研究表明，植物表面的微小结构具有生态功能，如抵御食草动物。本研究对毛泡桐植物表面此类微小结构的形态、分布、化学成分及其在枝条和叶片发育过程中的变化进行了研究。
利用光学显微镜研究了这些结构的形态和分布，并采用薄层色谱法和高效液相色谱法分析了它们的化学成分。为进一步探究这些结构的功能，还进行了一些简单的田间试验和观察。
研究了毛泡桐上的三种微小结构：碗状器官、腺毛和树状毛。碗状器官密集聚集在花芽附近的叶片上，经鉴定为花外蜜腺，可分泌糖分并吸引蚂蚁。人工损伤叶片会增加这些器官的花蜜分泌量，表明通过与蚂蚁共生具有抗食草动物的功能。腺毛存在于幼嫩和/或生殖器官表面。叶片、茎和花上的腺毛分泌含有甘油酯的黏液并捕获小昆虫。花和未成熟果实上腺毛的分泌物含有黄酮类化合物，可能对某些食草动物具有保护作用。叶片正面的黄色树状毛也含有与果实和花上腺毛分泌的相同的黄酮类化合物。在嫩梢顶端或花芽附近发育出三种特殊类型的叶片，其形状、大小和微小结构特征与标准叶片不同。这些叶片类型上微小结构的密度高于标准叶片，表明这些叶片类型可能专门用于保护幼叶或生殖器官。叶片发育过程中微小结构的变化表明，毛泡桐叶片在幼嫩阶段主要由腺毛和树状毛保护，在成熟阶段则由花外蜜腺保护。
结果表明，毛泡桐通过微小结构的分布和配置来保护幼嫩和/或生殖器官免受食草动物侵害，其微小结构的性质取决于叶片和枝条的发育阶段。
