Institute of Low Temperature Science, Hokkaido University , Sapporo 060-0819, Japan.
National Institute for Environmental Studies , 16-2 Onogawa, Tsukuba, Ibaraki 305-8506, Japan.
J Phys Chem B. 2017 Dec 14;121(49):11124-11131. doi: 10.1021/acs.jpcb.7b09173. Epub 2017 Dec 1.
The outermost surface of the leaves of land plants is covered with a lipid membrane called the cuticle that protects against various stress factors. Probing the molecular-level structure of the intact cuticle is highly desirable for understanding its multifunctional properties. We report the in situ characterization of the surface structure of Kalanchoe pinnata leaves using polarization-modulation infrared reflection-absorption spectroscopy (PM-IRRAS). Without sample pretreatment, PM-IRRAS measures the IR spectra of the leaf cuticle of a potted K. pinnata plant. The peak position of the CH-related modes shows that the cuticular waxes on the leaf surface are mainly crystalline, and the alkyl chains are highly packed in an all-trans zigzag conformation. The surface selection rule of PM-IRRAS revealed the average orientation of the cuticular molecules, as indicated by the positive and negative signals of the IR peaks. This unique property of PM-IRRAS revealed that the alkyl chains of the waxes and the main chains of polysaccharides are oriented almost perpendicular to the leaf surface. The nondestructive, background-free, and environmental gas-free nature of PM-IRRAS allows the structure and chemistry of the leaf cuticle to be studied directly in its native environment.
陆生植物叶片的最外层表面覆盖着一层脂质膜，称为角质层，可防止各种应激因素的侵害。深入了解完整角质层的分子级结构对于理解其多功能特性非常重要。我们使用偏振调制红外反射吸收光谱（PM-IRRAS）报告了对 Kalanchoe pinnata 叶片表面结构的原位表征。无需样品预处理，PM-IRRAS 即可测量盆栽 K. pinnata 植物叶片角质层的红外光谱。CH 相关模式的峰位置表明，叶片表面的角质层蜡主要是结晶的，烷基链以全反式锯齿构象高度堆积。PM-IRRAS 的表面选择规则揭示了角质层分子的平均取向，这可以通过 IR 峰的正负信号来表示。PM-IRRAS 的这一独特特性表明，蜡的烷基链和多糖的主链几乎垂直于叶片表面取向。PM-IRRAS 具有非破坏性、无背景和无环境气体的特点，允许在其天然环境中直接研究叶片角质层的结构和化学性质。
