Direct observation of bulk and surface chemical morphologies of Ginkgo biloba leaves by Fourier transform mid- and near-
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RESEARCH PAPER
Direct observation of bulk and surface chemical morphologies of Ginkgo biloba leaves by Fourier transform mid- and near-infrared microspectroscopic imaging Jianbo Chen & Suqin Sun & Qun Zhou
Received: 8 May 2013 / Revised: 11 July 2013 / Accepted: 11 September 2013 / Published online: 5 October 2013 # Springer-Verlag Berlin Heidelberg 2013
Abstract Fourier transform infrared microspectroscopy is a powerful tool to obtain knowledge about the spatial and/or temporal distributions of the chemical compositions of plants for better understanding of their biological properties. However, the chemical morphologies of plant leaves in the plane of the blade are barely studied, because sections in this plane for mid-infrared transmission measurements are difficult to obtain. Besides, native compositions may be changed by chemical reagents used when plant samples are microtomed. To improve methods for direct infrared microspectroscopic imaging of plant leaves in the plane of the blade, the bulk and surface chemical morphologies of nonmicrotomed Ginkgo biloba leaves were characterized by near-infrared transmission and mid-infrared attenuated total reflection microspectroscopic imaging. A new self-modeling curve resolution procedure was proposed to extract the spectral and concentration information of pure compounds. Primary and secondary metabolites of secretory cavities, veins, and mesophylls of Ginkgo biloba leaf blades were analyzed, and the distributions of cuticle, protein, calcium oxalate, cellulose, and ginkgolic acids on the adaxial surface were determined. By the integration of multiple infrared microspectroscopic imaging and chemometrics methods, it is possible to analyze nonmicrotomed leaves and other plant samples directly to understand their native chemical morphologies in detail. Keywords Infrared microspectroscopic imaging . Attenuated total reflection imaging . Self-modeling curve resolution . Chemical morphology . Ginkgo biloba leaf Electronic supplementary material The online version of this article (doi:10.1007/s00216-013-7366-3) contains supplementary material, which is available to authorized users. J. Chen : S. Sun : Q. Zhou (*) Department of Chemistry, Key Laboratory of Bioorganic Phosphorus Chemistry & Chemical Biology (Ministry of Education), Tsinghua University, Beijing 100084, China e-mail: [email protected]
Abbreviations ALS Alternating least squares ATR Attenuated total reflection CLS Classical least squares EC Estimated component FT Fourier transform HCA Hierarchical cluster analysis iEC Initial estimated component IR Infrared IRE Internal reflection element MIR Mid infrared NIR Near infrared PC Principal component PCA Principal component analysis PLS Partial least squares ROI Region of interest
Introduction Plant morphologies provide primary knowledge for the study of plant classification, physiology, ecology, genetics, pathology, etc. In a way, plant morphologies are formed by the spatial and/or temporal distributions of chemical compositions determined by both genetic and
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