A Multiscale Vibrational Spectroscopic Approach for Identification and Biochemical Characterization of Pollen.

Murat Bağcıoğlu,Boris Zimmermann,Achim Kohler,Jonathan A Coles

doi:10.1371/journal.pone.0137899

Murat Bağcıoğlu, Boris Zimmermann + Show 2 more

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https://doi.org/10.1371/journal.pone.0137899

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Journal: PloS one	Publication Date: Sep 16, 2015
Citations: 59	License type: CC BY 4.0

Affiliation: Norwegian University of Life Sciences

Abstract

BackgroundAnalysis of pollen grains reveals valuable information on biology, ecology, forensics, climate change, insect migration, food sources and aeroallergens. Vibrational (infrared and Raman) spectroscopies offer chemical characterization of pollen via identifiable spectral features without any sample pretreatment. We have compared the level of chemical information that can be obtained by different multiscale vibrational spectroscopic techniques.MethodologyPollen from 15 different species of Pinales (conifers) were measured by seven infrared and Raman methodologies. In order to obtain infrared spectra, both reflectance and transmission measurements were performed on ground and intact pollen grains (bulk measurements), in addition, infrared spectra were obtained by microspectroscopy of multigrain and single pollen grain measurements. For Raman microspectroscopy measurements, spectra were obtained from the same pollen grains by focusing two different substructures of pollen grain. The spectral data from the seven methodologies were integrated into one data model by the Consensus Principal Component Analysis, in order to obtain the relations between the molecular signatures traced by different techniques.ResultsThe vibrational spectroscopy enabled biochemical characterization of pollen and detection of phylogenetic variation. The spectral differences were clearly connected to specific chemical constituents, such as lipids, carbohydrates, carotenoids and sporopollenins. The extensive differences between pollen of Cedrus and the rest of Pinaceae family were unambiguously connected with molecular composition of sporopollenins in pollen grain wall, while pollen of Picea has apparently higher concentration of carotenoids than the rest of the family. It is shown that vibrational methodologies have great potential for systematic collection of data on ecosystems and that the obtained phylogenetic variation can be well explained by the biochemical composition of pollen. Out of the seven tested methodologies, the best taxonomical differentiation of pollen was obtained by infrared measurements on bulk samples, as well as by Raman microspectroscopy measurements of the corpus region of the pollen grain. Raman microspectroscopy measurements indicate that measurement area, as well as the depth of focus, can have crucial influence on the obtained data.

Highlights

Pollen grains are characteristic to plant families, genera or even species, revealing valuable information on ecology, forensics, climate change, insect migration, food sources and aeroallergens
The extensive differences between pollen of Cedrus and the rest of Pinaceae family were unambiguously connected with molecular composition of sporopollenins in pollen grain wall, while pollen of Picea has apparently higher concentration of carotenoids than the rest of the family
It is shown that vibrational methodologies have great potential for systematic collection of data on ecosystems and that the obtained phylogenetic variation can be well explained by the biochemical composition of pollen

Summary

Introduction

Pollen grains are characteristic to plant families, genera or even species, revealing valuable information on ecology, forensics, climate change, insect migration, food sources and aeroallergens They are extremely resilient to decay, and pollen microfossils can have well-preserved morphology for millions of years. In addition to optical microscopy, different microscopic techniques have been attempted for measurement of pollen, such as differential interference contrast microscopy, phase contrast microscopy, fluorescence microscopy, scanning electron microscopy, confocal laser scanning microscopy and other alternative methods for obtaining detailed morphology of pollen [1] These methods are time-consuming and expensive and provide only identification based on morphological analysis, while chemical characterization of samples cannot be obtained. We have compared the level of chemical information that can be obtained by different multiscale vibrational spectroscopic techniques.

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