Imaging linear and circular polarization features in leaves with complete Mueller matrix polarimetry

C.H Lucas Patty,David A Luo,Frans Snik,Freek Ariese,Wybren Jan Buma,Inge Loes Ten Kate,Rob J.M Van Spanning,William B Sparks,Thomas A Germer,Győző Garab,Michael W Kudenov

doi:10.1016/j.bbagen.2018.03.005

Abstract

Spectropolarimetry of intact plant leaves allows to probe the molecular architecture of vegetation photosynthesis in a non-invasive and non-destructive way and, as such, can offer a wealth of physiological information. In addition to the molecular signals due to the photosynthetic machinery, the cell structure and its arrangement within a leaf can create and modify polarization signals. Using Mueller matrix polarimetry with rotating retarder modulation, we have visualized spatial variations in polarization in transmission around the chlorophyll a absorbance band from 650 nm to 710 nm. We show linear and circular polarization measurements of maple leaves and cultivated maize leaves and discuss the corresponding Mueller matrices and the Mueller matrix decompositions, which show distinct features in diattenuation, polarizance, retardance and depolarization. Importantly, while normal leaf tissue shows a typical split signal with both a negative and a positive peak in the induced fractional circular polarization and circular dichroism, the signals close to the veins only display a negative band. The results are similar to the negative band as reported earlier for single macrodomains. We discuss the possible role of the chloroplast orientation around the veins as a cause of this phenomenon. Systematic artefacts are ruled out as three independent measurements by different instruments gave similar results. These results provide better insight into circular polarization measurements on whole leaves and options for vegetation remote sensing using circular polarization.

Highlights

One of the most distinctive and characteristic features of life is the homochirality of its molecular building blocks [1]
Some structure is visible in the Mueller matrix elements relating to linear polarizance (m21, m31) and dichroism (m12, m13)
For maize these elements show a much stronger and gradual signal as compared to maple, which might result from the positioning of the maize leaves within the setup, which was always very similar, in combination with the parallel venation

Summary

Introduction

One of the most distinctive and characteristic features of life is the homochirality of its molecular building blocks [1] Chiral molecules in their most simple form exist in left-handed (L-) and a right-handed (D-) versions, called enantiomers. There are a few exceptions [2], amino acids mainly occur in the Lconfiguration and sugars occur predominantly in the D-configuration Apart from these small molecules, many large scale molecular architectures, dimensions of which can range over several orders of magnitude, are chiral. Chirality can be observed in the chlorophylls and bacteriochlorophylls, in particular when utilized in photosynthesis (as their intrinsic signal is very weak due to their planar and almost symmetrical structure). These chlorophylls are organized in a supramolecular structure that itself is chiral too [4]

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Discussion

Conclusion