Optical spectroscopic microscopy targeted to oxygenic photosynthetic membranes and organisms

Spectral microscopy provides information about the spatial distribution and physiological functional states of pigment-protein complexes in photosynthetic organisms. This can be used to complement the newly developed techniques, such as cryogenic electron microscopy and atomic force microscopy, which are less effective in functional analysis of photosynthesis, despite having an excellent spatial resolution. The combination of optical microscopies with various spectroscopic techniques has extended the possibility of a multi-perspective investigation in photosynthesis research. Some of these spectroscopic techniques include fluorescence and absorption spectra, excitation spectra, time-resolved fluorescence measurement, Raman scattering spectroscopy, etc. These techniques can be applied to in vivo investigations of photosynthetic activity without introducing any artificial fluorophore since the photosynthetic pigments are informative probes. In particular, the technique has been effective in clarifying the dynamic physiological responses of photosynthetic organisms to variable environments. In this paper, we review the recent progress in spectral microscopy in the field of in vivo photosynthesis research. We have also introduced and discussed some distinctive spectral microscopies such as anti-Stokes fluorescence spectral microscopy, excitation spectral microscopy, cryo-microscopy, and Raman spectral microscopy.