Chlorophyll fluorescence emission spectroscopy of oxygenic organisms at 77 K

Abstract

Photosynthetic fluorescence emission spectra measurement at the temperature of 77 K (-196°C) is an often-used technique in photosynthesis research. At low temperature, biochemical and physiological processes that modulate fluorescence are mostly abolished, and the fluorescence emission of both PSI and PSII become easily distinguishable. Here we briefly review the history of low-temperature chlorophyll fluorescence methods and the characteristics of the acquired emission spectra in oxygen-producing organisms. We discuss the contribution of different photosynthetic complexes and physiological processes to fluorescence emission at 77 K in cyanobacteria, green algae, heterokont algae, and plants. Furthermore, we describe practical aspects for obtaining and presenting 77 K fluorescence spectra.

Autofluorescence in Plants

“…Chlorophyll autofluorescence is used both in lab-scale experiments and in remote sensing applications to evaluate plant health/vigor by directly measuring photosynthetic efficiency and has become a key technique for evaluating the response of plants to changes in the environment [16,17]. Chlorophyll is excited by UV, blue or green light and emits strongly in the red with a distinct bimodal emission with maxima at 685 and 720-730 nm ( Figure 2) [16]. The quantum yield, a measure of the brightness of fluorescence representing the ratio of photons absorbed to emitted, is 0.25 for chlorophyll a in solution and is independent of excitation wavelength or solvent [18].…”

Recycling of energy dissipated as heat accounts for high activity of Photosystem II

“…The opposite proportion can be observed at room temperature, in accordance with the numerous previous reports 20 . Determined at 77 K, the fluorescence yield of PSII core complex is about 2 times higher and the fluorescence yield of PSI about 20 times higher, as compared to room temperature 20,31 . The integration of the Chl a fluorescence emission spectra in leaves in the spectral region representing mostly PSII (wavelengths below 703 nm) and in the spectral region representing largely PSI (wavelengths higher than 703 nm) gives the ratio of photons emitted by PSII and PSI as high as 1.16  0.22 at 298 K but only 0.20  0.02 at 77 K (a mean value from three different leaves  S.D., Fig.…”

The Observation and Characterisation of Fluorescent Bioaerosols Using Real-Time UV-LIF Spectrometry in Hong Kong from June to November 2018

“…These are a taxon of green algae, for which previous literature suggests Chlorophyll-∝ as the dominant fluorophore [34]. Neither the PLAIR Rapid-E nor the WIBS-NEO are suited to algal identification because Chlorophyll-∝ has a much higher excitation wavelength of 400-485 nm [35]. Although Xe2 of the WIBS-Neo was close to the lower end of this excitation band, the emitted wavelengths were higher than the instrument's detection range, at 685 nm.…”