Comparative excitation-emission dependence of the F V /F M ratio in model green algae and cyanobacterial strains

The emission spectra collected under conditions of open (F ) and closed (F ) photosystem II (PSII) reaction centres are close-to-independent from the excitation wavelength in Chlamydomonas reinhardtii and Chlorella sorokiniana, whereas a pronounced dependence is observed in Synechocystis sp. PCC6803...

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Published in:Physiologia plantarum 2019-05, Vol.166 (1), p.351-364
Main Authors: Santabarbara, Stefano, Villafiorita Monteleone, Francesca, Remelli, William, Rizzo, Federico, Menin, Barbara, Casazza, Anna Paola
Format: Article
Language:English
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Summary:The emission spectra collected under conditions of open (F ) and closed (F ) photosystem II (PSII) reaction centres are close-to-independent from the excitation wavelength in Chlamydomonas reinhardtii and Chlorella sorokiniana, whereas a pronounced dependence is observed in Synechocystis sp. PCC6803 and Synechococcus PCC7942, instead. The differences in band-shape between the F and F emission are limited in green algae, giving rise only to a minor trough in the F /F spectrum in the 705-720 nm range, irrespectively of the excitation. More substantial variations are observed in cyanobacteria, resulting in marked dependencies of the measured F /F ratios on both the excitation and the detection wavelengths. In cyanobacteria, the maximal F /F values (0.5-0.7), observed monitoring at ~684 nm and exciting Chl a preferentially, are comparable to those of green algae; however, F /F decreases sharply below ~660 nm. Furthermore, in the red emission tail, the trough in the F /F spectrum is more pronounced in cyanobacteria with respect to green algae, corresponding to F /F values of 0.25-0.4 in this spectral region. Upon direct phycobilisomes excitation (i.e. >520 nm), the F /F value detected at 684 nm decreases to 0.3-0.5 and is close-to-negligible (~0.1) below 660 nm. At the same time, the F spectra are, in all species investigated, almost independent on the excitation wavelength. It is concluded that the excitation/emission dependencies of the F /F ratio arise from overlapped contributions from the three independent emissions of PSI, PSII and a fraction of energetically uncoupled external antenna, excited in different proportions depending on the respective optical cross-section and fluorescence yield. This article is protected by copyright. All rights reserved.
ISSN:0031-9317
1399-3054
DOI:10.1111/ppl.12931