Evaluation of visible-light wavelengths that reduce or oxidize the plastoquinone pool in green algae with the activated F0 rise method

Abbreviations : Chl – chlorophyll; F 0 rise – post-illumination rise of chlorophyll a fluorescence; FR – far-red; flv – flavodiiron; FWHM – full width at half maximum; LL – low light; ML – measuring light; PAM – pulse amplitude modulation; PG – propyl gallate; PQ – plastoquinone; PTOX – plastid terminal oxidase; SP – saturating pulse. Acknowledgements : Yagut Allahverdiyeva-Rinne and Martina Jokel-Toivanen are thanked for generously donating C. reinhardtii cc4533 and the flvB mutant. Olli Virtanen is thanked for sharing his expertise and helping with green algal cultivation. Iiris Kuusisto is thanked for assistance in experiments. The Emil Aaltonen Foundation is thanked for its financial support (HM). The studies were conducted in the Molecular Plant Biology unit, the Finnish Infrastructure for Photosynthesis Research. Conflict of interest : The authors declare that they have no conflict of interest. We recently developed a chlorophyll a fluorescence method (activated F 0 rise) for estimating if a light wavelength preferably excites PSI or PSII in plants. Here, the method was tested in green microalgae: Scenedesmus quadricauda , Scenedesmus ecornis , Scenedesmus fuscus , Chlamydomonas reinhardtii , Chlorella sorokiniana , and Ettlia oleoabundans . The Scenedesmus species displayed a plant-like action spectra of F 0 rise, suggesting that PSII/PSI absorption ratio is conserved from higher plants to green algae. F 0 rise was weak in a strain of C. reinhardtii , C. sorokiniana , and E. oleoabundans . Interestingly, another C. reinhardtii strain exhibited a strong F 0 rise. The result indicates that the same illumination can lead to different redox states of the plastoquinone pool in different algae. Flavodiiron activity enhanced the F 0 rise, presumably by oxidizing the plastoquinone pool during pre-illumination. The activity of plastid terminal oxidase, in turn, diminished the F 0 rise, but to a small degree.