Abstract
Cyanobacteria living in the harsh environment of the desert have to protect themselves against high light intensity and prevent photodamage. These cyanobacteria are in a desiccated state during the largest part of the day when both temperature and light intensity are high. In the desiccated state, their photosynthetic activity is stopped, whereas upon rehydration the ability to perform photosynthesis is regained. Earlier reports indicate that light-induced excitations in Leptolyngbya ohadii are heavily quenched in the desiccated state, because of a loss of structural order of the light-harvesting phycobilisome structures (Bar Eyal et al. in Proc Natl Acad Sci 114:9481, 2017) and via the stably oxidized primary electron donor in photosystem I, namely P700+ (Bar Eyal et al. in Biochim Biophys Acta Bioenergy 1847:1267–1273, 2015). In this study, we use picosecond fluorescence experiments to demonstrate that a third protection mechanism exists, in which the core of photosystem II is quenched independently.
Highlights
Cyanobacteria are photosynthetic organisms which are abundant in aquatic and terrestrial environments
We provide evidence that besides quenching of the light-harvesting PBS and photosystem I (PSI), direct photosystem II (PSII) excitation energy quenching occurs in the desiccated state
Desert-dwelling cyanobacteria need to protect themselves against high light intensity during the day, which in their natural habitat is accompanied by drought
Summary
Cyanobacteria are photosynthetic organisms which are abundant in aquatic and terrestrial environments. Terrestrial cyanobacteria constitute 28% of total global cyanobacterial biomass and 79% of this is constituted by cyanobacteria living in arid soil crusts (Garcia-Pichel et al 2003). We study Leptolyngbya ohadii, grown at low light intensities (60 μmol photons m −2 s−1), by timeresolved fluorescence spectroscopy. We provide evidence that besides quenching of the light-harvesting PBS and PSI, direct PSII excitation energy quenching occurs in the desiccated state
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