Photosystem II core quenching in desiccated Leptolyngbya ohadii

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.

A kaleidoscope of photosynthetic antenna proteins and their emerging roles

“…While the cytochrome b6f complex had been proposed as the redox sensor, a recent work had shown that it is not involved in cyanobacterial state transition ( Calzadi et al, 2019 ). In the cyanobacterial species, S ynechococcus elongatus and Synechocystis sp PCC 6803, there is no redistribution of PBS, nor is there any spillover from PSII to PSI ( Bhatti et al, 2020 ; Ranjbar Choubeh et al, 2020 ). However, in order to balance the excitation pressure between PSII and PSI, in state II, the PSII-core and not the PBS is quenched ( Bhatti et al, 2020 ; Ranjbar Choubeh et al, 2020 ).…”

“…In the cyanobacterial species, S ynechococcus elongatus and Synechocystis sp PCC 6803, there is no redistribution of PBS, nor is there any spillover from PSII to PSI ( Bhatti et al, 2020 ; Ranjbar Choubeh et al, 2020 ). However, in order to balance the excitation pressure between PSII and PSI, in state II, the PSII-core and not the PBS is quenched ( Bhatti et al, 2020 ; Ranjbar Choubeh et al, 2020 ). Furthermore, in S. elongatus , two (sub) populations of PSII, namely quenched and unquenched exist, in both states I and II.…”