Origin of pronounced differences in 77 K fluorescence of the green alga Chlamydomonas reinhardtii in state 1 and 2

Abstract

In response to changes in the reduction state of the plastoquinone pool in its thylakoid membrane, the green alga Chlamydomonas reinhardtti is performing state transitions: remodelling of its thylakoid membrane leads to a redistribution of excitations over photosystems I and II (PSI and PSII). These transitions are accompanied by marked changes in the 77 K fluorescence spectrum, which form the accepted signature of state transitions. The changes are generally thought to reflect a redistribution of light-harvesting complexes (LHCs) over PSII (fluorescing below 700 nm) and PSI (fluorescing above 700 nm). Here we studied the picosecond fluorescence properties of C. reinhardtti over a broad range of wavelengths with very low excitation intensities (0.2 nJ per laser pulse). Cells were directly used for time-resolved fluorescence measurements at 77 K without further treatment, such as medium exchange with glycerol. It is observed that upon going from state 1 (relatively more fluorescence below 700 nm) to state 2 (relatively more fluorescence above 700 nm), a large part of the fluorescence of LHC/PSII becomes substantially quenched in concurrence with LHC detachment from PSII, whereas the absolute amount of PSI fluorescence hardly changes. These results are in agreement with the recent proposal that the amount of LHC moving from PSII to PSI upon going from state 1 to state 2 is rather limited (Unlu et al. Proc Natl Acad Sci USA 111 (9):3460-3465, 2014).

Practical aspects of the measurements of non‐photochemical chlorophyll fluorescence quenching in green microalgae Chlamydomonas reinhardtii using Open FluorCam

“…Such a situation took place during dark‐adaptation and dark‐relaxation periods, as the gas diffusion inside the algal suspension in the microplate wells most probably was limited. A method used to provide the state 1 occurrence in dark‐adapted C. reinhardtii cells is strong agitation, which enables oxygen to penetrate into the culture (Ünlü et al ) but it is impossible to be applied for samples kept in multi‐well plate. On the other hand, portioning the well‐aerated, dark‐adapted cultures into the microplate in the darkness directly before the measurements is uncomfortable.…”

Structural basis of LhcbM5-mediated state transitions in green algae

“…State transitions were suggested to alter the thylakoid ultrastructure and protein-protein interactions in C. reinhardtii 16 . The process may also lead to switch of the detached LHCIIs into the energetically quenched form so as to avoid photodamage [16][17][18] .…”

Development of fluorescence quenching in Chlamydomonas reinhardtii upon prolonged illumination at 77 K

“…A primary example of a mechanism that regulates this distribution in higher plants, algae and cyanobacteria are state transitions (ST) (van Thor et al 1998 ; Allen 2003 ; Bellafiore et al 2005 ; Drop et al 2014 ), for the first time observed in 1969 in 77 K fluorescence spectra of Porphyridium cruentum (Murata 1969 ). Many subsequent studies on ST have routinely included low-temperature fluorescence spectroscopy (Allen et al 1981 ; Wollman and Delepelaire 1984 ; Bruce et al 1985 ; Delphin et al 1995 ; Cardol et al 2003 ; Bellafiore et al 2005 ; Kargul et al 2005 ; Chuartzman et al 2008 ; Iwai et al 2008 ; Allorent et al 2013 ; Drop et al 2014 ; Ünlü et al 2016 ). It is commonly accepted that redistribution of excitation energy between PSI and PSII upon state transitions is realized by a shift of a part of the light-harvesting antenna of PSII (LHCII) between PSII (state 1; St1) and PSI (state 2; St2).…”