Resolving the contribution of the uncoupled phycobilisomes to cyanobacterial pulse-amplitude modulated (PAM) fluorometry signals

Abstract

Pulse-amplitude modulated (PAM) fluorometry is extensively used to characterize photosynthetic organisms on the slow time-scale (1–1000 s). The saturation pulse method allows determination of the quantum yields of maximal (FM) and minimal fluorescence (F0), parameters related to the activity of the photosynthetic apparatus. Also, when the sample undergoes a certain light treatment during the measurement, the fluorescence quantum yields of the unquenched and the quenched states can be determined. In the case of cyanobacteria, however, the recorded fluorescence does not exclusively stem from the chlorophyll a in photosystem II (PSII). The phycobilins, the pigments of the cyanobacterial light-harvesting complexes, the phycobilisomes (PB), also contribute to the PAM signal, and therefore, F0 and FM are no longer related to PSII only. We present a functional model that takes into account the presence of several fluorescent species whose concentrations can be resolved provided their fluorescence quantum yields are known. Data analysis of PAM measurements on in vivo cells of our model organism Synechocystis PCC6803 is discussed. Three different components are found necessary to fit the data: uncoupled PB (PBfree), PB–PSII complexes, and free PSI. The free PSII contribution was negligible. The PBfree contribution substantially increased in the mutants that lack the core terminal emitter subunits allophycocyanin D or allophycocyanin F. A positive correlation was found between the amount of PBfree and the rate constants describing the binding of the activated orange carotenoid protein to PB, responsible for non-photochemical quenching.Electronic supplementary materialThe online version of this article (doi:10.1007/s11120-015-0141-x) contains supplementary material, which is available to authorized users.

Chlorosis as a Developmental Program in Cyanobacteria: The Proteomic Fundament for Survival and Awakening

“…In cyanobacteria, the basal PAM fluorescence signal (F0) results from overlapping PSII Chl a and phycobilisome fluorescence (38). In nitrogen-sufficient cells, the F0 levels of the mutants and wild-type were indistinguishable, but upon nitrogen depletion, F0 of the mutants was significantly lower than that of the wild-type (Figure 6B), which is in agreement with the lower phycobiliprotein level of the mutants.…”

Desiccation‐induced changes in photochemical processes of photosynthesis and spectral reflectance in Nostoc commune (Cyanobacteria, Nostocales) colonies from polar regions

“…The reason for such F m to F m ′ ratio is state 2 – state 1 transition caused by phycobilisomes during illumination of actinic light, that in cyanobacterial photosynthetic apparatus contributes to background ( F o ) and variable ( F v ) chlorophyll fluorescence to a larger extent than antennae and PSII chlorophyll molecules in higher plants (Papageorgiou ). Recently, contribution of phycobilisomes to F o and F m chlorophyll fluorescence could be assessed using a model presented by Acuña et al (). Non‐photochemical quenching increases under such situation as well (Maksimov et al ).…”

“…Recently, contribution of phycobilisomes to F o and F m chlorophyll fluorescence could be Phase I signifies the inhibition of photochemical processes at high RWC (100-80%), phase II denotes increase of ΦPSII due to better availability of CO 2 at RWC of 80-35% and phase III indicates decrease of ΦPSII because of dehydration. assessed using a model presented by Acuña et al (2016). Non-photochemical quenching increases under such situation as well (Maksimov et al 2014).…”

Toward Multiscale Models of Cyanobacterial Growth: A Modular Approach

“…While relevant for biophysical research, the respective models cannot be straightforwardly integrated into more comprehensive models of phototrophic growth, due to the focus on fast time scales and specific output variables. We note that the interpretation of results obtained from pulse-amplitude modulated (PAM) fluorimetry significantly differs between cyanobacteria and plants (Schuurmans et al, 2015; Acuña et al, 2016), with modeling approaches focusing almost exclusively on the latter.…”