A method to decompose spectral changes in Synechocystis PCC 6803 during light-induced state transitions

Abstract

Cyanobacteria have developed responses to maintain the balance between the energy absorbed and the energy used in different pigment-protein complexes. One of the relatively rapid (a few minutes) responses is activated when the cells are exposed to high light intensities. This mechanism thermally dissipates excitation energy at the level of the phycobilisome (PB) antenna before it reaches the reaction center. When exposed to low intensities of light that modify the redox state of the plastoquinone pool, the so-called state transitions redistribute energy between photosystem I and II. Experimental techniques to investigate the underlying mechanisms of these responses, such as pulse-amplitude modulated fluorometry, are based on spectrally integrated signals. Previously, a spectrally resolved fluorometry method has been introduced to preserve spectral information. The analysis method introduced in this work allows to interpret SRF data in terms of species-associated spectra of open/closed reaction centers (RCs), (un)quenched PB and state 1 versus state 2. Thus, spectral differences in the time-dependent fluorescence signature of photosynthetic organisms under varying light conditions can be traced and assigned to functional emitting species leading to a number of interpretations of their molecular origins. In particular, we present evidence that state 1 and state 2 correspond to different states of the PB-PSII-PSI megacomplex.Electronic supplementary materialThe online version of this article (doi:10.1007/s11120-016-0248-8) contains supplementary material, which is available to authorized users.

The phycobilisome terminal emitter transfers its energy with a rate of (20 ps)^-1 to photosystem II

“…In Fig. 5B we reproduced the steady state emission spectrum of the PB-PSII complex with open (black) or closed (red) RC from a decomposition of spectrally resolved fluorescence traces that were recorded over several minutes with 100 ms time resolution and were reported in Acuña et al (2016a). We note that the relative areas of the complexes with RCs open or closed are consistent.…”

“…The absence of a maximum at 682 nm in the black SS of Fig. 5B suggests that the decomposition reported in Acuña et al (2016a) was suboptimal. Fig.…”

“…Because the PB architecture possesses a C2 rotational symmetry axis, perpendicular to the membrane, the core can be described by three APC660 and one APC680 compartment (black). Three APC660 compartments are needed: the top cylinder (magenta), the APC660 pigments in the D and EF disks (orange), which are in the closest contact to the APC680 pigments, Acuña et al (2016a). and the remaining APC660 pigments of the basal cylinders (red).…”

“…2). The next challenge will be to establish the rate of energy transfer to PSI in the PB-PSII-PSI megacomplex that is present in WT Synechocystis (Liu et al 2013, Acuña et al 2016a.…”

Protein arrangement factor: a new photosynthetic parameter characterizing the organization of thylakoid membrane proteins

“…Researchers depicted changes in gene expression and protein content during HL stress and triggering different photoprotective mechanism operating in the first minutes up to few hours after exposition to HL (Fujita and Murakami 1987, Hihara and Ikeuchi 1997, Hihara et al 2001, Muramatsu and Hihara 2012. This short-term physiological response involves PBS uncoupling, state transition, protective energy dissipation in orange carotenoid protein (OCP)-dependent quenching (Kirilovsky et al 2014, Chukhutsina et al 2015, Acuña et al 2016 and changes in photosynthetic gene expression (Hihara et al 2001). Long-term acclimation involves compositional, functional and structural changes of thylakoid protein complexes (Oquist et al 1995, Muramatsu et al 2009, Allahverdiyeva et al 2015, Majumder et al 2017.…”