The acclimation of higher plants to different light intensities is associated with a reorganization of the photosynthetic apparatus. These modifications, namely, changes in the amount of peripheral antenna (LHCII) of photosystem (PS) II and changes in PSII/PSI stoichiometry, typically lead to an altered chlorophyll (Chl) a/b ratio. However, our previous studies show that in spruce, this ratio is not affected by changes in growth light intensity. The evolutionary loss of PSII antenna proteins LHCB3 and LHCB6 in the Pinaceae family is another indication that the light acclimation strategy in spruce could be different. Here we show that, unlike Arabidopsis, spruce does not modify its PSII/PSI ratio and PSII antenna size to maximize its photosynthetic performance during light acclimation. Its large PSII antenna consists of many weakly bound LHCIIs, which form effective quenching centers, even at relatively low light. This, together with sensitive photosynthetic control on the level of cytochrome b6f complex (protecting PSI), is the crucial photoprotective mechanism in spruce. High-light acclimation of spruce involves the disruption of PSII macro-organization, reduction of the amount of both PSII and PSI core complexes, synthesis of stress proteins that bind released Chls, and formation of "locked-in" quenching centers from uncoupled LHCIIs. Such response has been previously observed in the evergreen angiosperm Monstera deliciosa exposed to high light. We suggest that, in contrast to annuals, shade-tolerant evergreen land plants have their own strategy to cope with light intensity changes and the hallmark of this strategy is a stable Chl a/b ratio.

• Keywords
• Arabidopsis thaliana, LHCII antenna, Light acclimation, Non-photochemical quenching, Photoprotection, Photosynthetic control, Picea abies, Thylakoid membrane,
• MeSH
• Acclimatization MeSH
• Arabidopsis * metabolism   MeSH
• Chlorophyll A metabolism   MeSH
• Chlorophyll metabolism   MeSH
• Cytochromes b metabolism   MeSH
• Photosystem I Protein Complex metabolism   MeSH
• Photosystem II Protein Complex metabolism   MeSH
• Cytochrome b6f Complex metabolism   MeSH
• Heat-Shock Proteins metabolism   MeSH
• Picea * metabolism   MeSH
• Light MeSH
• Light-Harvesting Protein Complexes metabolism   MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Chlorophyll A MeSH
• Chlorophyll MeSH
• Cytochromes b MeSH
• Photosystem I Protein Complex MeSH
• Photosystem II Protein Complex MeSH
• Cytochrome b6f Complex MeSH
• Heat-Shock Proteins MeSH
• Light-Harvesting Protein Complexes MeSH

Antenna proteins play a major role in the regulation of light-harvesting in photosynthesis. However, less is known about a possible link between their sizes (oligomerization state) and fluorescence intensity (number of photons emitted). Here, we used a microscopy-based method, Fluorescence Correlation Spectroscopy (FCS), to analyze different antenna proteins at the particle level. The direct comparison indicated that Chromera Light Harvesting (CLH) antenna particles (isolated from Chromera velia) behaved as the monomeric Light Harvesting Complex II (LHCII) (from higher plants), in terms of their radius (based on the diffusion time) and fluorescence yields. FCS data thus indicated a monomeric oligomerization state of algal CLH antenna (at our experimental conditions) that was later confirmed also by biochemical experiments. Additionally, our data provide a proof of concept that the FCS method is well suited to measure proteins sizes (oligomerization state) and fluorescence intensities (photon counts) of antenna proteins per single particle (monomers and oligomers). We proved that antenna monomers (CLH and LHCIIm) are more "quenched" than the corresponding trimers. The FCS measurement thus represents a useful experimental approach that allows studying the role of antenna oligomerization in the mechanism of photoprotection.

• Keywords
• Chromera velia, antenna proteins, fluorescence correlation spectroscopy, light-harvesting, microscopy, photosynthesis, protein diffusion, protein oligomerization,
• MeSH
• Algal Proteins chemistry   metabolism   MeSH
• Fluorescence * MeSH
• Spectrometry, Fluorescence MeSH
• Photosynthesis * MeSH
• Kinetics MeSH
• Protein Multimerization MeSH
• Protein Transport MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Algal Proteins MeSH

We explored photoprotective strategies in a cryptophyte alga Rhodomonas salina. This cryptophytic alga represents phototrophs where chlorophyll a/c antennas in thylakoids are combined with additional light-harvesting system formed by phycobiliproteins in the chloroplast lumen. The fastest response to excessive irradiation is induction of non-photochemical quenching (NPQ). The maximal NPQ appears already after 20 s of excessive irradiation. This initial phase of NPQ is sensitive to Ca2+ channel inhibitor (diltiazem) and disappears, also, in the presence of non-actin, an ionophore for monovalent cations. The prolonged exposure to high light of R. salina cells causes photoinhibition of photosystem II (PSII) that can be further enhanced when Ca2+ fluxes are inhibited by diltiazem. The light-induced reduction in PSII photochemical activity is smaller when compared with immotile diatom Phaeodactylum tricornutum. We explain this as a result of their different photoprotective strategies. Besides the protective role of NPQ, the motile R. salina also minimizes high light exposure by increased cell velocity by almost 25% percent (25% from 82 to 104 μm/s). We suggest that motility of algal cells might have a photoprotective role at high light because algal cell rotation around longitudinal axes changes continual irradiation to periodically fluctuating light.

• MeSH
• Chlorophyll A metabolism   MeSH
• Chlorophyll metabolism   MeSH
• Cryptophyta cytology   metabolism   radiation effects   MeSH
• Photosystem II Protein Complex metabolism   MeSH
• Cell Movement radiation effects   MeSH
• Light MeSH
• Calcium metabolism   MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Chlorophyll A MeSH
• Chlorophyll MeSH
• chlorophyll c MeSH Browser
• Photosystem II Protein Complex MeSH
• Calcium MeSH

The extrinsic PsbU and PsbV proteins are known to play a critical role in stabilizing the Mn4CaO5 cluster of the PSII oxygen-evolving complex (OEC). However, most isolates of the marine cyanobacterium Prochlorococcus naturally miss these proteins, even though they have kept the main OEC protein, PsbO. A structural homology model of the PSII of such a natural deletion mutant strain (P. marinus MED4) did not reveal any obvious compensation mechanism for this lack. To assess the physiological consequences of this unusual OEC, we compared oxygen evolution between Prochlorococcus strains missing psbU and psbV (PCC 9511 and SS120) and two marine strains possessing these genes (Prochlorococcus sp. MIT9313 and Synechococcus sp. WH7803). While the low light-adapted strain SS120 exhibited the lowest maximal O2 evolution rates (Pmax per divinyl-chlorophyll a, per cell or per photosystem II) of all four strains, the high light-adapted strain PCC 9511 displayed even higher PChlmax and PPSIImax at high irradiance than Synechococcus sp. WH7803. Furthermore, thermoluminescence glow curves did not show any alteration in the B-band shape or peak position that could be related to the lack of these extrinsic proteins. This suggests an efficient functional adaptation of the OEC in these natural deletion mutants, in which PsbO alone is seemingly sufficient to ensure proper oxygen evolution. Our study also showed that Prochlorococcus strains exhibit negative net O2 evolution rates at the low irradiances encountered in minimum oxygen zones, possibly explaining the very low O2 concentrations measured in these environments, where Prochlorococcus is the dominant oxyphototroph.

• Keywords
• Marine cyanobacteria, Oxygen minimum zones, Oxygen-evolving complex, Photoacclimation, Photosystem II, Prochlorococcus, Synechococcus,
• MeSH
• Bacterial Proteins chemistry   genetics   physiology   MeSH
• Chlorophyll metabolism   MeSH
• Photosynthesis physiology   MeSH
• Photosystem II Protein Complex chemistry   genetics   physiology   MeSH
• Genome, Bacterial MeSH
• Oxygen metabolism   MeSH
• Models, Molecular MeSH
• Flow Cytometry MeSH
• Cyanobacteria genetics   metabolism   MeSH
• Light MeSH
• Publication type
• Journal Article MeSH
• Comparative Study MeSH
• Names of Substances
• Bacterial Proteins MeSH
• Chlorophyll MeSH
• Photosystem II Protein Complex MeSH
• Oxygen MeSH

Photoprotective non-photochemical quenching (NPQ) represents an effective way to dissipate the light energy absorbed in excess by most phototrophs. It is often claimed that NPQ formation/relaxation kinetics are determined by xanthophyll composition. We, however, found that, for the alveolate alga Chromera velia, this is not the case. In the present paper, we investigated the reasons for the constitutive high rate of quenching displayed by the alga by comparing its light harvesting strategies with those of a model phototroph, the land plant Spinacia oleracea. Experimental results and in silico studies support the idea that fast quenching is due not to xanthophylls, but to intrinsic properties of the Chromera light harvesting complex (CLH) protein, related to amino acid composition and protein folding. The pKa for CLH quenching was shifted by 0.5 units to a higher pH compared with higher plant antennas (light harvesting complex II; LHCII). We conclude that, whilst higher plant LHCIIs are better suited for light harvesting, CLHs are 'natural quenchers' ready to switch into a dissipative state. We propose that organisms with antenna proteins intrinsically more sensitive to protons, such as C. velia, carry a relatively high concentration of violaxanthin to improve their light harvesting. In contrast, higher plants need less violaxanthin per chlorophyll because LHCII proteins are more efficient light harvesters and instead require co-factors such as zeaxanthin and PsbS to accelerate and enhance quenching.

• MeSH
• Alveolata physiology   MeSH
• Algal Proteins metabolism   MeSH
• Photosynthesis * MeSH
• Protons * MeSH
• Protozoan Proteins metabolism   MeSH
• Plant Proteins metabolism   MeSH
• Spinacia oleracea physiology   MeSH
• Light-Harvesting Protein Complexes metabolism   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Comparative Study MeSH
• Names of Substances
• Algal Proteins MeSH
• Protons * MeSH
• Protozoan Proteins MeSH
• Plant Proteins MeSH
• Light-Harvesting Protein Complexes MeSH

The slow kinetic phases of the chlorophyll a fluorescence transient (induction) are valuable tools in studying dynamic regulation of light harvesting, light energy distribution between photosystems, and heat dissipation in photosynthetic organisms. However, the origin of these phases are not yet fully understood. This is especially true in the case of prokaryotic oxygenic photoautotrophs, the cyanobacteria. To understand the origin of the slowest (tens of minutes) kinetic phase, the M-T fluorescence decline, in the context of light acclimation of these globally important microorganisms, we have compared spectrally resolved fluorescence induction data from the wild type Synechocystis sp. PCC 6803 cells, using orange (λ = 593 nm) actinic light, with those of mutants, ΔapcD and ΔOCP, that are unable to perform either state transition or fluorescence quenching by orange carotenoid protein (OCP), respectively. Our results suggest a multiple origin of the M-T decline and reveal a complex interplay of various known regulatory processes in maintaining the redox homeostasis of a cyanobacterial cell. In addition, they lead us to suggest that a new type of regulatory process, operating on the timescale of minutes to hours, is involved in dissipating excess light energy in cyanobacteria.

• Keywords
• Fluorescence quenching, Interplay of regulatory processes, Kautsky effect, Photoprotection, Synechocystis, The M–T phase,
• MeSH
• Bacterial Proteins genetics   metabolism   MeSH
• Chlorophyll A MeSH
• Chlorophyll chemistry   genetics   metabolism   MeSH
• Diuron chemistry   MeSH
• Fluorescence MeSH
• Spectrometry, Fluorescence MeSH
• Phycobilisomes genetics   metabolism   MeSH
• Potassium Cyanide chemistry   MeSH
• Luminescent Measurements MeSH
• Light MeSH
• Synechocystis chemistry   genetics   metabolism   MeSH
• Temperature MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Bacterial Proteins MeSH
• Chlorophyll A MeSH
• Chlorophyll MeSH
• Diuron MeSH
• Phycobilisomes MeSH
• Potassium Cyanide MeSH
• orange carotenoid protein, Synechocystis MeSH Browser