Survival of phototrophic organisms depends on their ability to collect and convert enough light energy to support their metabolism. Phototrophs can extend their absorption cross section by using diverse pigments and by tuning the properties of these pigments via pigment-pigment and pigment-protein interaction. It is well known that some cyanobacteria can grow in heavily shaded habitats by utilizing far-red light harvested with far-red-absorbing chlorophylls d and f. We describe a red-shifted light-harvesting system based on chlorophyll a from a freshwater eustigmatophyte alga Trachydiscus minutus (Eustigmatophyceae, Goniochloridales). A comprehensive characterization of the photosynthetic apparatus of T. minutus is presented. We show that thylakoid membranes of T. minutus contain light-harvesting complexes of several sizes differing in the relative amount of far-red chlorophyll a forms absorbing around 700 nm. The pigment arrangement of the major red-shifted light-harvesting complex is similar to that of the red-shifted antenna of a marine alveolate alga Chromera velia. Evolutionary aspects of the algal far-red light-harvesting complexes are discussed. The presence of these antennas in eustigmatophyte algae opens up new ways to modify organisms of this promising group for effective use of far-red light in mass cultures.

• Keywords
• Chromatic acclimation, Eustigmatophyta, Light-harvesting protein, Oligomeric LHC, Red-shifted LHC, Violaxanthin,
• MeSH
• Pigments, Biological metabolism   MeSH
• Diuron MeSH
• Spectrometry, Fluorescence MeSH
• Stramenopiles metabolism   radiation effects   MeSH
• Membrane Proteins metabolism   MeSH
• Fresh Water * MeSH
• Light * MeSH
• Light-Harvesting Protein Complexes metabolism   MeSH
• Temperature MeSH
• Thylakoids metabolism   MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Pigments, Biological MeSH
• Diuron MeSH
• Membrane Proteins MeSH
• Light-Harvesting Protein Complexes MeSH

The soil chromophyte alga Xanthonema (X.) debile contains only non-carbonyl carotenoids and Chl-a. X. debile has an antenna system denoted Xanthophyte light-harvesting complex (XLH) that contains the carotenoids diadinoxanthin, heteroxanthin, and vaucheriaxanthin. The XLH pigment stoichiometry was calculated by chromatographic techniques and the pigment-binding structure studied by resonance Raman spectroscopy. The pigment ratio obtained by HPLC was found to be close to 8:1:2:1 Chl-a:heteroxanthin:diadinoxanthin:vaucheriaxanthin. The resonance Raman spectra suggest the presence of 8-10 Chl-a, all of which are 5-coordinated to the central Mg, with 1-3 Chl-a possessing a macrocycle distorted from the relaxed conformation. The three populations of carotenoids are in the all-trans configuration. Vaucheriaxanthin absorbs around 500-530 nm, diadinoxanthin at 494 nm and heteroxanthin at 487 nm at 4.5 K. The effective conjugation length of heteroxanthin and diadinoxanthin has been determined as 9.4 in both cases; the environment polarizability of the heteroxanthin and diadinoxanthin binding pockets is 0.270 and 0.305, respectively.

• Keywords
• Algae, Carotenoids, Chl-a, Diadinoxanthin, Heteroxanthin, Light-harvesting complex, Resonance Raman,
• MeSH
• Stramenopiles chemistry   MeSH
• Carotenoids chemistry   MeSH
• Protein Conformation MeSH
• Spectrum Analysis, Raman MeSH
• Light-Harvesting Protein Complexes chemistry   MeSH
• Chromatography, High Pressure Liquid MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Carotenoids MeSH
• Light-Harvesting Protein Complexes MeSH

We have used time-resolved absorption and fluorescence spectroscopy with nanosecond resolution to study triplet energy transfer from chlorophylls to carotenoids in a protective process that prevents the formation of reactive singlet oxygen. The light-harvesting complexes studied were isolated from Chromera velia, belonging to a group Alveolata, and Xanthonema debile and Nannochloropsis oceanica, both from Stramenopiles. All three light-harvesting complexes are related to fucoxanthin-chlorophyll protein, but contain only chlorophyll a and no chlorophyll c. In addition, they differ in the carotenoid content. This composition of the complexes allowed us to study the quenching of chlorophyll a triplet states by different carotenoids in a comparable environment. The triplet states of chlorophylls bound to the light-harvesting complexes were quenched by carotenoids with an efficiency close to 100%. Carotenoid triplet states were observed to rise with a ~5 ns lifetime and were spectrally and kinetically homogeneous. The triplet states were formed predominantly on the red-most chlorophylls and were quenched by carotenoids which were further identified or at least spectrally characterized.

• Keywords
• Algae, Energy transfer, Light harvesting, Photoprotection, Photosynthesis, Transient spectroscopy,
• MeSH
• Anaerobiosis MeSH
• Time Factors MeSH
• Chlorophyll metabolism   MeSH
• Spectrometry, Fluorescence MeSH
• Photochemical Processes * MeSH
• Stramenopiles metabolism   MeSH
• Carotenoids metabolism   MeSH
• Kinetics MeSH
• Chlorophyll Binding Proteins metabolism   MeSH
• Light-Harvesting Protein Complexes metabolism   MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Chlorophyll MeSH
• Carotenoids MeSH
• Chlorophyll Binding Proteins MeSH
• Light-Harvesting Protein Complexes MeSH

It has previously been shown that the long-term treatment of Arabidopsis thaliana with the chloroplast inhibitor lincomycin leads to photosynthetic membranes enriched in antennas, strongly reduced in photosystem II reaction centers (PSII) and with enhanced nonphotochemical quenching (NPQ) (Belgio et al. Biophys J 102:2761-2771, 2012). Here, a similar physiological response was found in the microalga Chromera velia grown under high light (HL). In comparison to cells acclimated to low light, HL cells displayed a severe re-organization of the photosynthetic membrane characterized by (1) a reduction of PSII but similar antenna content; (2) partial uncoupling of antennas from PSII; (3) enhanced NPQ. The decrease in the number of PSII represents a rather unusual acclimation response compared to other phototrophs, where a smaller PSII antenna size is more commonly found under high light. Despite the diminished PSII content, no net damage could be detected on the basis of the Photosynthesis versus irradiance curve and electron transport rates pointing at the excess capacity of PSII. We therefore concluded that the photoinhibition is minimized under high light by a lower PSII content and that cells are protected by NPQ in the antennas.

• Keywords
• Chromera velia alga, High light acclimation, Nonphotochemical quenching, Photoinhibition, Uncoupling of antennas from Photosystem II.,
• MeSH
• Acclimatization radiation effects   MeSH
• Alveolata cytology   physiology   radiation effects   MeSH
• Chlorophyll A MeSH
• Chlorophyll metabolism   MeSH
• Fluorescence MeSH
• Photochemical Processes radiation effects   MeSH
• Photosynthesis radiation effects   MeSH
• Photosystem II Protein Complex metabolism   MeSH
• Solubility MeSH
• Light * MeSH
• Light-Harvesting Protein Complexes metabolism   MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Chlorophyll A MeSH
• Chlorophyll MeSH
• Photosystem II Protein Complex MeSH
• Light-Harvesting Protein Complexes MeSH

Photosystem I (PSI) is a multi-subunit integral pigment-protein complex that performs light-driven electron transfer from plastocyanin to ferredoxin in the thylakoid membrane of oxygenic photoautotrophs. In order to achieve the optimal photosynthetic performance under ambient irradiance, the absorption cross section of PSI is extended by means of peripheral antenna complexes. In eukaryotes, this role is played mostly by the pigment-protein complexes of the LHC family. The structure of the PSI-antenna supercomplexes has been relatively well understood in organisms harboring the primary plastid: red algae, green algae and plants. The secondary endosymbiotic algae, despite their major ecological importance, have so far received less attention. Here we report a detailed structural analysis of the antenna-PSI association in the stramenopile alga Nannochloropsis oceanica (Eustigmatophyceae). Several types of PSI-antenna assemblies are identified allowing for identification of antenna docking sites on the PSI core. Instances of departure of the stramenopile system from the red algal model of PSI-Lhcr structure are recorded, and evolutionary implications of these observations are discussed.

• Keywords
• Electron microscopy, Light-harvesting complex, Nannochloropsis, Photosystem I, Stramenopila,
• MeSH
• Photosystem I Protein Complex metabolism   MeSH
• Plastids metabolism   MeSH
• Rhodophyta metabolism   MeSH
• Spectrophotometry, Ultraviolet MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Photosystem I Protein Complex MeSH

We present proteomic, spectroscopic, and phylogenetic analysis of light-harvesting protein (Lhc) function in oleaginous Nannochloropsis oceanica (Eustigmatophyta, Stramenopila). N. oceanica utilizes Lhcs of multiple classes: Lhcr-type proteins (related to red algae LHCI), Lhcv (VCP) proteins (violaxanthin-containing Lhcs related to Lhcf/FCP proteins of diatoms), Lhcx proteins (related to Lhcx/LhcSR of diatoms and green algae), and Lhc proteins related to Red-CLH of Chromera velia. Altogether, 17 Lhc-type proteins of the 21 known from genomic data were found in our proteomic analyses. Besides Lhcr-type antennas, a RedCAP protein and a member of the Lhcx protein subfamily were found in association with Photosystem I. The free antenna fraction is formed by trimers of a mixture of Lhcs of varied origins (Lhcv, Lhcr, Lhcx, and relatives of Red-CLH). Despite possessing several proteins of the Red-CLH-type Lhc clade, N. oceanica is not capable of chromatic adaptation under the same conditions as the diatom Phaeodactylum tricornutum or C. velia. In addition, a naming scheme of Nannochloropsis Lhcs is proposed to facilitate further work.

• Keywords
• Light harvesting, Thylakoid membrane, Vaucheriaxanthin, Violaxanthin–chlorophyll protein,
• MeSH
• Photosystem I Protein Complex metabolism   MeSH
• Phylogeny MeSH
• Stramenopiles genetics   metabolism   MeSH
• Spectrophotometry, Ultraviolet MeSH
• Light-Harvesting Protein Complexes chemistry   genetics   metabolism   MeSH
• Tandem Mass Spectrometry MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Photosystem I Protein Complex MeSH
• Light-Harvesting Protein Complexes MeSH

Fucoxanthin-chlorophyll proteins (FCP) are the major light-harvesting proteins of diatom algae, a major contributor to marine carbon fixation. FCP complexes from representatives of centric (Cyclotella meneghiniana) and pennate (Phaeodactylum tricornutum) diatoms were prepared by sucrose gradient centrifugation and studied by means of electron microscopy followed by single particle analysis. The oligomeric FCP from a centric diatom were observed to take the form of unusual chain-like or circular shapes, a very unique supramolecular assembly for such antennas. The existence of the often disputed oligomeric form of FCP in pennate diatoms has been confirmed. Contrary to the centric diatom FCP, pennate diatom FCP oligomers are very similar to oligomeric antennas from related heterokont (Stramenopila) algae. Evolutionary aspects of the presence of novel light-harvesting protein arrangement in centric diatoms are discussed.

• MeSH
• Chlorophyll Binding Proteins chemistry   metabolism   MeSH
• Diatoms chemistry   metabolism   MeSH
• Microscopy, Electron, Transmission MeSH
• Thylakoids chemistry   metabolism   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Chlorophyll Binding Proteins MeSH