Phytoplankton Assemblages and Their Dominant Pigments in the Nervion River Estuary

In the Nervion River estuary surface samples were taken from March to September 2003 at six sites covering most of the salinity range with the aim to know the biomass and taxonomic composition of phytoplankton assemblages in the different segments. Nine groups of algae including cyanobacteria, diatoms, dinoflagellates, chlorophytes, prasinophytes, euglenophytes, chrysophytes, haptophytes, raphidophytes and cryptophytes were identified by means of a combination of pigment analysis by high-performance liquid chromatography (HPLC) and microscopic observations of live and preserved cells. Diatoms, chlorophytes and cryptophytes were the most abundant algae in terms of cells number, whereas fucoxanthin, peridinin, chlorophyll b (Chl b) and alloxanthin were the most abundant auxiliary pigments. Based on multiple regression analysis, in the outer estuary (stations 0, 1, 2 and 3) about 93% of the chlorophyll a (Chl a) could be explained by algae containing fucoxanthin and by algae containing Chl b, whereas in the rest of the estuary most of the Chl a (about 98%) was accounted for by fucoxanthin, Chl b and alloxanthin containing algae. The study period coincided with that of most active phytoplankton growth in the estuary and fucoxanthin was by far the dominant among those signature pigments. Several diatoms, chrysophytes, haptophytes and raphydophytes were responsible for fucoxanthin among identified species. Besides, dinoflagellates with a pigment pattern corresponding to chrysophytes and type 4 haptophytes were identified among fucoxanthin-bearing algae. Cryptophytes were the most abundant species among those containing alloxanthin. The maximum of Chl b registered at the seaward end in April coincided with a bloom of the prasinophytes Cymbomonas tetramitiformis, whereas the Chl b maxima in late spring and summer were accounted for by prasinophytes in the middle and outer estuary and by several species of chlorophytes in the middle and inner estuary. Other Chl b containing algae were euglenophytes and the dinoflagellate Peridinium chlorophorum. Dinoflagellates constituted generally a minor component of the phytoplankton.     

Hyperdiversity of Genes Encoding Integral Light-Harvesting Proteins in the Dinoflagellate Symbiodinium sp

The superfamily of light-harvesting complex (LHC) proteins is comprised of proteins with diverse functions in light-harvesting and photoprotection. LHC proteins bind chlorophyll (Chl) and carotenoids and include a family of LHCs that bind Chl a and c. Dinophytes (dinoflagellates) are predominantly Chl c binding algal taxa, bind peridinin or fucoxanthin as the primary carotenoid, and can possess a number of LHC subfamilies. Here we report 11 LHC sequences for the chlorophyll a-chlorophyll c ₂-peridinin protein complex (acpPC) subfamily isolated from Symbiodinium sp. C3, an ecologically important peridinin binding dinoflagellate taxa. Phylogenetic analysis of these proteins suggests the acpPC subfamily forms at least three clades within the Chl a/c binding LHC family; Clade 1 clusters with rhodophyte, cryptophyte and peridinin binding dinoflagellate sequences, Clade 2 with peridinin binding dinoflagellate sequences only and Clades 3 with heterokontophytes, fucoxanthin and peridinin binding dinoflagellate sequences.     

A fluorometric method for the differentiation of algal populations in vivo and in situ

Fingerprints of excitation spectra of chlorophyll (Chl) fluorescence can be used to differentiate `spectral groups' of microalgae in vivo and in situ in, for example, vertical profiles within a few seconds. The investigated spectral groups of algae (green group, Chlorophyta; blue, Cyanobacteria; brown, Heterokontophyta, Haptophyta, Dinophyta; mixed, Cryptophyta) are each characterised by a specific composition of photosynthetic antenna pigments and, consequently, by a specific excitation spectrum of the Chl fluorescence. Particularly relevant are Chl a, Chl c, phycocyanobilin, phycoerythrobilin, fucoxanthin and peridinin. A laboratory-based instrument and a submersible instrument were constructed containing light-emitting diodes to excite Chl fluorescence in five distinct wavelength ranges. Norm spectra were determined for the four spectral algal groups (several species per group). Using these norm spectra and the actual five-point excitation spectrum of a water sample, a separate estimate of the respective Chl concentration is rapidly obtained for each algal group. The results of dilution experiments are presented. In vivo and in situ measurements are compared with results obtained by HPLC analysis. Depth profiles of the distribution of spectral algal groups taken over a time period of few seconds are shown. The method for algae differentiation described here opens up new research areas, monitoring and supervision tasks related to photosynthetic primary production in aquatic environments. This revised version was published online in June 2006 with corrections to the Cover Date.     

Triplet state spectra and dynamics of peridinin analogs having different extents of π-electron conjugation

The Peridinin-Chlorophyll a-Protein (PCP) complex has both an exceptionally efficient light-harvesting ability and a highly effective protective capacity against photodynamic reactions involving singlet oxygen. These functions can be attributed to presence of a substantial amount of the highly-substituted and complex carotenoid, peridinin, in the protein and the facts that the low-lying singlet states of peridinin are higher in energy than those of chlorophyll (Chl) a, but the lowest-lying triplet state of peridinin is below that of Chl a. Thus, singlet energy can be transferred from peridinin to Chl a, but the Chl a triplet state is quenched before it can sensitize the formation of singlet oxygen. The present investigation takes advantage of Chl a as an effective triplet state donor to peridinin and explores the triplet state spectra and dynamics of a systematic series of peridinin analogs having different numbers of conjugated carbon–carbon double bonds. The carotenoids investigated are peridinin, which has a C₃₇ carbon skeleton and eight conjugated carbon–carbon double bonds, and three synthetic analogs: C₃₃-peridinin, having two less double bonds than peridinin, C₃₅-peridinin which has one less double bond than peridinin, and C₃₉-peridinin which has one more double bond than peridinin. In this study, the behavior of the triplet state spectra and kinetics exhibited by these molecules has been investigated in polar and nonpolar solvents and reveals a substantial effect of both π-electron conjugated chain length and solvent environment on the spectral lineshapes. However, only a small dependence of these factors is observed on the kinetics of triplet energy transfer from Chl a and on carotenoid triplet state deactivation to the ground state.     

Variations in biochemical parameters of Heterocapsa sp. and Olisthodiscus luteus grown in 12:12 light:dark cycles II. Changes in pigment composition

Photosynthetic pigment composition was studied in batch cultures of Heterocapsa sp. and Olisthodiscus luteus growing exponentially in a 12:12 light:dark cycle. Both species divided in the dark. The synthesis of pigments was continuous for both species. However for chlorophyll c and peridinin, in Heterocapsa sp., and chlorophyll c and fucoxanthin, in O. luteus, (pigments belonging to light harvesting complexes) the synthesis was significantly higher during the light period. Concentrations per total cell volume (TCV) of chlorophyll a, chlorophyll c, peridinin and diadinoxanthin in Heterocapsa sp., and chlorophyll a, chlorophyll c, fucoxanthin and violaxanthin in O. luteus, showed a maximum at the onset of light and decreased during the light period. The values of the chlorophyll a:chlorophyll c, chlorophyll a:peridinin and chlorophyll a:fucoxanthin ratios are compared with data reported in the literature.     

Assembly of the photosynthetic apparatus in embryos from Fucus serratus L

The assembly of the photosynthetic apparatus was studied during the first six days of development of Fucus serratus L. embryos. HPLC analysis revealed that oospheres and zygotes contain the same photosynthetic pigments (i.e., chlorophyll a, chlorophyll c, fucoxanthin, violaxanthin, and β-carotene) as fully developed thalli. Total pigment amount increased after fertilization, mainly due to an active synthesis of Chl a and fucoxanthin. Spectral modifications revealing the progressive integration of Chl a and Chl c in the photosynthetic units are described. In particular, a distinct emission at 705 nm, reflecting the accumulation of LHC I, was clearly detected. The emission bands at 705 nm and 725 nm were characterized by 77 K excitation fluorescence measurements. Their spectra differed by the presence of a large band at approximately 550 nm due to fucoxanthin in the excitation spectrum of F705 nm. Room temperature variable fluorescence was first observed 30 h after fertilization indicating a functional Photosystem II electron transfer at this developmental stage. This revised version was published online in August 2006 with corrections to the Cover Date.     

Excitation relaxation dynamics and energy transfer in fucoxanthin–chlorophyll a/c-protein complexes,probed by time-resolved fluorescence

In algae, light-harvesting complexes contain specific chlorophylls (Chls) and keto-carotenoids; Chl a, Chl c, and fucoxanthin (Fx) in diatoms and brown algae; Chl a, Chl c, and peridinin in photosynthetic dinoflagellates; and Chl a, Chl b, and siphonaxanthin in green algae. The Fx–Chl a/c-protein (FCP) complex from the diatom Chaetoceros gracilis contains Chl c₁, Chl c₂, and the keto-carotenoid, Fx, as antenna pigments, in addition to Chl a. In the present study, we investigated energy transfer in the FCP complex associated with photosystem II (FCPII) of C. gracilis. For these investigations, we analyzed time-resolved fluorescence spectra, fluorescence rise and decay curves, and time-resolved fluorescence anisotropy data. Chl a exhibited different energy forms with fluorescence peaks ranging from 677 nm to 688 nm. Fx transferred excitation energy to lower-energy Chl a with a time constant of 300 fs. Chl c transferred excitation energy to Chl a with time constants of 500–600 fs (intra-complex transfer), 600–700 fs (intra-complex transfer), and 4–6 ps (inter-complex transfer). The latter process made a greater contribution to total Chl c-to-Chl a transfer in intact cells of C. gracilis than in the isolated FCPII complexes. The lower-energy Chl a received excitation energy from Fx and transferred the energy to higher-energy Chl a. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: Keys to Produce Clean Energy.     

Widespread occurrence and unexpected diversity of red-shifted chlorophyll producing cyanobacteria in humid subtropical forest ecosystems

Discovery of red-shifted chlorophyll d and f in cyanobacteria has opened up new avenues to estimate global carbon fixation driven by far-red light. Shaded habitats in humid subtropical forest ecosystems contain an increased proportion of far-red light components relative to residual white light. After an extensive survey of shaded ecosystems within subtropical forests, wide occurrence of red-shifted chlorophyll-producing cyanobacteria was demonstrated by isolated Chl f-producing and Chl d-containing cyanobacteria. Chl f-producing cyanobacteria were classified into the genera of Aphanocapsa and Chroococcidiopsis and two undescribed genera within Leptolyngbyaceae. Newly isolated Chl d-containing Acaryochloris sp. CCNUM4 showed the closest phylogenetic relationship with Acaryochloris species isolated from marine environments. Acaryochloris sp. CCNUM4 produced Chl d as major photopigment, and Chl f-producing cyanobacteria use Chl a under white light conditions but Chl a + f under far-red light conditions. Their habitats are widely distributed in subtropical forest ecosystems and varied from mosses on limestone to macrophyte and freshwater in the streams and ponds. This study presents a significant advance in the knowledge of distribution and diversity of red-shifted chlorophyll-producing cyanobacteria in terrestrial ecosystems. The results suggest that Chl f-producing and Chl d-containing cyanobacteria might be important primary producers in far-red light dominant niches worldwide.     

Pigment protein complexes and the concept of the photosynthetic unit: Chlorophyll complexes and phycobilisomes

The photosynthetic unit includes the reaction centers (RC 1 and RC 2) and the light-harvesting complexes which contribute to evolution of one O₂ molecule. The light-harvesting complexes, that greatly expand the absorptance capacity of the reactions, have evolved along three principal lines. First, in green plants distinct chlorophyll (Chl) a/b-binding intrinsic membrane complexes are associated with RC 1 and RC 2. The Chl a/b-binding complexes may add about 200 additional chromophores to RC 2. Second, cyanobacteria and red algae have a significant type of antenna (with RC 2) in the form of phycobilisomes. A phycobilisome, depending on the size and phycobiliprotein composition adds from 700 to 2300 light-absorbing chromophores. Red algae also have a sizable Chl a-binding complex associated with RC 1, contributing an additional 70 chromophores. Third, in chromophytes a variety of carotenoid-Chl-complexes are found. Some are found associated with RC 1 where they may greatly enhance the absorptance capacity. Association of complexes with RC 2 has been more difficult to ascertain, but is also expected in chromophytes. The apoprotein framework of the complexes provides specific chromophore attachment sites, which assures a directional energy transfer whithin complexes and between complexes and reaction centers. The major Chl-binding antenna proteins generally have a size of 16–28 kDa, whether of chlorophytes, chromophytes, or rhodophytes. High sequence homology observed in two of three transmembrane regions, and in putative chlorophyll-binding residues, suggests that the complexes are related and probably did not evolve from widely divergent polyphyletic lines.Abbreviations APC allophycocyanin - B phycoerythrin-large bangiophycean phycoerythrin - Chl chlorophyll - L_CM linker polypeptide in phycobilisome to thylakoid - FCP fucoxanthin Chl a/c complex - LHC(s) Chl-binding light harvesting complex(s) - LHC I Chl-binding complex of Photosystem I - LHC II Chl-binding complex of Photosystem II - PC phycocyanin - PCP peridinin Chl-binding complex - P700 photochemically active Chl a of Photosystem I - PS I Photosystem I - PS II Photosystem II - RC 1 reaction center core of PS I - RC 2 reaction center core of PS II - R phycoerythrin-large rhodophycean phycoerythrin - sPCP soluble peridinin Chl-binding complex     

Pigments and fatty acids of marine raphidophytes: A chemotaxonomic re-evaluation

The patterns of occurrence of photosynthetic pigments and fatty acids among seven available species (11 strains) of marine raphidophytes were determined and used as chemotaxonomic markers. All currently recognized genera of marine raphidophytes were included for analysis: that is, Chattonella, Fibrocapsa, Heterosigma, Olisthodiscus and Haramonas. The characteristic pigment composition was shown to be chlorophyll a, chlorophylls c₁ and/or c₂, fucoxanthin as the major carot-enoid, β,β-carotene and any or all of zeaxanthin, violaxanthin and an auroxanthin-like pigment as the minor carotenoids. The carotenoid composition of all marine raphidophyte genera investigated was virtually the same, except in Fibrocapsa and Haramonas, which differed due to the occurrence of fucoxanthinol and 19′-butanoyloxyfucoxanthin, respectively. These fucoxanthin derivatives, in addition to fucoxanthin, have potential chemotaxonomic use for differentiating the two species. In all 11 strains, 15 fatty acids (saturated, mono-unsaturated and polyunsaturated) were determined. Significant taxonomic distinctions between genera were reflected by their fatty acid profiles. A rapid key for the differentiation of genera, in addition to morphological features, may be the absence of the 18:4 fatty acid in Olisthodiscus; presence of 18:5 in Heterosigma; the presence of fucoxanthinol in Fibrocapsa and presence of 19′-butanoyloxyfucoxanthin in Haramonas.     

Does pigment composition reflect phytoplankton community structure in differing temperature and light conditions in a deep alpine lake? An approach using HPLC and delayed fluorescence techniques1

In vivo delayed fluorescence (DF) and HPLC/CHEMTAX pigment analyses were used to investigate seasonal and depth distributions of phytoplankton in a deep alpine mesotrophic lake, Mondsee (Austria). Using chl a equivalents, we determined significant relationships with both approaches. Community structure derived from pigment ratios of homogenous samples was compared with microscopic estimations using biovolume conversion factors. An advantage of the HPLC/CHEMTAX method was that it gave good discrimination among phytoplankton groups when based on a pigment ratio matrix derived from multiple regression analysis. When a single algal group was dominant, such as epilimnetic diatoms or hypolimnetic cyanobacteria in the deep chl maxima, HPLC/CHEMTAX results were significantly correlated with microscopic estimations (diatoms: r = 0.93; cyanobacteria: r = 0.94). Changes in the composition of photosynthetically active pigments were investigated with DF and benefited from excitation spectra that considered all light‐harvesting pigments, which made it possible to assess the enhancement of accessory photosynthetically active pigments relative to active chl a (chl a_DF672). Changes in similarity index, based on normalized DF spectra, confirmed compositional shifts observed by microscopy. At chosen wavelengths of DF spectra, 534 and 586 nm, we generally observed a significantly inverse relationship between normalized DF intensities and temperature and light along both seasonal and depth gradients. The relative increase in photosynthetically active pigments other than chl a_DF672 under low light and temperature was caused by an increasing dominance of diatoms and/or phycobilin‐rich cyanobacteria and Cryptophyta. DF spectra provided a more accurate picture of community pigments acclimated to light and temperature conditions than the β‐carotene:chl a ratio derived from HPLC.     

Seasonal variation in pigmentation of the dinoflagellate Peridinium gatunense (Dinophyceae) in Lake Kinneret, Israel

1. Pigment composition was measured in natural phytoplankton samples from Lake Kinneret, Israel. From March through June 1998, the dinoflagellate Peridinium gatunense Nygaard mostly contributed more than 95% of the algal biomass. Peak densities were found in April, close to the water surface, with >10⁹ cells m^?3, chlorophyll (Chl) a concentration of 380 mg m^?3 and areal Chl‐a density of >1300 mg m^?2. 2. Cellular concentrations of Chl‐a changed between 201 and 282 pg cell^?1, but did not show a defined temporal fluctuation. 3. The mass ratio of Chl‐c to Chl‐a changed from March to June between 0.16 and 0.22, and the peridinin to Chl‐a ratio changed from 0.25 to 0.41. Neither ratio showed a clear pattern of seasonal change. Conversely, there was a progressive increase in diadinoxanthin and β‐carotene ratios to Chl‐a through the season, parallel to the increase in photon flux impinging upon the lake surface. The diadinoxanthin to Chl‐a ratio changed from 0.11 to 0.28 and the β‐carotene to Chl‐a ratio varied from 0.03 to 0.08 from March through June. 4. Diatoxanthin was not detected in natural samples. However, it was present in experiments with P. gatunense cultures, when concentration of diatoxanthin increased rapidly, concurrent with a decrease in diadinoxanthin and β‐carotene concentrations, while Chl‐c and peridinin ratios to Chl‐a were almost stable with photon flux increase. 5. The seasonal variation in cellular pigmentation of P. gatunense in Lake Kinneret suggests that accumulation of photoprotective pigments is essential for optimisation of photosynthetic activity of this large dinoflagellate.     

Reconstitution of the Peridinin–chlorophyll a Protein (PCP): Evidence for Functional Flexibility in Chlorophyll Binding

The coding regions for the N-domain, and full length peridinin–chlorophyll a apoprotein (full length PCP), were expressed in Escherichia coli. The apoproteins formed inclusion bodies from which the peptides could be released by hot buffer. Both the above constructs were reconstituted by addition of a total pigment extract from native PCP. After purification by ion exchange chromatography, the absorbance, fluorescence excitation and CD spectra resembled those of the native PCP. Energy transfer from peridinin to Chl a was restored and a specific fluorescence activity calculated which was ~86% of that of native PCP. Size exclusion analysis and CD spectra showed that the N-domain PCP dimerized on reconstitution. Chl a could be replaced by Chl b, 3-acetyl Chl a, Chl d and Bchl using the N-domain apo protein. The specific fluorescence activity was the same for constructs with Chl a, 3-acetyl Chl a, and Chl d but significantly reduced for those made with Chl b. Reconstitutions with mixtures of chlorophylls were also made with eg Chl b and Chl d and energy transfer from the higher energy Qy band to the lower was demonstrated.     

Nucleotide sequence of two cDNAs encoding fucoxanthin chlorophyll a/c proteins in the diatom Odontella sinensis

Two cDNA clones encoding fucoxanthin chlorophyll a/c-binding proteins (FCP) in the diatom Odontella sinensis have been cloned and sequenced. The derived amino acid sequences of both clones are identical, comparison of the corresponding nucleic acids reveals differences only in the third codon position, suggesting a recent gene duplication. The derived proteins are similar to the chlorophyll a/b-binding proteins of higher plants. The presequences for plastid import resemble signal sequences for cotranslational import rather than transit peptides of higher plants. They are very similar to the presequences of FCP proteins in the diatom Phaeodactylum, but different from the presequences of the -subunit of CF₀CF₁ of Odontella and the peridinin chlorophyll a binding proteins (PCP) of the dinoflagellate Symbiodinium.Abbreviations CAB chlorophyll a/b-binding protein - FCP fucoxanthin chlorophyll a/c-binding protein - fcp the respective FCP genes - LHC light-harvesting complex - PCP peridinin chlorophyll a-binding protein - PAGE polyacrylamide gel electrophoresis - SDS sodium dodecyl sulfate     

Chlorophyll f production in two new subaerial cyanobacteria of the family Oculatellaceae

Chlorophyll (Chl) f was recently identified in a few cyanobacteria as the fifth chlorophyll of oxygenic organisms. In this study, two Leptolyngbya-like strains of CCNU0012 and CCNU0013 were isolated from a dry ditch in Chongqing city and a brick wall in Mount Emei Scenic Area in China, respectively. These two strains were described as new species: Elainella chongqingensis sp. nov. (Oculatellaceae, Synechococcales) and Pegethrix sichuanica sp. nov. (Oculatellaceae, Synechococcales) by the polyphasic approach based on morphological features, phylogenetic analysis of 16S rRNA gene and secondary structure comparison of 16S-23S internal transcribed spacer domains. Both strains produced Chl a under white light (WL) but additionally induced Chl f synthesis under far-red light (FRL). Unexpectedly, the content of Chl f in P. sichuanica was nearly half that in most Chl f-producing cyanobacteria. Red-shifted phycobiliproteins were also induced in both strains under FRL conditions. Subsequently, additional absorption peak beyond 700 nm in the FRL spectral region appeared in these two strains. This is the first report of Chl f production induced by FRL in the family Oculatellaceae. This study not only extended the diversity of Chl f-producing cyanobacteria but also provided precious samples to elucidate the essential binding sites of Chl f within cyanobacterial photosystems.     

Structural Confirmation of a Unique Carotenoid Lactoside,P457, in Symbiodinium sp. Strain nbrc 104787 Isolated from a Sea Anemone and its Distribution in Dinoflagellates and Various Marine Organisms

The molecular structure of the carotenoid lactoside P457, (3S,5R,6R,3′S,5′R,6′S)‐13′‐cis‐5,6‐epoxy‐3′,5′‐dihydroxy‐3‐(β‐d ‐galactosyl‐(1→4)‐β‐d ‐glucosyl)oxy‐6′,7′‐didehydro‐5,6,7,8,5′,6′‐hexahydro‐β,β‐caroten‐20‐al, was confirmed by spectroscopic methods using Symbiodinium sp. strain NBRC 104787 cells isolated from a sea anemone. Among various algae, cyanobacteria, land plants, and marine invertebrates, the distribution of this unique diglycosyl carotenoid was restricted to free‐living peridinin‐containing dinoflagellates and marine invertebrates that harbor peridinin‐containing zooxanthellae. Neoxanthin appeared to be a common precursor for biosynthesis of peridinin and P457, although neoxanthin was not found in peridinin‐containing dinoflagellates. Fucoxanthin‐containing dinoflagellates did not possess peridinin or P457; green dinoflagellates, which contain chlorophyll a and b, did not contain peridinin, fucoxanthin, or P457; and no unicellular algae containing both peridinin and P457, other than peridinin‐containing dinoflagellates, have been observed. Therefore, the biosynthetic pathways for peridinin and P457 may have been coestablished during the evolution of dinoflagellates after the host heterotrophic eukaryotic microorganism formed a symbiotic association with red alga that does not contain peridinin or P457.     

Tuning Energy Transfer in the Peridinin–chlorophyll Complex by Reconstitution with Different Chlorophylls

In vitro studies of the carotenoid peridinin, which is the primary pigment from the peridinin chlorophyll-a protein (PCP) light harvesting complex, showed a strong dependence on the lifetime of the peridinin lowest singlet excited state on solvent polarity. This dependence was attributed to the presence of an intramolecular charge transfer (ICT) state in the peridinin excited state manifold. The ICT state was also suggested to be a crucial factor in efficient peridinin to Chl-a energy transfer in the PCP complex. Here we extend our studies of peridinin dynamics to reconstituted PCP complexes, in which Chl-a was replaced by different chlorophyll species (Chl-b, acetyl Chl-a, Chl-d and BChl-a). Reconstitution of PCP with different Chl species maintains the energy transfer pathways within the complex, but the efficiency depends on the chlorophyll species. In the native PCP complex, the peridinin S₁/ICT state has a lifetime of 2.7 ps, whereas in reconstituted PCP complexes it is 5.9 ps (Chl-b) 2.9 ps (Chl-a), 2.2 ps (acetyl Chl-a), 1.9 ps (Chl-d), and 0.45 ps (BChl-a). Calculation of energy transfer rates using the Förster equation explains the differences in energy transfer efficiency in terms of changing spectral overlap between the peridinin emission and the absorption spectrum of the acceptor. It is proposed that the lowest excited state of peridinin is a strongly coupled S₁/ICT state, which is the energy donor for the major energy transfer channel. The significant ICT character of the S₁/ICT state in PCP enhances the transition dipole moment of the S₁/ICT state, facilitating energy transfer to chlorophyll via the Förster mechanism. In addition to energy transfer via the S₁/ICT, there is also energy transfer via the S₂ and hot S₁/ICT states to chlorophyll in all reconstituted PCP complexes.     

Spectroscopic Characterization of the Excitation Energy Transfer in the Fucoxanthin–Chlorophyll Protein of Diatoms

We characterized the energy transfer pathways in the fucoxanthin–chlorophyll protein (FCP) complex of the diatom Cyclotella meneghiniana by conducting ultrafast transient absorption measurements. This light harvesting antenna has a distinct pigment composition and binds chlorophyll a (Chl-a), fucoxanthin and chlorophyll c (Chl-c) molecules in a 4:4:1 ratio. We find that upon excitation of fucoxanthin to its S₂ state, a significant amount of excitation energy is transferred rapidly to Chl-a. The ensuing dynamics illustrate the presence of a complex energy transfer network that also involves energy transfer from the unrelaxed or ‘hot’ intermediates. Chl-c to Chl-a energy transfer occurs on a timescale of a 100 fs. We observe no significant spectral evolution in the Chl-a region of the spectrum. We have applied global and target analysis to model the measured excited state dynamics and estimate the spectra of the states involved; the energy transfer network is discussed in relation to the pigment organization of the FCP complex.     

Triplet-triplet energy transfer in Peridinin-Chlorophyll a-protein reconstituted with Chl a and Chl d as revealed by optically detected magnetic resonance and pulse EPR: Comparison with the native PCP complex from Amphidinium carterae

The triplet state of the carotenoid peridinin, populated by triplet-triplet energy transfer from photoexcited chlorophyll triplet state, in the reconstituted Peridinin-Chlorophyll a-protein, has been investigated by ODMR (Optically detected magnetic resonance), and pulse EPR spectroscopies. The properties of peridinins associated with the triplet state formation in complexes reconstituted with Chl a and Chl d have been compared to those of the main-form peridinin-chlorophyll protein (MFPCP) isolated from Amphidinium carterae. In the reconstituted samples no signals due to the presence of chlorophyll triplet states have been detected, during either steady state illumination or laser-pulse excitation. This demonstrates that reconstituted complexes conserve total quenching of chlorophyll triplet states, despite the biochemical treatment and reconstitution with the non-native Chl d pigment. Zero field splitting parameters of the peridinin triplet states are the same in the two reconstituted samples and slightly smaller than in native MFPCP. Analysis of the initial polarization of the photoinduced Electron-Spin-Echo detected spectra and their time evolution, shows that, in the reconstituted complexes, the triplet state is probably localized on the same peridinin as in native MFPCP although, when Chl d replaces Chl a, a local rearrangement of the pigments is likely to occur. Substitution of Chl d for Chl a identifies previously unassigned bands at ∼ 620 and ∼ 640 nm in the Triplet-minus-Singlet (T − S) spectrum of PCP detected at cryogenic temperature, as belonging to peridinin.     

Evolution of light-harvesting complex proteins from Chl c-containing algae

Background  

Light harvesting complex (LHC) proteins function in photosynthesis by binding chlorophyll (Chl) and carotenoid molecules that absorb light and transfer the energy to the reaction center Chl of the photosystem. Most research has focused on LHCs of plants and chlorophytes that bind Chl a and b and extensive work on these proteins has uncovered a diversity of biochemical functions, expression patterns and amino acid sequences. We focus here on a less-studied family of LHCs that typically bind Chl a and c, and that are widely distributed in Chl c-containing and other algae. Previous phylogenetic analyses of these proteins suggested that individual algal lineages possess proteins from one or two subfamilies, and that most subfamilies are characteristic of a particular algal lineage, but genome-scale datasets had revealed that some species have multiple different forms of the gene. Such observations also suggested that there might have been an important influence of endosymbiosis in the evolution of LHCs.