A Diatom Light-Harvesting Pigment-Protein Complex

Friedman, Alan L.; Alberte, Randall S.

doi:10.1104/pp.76.2.483

Cited by 79 publications

(50 citation statements)

References 12 publications

(19 reference statements)

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“…The Chl a/c-fucoxanthin complex can be extracted from diatom thylakoids under very mild conditions which leaves the remaining complexes in the membranes (7). The complex is also quite labile under conditions where intrinsic light-harvesting complexes (i.e.…”

Section: Discussionmentioning

confidence: 99%

“…Chl cl and c2 are widely distributed in the nonchlorophyte eucaryotic algae and differ from Chl a and b in that they are unsaturated in Ring IV and are not esterified to a hydrocarbon alcohol (16). Chl and Chl-carotenoid complexes have been isolated from dinoflagellates (4,24), cryptomonads (13), brown algae (1)(2)(3), and diatoms (7,10). In most cases, the functional role of these complexes in light-harvesting was assessed by the efficiency of energy coupling between the accessory pigments and Chl a, but their respective roles in regulation of excitation energy distribution between the two photosystems has not been addressed.…”

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confidence: 99%

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Light-Harvesting Function in the Diatom Phaeodactylum tricornutum

Owens

Wold²

1986

Plant Physiol.

109

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Three pigment-protein complexes were isolated from the marine diatom Phaeodactylum tricornutum (Bohlin) by treatment of thylakoid membrane fragments with 1% Triton X-100 at 4°C followed by centrifugation on sucrose density gradients. The major complex contains chlorophyll a, cl, C2, and the carotenoid fucoxanthin (chlorophyll a : c,: C2: fucoxanthin = 1.0: 0.09: 0.28 : 2.22) bound to an apoprotein doublet of 16.4 and 16.9 kilodaltons. This complex accounts for >70% of the total pigment and 20 to 40% of the protein in the thylakoid membranes. Efficient coupling of chlorophyll c and fucoxanthin absorption to chlorophyll a fluorescence supports a light-harvesting function for the complex. A minor light-harvesting complex containing chlorophyll a, cl, and C2 but no fucoxanthin (chlorophyll a: cl: C2 = 1.0: 0.23 : 0.26) was also isolated at Triton: chlorophyll a ratios between 20 and 40. These pigments are bound to a similar molecular weight apoprotein doublet. The third complex isolated was the P700-chlorophyll a protein, the reaction center of photosystem I, which showed characteristics similar to those isolated from other plant sources. The yield of the chlorophyll a/c-fucoxanthin complex was shown to respond strongly to changes in light intensity during growth, accounting for most of the changes in cellular pigmentation.The photosynthetically active pigments of plants are bound in discrete pigment-protein complexes (28) which can be divided functionally into two groups: the photochemical reaction center complexes where light energy is converted to chemical energy, and the light-harvesting complexes that serve as antennae to collect and transfer available light energy to the reaction centers.

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Section: Discussionmentioning

confidence: 99%

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confidence: 99%

Light-Harvesting Function in the Diatom Phaeodactylum tricornutum

Owens

Wold²

1986

Plant Physiol.

109

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“…Our purpose is to study fluorescence quenching processes in the diatom Phaeodactylum tricornutum. Diatoms possess both a major Chl a/c-fucoxanthin complex (accounting for about 80% of the total thylakoid pigment) and a minor Chl a/c complex (Friedman and Alberte, 1984;Owens and Wold, 1986). Although a primary site of q N is thought to be in the lightharvesting complex, it is currently unknown to what extent variations in antenna pigment and protein composition contribute to differences in fluorescence-quenching mechanisms.…”

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confidence: 99%

Photochemical and Nonphotochemical Fluorescence Quenching Processes in the Diatom Phaeodactylum tricornutum

1993

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Nonphotochemical fluorescence quenching was found to exist in the dark-adapted state in the diatom Pbaeodactyhm tricornutum. Pretreatment of cells with the uncoupler carbonylcyanide mchlorophenylhydrazone (CCCP) or with nigericin resulted in increases in dark-adapted minimum and maximum fluorescence yields. This suggests that a pH gradient exists across the thylakoid membrane in the dark, which serves to quench fluorescence levels nonphotochemically. The physiological processes involved in establishing this proton gradient were sensitive to anaerobiosis and antimycin A. Based on these results, it is likely that this energization of the thylakoid membrane is due in part to chlororespiration, which involves oxygen-dependent electron flow through the plastoquinone pool. Chlororespiration has been shown previously to occur in diatoms. In addition, we observed that cells treated with 3-(3,4-dichlorophenyI)-l,l-dimethylurea exhibited very strong nonphotochemical quenching when illuminated with actinic light.The rate and extent of this quenching were light-intensity dependent. This quenching was reversed upon addition of CCCP or nigericin and was thus due primarily to the establishment of a pH gradient across the thylakoid membrane. Preincubation of cells with CCCP or nigericin or antimycin A completely abolished this quenching. Cyclic electron transport processes around photosystem I may be involved in establishing this proton gradient across the thylakoid membrane under conditions where linear electron transport is inhibited. At steady state under normal physiological conditions, the qualitative changes in photochemical and nonphotochemical fluorescence quenching at increasing photon flux densities were similar to those in higher plants. However, important quantitative differences existed at limiting and saturating intensities. Dissimilarities in the factors that regulate fluorescence quenching mechanisms in these organisms may account for these differences.One process that competes directly with photochemistry for deactivation of excited-state energy is fluorescence emission from Chl a molecules of the PSII antenna. Changes in the proportion of excited states utilized for photochemistry will result in changes in fluorescence intensity. In recent years, it has been shown that both photochemical and nonphotochemical processes reduce the yield of fluorescence during photosynthesis (Krause et al., 1982). However, our current knowledge of these processes is based primarily on studies with higher plants and green algae. The components involved in qP are present in the PSII reaction center, which has been found to be highly conserved throughout evolution (Thornber, 1986). It is therefore likely that the mechanism of photochemical quenching has also been conserved. In contrast, a diverse group of underlying processes controls qN, whose primary site of action is thought to be in the lightharvesting antennae. With the extensive diversity in the composition of light-harvesting complexes among the algae, it is likely that the m...

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“…Fucoxanthin identified from C. magna possessed the same absorption features and HPLC retention time as that purified from Phaeodactylum tricornutum (9). The relative amount of fucoxanthin in C. magna is lower than that typically found in chyrsophytes (27) and the diatoms, P. tricornutum (9), and Skeletonema costatum (1 1), where it accounts for 60 to 80% of the total carotenoid.…”

Section: Resultsmentioning

confidence: 87%

Antheraxanthin, a Light Harvesting Carotenoid Found in a Chromophyte Alga

Alberte¹,

Andersen²

1986

Plant Physiol.

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The pigments of the chromophyte freshwater alga, Chrysophaera magna Belcher were analyzed by thin layer chromatography (TLC) and high performance liquid chromatography (HPLC) to reveal the presence of chlorophylls a and c, ,8-carotene, fucoxanthin, and antheraxanthin. The presence of antheraxanthin was verified by comparison of TLC RF values, HPLC retention times, and absorption features to those of authentic, synthetic antheraxanthin. Antheraxanthin accounted for about 15% of the total carotenoid content of C. magna. The molar ratio of the major carotenoids was antheraxanthin:fucoxanthin:j-carotene, 1:23:33. The whole-cell absorption spectrum revealed a broad band between 470 and 520 nanometers which was attributed to fucoxanthin and antheraxanthin in vivo. Upon extraction in hydrocarbon, this broad absorption region was lost. The in vivo fluorescence excitation spectrum for 680 nm emission revealed the energy transfer activities and light harvesting roles of chlorophylls a and c, and fucoxanthin. In addition, an excitation band was resolved at 487 nanometers which could be attributed only to antheraxanthin. Comparison of whole-cell fluorescence excitation spectra of C. magna with the diatom Phaeodactylum tricornutum, which possesses fucoxanthin but not antheraxanthin, supports the assignment of the 487 nm band to antheraxanthin. This is the first report of a photosynthetic light harvesting function of the xanthophylL antheraxanthin.This carotenoid broadens the absorption cross-section for photosynthesis in C. magna and extends light harvesting into the green portion of the spectrum.The role of accessory pigments in supporting photosynthetic 02 evolution in algae was established by the work of Dutton and Manning (8) (16,19). Even in clear, oligotrophic bodies of water, most of the red wavelengths are absorbed within the top few centimeters. Consequently, the Soret absorption bands of the Chl (400-440 nm) become far more important in driving photosynthesis than the red absorption region (650-690 nm). Further, dissolved substances in the water can very effectively filter the blue part of the spectrum, therefore leaving a 'green window' for light absorption. This effect is particularly pronounced at depth in the water column (19).The optical properties of natural bodies of water probably provided the selective pressures for the evolution of light harvesting pigments, such as certain xanthophyll carotenoids and the phycobiliproteins, that can effectively utilize light energy between 450 and 630 nm. Indeed, in all but the Chlorophyta, pigments with significant or major absorption in the green portion of the spectrum are not only common but are often more abundant than Chl a (2,11,16,23

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A Diatom Light-Harvesting Pigment-Protein Complex

Cited by 79 publications

References 12 publications

Light-Harvesting Function in the Diatom Phaeodactylum tricornutum

Light-Harvesting Function in the Diatom Phaeodactylum tricornutum

Photochemical and Nonphotochemical Fluorescence Quenching Processes in the Diatom Phaeodactylum tricornutum

Antheraxanthin, a Light Harvesting Carotenoid Found in a Chromophyte Alga

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