chlorophyll-a and diadinoxanthin

Carotenoids (Cars) exhibit two functions in photosynthesis, light-harvesting and photoprotective functions, which are performed through the excited states of Cars. Therefore, increasing our knowledge on excitation relaxation dynamics of Cars is important for understanding of the functions of Cars. In light-harvesting complexes, there exist Cars functioning by converting the π-conjugation number in response to light conditions. It is well known that some microalgae have a mechanism controlling the conjugation number of Cars, called as the diadinoxanthin cycle; diadinoxanthin (10 conjugations) is accumulated under low light, whereas diatoxanthin (11 conjugations) appears under high light. However, the excitation relaxation dynamics of these two Cars have not been clarified. In the present study, we investigated excitation relaxation dynamics of diadinoxanthin and diatoxanthin in relation to their functions, by the ultrafast fluorescence spectroscopy. After an excitation to the S

Topics: Acetone; Carotenoids; Chlorophyll; Chlorophyll A; Ethanol; Ether; Light-Harvesting Protein Complexes; Xanthophylls

Carotenoids are essential components of photosynthetic organisms including land plants, algae, cyanobacteria, and photosynthetic bacteria. Although the light-mediated regulation of carotenoid biosynthesis, including the light/dark cycle as well as the dependence of carotenoid biosynthesis-related gene translation on light wavelength, has been investigated in land plants, these aspects have not been studied in microalgae. Here, we investigated carotenoid biosynthesis in Euglena gracilis and found that zeaxanthin accumulates in the dark. The major carotenoid species in E. gracilis, namely β-carotene, neoxanthin, diadinoxanthin and diatoxanthin, accumulated corresponding to the duration of light irradiation under the light/dark cycle, although the translation of carotenoid biosynthesis genes hardly changed. Irradiation with either blue or red-light (3 μmol photons m

Topics: Acclimatization; beta Carotene; Chlorophyll; Euglena gracilis; Gene Expression Regulation; Light; Photosystem II Protein Complex; Xanthophylls; Zeaxanthins

The influence of six different light regimes throughout the photosynthetically active radiation range (from 400 to 700 nm, including blue, green, yellow, red-orange, red, and white) at two intensities (100 and 300 µmol photons m

Topics: beta Carotene; Chlorophyll; Diatoms; Light; Photosynthesis; Pigments, Biological; Xanthophylls; Zeaxanthins

Diatoms are abundant photosynthetic organisms in aquatic environments and contribute 40% of its primary productivity. An important factor that contributes to the success of diatoms is their fucoxanthin chlorophyll a/c-binding proteins (FCPs), which have exceptional light-harvesting and photoprotection capabilities. Here, we report the crystal structure of an FCP from the marine diatom

Topics: Chlorophyll; Chlorophyll A; Chlorophyll Binding Proteins; Diatoms; Energy Transfer; Light; Photosynthesis; Protein Structure, Quaternary; Thylakoids; Xanthophylls

Fucoxanthin chlorophyll (Chl) a/ c-binding proteins (FCPs) are unique light-harvesting antennas in diatoms. Recent time-resolved fluorescence analysis of photosystem I with FCP associated (PSI-FCPI) has mainly shown excitation energy transfer among Chls a from FCPI to PSI in tens of picoseconds. However, it remains unclear how each pigment, especially carotenoids and Chl c, in the FCPI is functionally related to the energy transfer in a femtosecond time range. Here, we reveal ultrafast excitation energy transfer mechanism in the PSI-FCPI preparations isolated from a diatom, Chaetoceros gracilis, by means of femtosecond time-resolved fluorescence spectroscopy with an upconversion system. Compared with the fluorescence lifetime components of PSI core-like complexes, the energy transfer of Chl c → Chl a in the FCPI was observed within hundreds of femtoseconds, and the energy in the FCPI was transferred to PSI in ∼2 ps. The comparative fluorescence analyses provide physical insights into the energy transfer machinery within FCPI and from FCPI to PSI.

Topics: Carotenoids; Chlorophyll; Chlorophyll A; Chlorophyll Binding Proteins; Diatoms; Energy Transfer; Fluorescence; Photosystem I Protein Complex; Spectrometry, Fluorescence; Xanthophylls

Diatoms contain a highly flexible capacity to dissipate excessively absorbed light by nonphotochemical fluorescence quenching (NPQ) based on the light-induced conversion of diadinoxanthin (Dd) into diatoxanthin (Dt) and the presence of Lhcx proteins. Their NPQ fine regulation on the molecular level upon a shift to dynamic light conditions is unknown. We investigated the regulation of Dd + Dt amount, Lhcx gene and protein synthesis and NPQ capacity in the diatom Phaeodactylum tricornutum after a change from continuous low light to 3 d of sine (SL) or fluctuating (FL) light conditions. Four P. tricornutum strains with different NPQ capacities due to different expression of Lhcx1 were included. All strains responded to dynamic light comparably, independently of initial NPQ capacity. During SL, NPQ capacity was strongly enhanced due to a gradual increase of Lhcx2 and Dd + Dt amount. During FL, cells enhanced their NPQ capacity on the first day due to increased Dd + Dt, Lhcx2 and Lhcx3; already by the second day light acclimation was accomplished. While quenching efficiency of Dt was strongly lowered during SL conditions, it remained high throughout the whole FL exposure. Our results highlight a more balanced and cost-effective photoacclimation strategy of P. tricornutum under FL than under SL conditions.

Topics: Chlorophyll; Chlorophyll A; Diatoms; Fluorescence; Gene Expression Regulation, Bacterial; Light; Light-Harvesting Protein Complexes; Photosynthesis; Protein Biosynthesis; RNA, Messenger; Xanthophylls

Various life cycle stages of cyst-producing dinoflagellates often appear differently colored under the microscope; gametes appear paler while zygotes are darker in comparison to vegetative cells. To compare physiological and photochemical competency, the pigment composition of discrete life cycle stages was determined for the common resting cyst-producing dinoflagellate Scrippsiella lachrymosa. Vegetative cells had the highest cellular pigment content (25.2 ± 0.5 pg · cell(-1) ), whereas gamete pigment content was 22% lower. The pigment content of zygotes was 82% lower than vegetative cells, even though they appeared darker under the microscope. Zygotes of S. lachrymosa contained significantly higher cellular concentrations of β-carotene (0.65 ± 0.15 pg · cell(-1) ) than all other life stages. Photoprotective pigments and the de-epoxidation ratio of xanthophylls-cycle pigments in S. lachrymosa were significantly elevated in zygotes and cysts compared to other stages. This suggests a role for accessory pigments in combating intracellular oxidative stress during sexual reproduction or encystment. Resting cysts contained some pigments even though chloroplasts were not visible, suggesting that the brightly colored accumulation body contained photosynthetic pigments. The differences in pigmentation between life stages have implications for interpretation of pigment data from field samples when sampled during dinoflagellate blooms.

Topics: beta Carotene; Chlorophyll; Dinoflagellida; Life Cycle Stages; Oxidative Stress; Photosynthesis; Pigmentation; Xanthophylls; Zygote

The major light-harvesting pigment protein complex (fucoxanthin-chlorophyll-binding protein complex; FCP) was purified from a marine centric diatom, Chaetoceros gracilis, by mild solubilization followed by sucrose density gradient centrifugation, and then characterized. The dynamic light scattering measurement showed unimodality, indicating that the complex was highly purified. The amount of chlorophyll a (Chl a) bound to the purified FCP accounted for more than 60 % of total cellular Chl a. The complex was composed of three abundant polypeptides, although there are nearly 30 FCP-related genes. The two major components were identified as Fcp3 (Lhcf3)- and Fcp4 (Lhcf4)-equivalent proteins based on their internal amino acid sequences and a two-dimensional isoelectric focusing electrophoresis analysis developed in this work. Compared with the thylakoids, the FCP complex showed higher contents of fucoxanthin and chlorophyll c but lower contents of the xanthophyll cycle pigments diadinoxanthin and diatoxanthin. Fluorescence excitation spectra analyses indicated that light harvesting, rather than photosystem protection, is the major function of the purified FCP complex, which is associated with more than 60 % of total cellular Chl a. These findings suggest that the huge amount of Chl bound to the FCP complex composed of Lhcf3, Lhcf4, and an unidentified minor protein has a light-harvesting function to allow efficient photosynthesis under the dim-light conditions in the ocean.

Topics: Carrier Proteins; Chlorophyll; Chlorophyll A; Diatoms; Light; Light-Harvesting Protein Complexes; Photosystem II Protein Complex; Spectrometry, Fluorescence; Thylakoids; Xanthophylls

Phytoplankton dominant species and their light absorption properties during the blooms occurred in August 2013 in adjacent waters of the Changjiang Estuary were analyzed. The results showed that phytoplankton blooms broke out in 10 out of 34 investigation stations, among which diatom blooms occurred in 6 stations while 3 stations were predominated by dinoflagellate. Phytoplankton absorption coefficients of both bloom and non-bloom waters exhibited large variations, with respective ranges of 0.199-0.832 m(-1) and 0.012-0.109 m(-1), while phytoplankton specific absorption coefficients spanned much narrower range, with the average values of bloom and non-bloom waters being 0.023 and 0.035 m2 x mg(-1), respectively. When transitioned from bloom to non-bloom waters, the proportion of phytoplankton with larger cell size lowered while that of smaller phytoplankton elevated, causing a less extent of package effect and thus higher specific absorption coefficients. Distinctive absorption spectra were observed between different types of bloom (such as diatom and dinoflagellate blooms) with similar phytoplankton cell size, mostly attributed to distinctive accessory pigment composition. The ratios of diadinoxanthin and chlorophyll-c2 concentrations to chlorophyll-a concentration in dinoflagellate blooms were higher than those in diatom blooms, which largely contributed to the shoulder peaks at 465 nm in dinoflagellate blooms.

Topics: Chlorophyll; Chlorophyll A; Diatoms; Dinoflagellida; Estuaries; Eutrophication; Light; Phytoplankton; Xanthophylls

Benthic marine dioflagellate microalgae belonging to the genus Prorocentrum are a major source of okadaic acid (OA), OA analogues and polyketides. However, dinoflagellates produce these valuable toxins and bioactives in tiny quantities, and they grow slowly compared to other commercially used microalgae. This hinders evaluation in possible large-scale applications. The careful selection of producer species is therefore crucial for success in a hypothetical scale-up of culture, as are appropriate environmental conditions for optimal growth. A clone of the marine toxic dinoflagellate P. belizeanum was studied in vitro to evaluate its capacities to grow and produce OA as an indicator of general polyketide toxin production under the simultaneous influence of temperature (T) and irradiance (I0). Three temperatures and four irradiance levels were tested (18, 25 and 28 °C; 20, 40, 80 and 120 µE·(m-2)·s(-1)), and the response variables measured were concentration of cells, maximum photochemical yield of photosystem II (PSII), pigments and OA. Experiments were conducted in T-flasks, since their parallelepipedal geometry proved ideal to ensure optically thin cultures, which are essential for reliable modeling of growth-irradiance curves. The net maximum specific growth rate (µ(m)) was 0.204 day(-1) at 25 °C and 40 µE·(m-2)·s(-1). Photo-inhibition was observed at I0 > 40 μEm(-2)s(-1), leading to culture death at 120 µE·m(-2)·s(-1) and 28 °C. Cells at I0 ≥ 80 µE·m(-2)·s(-1) were photoinhibited irrespective of the temperature assayed. A mechanistic model for µ(m)-I0 curves and another empirical model for relating µ(m)-T satisfactorily interpreted the growth kinetics obtained. ANOVA for responses of PSII maximum photochemical yield and pigment profile has demonstrated that P. belizeanum is extremely light sensitive. The pool of photoprotective pigments (diadinoxanthin and dinoxanthin) and peridinin was not able to regulate the excessive light-absorption at high I0-T. OA synthesis in cells was decoupled from optimal growth conditions, as OA overproduction was observed at high temperatures and when both temperature and irradiance were low. T-flask culture observations were consistent with preliminary assays outdoors.

Topics: beta Carotene; Carotenoids; Chlorophyll; Chromatography, High Pressure Liquid; Dinoflagellida; Light; Models, Theoretical; Okadaic Acid; Photobioreactors; Temperature; Xanthophylls

Phytoplankton, such as diatoms, experience great variations of photon flux density (PFD) and light spectrum along the marine water column. Diatoms have developed some rapidly-regulated photoprotective mechanisms, such as the xanthophyll cycle activation (XC) and the non-photochemical chlorophyll fluorescence quenching (NPQ), to protect themselves from photooxidative damages caused by excess PFD. In this study, we investigate the role of blue fluence rate in combination with red radiation in shaping photoacclimative and protective responses in the coastal diatom Pseudo-nitzschia multistriata. This diatom was acclimated to four spectral light conditions (blue, red, blue-red, blue-red-green), each of them provided with low and high PFD. Our results reveal that the increase in the XC pool size and the amplitude of NPQ is determined by the blue fluence rate experienced by cells, while cells require sensing red radiation to allow the development of these processes. Variations in the light spectrum and in the blue versus red radiation modulate either the photoprotective capacity, such as the activation of the diadinoxanthin-diatoxanthin xanthophyll cycle, the diadinoxanthin de-epoxidation rate and the capacity of non-photochemical quenching, or the pigment composition of this diatom. We propose that spectral composition of light has a key role on the ability of diatoms to finely balance light harvesting and photoprotective capacity.

Topics: Acclimatization; Chlorophyll; Diatoms; Photons; Photosynthesis; Phytoplankton; Radiation; Xanthophylls

The physiological response of the scleractinian coral Turbinaria reniformis to ammonium enrichment (3 μmol l(-1)) was examined at 26°C as well as during a 7 day increase in temperature to 31°C (thermal stress). At 26°C, ammonium supplementation had little effect on the coral physiology. It induced a decrease in symbiont density, compensated by an increase in chlorophyll content per symbiont cell. Organic carbon release was reduced, likely because of a better utilization of the photosynthesized carbon (i.e. incorporation into proteins, kept in the coral tissue). The δ(15)N signatures of the ammonium-enriched symbionts and host tissue were also significantly decreased, by 4 and 2‰, respectively, compared with the non-enriched conditions, suggesting a significant uptake of inorganic nitrogen by the holobiont. Under thermal stress, coral colonies that were not nitrogen enriched experienced a drastic decrease in photosynthetic and photoprotective pigments (chlorophyll a, β-carotene, diadinoxanthin, diatoxanthin and peridinin), followed by a decrease in the rates of photosynthesis and calcification. Organic carbon release was not affected by this thermal stress. Conversely, nitrogen-enriched corals showed an increase in their pigment concentrations, and maintained rates of photosynthesis and calcification at ca. 60% and 100% of those measured under control conditions, respectively. However, these corals lost more organic carbon into the environment. Overall, these results indicate that inorganic nitrogen availability can be important to determining the resilience of some scleractinian coral species to thermal stress, and can have a function equivalent to that of heterotrophic feeding concerning the maintenance of coral metabolism under stress conditions.

Topics: Ammonium Compounds; Analysis of Variance; Animals; Anthozoa; beta Carotene; Calcification, Physiologic; Carotenoids; Chlorophyll; Chlorophyll A; Dinoflagellida; Fluorescence; Hot Temperature; Indian Ocean; Nitrogen; Photosynthesis; Stress, Physiological; Symbiosis; Xanthophylls

Chromophytes are an important group of microorganisms that contribute significantly to the carbon cycle on Earth. Their photosynthetic capacity depends on efficiency of the light-harvesting system that differs in pigment composition from that of green plants and other groups of algae. Here we employ femtosecond transient absorption spectroscopy to study energy transfer pathways in the main light-harvesting complex of Xanthonema debile, denoted XLH, which contains four carotenoids--diadinoxanthin, heteroxanthin, diatoxanthin, and vaucheriaxanthin--and Chl-a. Overall carotenoid-to-chlorophyll energy transfer efficiency is about 60%, but energy transfer pathways are excitation wavelength dependent. Energy transfer from the carotenoid S(2) state is active after excitation at both 490 nm (maximum of carotenoid absorption) and 510 nm (red edge of carotenoid absorption), but this channel is significantly more efficient after 510 nm excitation. Concerning the energy transfer pathway from the S(1) state, XLH contains two groups of carotenoids: those that have the S(1) route active (~25%) and those having the S(1) pathway silent. For a fraction of carotenoids that transfer energy via the S(1) channel, energy transfer is observed after both excitation wavelengths, though energy transfer times are different, yielding 3.4 ps (490 nm excitation) and 1.5 ps (510 nm excitation). This corresponds to efficiencies of the S(1) channel of ~85% that is rather unusual for a donor-acceptor pair consisting of a noncarbonyl carotenoid and Chl-a. Moreover, major carotenoids in XLH, diadinoxanthin and diatoxanthin, have their S(1) energies in solution lower than the energy of the acceptor state, Q(y) state of Chl-a. Thus, binding of these carotenoids to XLH must tune their S(1) energy to allow for efficient energy transfer. Besides the light-harvesting function, carotenoids in XLH also have photoprotective role; they quench Chl-a triplets via triplet-triplet energy transfer from Chl-a to carotenoid.

Topics: Carotenoids; Chlorophyll; Chlorophyta; Energy Transfer; Light-Harvesting Protein Complexes; Xanthophylls

Photosynthetic diatoms are exposed to rapid and unpredictable changes in irradiance and spectral quality, and must be able to acclimate their light harvesting systems to varying light conditions. Molecular mechanisms behind light acclimation in diatoms are largely unknown. We set out to investigate the mechanisms of high light acclimation in Phaeodactylum tricornutum using an integrated approach involving global transcriptional profiling, metabolite profiling and variable fluorescence technique. Algae cultures were acclimated to low light (LL), after which the cultures were transferred to high light (HL). Molecular, metabolic and physiological responses were studied at time points 0.5 h, 3 h, 6 h, 12 h, 24 h and 48 h after transfer to HL conditions. The integrated results indicate that the acclimation mechanisms in diatoms can be divided into an initial response phase (0-0.5 h), an intermediate acclimation phase (3-12 h) and a late acclimation phase (12-48 h). The initial phase is recognized by strong and rapid regulation of genes encoding proteins involved in photosynthesis, pigment metabolism and reactive oxygen species (ROS) scavenging systems. A significant increase in light protecting metabolites occur together with the induction of transcriptional processes involved in protection of cellular structures at this early phase. During the following phases, the metabolite profiling display a pronounced decrease in light harvesting pigments, whereas the variable fluorescence measurements show that the photosynthetic capacity increases strongly during the late acclimation phase. We show that P. tricornutum is capable of swift and efficient execution of photoprotective mechanisms, followed by changes in the composition of the photosynthetic machinery that enable the diatoms to utilize the excess energy available in HL. Central molecular players in light protection and acclimation to high irradiance have been identified.

Topics: Acclimatization; Carbon; Chlorophyll; Diatoms; Electron Transport; Light; Models, Biological; Photosynthesis; Pigmentation; Plastids; RNA, Complementary; Time Factors; Transcription, Genetic; Xanthophylls

In the present study we report that in the diatom Cyclotella meneghiniana the diatoxanthin-dependent non-photochemical quenching of chlorophyll fluorescence (NPQ) is heterogeneous and consists of three different components. (i) A transient NPQ component that generates immediately upon illumination, depends on the transthylakoid proton gradient as well as on the light intensity, and is modulated by the initial diatoxanthin content of the cells. It is located in the antenna complexes of C. meneghiniana and is comparable with the transient NPQ observed in vascular plants. (ii) A steady-state NPQ component is observed during later stages of the high-light illumination and depends on the diatoxanthin content formed by the light-activated diadinoxanthin cycle. (iii) A fast relaxing NPQ component is seen upon a transition of high-light-illuminated cells to complete darkness. This component relaxes within a time frame of tens of seconds and its extent is correlated with the amount of diatoxanthin formed during the phase of actinic illumination. It cannot be observed in dithiothreitol-treated cells where the de-epoxidation of diadinoxanthin to diatoxanthin is suppressed. The fast relaxing component can be interpreted as a relaxation of part of the steady-state NPQ. The different diatoxanthin-dependent components are characterized by different quenching efficiencies of diatoxanthin. Diatoxanthin involved in the transient NPQ exhibits a 2-fold higher quenching efficiency compared with diatoxanthin participating in the steady-state NPQ. It is proposed that the different quenching efficiencies of diatoxanthin are caused by the existence of different diatoxanthin pools within the antenna system of C. meneghiniana.

Topics: beta Carotene; Chlorophyll; Diatoms; Fluorescence; Light; Photosynthesis; Signal Transduction; Time Factors; Xanthophylls

Two different fucoxanthin-chlorophyll protein complexes (FCP) were purified from the centric diatom Cyclotella meneghiniana and characterized with regard to their polypeptide and pigment composition. Whereas the oligomeric FCPb complex is most probably composed of fcp5 gene products, the trimeric FCPa has subunits encoded by fcp1-3 and fcp6/7. The amount of the latter polypeptide is enhanced when FCPa is isolated from algae grown under HL conditions. This increase in Fcp6/7 polypeptides is accompanied by an increase in the pool of xanthophyll cycle pigments, diadinoxanthin and diatoxanthin, and a concomitant decrease in fucoxanthin content. In addition, the de-epoxidation ratio, i.e., the amount of diatoxanthin in relation to the pool of xanthophyll cycle pigments, is increased by a factor of 2. With regard to fluorescence yield, HL FCPa was quenched in comparison to LL FCPa. This is in accordance with the larger amount of diatoxanthin that is bound, which is supposed to act as a quencher like zeaxanthin in higher plants. Thus, we conclude that the enhanced content of diatoxanthin in FCPa plays a protective role, which is paralleled by a weakened light harvesting function due to a smaller amount of fucoxanthin.

Topics: Blotting, Western; Chlorophyll; Diatoms; Light-Harvesting Protein Complexes; Spectrometry, Fluorescence; Xanthophylls

Bleaching of corals by loss of symbiotic dinoflagellate algae and/or photosynthetic pigments is commonly triggered by elevated temperatures coupled with high irradiance, and is a first-order threat to coral reef communities. In this study, a high-resolution high-performance liquid chromatography method integrated with mass spectrometry was applied to obtain the first definitive identification of chlorophyll and carotenoid pigments of three clades of symbiotic dinoflagellate algae (Symbiodinium) in corals, and their response to experimentally elevated temperature and irradiance. The carotenoids peridinin, dinoxanthin, diadinoxanthin (Dn), diatoxanthin (Dt) and beta-carotene were detected, together with chlorophylls a and c2, and phaeophytin a, in all three algal clades in unstressed corals. On exposure to elevated temperature and irradiance, three coral species (Montastrea franksi and Favia fragum with clade B algae, and Montastrea cavernosa with clade C) bleached by loss of 50-80% of their algal cells, with no significant impact to chlorophyll a or c2, or peridinin in retained algal cells. One species (Agaricia sp. with clade C) showed no significant reduction in algal cells at elevated temperature and irradiance, but lost substantial amounts of chlorophyll a and carotenoid pigments, presumably through photo-oxidative processes. Two coral species (Porites astreoides and Porites porites both bearing clade A algae) did not bleach. The impact of elevated temperature and irradiance on the levels of the photoprotective xanthophylls (Dn + Dt) and beta-carotene varied among the corals, both in pool size and xanthophyll cycling, and was not correlated to coral bleaching resistance.

Topics: Animals; Anthozoa; Cell Count; Chlorophyll; Chromatography, High Pressure Liquid; Eukaryota; Light; Mass Spectrometry; Phylogeny; Pigments, Biological; Symbiosis; Temperature; Xanthophylls

Diatoms differ from higher plants by their antenna system, in terms of both polypeptide and pigment contents. A rapid isolation procedure was designed for the membrane-intrinsic light harvesting complexes (LHC) of the diatom Phaeodactylum tricornutum to establish whether different LHC subcomplexes exist, as well to determine an uneven distribution between them of pigments and polypeptides. Two distinct fractions were separated that contain functional oligomeric complexes. The major and more stable complex ( approximately 75% of total polypeptides) carries most of the chlorophyll a, and almost only one type of carotenoid, fucoxanthin. The minor complex, carrying approximately 10-15% of the total antenna chlorophyll and only a little chlorophyll c, is highly enriched in diadinoxanthin, the main xanthophyll cycle carotenoid. The two complexes also differ in their polypeptide composition, suggesting specialized functions within the antenna. The diadinoxanthin-enriched complex could be where the de-epoxidation of diadinoxanthin into diatoxanthin mostly occurs.

Topics: Carotenoids; Centrifugation, Density Gradient; Chlorophyll; Chromatography, Gel; Diatoms; Light-Harvesting Protein Complexes; Macromolecular Substances; Phytoplankton; Xanthophylls

The effect of Fe(III) deficiency on qualitative and quantitative changes in pigment composition in Phaeodactylum tricornutum Bohlin was demonstrated by HPLC and AAS. Maximum content of pigments showed the diatom cells incubated at the optimum iron concentration, i.e., 10 microM. The contents of chlorophyll a, chlorophyll c1 + c2, fucoxanthin, diadinoxanthin and beta,beta-carotene were 109.99, 20.16, 40.39, 1.29 and 1.48 fg per cell, respectively. The results obtained showed that Fe(III) affected qualitative and quantitative pigment composition in P. tricornutum. The content of individual pigments, proportions between accompanying pigments and their ratios to chlorophyll a were important indicators of phytoplankton response to iron stress. The strong reduction in beta,beta-carotene content, several times (2-5) increase in diadinoxanthin level as compared to beta,beta-carotene, and high amount of diadinoxanthin in relation to chlorophyll a were observed in algae growing at very low Fe(III) concentrations, 0.001 and 0.01 microM. The data suggested that phytoplankton pigments could be a potential physiological marker.

Topics: beta Carotene; Chlorophyll; Chromatography, High Pressure Liquid; Diatoms; Iron; Pigments, Biological; Xanthophylls

The pool size of the xanthophyll cycle pigment diadinoxanthin (DD) in the diatom Phaeodactylum tricornutum depends on illumination conditions during culture. Intermittent light caused a doubling of the DD pool without significant change in other pigment contents and photosynthetic parameters, including the photosystem II (PSII) antenna size. On exposure to high-light intensity, extensive de-epoxidation of DD to diatoxanthin (DT) rapidly caused a very strong quenching of the maximum chlorophyll fluorescence yield (F(m), PSII reaction centers closed), which was fully reversed in the dark. The non-photochemical quenching of the minimum fluorescence yield (F(o), PSII centers open) decreased the quantum efficiency of PSII proportionally. For both F(m) and F(o), the non-photochemical quenching expressed as F/F' - 1 (with F' the quenched level) was proportional to the DT concentration. However, the quenching of F(o) relative to that of F(m) was much stronger than random quenching in a homogeneous antenna could explain, showing that the rate of photochemical excitation trapping was limited by energy transfer to the reaction center rather than by charge separation. The cells can increase not only the amount of DT they can produce, but also its efficiency in competing with the PSII reaction center for excitation. The combined effect allowed intermittent light grown cells to down-regulate PSII by 90% and virtually eliminated photoinhibition by saturating light. The unusually rapid and effective photoprotection by the xanthophyll cycle in diatoms may help to explain their dominance in turbulent waters.

Topics: Algorithms; Chlorophyll; Diatoms; Fluorescence; Light; Light-Harvesting Protein Complexes; Oxygen; Photosynthesis; Photosynthetic Reaction Center Complex Proteins; Photosystem II Protein Complex; Phytoplankton; Xanthophylls

Non-photochemical fluorescence quenching (NPQ) in diatoms is associated with a xanthophyll cycle involving diadinoxanthin (DD) and its de-epoxidized form, diatoxanthin (DT). In higher plants, an obligatory role of de-epoxidized xanthophylls in NPQ remains controversial and the presence of a transthylakoid proton gradient (DeltapH) alone may induce NPQ. We used inhibitors to alter the amplitude of DeltapH and/or DD de-epoxidation, and coupled NPQ. No DeltapH-dependent quenching was detected in the absence of DT. In diatoms, both DeltapH and DT are required for NPQ. The binding of DT to protonated antenna sites could be obligatory for energy dissipation.

Topics: Chlorophyll; Diatoms; Fluorescence; Photochemistry; Proton Pumps; Thylakoids; Xanthophylls

Cd has pleiotropic effects on plant physiology and in particular on photosynthesis. It has not been established yet if Cd alters the functioning of the xanthophyll cycle. To answer this question, an exponentially growing culture of the marine diatom Phaeodactylum tricornutum was incubated with Cd (20 mg/l) for 24 h and irradiated with a light activating the xanthophyll cycle, which in diatoms, consists of the reversible deepoxidation of diadinoxanthin to diatoxanthin. The measurements show that the deepoxidation step is not influenced by Cd. In contrast, the Cd concentration used sharply inhibits the epoxidation of diatoxanthin to diadinoxanthin.

Topics: Cadmium; Chlorophyll; Diatoms; Light; Photosynthesis; Spectrometry, Fluorescence; Xanthophylls

The lifetimes of the first excited singlet states (2(1)A(g)) of diadinoxanthin and diatoxanthin, carotenoids involved in the xanthophyll cycle in some genera of algae, have been measured by femtosecond time-resolved optical spectroscopy to be 22.8 +/- 0.1 ps and 13.3 +/- 0.1 ps, respectively. Using the energy gap law for radiationless transitions set forth by Englman and Jortner (Mol. Phys. 18 (1970) 145-164), these lifetimes correspond to S1 excited state energies of 15210 cm-1 for diadinoxanthin and 14620 cm-1 for diatoxanthin. The lowest excited singlet state energy of Chl a has an energy of 14700 cm-1. The fact that the S1 state energy of diadinoxanthin lies above that of Chl a, whereas the S1 state energy of diatoxanthin lies below that of Chl a, suggests that the xanthophyll cycle involving the enzymatic interconversion of diadinoxanthin and diatoxanthin may play a role in regulating energy flow between these molecules and Chl a in many species of algae, essentially fulfilling a role identical to that proposed for violaxanthin and zeaxanthin in higher plants and green algae (Frank et al. (1994) Photosyn. Res. 41, 389-395).

Topics: Carotenoids; Chlorophyll; Chlorophyll A; Energy Metabolism; Eukaryota; Hydrogen-Ion Concentration; Spectrometry, Fluorescence; Spectrophotometry; Thermodynamics; Xanthophylls