Vertical structure and photosynthetic activity of Lake Shira phytoplankton

This study was conducted to analyse vertical dynamics of phytoplankton distribution in Shira Lake during the summer stratification regime. From late June to September phytoplankton in Shira Lake were stratified with the maximum in the lower part of the thermocline, at a depth of 8–12 m, with a chlorophyll concentration up to 23 g and biomass up to 5 mg l^–1. Maxima of chlorophyll and biomass of cyanobacteria and green algae were in different layers. From June to September a major part of chlorophyll a was in green algae, while under ice – in cyanobacteria. The variable fluorescence proves high photosynthetic activity of algae in the depth assemblage. Epifluorescent analysis disclosed that additional light-harvesting pigments were better developed in cells from the depth maximum. The maximum of gross primary production calculated from fluorescence corresponded to the depth maximum of phytoplankton. Primary production over a season was 2.7 gO₂ m^–2. Formation mechanisms of the depth maximum of phytoplankton are discussed in this paper.     

Genome-wide analysis of the family of light-harvesting chlorophyll a/b-binding proteins in arabidopsis and rice

Light-harvesting antenna system possesses an inherent property of photoprotection. The single-helix proteins found in cyanobacteria play role in photoprotection and/or pigment metabolism. The photoprotective functions are also manifested by the two- and four-helix proteins. The photoprotection mechanism evolved earlier to the mechanism of light-harvesting of the antenna complex. Here, the light-harvesting complex genes of photosystems I and II from Arabidopsis are enlisted, and almost similar set of genes are identified in rice. Also, the three-helix early light-inducible proteins (ELIPs), two-helix stress-enhanced proteins (SEPs) and one-helix high light-inducible proteins [one-helix proteins (OHPs)] are identified in rice. Interestingly, two independent genomic loci encoding PsbS protein are also identified with implications on additional mode of non-photochemical quenching (NPQ) mechanism in rice. A few additional LHC-related genes are also identified in rice (LOC_Os09g12540, LOC_Os02g03330). This is the first report of identification of light-harvesting complex genes and light-inducible genes in rice.Key words: Lhca and Lhcb proteins, Lhc proteins evolution, light-inducible proteins, protein alignment, PsbSThe light-harvesting proteins are present in different taxa. The proteins of light-harvesting systems from higher plants, cyano-bacteria, purple bacteria and green sulphur bacteria share no sequence similarity however little structural similarity can be seen.¹ Apparently, the light-harvesting systems in these different taxa might have evolved independently from each other.¹ To enable efficient transfer of excitation energy into the reaction centers, where charge separation takes place, different proteins are recruited in order to coordinate the photosynthetic pigment molecules. The light-harvesting and light dissipation are tightly coupled processes involving the higher plant light-harvesting antenna. Here, genome-wide analysis of the light-harvesting chlorophyll a/b-binding proteins and light-inducible proteins in Arabidopsis thaliana L. and Oryza sativa L. (rice) is conducted. This study wherein genes coding for antenna proteins are identified and named can be used as a nomenclature guide to the light-harvesting complex gene family members and their relatives in rice.     

Light-harvesting systems of brown algae and diatoms. Isolation and characterization of chlorophyll ac and chlorophyll afucoxanthin pigment-protein complexes

The present study examined the protein associations and energy transfer characteristics of chlorophyll c and fucoxanthin which are the major light-harvesting pigments in the brown and diatomaceous algae. It was demonstrated that sodium dodecyl sulfate (SDS)-solubilized photosynthetic membranes of these species when subjected to SDS polyacrylamide gel electrophoresis yielded three spectrally distinct pigment-protein complexes. The slowest migrating zone was identical to complex I, the SDS-altered form of the P-700 chlorophyll a-protein. The zone of intermediate mobility contained chlorophyll c and chlorophyll a in a molar ratio of 2 : 1, possessed no fucoxanthin, and showed efficient energy transfer from chlorophyll c to chlorophyll a. The fastest migrating pigment-protein zone contained fucoxanthin and chlorophyll a, possessed no chlorophyll c, and showed efficient energy transfer from fucoxanthin to chlorophyll a. It is demonstrated that the chlorophyll $\text{a}\text{c-}\text{protein}$ and the chlorophyll $\text{a}\text{fucoxanthin-protein}$ complexes are common to the brown algae and diatoms examined, and likely share similar roles in the photosynthetic units of these species.     

Photoacclimation impacts the molecular features of photosystem supercomplexes in the centric diatom Thalassiosira pseudonana

In diatoms, light-harvesting processes take place in a specific group of proteins, called fucoxanthin chlorophyll a/c proteins (FCP). This group includes many members and represents the major characteristic of the diatom photosynthetic apparatus, with specific pigments bound (chlorophyll c, fucoxanthin, diadino- and diatoxanthin besides chlorophyll a). In thylakoids, FCP and photosystems (PS) form multimeric supercomplexes.In this study, we compared the biochemical properties of PS supercomplexes isolated from Thalassiosira pseudonana cells grown under low light or high light conditions, respectively. High light acclimation changed the molecular features of the PS and their ratio in thylakoids. In PSII, no obvious changes in polypeptide composition were observed, whereas for PSI changes in one specific group of FCP proteins were detected. As reported before, the amount of xanthophyll cycle pigments and their de-epoxidation ratio was increased in PSI under HL. In PSII, however, no additional xanthophyll cycle pigments occurred, but the de-epoxidation ratio was increased as well. This comparison suggests how mechanisms of photoprotection might take place within and in the proximity of the PS, which gives new insights into the capacity of diatoms to adapt to different conditions and in different environments.     

Redox functions of carotenoids in photosynthesis

Carotenoids are well-known as light-harvesting pigments. They also play important roles in protecting the photosynthetic apparatus from damaging reactions of chlorophyll triplet states and singlet oxygen in both plant and bacterial photosynthesis. Recently, it has been found that beta-carotene functions as a redox intermediate in the secondary pathways of electron transfer within photosystem II and that carotenoid cation radicals are transiently formed after photoexcitation of bacterial light-harvesting complexes. The redox role of beta-carotene in photosystem II is unique among photosynthetic reaction centers and stems from the very strongly oxidizing intermediates that form in the process of water oxidation. Because of the extended pi-electron-conjugated system of carotenoid molecules, the cation radical is delocalized. This enables beta-carotene to function as a "molecular wire", whereby the centrally located oxidizing species is shuttled to peripheral redox centers of photosystem II where it can be dissipated without damaging the system. The physiological significance of carotenoid cation radical formation in bacterial light-harvesting complexes is not yet clear, but may provide a novel mechanism for excitation energy dissipation as a means of photoprotection. In this paper, the redox reactions of carotenoids in photosystem II and bacterial light-harvesting complexes are presented and the possible roles of carotenoid cation radicals in photoprotection are discussed.     

Photosynthetic action spectra of marine algae

A polarographic oxygen determination, with tissue in direct contact with a stationary platinum electrode, has been used to measure the photosynthetic response of marine algae. These were exposed to monochromatic light, of equal energy, at some 35 points through the visible spectrum (derived from a monochromator). Ulva and Monostroma (green algae) show action spectra which correspond very closely to their absorption spectra. Coilodesme (a brown alga) shows almost as good correspondence, including the spectral region absorbed by the carotenoid, fucoxanthin. In green and brown algae, light absorbed by both chlorophyll and carotenoids seems photosynthetically effective, although some inactive absorption by carotenoids is indicated. Action spectra for a wide variety of red algae, however, show marked deviations from their corresponding absorption spectra. The photosynthetic rates are high in the spectral regions absorbed by the water-soluble "phycobilin" pigments (phycoerythrin and phycocyanin), while the light absorbed by chlorophyll and carotenoids is poorly utilized for oxygen production. In red algae containing chiefly phycoerythrin, the action spectrum closely resembles that of the water-extracted pigment, with peaks corresponding to its absorption maxima (495, 540, and 565 mµ). Such algae include Delesseria, Schizymenia, and Porphyrella. In the genus Porphyra, there is a series P. nereocystis, P. naiadum, and P. perforata, with increasingly more phycocyanin and less phycoerythrin: the action spectra reflect this, with increasing activity in the orange-red region (600 to 640 mµ) where phycocyanin absorbs. In all these red algae, photosynthesis is almost minimal at 435 mµ and 675 mµ, where chlorophyll shows maximum absorption. Although the chlorophylls (and carotenoids) are present in quantities comparable to the green algae, their function is apparently not that of a primary light absorber; this role is taken over by the phycobilins. In this respect the red algae (Rhodophyta) appear unique among photosynthetic plants.     

Regulation and possible function of the violaxanthin cycle

This paper discusses biochemical and regulatory aspects of the violaxanthin cycle as well as its possible role in photoprotection. The violaxanthin cycle responds to environmental conditions in the short-term and long-term by adjusting rates of pigment conversions and pool sizes of cycle pigments, respectively. Experimental evidence indicating a relationship between zeaxanthin formation and non-photochemical energy dissipation is reviewed. Zeaxanthin-associated energy dissipation appears to be dependent on transthylakoid pH. The involvement of light-harvesting complex II in this quenching process is indicated by several studies. The current hypotheses on the underlying mechanism of zeaxanthin-dependent quenching are alterations of membrane properties, including conformational changes of the light-harvesting complex II, and singlet-singlet energy transfer from chlorophyll to zeaxanthin     

Spectral and functional studies on siphonaxanthin-type light-harvesting complex of photosystem II from Bryopsis corticulans

Carotenoids with conjugated carbonyl groups possess special photophysical properties which have been studied in some water-soluble light-harvesting proteins (Polívka and Sundström, Chem Rev 104:2021–2071, 2004). However, siphonaxanthin-type light-harvesting complexes of photosystem II (LHCII) in siphonous green alga have received fewer studies. In the present study, we determined sequences of genes for several Bryopsis corticulans Lhcbm proteins, which showed that they belong to the group of major LHCII and diverged early from green algae and higher plants. Analysis of pigment composition indicated that this siphonaxanthin-type LHCII contained in total 3 siphonaxanthin and siphonein but no lutein and violaxanthin. In addition, 2 chlorophylls a in higher plant LHCII were replaced by chlorophyll b. These changes led to an increased absorption in green and blue-green light region compared with higher plant LHCII. The binding sites for chlorophylls, siphonaxanthin, and siphonein were suggested based on the structural comparison with that of higher plant LHCII. All of the ligands for the chlorophylls were completely conserved, suggesting that the two chlorophylls b were replaced by chlorophyll a without changing their binding sites in higher plant LHCII. Comparisons of the absorption spectra of isolated siphonaxanthin and siphonein in different organic solutions and the effect of heat treatment suggested that these pigments existed in a low hydrophobic protein environment, leading to an enhancement of light harvesting in the green light region. This low hydrophobic protein environment was maintained by the presence of more serine and threonine residues in B. corticulans LHCII. Finally, esterization of siphonein may also contribute to the enhanced harvesting of green light.     

Spectroscopic properties of the Chlorophyll a–Chlorophyll c 2–Peridinin-Protein-Complex (acpPC) from the coral symbiotic dinoflagellate Symbiodinium

Femtosecond time-resolved transient absorption spectroscopy was performed on the chlorophyll a–chlorophyll c ₂–peridinin-protein-complex (acpPC), a major light-harvesting complex of the coral symbiotic dinoflagellate Symbiodinium. The measurements were carried out on the protein as well on the isolated pigments in the visible and the near-infrared region at 77 K. The data were globally fit to establish inter-pigment energy transfer paths within the scaffold of the complex. In addition, microsecond flash photolysis analysis was applied to reveal photoprotective capabilities of carotenoids (peridinin and diadinoxanthin) in the complex, especially the ability to quench chlorophyll a triplet states. The results demonstrate that the majority of carotenoids and other accessory light absorbers such as chlorophyll c ₂ are very well suited to support chlorophyll a in light harvesting. However, their performance in photoprotection in the acpPC is questionable. This is unusual among carotenoid-containing light-harvesting proteins and may explain the low resistance of the acpPC complex against photoinduced damage under even moderate light conditions.     

Phytoplankton and phytobenthos pigment strategies: implications for algal survival in the changing Arctic

We compared phytoplankton and phytobenthos pigment strategies in 17 shallow lakes and ponds from northern Canada and Alaska, sampled during mid to late summer. Benthic chlorophyll a concentrations (8–261 mg m⁻²) greatly exceeded those of the phytoplankton (0.008–1.4 mg m⁻²) in all sites. Cyanobacteria dominated the phytobenthos, while green algae and fucoxanthin-groups characterized the plankton. Both communities had higher photoprotection in cold, UV-transparent, high latitude waters. Phytoplankton had higher concentrations of photoprotective carotenoids per unit chlorophyll a than the phytobenthos. The planktonic photoprotective pigments were positively correlated with UV-penetration, and inversely correlated with temperature and coloured dissolved organic matter. A partial redundancy analysis showed that the benthic pigments were related to latitude, area and temperature. The UV-screening compound scytonemin occurred in high concentrations in the phytobenthos and was inversely related to temperature, while benthic carotenoids per unit chlorophyll a showed much lower variability among sites. These differing pigment strategies imply divergent responses to environmental change between the phytobenthos and phytoplankton in high latitude lakes.     

Relationship between photosynthetic pigments and chlorophyll fluorescence in soybean under varying phosphorus nutrition at ambient and elevated CO<Subscript>2</Subscript>

To assess the relationship between chlorophyll (Chl) fluorescence (CF) and photosynthetic pigments, soybean was grown under varying phosphorus (P) nutrition at ambient and elevated CO₂ (EC). The EC stimulated, but P deficiency decreased plant height, node numbers, and leaf area concomitantly with the rates of stem elongation, node addition, and leaf area expansion. Under P deficiency, CF parameters and pigments declined except that carotenoids (Car) were relatively stable indicating its role in photoprotection. The CF parameters were strongly related with Chl concentration but not with Chl a/b or Car. However, total Chl/Car showed the strongest association with CF parameters such as quantum efficiency and yield of photosystem II. This relationship was not affected by CO₂ treatment. The high correlation between CF and total Chl/Car underscores the significance of the quantification of both, Chl and Car concentrations, to understand the photochemistry and underlying processes of photoprotection and mechanisms of excess energy dissipation in a given environment.     

Characteristics of Myeloid Differentiation and Maturation Pathway Derived from Human Hematopoietic Stem Cells Exposed to Different Linear Energy Transfer Radiation Types

Exposure of hematopoietic stem/progenitor cells (HSPCs) to ionizing radiation causes a marked suppression of mature functional blood cell production in a linear energy transfer (LET)- and/or dose-dependent manner. However, little information about LET effects on the proliferation and differentiation of HSPCs has been reported. With the aim of characterizing the effects of different types of LET radiations on human myeloid hematopoiesis, in vitro hematopoiesis in Human CD34⁺ cells exposed to carbon-ion beams or X-rays was compared. Highly purified CD34⁺ cells exposed to each form of radiation were plated onto semi-solid culture for a myeloid progenitor assay. The surviving fractions of total myeloid progenitors, colony-forming cells (CFC), exposed to carbon-ion beams were significantly lower than of those exposed to X-rays, indicating that CFCs are more sensitive to carbon-ion beams (D ₀ = 0.65) than to X-rays (D ₀ = 1.07). Similar sensitivities were observed in granulocyte-macrophage and erythroid progenitors, respectively. However, the sensitivities of mixed-type progenitors to both radiation types were similar.In liquid culture for 14 days, no significant difference in total numbers of mononuclear cells was observed between non-irradiated control culture and cells exposed to 0.5 Gy X-rays, whereas 0.5 Gy carbon-ion beams suppressed cell proliferation to 4.9% of the control, a level similar to that for cells exposed to 1.5 Gy X-rays. Cell surface antigens associated with terminal maturation, such as CD13, CD14, and CD15, on harvest from the culture of X-ray-exposed cells were almost the same as those from the non-irradiated control culture. X-rays increased the CD235a⁺ erythroid-related fraction, whereas carbon-ion beams increased the CD34⁺CD38⁻ primitive cell fraction and the CD13⁺CD14^+/−CD15⁻ fraction. These results suggest that carbon-ion beams inflict severe damage on the clonal growth of myeloid HSPCs, although the intensity of cell surface antigen expression by mature myeloid cells derived from HSPCs exposed to each type of radiation was similar to that by controls.     

Xanthophyll-induced aggregation of LHCII as a switch between light-harvesting and energy dissipation systems

The xanthophyll cycle pigments, violaxanthin and zeaxanthin, present outside the light-harvesting pigment-protein complexes of Photosystem II (LHCII) considerably enhance specific aggregation of proteins as revealed by analysis of the 77 K chlorophyll a fluorescence emission spectra. Analysis of the infrared absorption spectra in the Amide I region shows that the aggregation is associated with formation of intermolecular hydrogen bonding between the α helices of neighboring complexes. The aggregation gives rise to new electronic energy levels, in the Soret region (530 nm) and corresponding to the Q spectral region (691 nm), as revealed by analysis of the resonance light scattering spectra. New electronic energy levels are interpreted in terms of exciton coupling of protein-bound photosynthetic pigments. The energy of the Q excitonic level of chlorophyll is not high enough to drive the light reactions of Photosystem II but better suited to transfer excitation energy to Photosystem I, which creates favourable energetic conditions for the state I-state II transition. The lack of fluorescence emission from this energy level, at physiological temperatures, is indicative of either very high thermal energy conversion rate or efficient excitation quenching by carotenoids. Chlorophyll a fluorescence was quenched up to 61% and 34% in the zeaxanthin- and violaxanthin-containing samples, respectively, as compared to pure LHCII. Enhanced aggregation of LHCII, observed in the presence of the xanthophyll cycle pigments, is discussed in terms of the switch between light-harvesting and energy dissipation systems.     

First solid-state NMR analysis of uniformly ¹³C-enriched major light-harvesting complexes from Chlamydomonas reinhardtii and identification of protein and cofactor spin clusters

The light-harvesting complex II (LHCII) is the main component of the antenna system of plants and green algae and plays a major role in the capture of sun light for photosynthesis. The LHCII complexes have also been proposed to play a key role in the optimization of photosynthetic efficiency through the process of state 1-state 2 transitions and are involved in down-regulation of photosynthesis under excess light by energy dissipation through non-photochemical quenching (NPQ). We present here the first solid-state magic-angle spinning (MAS) NMR data of the major light-harvesting complex (LHCII) of Chlamydomonas reinhardtii, a eukaryotic green alga. We are able to identify nuclear spin clusters of the protein and of its associated chlorophyll pigments in 13C-13C dipolar homonuclear correlation spectra on a uniformly 13C-labeled sample. In particular, we were able to resolve several chlorophyll 131 carbon resonances that are sensitive to hydrogen bonding to the 131-keto carbonyl group. The data show that 13C NMR signals of the pigments and protein sites are well resolved, thus paving the way to study possible structural reorganization processes involved in light-harvesting regulation through MAS solid-state NMR.     

Chlorophyll-protein complexes of a Codium species,including a light-harvesting siphonaxanthin-Chlorophylla ab-protein complex,an evolutionary relic of some Chlorophyta

Eight chlorophyll-protein complexes were isolated from thylakoid membranes of a Codium species, a marine green alga, by mild SDS-polyacrylamide gel electrophoresis. CP 1a¹, CP 1a², CP 1a³ and CP 1a⁴ were partially dissociated Photosystem (PS) I complexes, which in addition to the core reaction centre complex, CP 1, possessed PS I light-harvesting complexes containing chlorophyll (Chl) a, Chl b and siphonaxanthin. LHCP¹ and LHCP³ are orange-brown green chlorophyll $\text{a}\text{b-}\text{proteins}$ ($\text{Chl}\text{a}\text{Chl}\text{b}$ ratios of 0.66) that contain siphonaxanthin and its esterified form, siphonein. CP a and CP 1, the core reaction centre complexes of PS II and PS I, respectively, had similar spectral properties to those isolated from other algae or higher plants. These P-680- or P-700-Chl a-proteins are universally distributed among algae and terrestrial plants; they appear to be highly conserved and have undergone little evolutionary adaptation. Siphonaxanthin and siphonein which are present in the Codium light-harvesting complexes of PS II and PS I are responsible for enhanced absorption in the green region (518 and 538 nm). Efficient energy transfer from both xanthophylls and Chl b to only Chl a in Codium light-harvesting complexes, which have identical fluorescence emission spectra at 77 K to those of the lutein-Chl $\text{a}\text{b-}\text{proteins}$ ($\text{Chl}\text{a}\text{Chl}\text{b}$ ratios of 1.2) of most green algae and all higher plants, proved that the molecular arrangement of these light-harvesting pigments was maintained in the isolated Codium complexes. The siphonaxanthin-Chl $\text{a}\text{b-}\text{proteins}$ allow enhanced absorption of blue-green and green light, the predominant light available in deep ocean waters or shaded subtidal marine habitats. Since there is a variable distribution of lutein, siphonaxanthin and siphonein in marine green algae and siphonaxanthin is found in very ancient algae, these novel siphonein-siphonaxanthin-Chl $\text{a}\text{b-}\text{proteins}$ may be ancient light-harvesting complexes which were evolved in deep water algae.     

The quantum efficiency of photosynthesis in macroalgae and submerged angiosperms

Summary Photon absorption and photosynthesis under conditions of light limitation were determined in six temperate marine macroalgae and eight submerged angiosperms. Photon absorption and photosynthetic efficiency based on incident light increased in proportion to chlorophyll density per area and approached saturation at the highest densities (300 mg chlorophyll m^–2) encountered. Absorption and photosynthetic efficiency were higher in brown and red algae than in green algae and angiosperms for the same chlorophyll density because of absorption by accessory pigments. Among thin macroalgae and submerged angiosperms chlorophyll variations directly influence light absorption and photosynthesis, whereas terrestrial leaves have chlorophyll in excess and thus there is only a minor influence of pigment variability on light-limited photosynthesis. The quantum efficiency of photosynthesis averaged 0.062±0.019 (±SD) mol O₂ mol^–1 photons absorbed for macroalgae and, significantly less, 0.049±0.016 mol O₂ mol^–1 photons for submerged angiosperms. Of the measurements 80% were between 0.037 and 0.079 mol O₂ mol^–1 photons. The results are lower than values given in the literature for unicellular algae and terrestrial C₃ species at around 0.1 mol O₂ mol^–1 photons, but resemble values for other marine macroalgae and terrestrial C₄ species. The reason for these differences remains unknown, but may be sought for in differential operation of cyclic photophosphorylation and photorespiration.     

Excitation Energy Transfer between Pigments in Photosynthetic Cells

The excitation lifetimes of photosynthetic pigments and the times needed for energy transfer between pigments in various algae, were determined in vitro and in vivo. For this purpose, the time curves of fluorescence rise and decay were measured by means of Brody''s instrument (10), and compared with theoretical curves obtained by the method of “convolution of the first kind.”¹     

A Mechanism of Energy Dissipation in Cyanobacteria

When grown under a variety of stress conditions, cyanobacteria express the isiA gene, which encodes the IsiA pigment-protein complex. Overexpression of the isiA gene under iron-depletion stress conditions leads to the formation of large IsiA aggregates, which display remarkably short fluorescence lifetimes and thus a strong capacity to dissipate energy. In this work we investigate the underlying molecular mechanism responsible for chlorophyll fluorescence quenching. Femtosecond transient absorption spectroscopy allowed us to follow the process of energy dissipation in real time. The light energy harvested by chlorophyll pigments migrated within the system and eventually reaches a quenching site where the energy is transferred to a carotenoid-excited state, which dissipates it by decaying to the ground state. We compare these findings with those obtained for the main light-harvesting complex in green plants (light-harvesting complex II) and artificial light-harvesting antennas, and conclude that all of these systems show the same mechanism of energy dissipation, i.e., one or more carotenoids act as energy dissipators by accepting energy via low-lying singlet-excited S₁ states and dissipating it as heat.     

Alterations in architecture and metabolism induced by ultraviolet radiation-B in the carragenophyte <Emphasis Type="Italic">Chondracanthus teedei</Emphasis> (Rhodophyta,Gigartinales)

The in vivo effect of ultraviolet radiation-B (UVBR) in apical segments of Chondracanthus teedei was examined. Over a period of 7 days, the segments were cultivated and exposed to photosynthetically active radiation (PAR) at 80 μmol photons m⁻² s⁻¹ and PAR + UVBR at 1.6 W m⁻² for 3 h per day. The samples were processed for electron microscopy and histochemistry; also was analyzed growth rates, mitochondrial activity, protein levels, content of photosynthetic pigments and photosynthetic performance. UVBR elicited increased cell wall thickness and accumulation of plastoglobuli, changes in mitochondrial organization and destruction of chloroplast internal organization. Compared to controls, algae exposed to PAR + UVBR showed a growth rate reduction of 55%. The content of photosynthetic pigments, including chlorophyll a and phycobiliproteins, decreased after exposure to PAR + UVBR. This result agrees with the decreased photosynthetic performance observed after exposing algae to PAR + UVBR. Irradiation also elicited increased activity of the antioxidant enzyme glutathione peroxidase and decreased mitochondrial NADH dehydrogenase activity, which correlated with the decreased protein content in plants exposed to PAR + UVBR. Taken together, these findings strongly indicate that UVBR negatively affects the architecture and metabolism of the carragenophyte C. teedei.     

Utilizing the effective xanthophyll cycle for blooming of Ochromonas smithii and O. itoi (Chrysophyceae) on the snow surface

Snow algae inhabit unique environments such as alpine and high latitudes, and can grow and bloom with visualizing on snow or glacier during spring-summer. The chrysophytes Ochromonas smithii and Ochromonas itoi are dominant in yellow-colored snow patches in mountainous heavy snow areas from late May to early June. It is considered to be effective utilizing the xanthophyll cycle and holding sunscreen pigments as protective system for snow algae blooming in the vulnerable environment such as low temperature and nutrients, and strong light, however the study on the photoprotection of chrysophytes snow algae has not been shown. To dissolve how the chrysophytes snow algae can grow and bloom under such an extreme environment, we studied with the object of light which is one point of significance to this problem. We collected the yellow snows and measured photosynthetically active radiation at Mt. Gassan in May 2008 when the bloom occurred, then tried to establish unialgal cultures of O. smithii and O. itoi, and examined their photosynthetic properties by a PAM chlorophyll fluorometer and analyzed the pigment compositions before and after illumination with high-light intensities to investigate the working xanthophyll cycle. This experimental study using unialgal cultures revealed that both O. smithii and O. itoi utilize only the efficient violaxanthin cycle for photoprotection as a dissipation system of surplus energy under prolonged high-light stress, although they possess chlorophyll c with diadinoxanthin.