Immunocytochemical localization of photosystem I and the fucoxanthin-chlorophylla/c light-harvesting complex in the diatomPhaeodactylum tricornutum

Summary iserum against two polypeptides of the major fucoxanthin-chlorophylla/c light-harvesting complex of the diatomPhaeodactylum tricornutum and heterologous antiserum against purified photosystem I particles of maize were used to localize these two complexes on the thylakoid membranes ofP. tricornutum. As in many chromophyte algae, the thylakoids are loosely appressed and organized into extended bands of three, giving a ratio of 21 for appressed versus non-appressed membranes. Immunoelectron microscopy demonstrated that the fucoxanthin-chlorophylla/c light-harvesting complex, which is believed to be associated with photosystem II, was equally distributed on the appressed and non-appressed thylakoid membranes. Photosystem I was also found on both types of membranes, but was slightly more concentrated on the two outer non-appressed membranes of each band. Similarly, photosystem I activity, as measured by the photooxidation of 3,3-diaminobenzidine, was higher in the outer thylakoids than in the central thylakoid of each band. We conclude that the thylakoids of diatoms differ from those of green algae and higher plants in their macromolecular organization as well as in their morphological arrangement.Abbreviations BSA bovine serum albumin - DAB 3,3-diaminobenzidine - FCPC fucoxanthin-chlorophylla/c light-harvesting complex - LHC light-harvesting complex - PBS phosphate-buffered saline - PS photosystem     

Leaf senescence in a non-yellowing mutant of Festuca pratensis Huds.

A study was made of linolenic acid-dependent oxidative chlorophyll bleaching (CHLOX) by thylakoid membranes from senescing leaf tissue of a normal cultivar (cv. Rossa) and a non-yellowing mutant genotype (Bf 993) of Festuca pratensis Huds. To overcome the problem of variation in levels of endogenous chlorophyll substrate in membranes from different sources, light-harvesting complex (LHC) was used to supplement thylakoid pigment. It was shown that CHLOX is associated with both Photosystem I and LHC-rich thylakoid subfractions but that purified LHC has negligible associated CHLOX activity and stimulates the rate of bleaching by isolated entire chloroplast membranes. Non-senescent tissue of Bf 993 and Rossa had essentially identical thylakoid CHLOX levels, which subsequently declined during senescence in darkness. The half-life of CHLOX from the mutant was three times greater than that of the normal genotype. In both cultivars, the amount of CHLOX assayed in thylakoids isolated at different times during senescence was more than adequate to support the corresponding in-vivo rate of pigment degradation as calculated from the half-life for chlorophyll. It was concluded that the non-yellowing mutation is not expressed through a lack of CHLOX activity. The role of linolenic acid metabolism in the regulation of thylakoid structure and function during senescence, and as a likely site of the non-yellowing lesion, are discussed.Abbreviations CHLOX linolenic acid-dependent oxidative chlorophyll bleaching activity - CHLPX chlorophyll peroxidase - CPI chlorophyll-protein complex I - LHC light-harvesting complex - LNA linolenic acid - PSI photosystem I - PSII photosystem II - S relative senescence rate - t _1/2 lialf time for degradation     

The supramolecular architecture, function, and regulation of thylakoid membranes in red algae: an overview

Red algae are a group of eukaryotic photosynthetic organisms. Phycobilisomes (PBSs), which are composed of various types of phycobiliproteins and linker polypeptides, are the main light-harvesting antennae in red algae, as in cyanobacteria. Two morphological types of PBSs, hemispherical- and hemidiscoidal-shaped, are found in different red algae species. PBSs harvest solar energy and efficiently transfer it to photosystem II (PS II) and finally to photosystem I (PS I). The PS I of red algae uses light-harvesting complex of PS I (LHC I) as a light-harvesting antennae, which is phylogenetically related to the LHC I found in higher plants. PBSs, PS II, and PS I are all distributed throughout the entire thylakoid membrane, a pattern that is different from the one found in higher plants. Photosynthesis processes, especially those of the light reactions, are carried out by the supramolecular complexes located in/on the thylakoid membranes. Here, the supramolecular architecture, function and regulation of thylakoid membranes in red algal are reviewed.     

IMMUNOLOGICAL AND ULTRASTRUCTURAL CHARACTERIZATION OF THE PHOTOSYNTHETIC COMPLEXES OF THE PROCHLOROPHYTE PROCHLOROCOCCUS (OXYCHLOROBACTERIA)

Ultrastructural features and immunological properties of some thylakoid proteins were examined in two strains of the prochlorophyte Prochlorococcus and compared to those of other photosynthetic prokaryotes and eukaryotes. Both strains exhibited two or three rows of tightly appressed thylakoidal membranes, located at the cell periphery. However, thylakoids were concentrically arranged in the strain from the Sargasso Sea (SARG) and horseshoe-shaped in the Mediterranean isolate (CCMP 1378). Although lacking phycobilisomes, both cell types shared with cyanobacteria the presence of carboxysome-like structures and glycogen granules as storage compounds. The main thylakoid polypeptides separated by sodium dodecyl sulfate—polyacrylamide gel electrophoresis were characterized by Western blotting using several antibodies. The 30-kDa polypeptide of the light-harvesting complex (LHC) of Prochlorococcus showed a weak positive immunological cross-reaction with an antibody raised against the 32-kDa apoprotein of the LHC of the prochlorophyte Prochlorothrix hollandica. In contrast, it showed no immunological relationships with the chlorophyll a/b (Chl a/b) LHCs of green algae and higher plants. Protein membranes from Prochlorococcus strongly cross-reacted with antibodies raised against reaction center polypeptides of photosystems II and I (PSs II and I) of other photosynthetic organisms, confirming the high degree of conservation of these basic compounds of the photosynthetic machinery during evolution. Immunolocalization of thylakoid proteins showed that the LHC proteins, the major PS II reaction center proteins (CP 43 and D2), and the PS I reaction center proteins were equally distributed within the thylakoid membranes in contrast to the segregation observed in higher plants and green alga thylakoids. We also identified ribulose-1, 5-bisphosphate carboxylase/oxygenase in the carboxysomes. These results suggest that Prochlorococcus is more closely related to cyanobacteria than to green plastids even though it contains Chl b.     

Biogenesis of thylakoid membranes with emphasis on the process in Chlamydomonas

Recent results obtained by electron microscopic and biochemical analyses of greening Chlamydomonas reinhardtii y1 suggest that localized expansion of the plastid envelope is involved in thylakoid biogenesis. Kinetic analyses of the assembly of light-harvesting complexes and development of photosynthetic function when degreened cells of the alga are exposed to light suggest that proteins integrate into membrane at the level of the envelope. Current information, therefore, supports the earlier conclussion that the chloroplast envelope is a major biogenic structure, from which thylakoid membranes emerge. Chloroplast development in Chlamydomonas provides unique opportunities to examine in detail the biogenesis of thylakoids.Abbreviations Rubisco ribulose bisphosphate carboxylase/oxygenase - CAB Chl a/b-binding (proteins) - Chlide chlorophyllide - LHC I light-harvesting complex of PS I - LHC II light-harvesting complex of PS II - Pchlide protochlorophyllide     

The effect of the dark interval in intermittent light on thylakoid development: photosynthetic unit formation and light harvesting protein accumulation

Etiolated bean plants were grown in intermittent light with dark intervals of shorter or longer duration, to modulate the rate of chlorophyll accumulation, relative to that of the other thylakoid components formed. We thus produced conditions under which chlorophyll becomes more or less a limiting factor. We then tested whether LHC complexes can be incorporated in the thylakoid. It was found that an equal amount of chlorophyll, formed under the same total irradiation received, may be used for the stabilization of few and large-in-size PS units containing LHC components (short dark-interval intermittent light), or for the stabilization of many and small-in-size PS units with no LHC components (long dark-interval intermittent light). The size of the PS units diminishes as the dark-interval duration is increased, with no further change after 98 minutes. The PSII/cytf ratio remains constant throughout development in intermittent light and equal to that of mature chloroplasts (PSII/cytf = 1) except in the case of very long dark-interval regimes, where about half PSII units per cytf are present. The PSII/PSI ratio was found to be correlated with the PSII unit size (the larger the size, the lower the ratio). The number of PSI units operating on the same electron transfer chain varied depending on the size of the PSII unit (the larger the PSII unit size, the more the PSI units per chain). The results suggest that it is not the chlorophyll content per se which regulates the stabilization of LHC in developing thylakoids and consequently the size of the PS units, but rather the rate by which it is accumulated, relative to that of the other thylakoid components.Abbreviations Chl Chlorophyll - CL Continuous light - CPa the reaction center complex of PSII - CPI the reaction center complex of PSI - CPIa Chlorophyll protein complex containing the CPI and the light harvesting complex of PSI - fr w fresh weight - LDC Light dark cycles - LHC-I Light-harvesting complex of PSI - LHC-II Light harvesting complex of PSII - PS photosystem - PSI photosystem I - PSII photosystem II     

Light-induced fluorescence quenching in the light-harvesting chlorophyll a/b protein complex

Summary Irradiation of the principal photosystem II light-harvesting chlorophyll-protein antenna complex, LHC II, with high light intensities brings about a pronounced quenching of the chlorophyll fluorescence. Illumination of isolated thylakoids with high light intensities generates the formation of quenching centres within LHC II in vivo, as demonstrated by fluorescence excitation spectroscopy. In the isolated complex it is demonstrated that the light-induced fluorescence quenching: a) shows a partial, biphasic reversibility in the dark; b) is approximately proportional to the light intensity; c) is almost independent of temperature in the range 0–30°C; d) is substantially insensitive to protein modifying reagents and treatments; e) occurs in the absence of oxygen. A possible physiological importance of the phenomenon is discussed in terms of a mechanism capable of dissipating excess excitation energy within the photosystem II antenna.Abbreviations chla chlorophyll a - chlb chlorophyll b - F₀ fluorescence yield with reaction centers open - F_m fluorescence yield with reaction centres closed - F_i fluorescence at the plateau level of the fast induction phase - LHC II light-harvesting chlorophyll a/b protein complex II - PS II photosystem II - PSI photosystem I - Tricine N-[2-hydroxy-1,1-bis(hydroxymethyl)ethyl]glycine     

CHARACTERIZATION OF THE LIGHT-HARVESTING COMPLEX OF GIRAUDYOPSIS STELLIFER (CHRYSOPHYCEAE) AND EFFECTS OF LIGHT STRESS1

The light-harvesting complex (LHC) of Giraudyopsis stellifer Dangeard was isolated on a sucrose density gradient after digitonin treatment, and the pigment composition was analyzed by reverse-phase high-pressure liquid chromatography. The LHC is a chlorophyll (Chl) a/c/ fucoxanthin/violaxanthin complex, depleted of β-carotene, comparable to the LHC of Fucophyceae. The excitation transfer from Chl c and fucoxanthin to Chl a is efficient in whole cells. Immunological reactions indicate a close relationship between Chrysophyceae and Fucophyceae. The immunocytochemical labeling confirms the lack of segregation of the LHC in the appressed membranes of the three associated thylakoids and its localization in the intrapyrenoid thylakoid. The violaxanthin-antheraxanthin-zeaxanthin cycle is operative in the cells and efficiently protects photosystem II reaction centers against photoinhibition.     

The role of chlorophyll-protein complexes in the function and structure of chloroplast thylakoids

Summary The photosynthetic pigments of chloroplast thylakoid membranes are complexed with specific intrinsic polypeptides which are included in three supramolecular complexes, photosystem I complex, photosystem II complex and the light-harvesting complex. There is a marked lateral heterogeneity in the distribution of these complexes along the membrane with photosystem II complex and its associated light-harvesting complex being located mainly in the stacked membranes of the grana partitions, while photosystem I complex is found mainly in unstacked thylakoids together with ATP synthetase. In contrast, the intermediate electron transport complex, the cylochrome b-f complex, is rather uniformly distributed in these two membrane regions. The consequences of this lateral heterogeneity in the location of the thylakoid complexes are considered in relation to the function and structure of chloroplasts of higher plants.     

Characterization of photosystem I antenna proteins in the prasinophyte Ostreococcus tauri

Prasinophyceae are a broad class of early-branching eukaryotic green algae. These picophytoplankton are found ubiquitously throughout the ocean and contribute considerably to global carbon-fixation. Ostreococcus tauri, as the first sequenced prasinophyte, is a model species for studying the functional evolution of light-harvesting systems in photosynthetic eukaryotes. In this study we isolated and characterized O. tauri pigment-protein complexes. Two photosystem I (PSI) fractions were obtained by sucrose density gradient centrifugation in addition to free light-harvesting complex (LHC) fraction and photosystem II (PSII) core fractions. The smaller PSI fraction contains the PSI core proteins, LHCI, which are conserved in all green plants, Lhcp1, a prasinophyte-specific LHC protein, and the minor, monomeric LHCII proteins CP26 and CP29. The larger PSI fraction contained the same antenna proteins as the smaller, with the addition of Lhca6 and Lhcp2, and a 30% larger absorption cross-section. When O. tauri was grown under high-light conditions, only the smaller PSI fraction was present. The two PSI preparations were also found to be devoid of the far-red chlorophyll fluorescence (715-730 nm), a signature of PSI in oxygenic phototrophs. These unique features of O. tauri PSI may reflect primitive light-harvesting systems in green plants and their adaptation to marine ecosystems. Possible implications for the evolution of the LHC-superfamily in photosynthetic eukaryotes are discussed.     

Cytochrome b 6 f complex: Dynamic molecular organization,function and acclimation

The cytochrome b ₆ f complex occupies a central position in photosynthetic electron transport and proton translocation by linking PS II to PS I in linear electron flow from water to NADP⁺, and around PS I for cyclic electron flow. Cytochrome b ₆ f complexes are uniquely located in three membrane domains: the appressed granal membranes, the non-appressed stroma thylakoids and end grana membranes, and also the non-appressed grana margins, in contrast to the marked lateral heterogeneity of the localization of all other thylakoid multiprotein complexes. In addition to its vital role in vectorial electron transfer and proton translocation across the membrane, cytochrome b ₆ f complex is also involved in the regulation of balanced light excitation energy distribution between the photosystems, since its redox state governs the activation of LHC II kinase (the kinase that phosphorylates the mobile peripheral fraction of the chlorophyll a/b-proteins of LHC II of PS II). Hence, cytochrome b ₆ f complex is the molecular link in the interactive co-regulation of light-harvesting and electron transfer.The importance of a highly dynamic, yet flexible organization of the thylakoid membranes of plants and green algae has been highlighted by the exciting discovery that a lateral reorganization of some cytochrome b ₆ f complexes occurs in the state transition mechanism both in vivo and in vitro (Vallon et al. 1991). The lateral redistribution of phosphorylated LHC II from stacked granal membrane regions is accompanied by a concomitant movement of some cytochrome b ₆ f complexes from the granal membranes out to the PS I-containing stroma thylakoids. Thus, the dynamic movement of cytochrome b ₆ f complex as a multiprotein complex is a molecular mechanism for short-term adaptation to changing light conditions. With the concept of different membrane domains for linear and cyclic electron flow gaining credence, it is thought that linear electron flow occurs in the granal compartments and cyclic electron flow is localised in the stroma thylakoids at non-limiting irradiances. It is postulated that dynamic lateral reversible redistribution of some cytochrome b ₆ f complexes are part of the molecular mechanism involved in the regulation of linear electron transfer (ATP and NADPH) and cyclic electron flow (ATP only). Finally, the molecular significance of the marked regulation of cytochrome b ₆ f complexes for long-term regulation and optimization of photosynthetic function under varying environmental conditions, particularly light acclimation, is discussed.Abbreviations Chl chlorophyll - cyt cytochrome - PS Photosystem     

Light regulation of photosynthetic membrane structure,organization, and function

The light environment during plant growth determines the structural and functional properties of higher plant chloroplasts, thus revealing a dynamically regulated developmental system. Pisum sativum plants growing under intermittent illumination showed chloroplasts with fully functional photosystem (PS) II and PSI reaction centers that lacked the peripheral chlorophyll (Chi) a/b and Chl a light-harvesting complexes (LHC), respectively. The results suggest a light flux differential threshold regulation in the biosynthesis of the photosystem core and peripheral antenna complexes. Sun-adapted species and plants growing under far-red-depleted illumination showed grana stacks composed of few (3–5) thylakoids connected with long intergrana (stroma) thylakoids. They had a PSII/PSI reaction center ratio in the range 1.3–1.9. Shade-adapted species and plants growing under far-red-enrichcd illumination showed large grana stacks composed of several thylakoids, often extending across the entire chloroplast body, and short intergrana stroma thylakoids. They had a higher PSII/PSI reaction center ratio, in the range of 2.2–4.0. Thus, the relative extent of grana and stroma thylakoid formation corresponds with the relative amounts of PSII and PSI in the chloroplast, respectively. The structural and functional adaptation of the photosynthetic membrane system in response to the quality of illumination involves mainly a control on the rate of PSII and PSI complex biosynthesis.     

Modification of excitation energy distribution to photosystem I by protein phosphorylation and cation depletion during thylakoid biogenesis in wheat

The effects of protein phosphorylation and cation depletion on the electron transport rate and fluorescence emission characteristics of photosystem I at two stages of chloroplast development in light-grown wheat leaves are examined. The light-harvesting chlorophyll a/b protein complex associated with photosystem I (LHC I) was absent from the thylakoids at the early stage of development, but that associated with photosystem II (LHC II) was present. Protein phosphorylation produced an increase in the light-limited rate of photosystem I electron transport at the early stage of development when chlorophyll b was preferentially excited, indicating that LHC I is not required for transfer of excitation energy from phosphorylated LHC II to the core complex of photosystem I. However, no enhancement of photosystem I fluorescence at 77 K was observed at this stage of development, demonstrating that a strict relationship between excitation energy density in photosystem I pigment matrices and the long-wavelength fluorescence emission from photosystem I at 77 K does not exist. Depletion of Mg²⁺ from the thylakoids produced a stimulation of photosystem I electron transport at both stages of development, but a large enhancement of the photosystem I fluorescence emission was observed only in the thylakoids containing LHC I. It is suggested that the enhancement of PS I electron transport by Mg²⁺-depletion and phosphorylation of LHC II is associated with an enhancement of fluorescence at 77 K from LHC I and not from the core complex of PS I.     

Ultrastructure and freeze-fracture studies of the thylakoids ofMantoniella squamata (Prasinophyceae)

Summary The ultrastructure and the supramolecular organization of the thylakoids of the small green flagellate,Mantoniella squamata, were examined in thin sections and freeze-fracture preparations. The whole chloroplast is tightly packed with thylakoids, which show a pattern of meandering, branching and/or anastomosing membranes. In freeze-fracture preparations only two fracture-faces can be distinguished: the PF- and the EF-face. The PF-face has a much higher particle density than the EF-face (PF: 4086 particles/m²; EF: 865 particles/m²). The EF-face is not as uniform as the PF-face. The areas which are packed with particles probably correspond to closely appressed thylakoid regions or adhesive patches, noticed in thin sections in some areas. The mean particle size on both faces is also different (EF: 10.5 nm; PF: 8.6 nm), but no information about the classification of the particles to special protein complexes is available at this time.Abbreviations chl chlorophyll - EF exoplasmic fracture face - ER endoplasmic reticulum - LHC light-harvesting chlorophyll-protein complex - PF protoplasmic fracture face - PS I photosystem I - PS II photosystem II     

The major light-harvesting complex of Photosystem II: aspects of its molecular and cell biology

The light-harvesting complex of photosystem II (LHC II) contains one major (LHC IIb) and at least three minor chlorophyll-protein components. The apoproteins of LHC IIb (LHCP) are encoded by nuclear genes and synthesized in the cytoplasm as a higher molecular weight precursor(s) (pLHCP). Several genes coding for pLHCP have been cloned from various higher plant species. The expression of these genes is dependent upon a variety of factors such as light, the developmental stage of the plastids and the plant. After its synthesis in the cytoplasm, pLHCP is imported into plastids, inserted into thylakoids, processed to its mature form, and assembled into LHC IIb. The pathway of assembly of LHC IIb in the thylakoid membranes is currently being investigated in several laboratories. We present a model that gives some details of the steps in the assembly process. Many of the steps involved in the synthesis and assembly are dependent on light and the stage of plastid development.Abbreviations PS Photosystem - LHC II Light-harvesting complex of PS II - LHCP Apoproteins of LHC IIb - pLHCP Precursor of LHCP - PAGE Polyacrylamide gel electrophoresis     

Evidence for an association of the early light-inducible protein (ELIP) of pea with photosystem II

The precursor to the nuclear-coded 17 kDa early light-inducible protein (ELIP) of pea has been transported into isolated intact chloroplasts. The location of the mature protein in the thylakoid membranes was investigated after using cleavable crosslinkers such as DSP and SAND in conjunction with immuno-fractionation methods and by application of mild detergent fractionation. We show that ELIP is integrated into the membranes via the unstacked stroma thylakoids. After isolation of protein complexes by solubilization of membranes with Triton X-100 and sucrose density-gradient centrifugation the crosslinked ELIP comigrates with the PS II core complex. Using SAND we identified ELIP as a 41–51 kDa crosslinked product while with DSP four products of 80 kDa, 70 kDa, 50–42 kDa and 23–21 kDa were found. The immunoprecipitation data suggested that the D₁-protein of the PS II complex is one of the ELIP partners in crosslinked products.Abbreviations chl chlorophyll - D₁ herbicide-binding protein - DSP dithiobis-(succinimidylpropionate) - ELIP early light-inducible protein - LHC I and LHC II light-harvesting chlorophyll a/b complex associated with photosystem I or II - PAGE polyacrylamide gel electrophoresis - poly(A)-rich RNA polyadenyd mRNA - PS I and PS II photosystems I and II - SAND sulfosuccinimidyl 2-(m-azido-o-nitro-benzamido)-ethyl-1,3-dithiopropionate - Triton X-100 octylphenoxypolyethoxyethanol     

Functional assembly in vitro of phycobilisomes with isolated photosystem II particles of eukaryotic chloroplasts

Phycobiliproteins obtained by dissociation of phycobilisomes were reassociated in vitro with intact thylakoids or isolated photosystems I and II preparations obtained from cyanophytes (prokaryotes) or green algae (eukaryotes) to form bound phycobilisome complexes. Energy transfer from Fremyella diplosiphon phycobiliproteins to chlorophyll a of reaction centers I and II was measured in: complexes containing intact thylakoids of the cyanophytes F. diplosiphon or Anacystis nidulans and the eukaryotic algae Euglena gracilis and mutants of Chlamydomonas reinhardtii; complexes containing isolated photosystem II particles of A. nidulans or C. reinhardtii; and complexes containing reaction center I of F. diplosiphon or C. reinhardtii. Energy transfer from phycoerythrin to chlorophyll a of photosystem II could be demonstrated in complexes containing phycobilisomes bound to cyanophyte thylakoids or isolated photosystem II particles of A. nidulans or C. reinhardtii. Bound phycobilisomes did not transfer energy to photosystem II within green algae thylakoids containing altered forms of light-harvesting chlorophyll a/b-protein complex (LHC) II antenna, reduced amounts of LHC II, or chlorophyll b, or chlorophyll b-less mutants, nor to chlorophyll a of photosystem I of intact thylakoids or isolated reaction centers. We conclude that phycobilisomes can form a specific and functional association with photosystem II particles of both cyanophytes and eukaryotic thylakoids. This interaction appears to be hindered by the presence of LHC II antenna in the eukaryotic thylakoids.     

CHARACTERIZATION OF PHOTOSYSTEM I-ASSOCIATED POLYPEPTIDES FROM THE CHLOROPHYLL b-RICH ALGA TETRASELMIS SPP. (PLEURASTROPHYCEAE) AND OTHER CHLOROPHYTE ALGAE1

The phylogenetic distribution of photosystem I-associated polypeptides was assessed by immunoblotting algal thylakoid membrane polypeptides with antisera generated against the P700-chlorophyll a protein (CC I) and a photosystem I light-harvesting chlorophyll-protein (LHC Ib). Polypeptides cross-reacting with the CC I apoprotein were found in 20 species representing four classes of unicellular algae. Polypeptides sharing antigenicity with spinach LHC Ib were observed only in algal species containing chlorophyll b. Tetraselmis spp. (Pleurastrophyceae), rich in chlorophyll b (Chl a:b 1.2), exhibited marked heterogeneity in the composition of their CC I and LHC Ib cross-reactive polypeptides. When immunoblotted with antisera against CC I, all Tetraselmis clones examined exhibited a 25-kD polypeptide in greater abundance than the 58-kD CC I apoprotein characteristic of higher plants and other green algal thylakoids. Three Tetraselmis clones (RG 6, RG 11, and RG 12) exhibited an 81-kD polypeptide with strong antigenicity toward the LHC Ib antisera, in contrast to the 17- to 24-kD cross-reactive polypeptides found in spinach, green algae, and one Tetraselmis clone (RG 5). Associated with the unique photosystem I polypeptide composition in Tetraselmis spp., Chl: P700 ratios for the group are 2–5 times greater than those observed for higher plants or other green algae. The chlorophyll b enrichment, unusual composition of photosystem I cross-reactive polypeptides, and heterogeneity of these polypeptides within isolates of Tetraselmis might make this genus useful for investigations of the functional organization of chlorophyll b in light-harvesting systems. These features also support the view of an alternative phyletic origin for the Pleurastrophyceae.     

Immunogold localization of LHC II proteins in chloroplasts with different degrees of grana stacking induced by SAN-9789.

The amount and distribution of proteins of the light-harvesting complex associated with photosystem II (PS II) were investigated using immunogold labelling of chloroplasts of wheat ( Triticum aestivum L. cv. Walde). The seedlings were grown in weak red light (16 mW m⁻²) after imbibition of grains with SAN-9789 (Norflurazon, 0.028 to 28 mg I⁻¹). Chloroplasts of these plants exhibited thylakoids with different degrees of stacking. Thylakoids of untreated plants grown in a greenhouse had most gold particles per unit membrane length in both appressed and non-appressed regions compared to red light grown plants. The ratios of labelling between appressed and non-appressed membranes were fairly constant in red light- and greenhouse-grown plants. The labelling densities were 2.5–3 times higher in the appressed thylakoids compared to the non-appressed thylakoids. However, at a SAN concentration of 2.8 mg I⁻¹ there was a sharp decrease in thylakoid appressions and in labelling density of both appressed and non-appressed membranes. The total amount of particles per chloroplast was also much lower as compared to that at lower SAN concentrations. Plants treated with the highest concentration of SAN (28 mg I⁻¹) contained chloroplasts devoid of normal grana structures. In these plastids, the thylakoids were elongated and single. The labelling density in these membranes was ca 50% of that observed at 2.8 mg I⁻¹. This paper thus supports earlier observations that proteins of the light-harvesting complex of PS II (LHC II) are mainly localized in the appressed regions of the grana membranes, and may be involved in the formation of grana.     

Composition and Characteristic Differences in Photosynthetic Membranes of Two Ecotypes of Reed (Phragmites communis L.) from Different Habitats

As compared with the swamp reed (SR) ecotype of Phragmites communis growing in the desert region of northwest China, plants of the dune reed (DR) ecotype from the same region possessed lower chlorophyll (Chl) content in leaves, and less thylakoids and grana stacks in chloroplasts. Tube gel electrophoresis without stain showed that the contents of Chl-protein (Pro) components related to photosystem 2 (PS2) were markedly lower in the DR thylakoid membranes than in the SR thylakoid membranes, while the contents of Chl-Pro components associated with PS1 were almost the same in both types. SDS-PAGE analysis indicated that the content of polypeptides of the light-harvesting Chl a/b complex of PS2 (LHC2) was lower in the DR thylakoids. Besides, the conformation of LHC2 within the DR thylakoid membranes was also altered as indicated by circular dichroism spectra. Hence in the DR, reduced energy harvesting by declining the size of LHC2 might be responsible for the down-regulated PS2 activity. Chl fluorescence parameters. F_v/F_m and quantum efficiency of PS2 (_PS2), were lower in the DR leaves than in the SR ones. However, non-photochemical quenching coefficient (q_N) was greater in DR than that in SR, implying other energy dissipation way exists in the DR photosynthetic membranes.