Carotenoid distribution and deepoxidation in thylakoid pigment-protein complexes from cotton leaves and bundle-sheath cells of maize

In response to excess light, the xanthophyll violaxanthin (V) is deepoxidized to zeaxanthin (Z) via antheraxanthin (A) and the degree of this deepoxidation is strongly correlated with dissipation of excess energy and photoprotection in PS II. However, little is known about the site of V deepoxidation and the localization of Z within the thylakoid membranes. To gain insight into this problem, thylakoids were isolated from cotton leaves and bundle-sheath strands of maize, the pigment protein-complexes separated on Deriphat gels, electroeluted, and the pigments analyzed by HPLC. In cotton thylakoids, 30% of the xanthophyll cycle pigments were associated with the PS I holocomplex, including the PS I light-harvesting complexes and PS I core complex proteins (CC I), and about 50% with the PS II light-harvesting complexes (LHC II). The Chl was evenly distributed between PS I and PS II. Less than 2% of the neoxanthin, about 18% of the lutein, and as much as 76% of the -carotene of the thylakoids were associated with PS I. Exposure of pre-darkened cotton leaves to a high photon flux density for 20 min prior to thylakoid isolation caused about one-half of the V to be converted to Z. The distribution of Z among the pigment-protein complexes was found to be similar to that of V. The distribution of the other carotenoids was unaffected by the light treatment. Similarly, in field-grown maize leaves and in the bundle-sheath strands isolated from them, about 40% of the V present at dawn had been converted to Z at solar noon. Light treatment of isolated bundle-sheath strands which initially contained little Z caused a similar degree of conversion of V to Z. As in cotton thylakoids, about 30% the V+A+Z pool in bundle-sheath thylakoids from maize was associated with the PS I holocomplex and the CC I bands and 46% with the LHC II bands, regardless of the extent of deepoxidation. These results demonstrate that Z is present in PS I as well as in PS II and that deepoxidation evidently takes place within the pigment-protein complexes of both photosystems.Abbreviations A antheraxanthin - CC I, CC II Core or reaction center complex of PS I, PS II - CP Chl protein - EPS epoxidation state - F_m Chl fluorescence at closed PS II reaction centers - IEF isoelectric focussing gels - LHC I, LHC II light-harvesting complex of PS I, PS II - OE oxygen evolving polypeptide - PFD photon flux density - PS I^* PS I holocomplex - V violaxanthin - Z zeaxanthin - antibody against C.I.W.-D.P.B. Publication No. 1127.     

Role of Light-harvesting Complex 2 Dissociation in Protecting the Photosystem 2 Reaction Centres Against Photodamage in Soybean Leaves and Thylakoids

The protective role of light-harvesting complex 2 (LHC2) dissociation from photosystem 2 (PS2) complex was explored by the 5-p-fluorosulfonylbenzoyl adenosine (FSBA, an inhibitor of protein kinase) treatment at saturating irradiance (SI) in soybean leaves and thylakoids. The dissociation of some LHC2s from PS2 complex occurred after SI treatment, but FSBA treatment inhibited the dissociation as demonstrated by analysis of sucrose density gradient centrifugation of thylakoid preparation and low-temperature (77 K) chlorophyll (Chl) fluorescence. A significant increase in F₀ and decrease in F_v/F_m occurred after SI, and the two parameters could largely recover to the levels of dark-adapted leaves after subsequent 3 h in the dark, but they could not recover in the FSBA-treated leaves at SI. Neither the electron transport activity of PS2 nor the D1 protein amount in vivo had significant change after SI without FSBA, whereas FSBA treatment at SI could result in significant decreases in both the PS2 electron transport activity and the D1 protein amount. When thylakoids instead of leaves were used, the PS2 electron transport activity and the D1 protein amount declined more after SI with FSBA than without FSBA. The phosphorylation level of PS2 core proteins increased, while the phosphorylation level of LHC2 proteins was reduced after SI. Also, the phosphorylation of PS2 core proteins could be greatly inhibited by the FSBA treatment at SI. Hence in soybean leaf the LHC2 dissociation is an effective strategy protecting PS2 reaction centres against over-excitation and photodamage by reducing the amount of photons transferred to the centres under SI, and the phosphorylation of PS2 core proteins plays an important role in the dissociation.     

Development of Photosystem II in dark grown Chlamydomonas reinhardtii. A light-dependent conversion of PS IIβ, QB-nonreducing centers to the PS IIα, QB-reducing form

The green alga Chlamydomonas reinhardtii is a facultative heterotroph and, when cultured in the presence of acetate, will synthesize chlorophyll (Chl) and photosystem (PS) components in the dark. Analysis of the thylakoid membrane composition and function in dark grown C. reinhardtii revealed that photochemically competent PS II complexes were synthesized and assembled in the thylakoid membrane. These PS II centers were impaired in the electron-transport reaction from the primary-quinone electron acceptor, Q_A, to the secondary-quinone electron acceptor, Q_B (Q_B-nonreducing centers). Both complements of the PS II Chl a–b light harvesting antenna (LHC II-inner and LHC II-peripheral) were synthesized and assembled in the thylakoid membrane of dark grown C. reinhardtii cells. However, the LHC II-peripheral was energetically uncoupled from the PS II reaction center. Thus, PS II units in dark grown cells had a -type Chl antenna size with only 130 Chl (a and b) molecules (by definition, PS II units lack LHC II-peripheral). Illumination of dark grown C. reinhardtii caused pronounced changes in the organization and function of PS II. With a half-time of about 30 min, PS II centers were converted froma Q_B-nonreducing form in the dark, to a Q_B-reducing form in the light. Concomitant with this change, PS II units were energetically coupled with the LHC II-peripheral complement in the thylakoid membrane and were converted to a PS II form. The functional antenna of the latter contained more than 250 Chl(a+b) molecules. The results are discussed in terms of a light-dependent activation of the Q_A-Q_B electron-transfer reaction which is followed by association of the PS II unit with a LHC II-peripheral antenna and by inclusion of the mature form of PS II (PS II) in the membrane of the grana partition region.Abbreviations Chl chlorophyll - PS photosystem - Q_A primary quinone electron acceptor of PS II - Q_B secondary quinone electron acceptor of PS II - LHC light harvesting complex - F₀ non-variable fluorescence yield - F_plf intermediate fluorescence yield plateau leyel - F_max maximum fluorescence yield - F_i initial fluorescence yield increase from F₀ to F_pl (F_pl–F₀) - F_v total variable fluorescence yield (F_m–F0) - DCMU dichlorophenyl-dimethylurea     

The quenching characteristics of potassium iridic chloride and their meaning for the origin of chlorophyll fluorescence components

To understand the origins of the different lifetime components of photosystem 2 (PS2) chlorophyll (Chl) fluorescence we have studied their susceptibility to potassium iridic chloride (K₂IrCl₆) which has been shown to bleach antenna pigments of photosynthetic bacteria (Loach et al. 1963). The addition of K₂IrCl₆ to PS2 particles gives rise to a preferential quenching of the variable Chl fluorescence (F_v). At concentrations lower than 20 M, this is brought about mainly by a decrease in the yield, but not in the lifetime, of the slowest component when all the PS2 reaction centres are closed (F_M). The yield of the middle and fast decays are not significantly altered. This type of quenching is not seen with DNB. The iridate-induced quenching of the initial fluorescence level (F₀) is due to a proportional decrease in the yield and lifetime of the three components and correlates with the observed modification in the relative quantum yield of oxygen evolution. In this concentration range a bleaching of Chl a is seen. At higher iridate levels, greater than 20 M, a proportional decrease in the lifetimes and yields of the three kinetic components is seen at F_M. These changes are associated with a carotenoid bleaching. In isolated light harvesting Chl a/b complexes of PS2 (LHC2), iridate addition converts a 4 ns decay into a 200 ps emission and both types of bleaching are observed. By also measuring the rate of PS2 trap closure versus iridate concentration, we have discussed the results in terms of excitation energy transfer.Abbreviations DNB m-dinitrobenzene - F_M maximum Chl fluorescence - F₀ initial fluorescence - F_v variable fluorescence - I pheophytin a primary electron acceptor of PS2 - P₆₈₀ chlorophyll a of photochemical centre - PS2 photosystem 2 - Q_A primary stable electron acceptor of PS2 - Chl chlorophyll - LHC2 light harvesting Chl a/b complex of PS2 - MES 2(N-morpholino) ethanesulfonic acid - DCMU 3-(3-4-dichlorophenyl) 1-1 dimethylurea - PPBQ phenyl-p-benzo-quinone - BBY PS2-enriched membranes prepared as in Berthold et al. (1981) - Q₄₀₀ PS2 electron acceptor with a midpoint potential of 400 mV     

Phospholipase A2 induced effects on the structural organization and physical properties of pea chloroplast membranes

Phospholipase A₂ (PLA₂)-induced effects on the membrane organization, fluidity properties and surface charge density of pea chloroplasts were investigated. It was observed that lipolytic treatment with PLA₂ altered the chloroplast structure having as a result a swelling of thylakoids and a total destruction of normal granal structure. In spite of this, the thylakoid membranes remained in close contact. At the same time, a slight decrease of surface charge density was registered, thus explaining the adhesion of swelled membranes. Fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene (DPH) was measured during PLA₂ treatment. A pronounced decrease of DPH fluorescence polarization was found, indicating that phospholipase treatment resulted in considerable disordering and/or fluidization of the thylakoid membranes. The increased fluidity could be attributed to the destabilizing effect of the products of enzymatic hydrolysis of the phospholipids (free fatty acids, lysophospholipids) on the bilayer structure of thylakoids membranes.Abbreviations 9-AA 9-aminoacridine - BSA bovine serium albumin - DCMU 3-/3,4-dichlorophenyl-1,1-dimethyl/urea - DPH 1,6-diphenyl-1,3,5-hexatriene - EDTA ethylenediaminetetraacetic acid - HEPES N-2-hydroxyethylpiperazine-N-2-ethanesulfonic acid - LHC light harvesting chlorophyll a/b-protein complex of PS II - MES 2/N-morpholine/ethanesulfonic acid - PLA₂ phospholipase A₂ - PS I, PS II photosystem I and photosystem II, respectively - S lipid structural order parameter - THF tetrahydrofuran - TRICINE N-/tris/hydroxymethyl/methyl/glicine     

Action spectra and functional antenna sizes of Photosystems I and II in relation to the thylakoid membrane organization and pigment composition

The functional organization of competent photosynthetic units in developing thylakoids from intermittent-light grown pea as well as in the unstacked, stacked and phosphorylated stacked thylakoids from its mature chloroplasts was characterized by polarographic measurements of action spectra, reaction centre contents and optical cross-sections for PS I-mediated O2 uptake and PS II-mediated O2 evolution. The minimum antenna sizes of 60 and 37 chlorophyll a molecules for PS I and PS II, respectively, were determined in developing thylakoids with a ratio of Chl a/Chl b>50. In mature chloroplasts, the embedded light-harvesting chlorophyll a/b-binding (LHC) protein complexes increased the PS I and PS II effective antenna sizes by 3–6 times depending on the thylakoid membrane organization. In unstacked thylakoids, a randomization of PS I, PS II and LHC II led to the most uniform spectral distribution of light harvesting between the two photosystems but caused the maximal difference of their antenna sizes to be 370 and 100 Chls for the competent PS I and PS II units, respectively. Following the Mg2+-induced stacking of thylakoids, opposite complementary changes of the action spectra, antenna sizes and Chl a/Chl b ratios indicated a redistribution of a LHC II pool of 100 Chl ( a + b) molecules from PS I to PS II. Unlike to the stroma-exposed PS II in unstacked thylakoids, the granal PS II units of 200 Chls demonstrated an additional 2-fold increase of the effective antenna size due to energy transfer within PS II dimers under strong background illumination, which closed >90% of reaction centres. Protein phosphorylation of the stacked thylakoids induced a significant inactivation of the O2-evolving PS II centres but did not cause complementary changes of the action spectra and antenna sizes of the competent PS I and PS II. In this case, light harvesting parameters of the O2-evolving PS II units were nearly unaffected, whereas the obvious relative increase of the PS I activity at 650 nm and its decrease at >700 nm both in the action spectrum and optical cross-section measurements might suggest a substitution of PS I units in the O2-reducing fraction by another distinct fraction of -type which in turn is not the same to PS I units in unstacked thylakoids.     

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     

Immunogold localization of light-harvesting and photosystem I complexes in the thylakoids ofFucus serratus (Phaeophyceae)

Summary The repartition of light-harvesting complex (LHC) and photosystem I (PS I) complex has been examined in isolated plastids ofFucus serratus by immunocytochemical labelling. LHC is distributed equally all along the length of thylakoid membranes, without any special repartition in the appressed membranes of the three associated thylakoids ofFucus. PS I is present on all the thylakoid membranes, but the external membranes of the three associated thylakoids are largely enriched relatively to the inner ones. This specific repartition of PSI on non-appressed membranes can be compared to the localization of PSI on stroma thylakoid membranes of higher plants and green algae. Consequently, although they share some common features with those of higher plants and green algae, the appressions of thylakoids in brown algae has neither the same structure nor the same functional role as typical grana stacked membranes in the repartition of the harvested energy.Abbreviations BSA bovine serum albumin - GAR goat anti-rabbit immunoglobulin G - LHC light-harvesting complex - PBS phosphatebuffered saline - PS I photosystem I - PS II photosystem II     

On the long-wavelength spectral forms of chlorophyll a in Photosystem I: Spectroscopic and immunological investigations on a greening mutant of the green alga Scenedesmus obliquus

The origin of the long-wavelength chlorophyll (Chl) absorption (_peak > 680 nm) and fluorescence emission (_peak > 685 nm) has been investigated on Scenedesmus mutants (C-2A-series, lacking the ability to synthesize chlorophyll in the dark) grown at 0.3 (LL), 10 (ML) and 240 µE s^–1 m^–2(HL). LL cells are arrested in an early greening state; consequently, Chl availability determines the phenotype. LL thylakoids are totally lacking long-wavelength Chl; nonetheless, PS I and PS II are fully functional. Gel electrophoresis and Western blots indicate that four out of seven resolved LHC polypeptides seem to require a high Chl availability for assembly of functional chlorophyll-protein complexes. The PS I core-complex of ML and HL thylakoids contains long-wavelength chlorophylls, but in the PS I core-complex of LL thylakoids these pigments are lacking. We conclude that long-wavelength pigments are only present in the PS I core in the case of high Chl availability. The following hypothesis is discussed: Chl availability determines not only the LHC polypeptide pattern, but also the number of bound Chl molecules per individual pigment-protein complex. Chl-binding at non-obligatory, peripheral sites of the pigment-protein complex results in long-wavelength Chl. In the case of low Chl availability, these sites are not occupied and, therefore, the long-wavelength Chl is absent.     

Alteration of Components of Chlorophyll-Protein Complexes and Distribution of Excitation Energy Between the Two Photosystems in Two New Rice Chlorophyll b-less mutants

Two new yellow rice chlorophyll (Chl) b-less (lack) mutants VG28-1 and VG30-5 differ from the other known Chl b-less mutants with larger amounts of soluble protein and ribulose-1,5-bisphosphate carboxylase/oxygenase small sub-unit and smaller amounts of Chl a. We investigated the altered features of Chl-protein complexes and excitation energy distribution in these two mutants, as compared with wild type (WT) rice cv. Zhonghua 11 by using native mild green gel electrophoresis and SDS-PAGE, and 77 K Chl fluorescence in the presence of Mg²⁺. WT rice revealed five pigment-protein bands and fourteen polypeptides in thylakoid membranes. Two Chl b-less mutants showed only CPI and CPa pigment bands, and contained no 25 and 26 kDa polypeptides, reduced amounts of the 21 kDa polypeptide, but increased quantities of 32, 33, 56, 66, and 19 kDa polypeptides. The enhanced absorption of CPI and CPa and the higher Chl fluorescence emission ratio of F685/F720 were also observed in these mutants. This suggested that the reduction or loss of the antenna LHC1 and LHC2 was compensated by an increment in core component and the capacity to harvest photon energy of photosystem (PS) 1 and PS2, as well as in the fraction of excitation energy distributed to PS2 in the two mutants. 77 K Chl fluorescence spectra of thylakoid membranes showed that the PS1 fluorescence emission was shifted from 730 nm in WT rice to 720 nm in the mutants. The regulation of Mg²⁺ to excitation energy distribution between the two photosystems was complicated. 10 mM Mg²⁺ did not affect noticeably the F685/F730 emission ratio of WT thylakoid membranes, but increased the ratio of F685/F720 in the two mutants due to a reduced emission at 685 nm as compared to that at 720 nm.     

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     

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     

The coleoptile chloroplast: Distinct distribution of xanthophyll cycle pigments,and enrichment in Photosystem II

Recent studies have shown that coleoptile chloroplasts operate the xanthophyll cycle, and that their zeaxanthin concentration co-varies with their sensitivity to blue light. The present study characterized the distribution of photosynthetic pigments in thylakoid pigment–protein complexes from dark-adapted and light-treated coleoptile and mesophyll chloroplasts, the low temperature fluorescence emission spectra, and the rates of PS I and PS II electron transport in both types of chloroplasts from 5-day-old corn seedlings. Pigments were extracted from isolated PS I holocomplex, LHC IIb trimeric and LHC II monomeric complexes and analyzed by HPLC. Chlorophyll distribution in coleoptile thylakoids showed 31% of the total collected Chl in PS I and 65% in the light harvesting complexes of PS II. In mesophyll thylakoids, the values were 44% and 54%, respectively. Mesophyll and coleoptile PS I holocomplexes differed in their Chl t a/Chl t b ratios (8.1 and 6.1, respectively) and -carotene content. In contrast, mesophyll and coleoptile LHC IIb trimers and LHC II monomers had similar Chl t a/Chl t b ratios and -carotene content. The three analyzed pigment–protein complexes from dark-adapted coleoptile chloroplasts contained zeaxanthin, whereas there was no detectable zeaxanthin in the complexes from dark-adapted mesophyll chloroplasts. In both chloroplast types, zeaxanthin and antheraxanthin increased markedly in the three pigment–protein complexes upon illumination, while violaxanthin decreased. In mesophyll thylakoids, zeaxanthin distribution as a percentage of the xanthophyll cycle pool was: LHC II monomers > LHC IIb trimers > PS I holocomplex, and in coleoptile thylakoids, it was: LHC IIb trimers > LHC II monomers = PS I holocomplex. Low temperature (77 K) fluorescence emission spectra showed that the 686 nm emission of coleoptile chloroplasts was approximately 50% larger than that of mesophyll chloroplasts when normalized at 734 nm. The pigment and fluorescence analysis data suggest that there is relatively more PS II per PS I and more LHC I per CC I in coleoptile chloroplasts than in mesophyll chloroplasts. Measurements of t in vitro uncoupled photosynthetic electron transport showed approximately 60% higher rates of electron flow through PS II in coleoptile chloroplasts than in mesophyll chloroplasts. Electron transport rates through PS I were similar in both chloroplast types. Thus, when compared to mesophyll chloroplasts, coleoptile chloroplasts have a distinct PS I pigment composition, a distinct chlorophyll distribution between PS I and PS II, a distinct zeaxanthin percentage distribution among thylakoid pigment–protein complexes, a higher PS II-related fluorescence emission, and higher PS II electron transport capacity. These characteristics may be associated with a sensory transducing role of coleoptile chloroplasts.     

Pigment composition and functional state of the thylakoid membranes during preparation of samples for pigment-protein complexes separation by nondenaturing gel electrophoresis

The present study was conducted to examine changes in photosynthetic pigment composition and functional state of the thylakoid membranes during the individual steps of preparation of samples that are intended for a separation of pigmentprotein complexes by nondenaturing polyacrylamide gel electrophoresis. The thylakoid membranes were isolated from barley leaves (Hordeum vulgare L.) grown under low irradiance (50 μmol m⁻² s⁻¹). Functional state of the thylakoid membrane preparations was evaluated by determination of the maximal photochemical efficiency of photosystem (PS) II (F_V/F_M) and by analysis of excitation and emission spectra of chlorophyll a (Chl a) fluorescence at 77 K. All measurements were done at three phases of preparation of the samples: (1) in the suspensions of osmotically-shocked broken chloroplasts, (2) thylakoid membranes in extraction buffer containing Tris, glycine, and glycerol and (3) thylakoid membranes solubilized with a detergent decyl-β-D-maltosid. F_V/F_M was reduced from 0.815 in the first step to 0.723 in the second step and to values close to zero in solubilized membranes. Pigment composition was not pronouncedly changed during preparation of the thylakoid membrane samples. Isolation of thylakoid membranes affected the efficiency of excitation energy transfer within PSII complexes only slightly. Emission and excitation fluorescence spectra of the solubilized membranes resemble spectra of trimers of PSII light-harvesting complexes (LHCII). Despite a disrupted excitation energy transfer from LHCII to PSII antenna core in solubilized membranes, energy transfer from Chl b and carotenoids to emission forms of Chl a within LHCII trimers remained effective.     

Photosynthetic Electron Transport,Photophosphorylation, and Antioxidants in Two Ecotypes of Reed (Phragmites Communis Trin.) from Different Habitats

We compared chloroplast photochemical properties and activities of some chloroplast-localised enzymes in two ecotypes of Phragmites communis, swamp reed (SR, C₃-like) and dune reed (DR, C₄-like) plants growing in the desert region of north-west China. Electron transport rates of whole electron transport chain and photosystem (PS) 2 were remarkably lower in DR chloroplasts. However, the electron transport rate for PS1 in DR chloroplasts was more than 90 % of the activity similar in the SR chloroplasts. Activities of Mg²⁺-ATPase and cyclic and non-cyclic photophosphorylations were higher in DR chloroplasts than in the SR ones. The activities of chloroplast superoxide dismutase (SOD) and ascorbate peroxidase (APX), both localised at or near the PS1 complex and serving to scavenge active oxygen around PS1, and the content of ascorbic acid, a special substrate of APX in chloroplast, were all higher in DR chloroplasts. Hence reed, a hydrophytic plant, when subjected to intense selection pressure in dune habitat, elevates its cyclic electron flow around PS1. In consequence, it provides extra ATP required by C₄ photosynthesis. Combined high activities of active oxygen scavenging components in DR chloroplasts might improve protection of photosynthetic apparatus, especially PS1, from the damage of reactive oxygen species. This offers new explanation of photosynthetic performance of plant adaptation to long-term natural drought habitat, which is different from those, subjected to the short-term stress treatment or even to the artificial field drought.     

Chlorophyll fluorescence changes at high temperatures induced by linear heating of greening barley leaves

A relative decrease of the high temperature part (above 60°C) of the chlorophyll fluorescence temperature curve during 3 h to 10 h greening period of barley (Hordeum vulgare L.) leaves was found to be concomitant to a decrease of Chl alb ratio and to a gradual increase of LHCP/core ratio found by electrophoresis and the ratio of granal to total length of thylakoid membranes. It is suggested that the high temperature part of the fluorescence temperature curve depends inversely on the relative amount of LHC II in thylakoid membranes.Abbreviations Chl a(b) chlorophyll a(b) - CPa chlorophyll a protein complex of PS II - CP1 P700 chlorophyll a protein complex of PS I - FP free pigments - FTC fluorescence temperature curve - F(T30) fluorescence intensity at 30°C - LHC II light harvesting complex II - LHCP light harvesting chlorophyll protein - LHCP3 (LHCPm) monomeric form of LHC II - LHCPo oligomeric form of LHC II complex - M1 first maximum of FTC - M2 second maximum (region) of FTC - PAA polyacrylamide - PAR photosynthetically active radiation - PS I(II) Photosystem I(II) - SDS-PAGE sodium dodecyl sulfate polyacrylamide gel electrophoresis     

Characterization of photosystem II in stroma thylakoid membranes

The functional state of the PS II population localized in the stroma exposed non-appressed thylakoid region was investigated by direct analysis of the PS II content of isolated stroma thylakoid vesicles. This PS II population, possessing an antenna size typical for PS II, was found to have a fully functional oxygen evolving capacity in the presence of an added quinone electron acceptor such as phenyl-p-benzoquinone. The sensitivity to DCMU for this PS II population was the same as for PS II in control thylakoids. However, under more physiological conditions, in the absence of an added quinone acceptor, no oxygen was evolved from stroma thylakoid vesicles and their PS II centers were found to be incapable to pass electrons to PS I and to yield NADPH. By comparison of the effect of a variety of added quinone acceptors with different midpoint potentials, it is concluded that the inability of PS II in the stroma thylakoid membranes to contribute to NADPH formation probably is due to that Q_A of this population is not able to reduce PQ, although it can reduce some artificial acceptors like phenyl-p-benzoquinone. These data give further support to the notion of a discrete PS II population in the non-appressed stroma thylakoid region, PS II, having a higher midpoint potential of Q_A than the PS II population in the appressed thylakoid region, PS II. The physiological significance of a PS II population that does not produce any NADPH is discussed.Abbreviations pBQ p-benzoquinone - Chl chlorophyll - DCBQ 2,6-dichloro-p-benzoquinone - DCIP 2,6-dichloroindophenol - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - DMBQ 2,5-dimethyl-p-benzoquinone - DQ duroquinone(tetramethyl-p-benzoquinone) - FeCN ferricyanide (potassium hexacyanoferrat) - MV methylviologen - NADPH,NADP⁺ reduced or oxidized form of nicotinamide adenine dinucleotide phosphate respectively - PpBQ phenyl-p-benzoquinone - PQ plastoquinone - PS II photosystem II - PS I photosystem I - Q_A primary quinone acceptor of PS II - Q_B secondary quinone acceptor of PS II - E microEinstein     

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     

Polyamines in the photosynthetic apparatus

The three main polyamines putrescine (Put), spermidine (Spd) and spermine (Spm) were characterized by HPLC in intact spinach leaf cells, intact chloroplasts, thylakoid membranes, Photosystem II membranes, the light-harvesting complex and the PS II complex. All contain the three polyamines in various ratios; the HPLC polyamine profiles of highly resolved PS II species (a Photosystem II core and the rection center) suggest an enrichment in the polyamine Spm.Abbreviations Chl chlorophyll - HPLC high performance liquid chromatography - LHC light-harvesting complex - PS II Photosystem II - PS II-RC Photosystem II reaction center - Put putrescine - Spd spermidine - Spm spermine - 10%S-core D₁-D₂-Cyt b559-47 kD-43 kD complex     

ATP-induced quenching of chlorophyll fluorescence in chloroplasts of higher plants. Dependence on structural properties of the membranes

The ATP-induced quenching of chlorophyll fluorescence in chloroplasts of higher plants is shown to be inhibited when the mobility of the protein complexes into the thylakoid membranes is reduced. Its occurrence also requires the presence of LHC complexes and the ability of the membranes to unstack.These observations, in addition to a slight increase of charge density of the surface-as indicated by 9-aminoacridine fluorescence and high salt-induced chlorophyll fluorescence studies-and partial unstacking of the membranes-as monitored by digitonin method and 540 nm light scattering changes-after phosphorylation, suggest that the ATP-induced quenching of chlorophyll fluorescence could reflect some lateral redistribution of membrane proteins in the lipid matrix of the thylakoids.Abbreviations ATP adenosine triphosphate - 9-AA 9-aminoacridine - Chl chlorophyll - EDTA ethylenediaminetetraacetate - GDA glutaraldehyde - Hepes N-2-hydroxyethylpiperazine-N-2-ethane-sulphonic acid - LHC light-harvesting chlorophyll a/b complex PS photosystem