Composition Of Thylakoid Membranes Research Articles

Effects of natural shade on soybean thylakoid membrane composition

The effect of natural shade on chloroplast thylakoid membrane activity and composition was examined for soybean (Glycine Max. cv. Young) grown under field conditions. Plots with high (10 plants m(-1) row) or low (1 plant m(-1) row) plant density were established. Expanding leaves were tagged at 50, 58 and 65 days after planting (DAP). At 92 DAP, tagged leaves were used as reference points to characterize canopy light environments and isolate thylakoid membranes. Light environments ranged from a photosynthetic photon flux density (PPFD) of 87% of full sun to a PPFD of 10% of full sun. The decline in PPFD was accompanied by an increase in the far-red/red (735 nm/645 nm) ratio from 0.9 to approximately six. The major effects of shade on chloroplast thylakoid membranes were a reduction in chloroplast coupling factor and a shift in light-harvesting capacity from Photosystem I to Photosystem II. Photosynthetic electron transport capacity was not affected by differences in PPFD, but was 20 to 30% higher in the 1 plant m(-1) row treatment. The plant density effect on electron transport was associated with differences in plastocyanin concentration, suggesting that plastocyanin is a limiting factor in soybean. Shade did not have a significant effect on the concentration of Photosystem II, Cyt b6f, or Photosystem I complexes.

Sunflower seedlings subjected to increasing stress by water deficit: Changes in O2.- production related to the composition of thylakoid membranes

Sunflower seedlings subjected to increasing stress by water deficit: Changes in O2.- production related to the composition of thylakoid membranes

Sunflower seedlings subjected to increasing stress by water deficit: Changes in O2− production Aated to the composition of thylakoid membranes

Free radicals, such as the superoxide anion, can damage the photosynthetic apparatus. At the same time they are increasingly formed as by-products of electron transport during stress conditions. For this reason, we studied the kinetics of formation and decay of superoxide anions in relation to changes, induced by increasing water deficit, in the composition of thylakoids. Seedlings of sunflower (Helianthus annuus L. cv. Licia Stella) were subjected to either a mild, a moderate, or a severe water deficit. Upon illumination of thylakoid membranes containing Tiron, we found first order kinetics of formation and decay of the Tiron semiquinone radical. At each stress intensity a higher rate of superoxide formation than in the control was observed. The different decay rates suggested a changed chemical environment around the radical. In comparison with the control, the levels of carotenoids and hydrophobic proteins in the thylakoids decreased, and the lipid/protein ratio increased after a mild water deficit. After moderate drought, the increased levels of hydrophilic proteins and carotenoids seem unsufficient to limit the improved capacity to leak electrons from the thylakoids. After a severe water stress, a decrease in unsaturation and in linolenic acid as well as a loss of lipolytic antioxidants took place, which may have rendered the thylakoids more sensitive to attack by activated forms of oxygen. The results suggest that during water deficit, the interactions among membrane components change in relation to a changed chemical composition. Such changes are probably among the causes for changes in the conformation of proteins and in the position of various molecular species in the lipid bilayer, so that they become more exposed to molecular oxygen.

Characterization of the Fad12 mutant of Synechocystis that is defective in Δ12 acyl-lipid desaturase activity

The Fad12 mutant of Synechocystis sp. PCC 6803 has a defect in the desA gene for Δ12 acyl-lipid desaturase. We identified a change in the nucleotide sequence of the structural gene for the desaturase, in which a leucine codon has been converted to a stop codon. Western blot analysis revealed that the Δ12 acyl-lipid desaturase was localized in both plasma membranes and thylakoid membranes of wild-type cells but was absent from both types of membrane in Fad12 cells. These findings suggest that the desaturation of fatty acids takes place in both types of membrane in Synechocystis sp. PCC 6803. The mutation in the Δ12 desaturase did not affect the lipid composition of thylakoid and plasma membranes, but it changed the fatty acid composition of lipids in similar ways in both types of membrane.

Lipid composition of thylakoid membranes from leaves and regreened spathes of Zantedeschia aethiopica

The glycerolipid and fatty acid composition of thylakoid membranes from two photosynthetic organs, the leaf and regreened spathe, of Zantedeschia aethiopica was studied. In regreened spathes, there was a decrease in the monogalactosyl- and digalactosyldiacylglycerols, and an increase in the contents of the sulpholipid, sulphoquinovosyldiacylglycerol and in the phospholipids phosphatidylglycerol and phosphatidylcholine, when compared with those isolated from the leaf. The major difference detected in fatty acid composition of both photosynthetic structures was the absence of the unusual fatty acid, Δ 3- trans-hexadecenoic, from phosphatidylglycerol in regreened spathe thylakoid membranes. In spite of these differences, chloroplasts from regreened spathes exhibited a typical organization, with grana and stromal regions. The results obtained suggest, that in Z. aethiopica, there is no evident correlation between the presence of Δ 3- trans-hexadecenoic acid in thylakoid membranes and thylakoid-stacking. The absence of this fatty acid in the regreened spathe is discussed in terms of chloroplast function.

Unusual composition of thylakoid membranes of the resurrection plant Boea hygroscopica: Changes in lipids upon dehydration and rehydration

Boea hygroscopica is a resurrection plant that is able to pass from biosis to anabiosis and vice versa following slow dehydration, but loses this ability following a rapid water loss. Fresh leaves were detached from plants grown in well‐watered conditions and subjected to either rapid or slow dehydration and rehydration. Upon rehydration only slowly dried leaves revived. Analysis of thylakoid membranes revealed a rather small amount of total lipids (1,4–2 μmol g−1 dry weight) in comparison with other flowering plants. The main glycolipid was digalactosyldiacylglycerol (DGDG) rather than monogalactosyldiacylglycerol (MGDG) as is common in higher plants.Linoleic acid was the main fatty acid (30–40 mol% of total fatty acids), while linolenic acid was present from 14 to 26 mol%. In both the fresh and rehydrated leaves nearly all lipid components were present in similar amounts. Following dehydration the DGDG/MGDG molar ratio, which was 1.1 in control and rehydrated leaves, doubled by the end of the rapid drying period and was three times as high in slowly dried leaves. The total polar lipid/free sterol molar ratio as well as the free fatty acid level assumed the highest values in the rapidly dehydrated leaves. A shift towards the more unsaturated fatty acids was observed in all lipid classes upon dehydration irrespective of whether it was slow or rapid. Our data show only small differences between rapidly and slowly dehydrated leaves which can be correlated to the capacity of slowly dehydrated leaves to revive.

Unusual composition of thylakoid membranes of the resurrection plant Boea hygroscopica: Changes in lipids upon dehydration and rehydration

Unusual composition of thylakoid membranes of the resurrection plant Boea hygroscopica: Changes in lipids upon dehydration and rehydration

Heat-Induced Alterations in Thylakoid Membrane Protein Composition in Barley

Biochemical and spectroscopic studies on the effects of high temperatures (45-47� C) over a 1 h period on the protein composition, fluorescence and photochemical activities of the barley thylakoid membrane were made. Photosystem II (PS II) activity decreased as expected, and photosystem I (PS I) activity also unexpectedly decreased. Our data support previous conclusions that the decrease in PS I activity is largely due to inactivation (or loss) of a component between the two photosystems. A two-dimensional electrophoretic system permitted first the separation of the thylakoid pigment-protein complexes of unstressed and stressed plants, followed by a determination of their subunit composition. The changes in the protein composition of each pigment-protein complex in response to elevated temperatures were monitored. Heat changed the quaternary structure of PS II and resulted in removal of the oxygen-evolving enhancer proteins from the thylakoid, but did essentially no damage to the PS I complex. The PS II core complex dissociated from a dimeric form to a monomeric one, and the major LHC II component (LHC IIb) changed from a trimeric to a monomeric form. The pigments that are lost from thylakoids during heat stress are mainly removed from the PS II pigment-proteins.

Dynamics of Photosystem Stoichiometry Adjustment by Light Quality in Chloroplasts.

Long-term imbalance in light absorption and electron transport by photosystem I (PSI) and photosystem II (PSII) in chloroplasts brings about changes in the composition, structure, and function of thylakoid membranes. The response entails adjustment in the photosystem ratio, which is optimized to help the plant retain a high quantum efficiency of photosynthesis (W.S. Chow, A. Melis, J.M. Anderson [1990] Proc Nat Acad Sci USA 87: 7502-7506). The dynamics of photosystem ratio adjustment were investigated upon the transfer of pea {Pisum sativum} plants from a predominantly PSI-light to a predominantly PSII-light environment and vice versa. The concentration of functional components (primary electron accepting plastoquinone of PSII [QA], P700) and that of constituent proteins were monitored during acclimation by A difference spectrophotometry and immunoblot analysis, respectively. Fully reversible changes in photosystem ratio occurred with a half-time of about 20 h. They involved closely coordinated changes in the concentration of the QA, reaction center protein D1, D2, and the 9-kD apoprotein of the cytochrome b559 for PSII. Similarly, closely coordinated changes in the relative concentration of P700 and reaction center proteins of PSI were observed. The level of chlorophyll b and that of the light-harvesting complex II changed in accordance with the concentration of PSII in the acclimating thylakoids. Overall, adjustments in the photosystem ratio in response to PSI- or PSII-light conditions appeared to be a well-coordinated reaction in the chloroplast. The response was absent in the chlorophyll b-less chlorina f2 mutant of barley (Hordeum vulgare) and in a phycobilisomeless mutant of Agmenellum quadruplicatum, suggesting that photosystem accessory pigments act as the light-quality perception molecules and that PSI and PSII themselves play a role in the signal transduction pathway.

Photoacclimation in the Red Alga Porphyridium cruentum

Acclimation of the photosynthetic apparatus to changes in the light environment was studied in the unicellular red alga Porphyridium cruentum (American Type Culture Collection No. 50161). Absolute or relative amounts of four photosynthetic enzymes and electron carriers were measured, and the data were compared with earlier observations on light-harvesting components (F.X. Cunningham, Jr., R.J. Dennenberg, L. Mustárdy, P.A. Jursinic, E. Gantt [1989] Plant Physiol 91: 1179-1187; F.X. Cunningham, Jr., R.J. Dennenberg, P.A. Jursinic, E. Gantt [1990] Plant Physiol 93: 888-895) and with measurements of photosynthetic capacity. P(max), the light-saturated rate of photosynthesis on a chlorophyll (Chl) basis, increased more than 4-fold with increase in growth irradiance from 6 to 280 mueinsteins.m(-2).s(-1). Amounts of ferredoxin-NADP(+) reductase, ribulose-1,5-bisphosphate carboxylase, and cytochrome f increased in parallel with P(max), whereas numbers of the light-harvesting complexes (photosystem [PS] I, PSII, and phycobilisomes) changed little, and ATP synthase increased 7-fold relative to Chl. The calculated minimal turnover time for PSII under the highest irradiance, 5 ms, was thus about 4-fold faster than that calculated for cultures grown under the lowest irradiance (19 ms). A change in the spectral composition of the growth light (irradiance kept constant at 15 mueinsteins.m(-2).s(-1)) from green (absorbed predominantly by the phycobilisome antenna of PSII) to red (absorbed primarily by the Chl antenna of PSI) had little effect on the amounts of ribulose-1,5-bisphosphate carboxylase, ATP synthase, and phycobilisomes on a Chl, protein, or thylakoid area basis. However, the number of PSI centers declined by 40%, cytochrome f increased by 40%, and both PSII and ferredoxin-NADP(+) reductase increased approximately 3-fold on a thylakoid area basis. The substantial increase in ferredoxin-NADP(+) reductase under PSI light is inconsistent with a PSI-mediated reduction of NADP as the sole function of this enzyme. Our results demonstrate a high degree of plasticity in content and composition of thylakoid membranes of P. cruentum.

Chlorophyll Proteins and Lipids in Paraquat Treated Sensitive and Resistant Conyza Canadensis Leaves

Photosynthetic activity and molecular composition of thylakoid membranes of sensitive and atrazine/paraquat coresistant biotypes of Conyza canadensis (L.) Cronq was compared before and after 5 × 10-4 molar paraquat spraying. In contrast to the irreversibly damaged sensitive plants the Rfd values (vitality indices) calculated from parameters of fluorescence induction curves, and the in vivo CO2 fixation in resistant plants showed - after a transitory inhibition - a recovery. Resistant thylakoids contained higher amount of PS II and LHC II, (i.e. lower relative amount of CP I) which can be the result of an adaptation process. Fatty acid composition of total leaf extract was almost the same in both biotype even after spraying. The amount of the oligomeric form of LHCP II decreased in paraquat treated sensitive thylakoids, which was in correlation with the reduction of Δ3-transhexadecanoic acid content. Decrease in oligomeric LHCP II and/or special lipids (PG) in sensitive thylakoids may change the association of LHCP II and photosystem II core as it is evidenced from lowering of the Mg2+ induced changes of the short wavelength fluorescence intensity and increase in the relative quantum requirement values. The results are discussed in connection with a possible effect of paraquat on PS II.

The D1 protein of the photosystem II reaction‐centre complex accumulates in the absence of D2: analysis of a mutant of the cyanobacterium Synechocystis sp. PCC 6803 lacking cytochrome d559

The reaction center core of photosystem II, a multiprotein membrane bound complex, is composed of a heterodimer of two proteins, D1 and D2. A random mutagenesis technique was used to isolate a photosystem II deficient mutant, CP6t16, of the unicellular cyanobacterium, Synechocystis sp. PCC 6803. Nucleotide sequence analysis showed that the primary lesion in CP6t16 is an ochre mutation introducing a translational stop codon in the psbE gene, encoding the alpha-subunit of cytochrome b559, an integral component of the PSII complex. Analysis of the protein composition of CP6t16 thylakoid membranes isolated in the presence of serine protease inhibitors revealed that, in the absence of cytochrome b559, the D2 protein is also absent. However, the D1 protein is stably incorporated in these membranes, suggesting that the synthesis and integration of D1 are independent of those of D2 and cytochrome b559.

Physiological effects of sublethal atrazine on barley chloroplast thylakoid membranes

This study was conducted to more clearly define the physiological effects of PS II herbicides on chloroplast thylakoid membrane activity and composition. Barley (Hordeum vulgare L. cv Boone) was grown in hydroponic culture at 20°C in a growth chamber with a light intensity of 500 μmole photons m(-2) s(-1). Atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine), a Photosystem II herbicide, was supplied continuously via the roots to 7-day-old plants. Atrazine concentrations greater than 0.07 ppm (0.32 μM) were associated with decreased leaf chlorophyll (chl), lowered chl a/b ratio, inhibition of chloroplast electron transport, and plant death within 1 to 2 weeks. Atrazine at 0.07 ppm was defined as sublethal because no toxic effects were observed. Sublethal atrazine induced a decrease in chl a/b ratio with no effect on leaf chl content. Photosynthetic electron transport was either unaffected in fully expanded leaves or slightly stimulated in expanding leaves by treatment of intact plants with 0.07 ppm atrazine. The major effect of sublethal atrazine was on the chl-protein complex composition. Sublethal atrazine increased the level of the Photosystem II light-harvesting complex (LHC-II) and lowered the level of the CP1a Photosystem I complex relative to controls. The numbers of Photosystem II and Photosystem I reaction centers and cytochrome b 6/f complexes per unit chl were not affected by sublethal atrazine. The overall result was an atrazine-induced redistribution of light-harvesting chl from Photosystem I to Photosystem II with no effect on the number of thylakoid membrane-protein complexes associated with electron transport.

Photosynthetic activity and chloroplast structural characteristics in triazine‐resistant biotypes of three weed species

Triazine‐resistant (R) and susceptible (S) biotypes of Chenopodium album, Conyza bonaeriensis and Setaria glauca were compared in terms of photosynthetic activity, chloroplast ultrastructure, and polar‐lipid composition of thylakoid membranes. Concerning photosynthetic activity, R relative to S biotypes showed lower rates in photosystem II electron transport (R/S ratios in the 0.3‐0.5 range), which were correlated with increases in the ratio of I to P levels of the fluorescence emission curve, but similar rates in both whole‐chain electron transport by thylakoids and photosynthetic oxygen evolution at different light intensities and at temperatures of 20 and 30°C by leaf discs. Concerning chloroplast structural characteristics, R and S biotypes did not show differences in degree of thylakoid appression and chlorophyll a/b ratio. However, thylakoid polar‐lipids of R biotypes exhibited a higher degree of unsaturation, specially, in its monogalactosyl diglyceride fraction; they were richer in trans‐hexadecenoic acid in its phospholipid fraction and they had higher contents in monoglactosyl diglyceride. The above results are discussed in relation to possible differences in photosynthetic performance between R and S plants.

Composition and biosynthesis of thylakoid membrane polypeptides in the red alga Cyanidium caldarium: Comparison with the thylakoid polypeptide composition of higher plants and cyanobacteria

The polypeptide composition of thylakoid membranes of the red alga Cyanidium caldarium was studied by PAGE in the presence of lithium dodecyl sulfate. The thylakoid membranes were shown to contain 65 polypeptides with mol wt from 110 to 10 kDa. PS I isolated from C. caldarium cells is composed of at least 5 components, one of which is the chlorophyll-protein complex with mol wt of 110 kDa typical of higher plants. Cyt f, c 552, b 6 and b 559 were identified. Inhibition of carotenoid biosynthesis with norflurazon caused no changes in the polypeptide composition of thylakoid membranes of the algae grown in dark. The suppression of the biosynthesis rate of some thylakoid polypeptides in the algae grown with norflurazon in light is a result of membrane photodestruction. Thylakoid membranes from C. caldarium cells are more similar in the number of protein components to thylakoid membranes from cells of the cyanobacterium Anacystis nidulans than to those of higher plants (Pisum sativum), which was proved by immune-blotting assays: Thylakoid membranes of the red alga and cyanobacteria contain 28 homologous polypeptides, while thylakoid membranes of the alga and pea, only 15.

Chlororespiration: an adaptation to nitrogen deficiency in Chlamydomonas reinhardtii.

When grown under nitrogen limitation, pronounced chlororespiratory activity develops together with an altered composition of thylakoid membranes in Chlamydomonas reinhardtii. Relative to control cultures, the flash-inhibited, chlororespiration-dependent O2 consumption signal increases 10-fold. Also augmented is the light-sensitive respiratory activity responsible for the "Kok effect," reflecting competitive inhibition of chlororespiratory electron transport by photosystem I. Fluorescence measurements show that the thylakoid plastoquinone pool is extensively reduced in dark-adapted, N-limited cells. Thylakoids of N-limited cells have reduced amounts of cytochrome b6, cytochrome f, and light-harvesting complexes. However, thylakoid-bound NADH-PQ oxidoreductase, with major subunits of 51 kDa and 17 kDa, is increased 7-fold and two novel cytochromes of 34 and 12.5 kDa are highly abundant. Thus, components of photosynthetic and chlororespiratory electron transport pathways are differentially regulated by N availability.

The Chlorophyll-Proteins of pine ( Pinus sylvestris L.) as Influenced by SO 2-Incubation

Summary The 4th derivative of the red chlorophyll a absorption band shows two characteristic peaks, the amplitudes of which are changed in conifer needles exposed to SO2. To study the molecular basis of this effect the chlorophyll-protein composition of thylakoid membranes from un-treated Pinus sylvestris seedlings and from seedlings incubated with 810 µg/m3 SO2 for 90 h was analysed. It was found that SO2 incubation preferentially decreases the amount of one of the two chlorophyll a-proteins that are associated with the core complex of photosystem II. Additionally, the structure of the complete photosynthetic apparatus was impaired as concluded from the complete dissociation of PS I even under mild conditions of detergent incubation and electrophoresis.

Development of Photosystem II in dark grown Chlamydomonas reinhardtii. A light-dependent conversion of PS II?, QB-nonreducing centers to the PS II?, 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, QA, to the secondary-quinone electron acceptor, QB (QB-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 β-type Chl antenna size with only 130 Chl (a and b) molecules (by definition, PS IIβ 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 QB-nonreducing form in the dark, to a QB-reducing form in the light. Concomitant with this change, PS IIβ units were energetically coupled with the LHC II-peripheral complement in the thylakoid membrane and were converted to a PS IIα 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 QA-QB electron-transfer reaction which is followed by association of the PS IIβ unit with a LHC II-peripheral antenna and by inclusion of the mature form of PS II (PS IIα) in the membrane of the grana partition region.

The composition and function of thylakoid membranes from pea plants grown under white or green light with or without far‐red light

Pea plants (Pisum sativum L. ev. Greenfeast) were grown for 2 to 3 weeks in while (˜ 50 μmol photons m−2 s−1; 400–700 nm) or green (˜ 30 μmol photons m−2 s −1 400–700 nm) light (16 h day/8 h night), with or without far‐red light. Supplementary far‐red light decreased leaf area and increased internodal length in both white and green light, demonstrating that phytochrome influenced leaf size and plant growth. However, there was no effect of far‐red light on chlorophyll a/chlorophyll b ratios, chlorophyll‐protein composition, the stoichiometry of electron transport complexes or photosynthetic function of isolated thylakoids. These results suggest that phytochrome is ineffective in modulating the composition and function of thylakoids in pea plants grown at low irradiance. One possible explanation of the ineffectiveness of phytochrome on thylakoids is discussed in terms of the drastic attenuation of red relative to far‐red light in green tissue.

Changes in leaf phosphate status have only small effects on the photochemical apparatus of sugar beet leaves

The effects of orthophosphate (P i) on the structure and function of thylakoid membranes was investigated by monitoring changes in thylakoid polypeptides, pigment-proteins, cytochromes (Cyt), atrazine-binding sites, leaf fluorescence characteristics, photosynthesis quantum yield and electron transport (including Cyt f dark reduction) in leaves of sugar beet ( Beta vulgaris L. cv. F58-554H1) plants cultured hydroponically with different levels of P i supply. Low-P treatment (i.e. low external P i supply) decreased soluble leaf phosphorus (P) by 78% and total plant dry matter by 77%, and decreased light-saturated photosynthetic CO 2 fixation by 32%. The results show that low-P treatment had only minor effects on thylakoid membrane composition and function. There was some evidence that low-P increased the amounts of photosystem (PS) I and light harvesting chlorophyll-protein complexes and of the Cyt f and b 563 , relative to the amounts of PS II reaction center complex, the number of atrazine binding sites and Cyt b 559 . Low-P treatment had very little effect, if any, on photosynthetic quantum yield and small effects on chlorophyll fluorescence.