The induction of CP43′ by iron-stress in Synechococcus sp. PCC 7942 is associated with carotenoid accumulation and enhanced fatty acid unsaturation

Comparative lipid analysis demonstrated reduced amount of PG (50%) and lower ratio of MGDG/DGDG in iron-stressed Synechococcus sp. PCC 7942 cells compared to cells grown under iron sufficient conditions. In parallel, the monoenoic (C:1) fatty acids in MGDG, DGDG and PG increased from 46.8%, 43.7% and 45.6%, respectively in control cells to 51.6%, 48.8% and 48.7%, respectively in iron-stressed cells. This suggests increased membrane dynamics, which may facilitate the diffusion of PQ and keep the PQ pool in relatively more oxidized state in iron-stressed compared to control cells. This was confirmed by chlorophyll fluorescence and thermoluminescence measurements. Analysis of carotenoid composition demonstrated that the induction of isiA (CP43′) protein in response to iron stress is accompanied by significant increase of the relative abundance of all carotenoids. The quantity of carotenoids calculated on a Chl basis increased differentially with nostoxanthin, cryptoxanthin, zeaxanthin and β-carotene showing 2.6-, 3.1-, 1.9- and 1.9-fold increases, respectively, while the relative amount of caloxanthin was increased only by 30%. HPLC analyses of the pigment composition of Chl-protein complexes separated by non-denaturating SDS-PAGE demonstrated even higher relative carotenoids content, especially of cryptoxanthin, in trimer and monomer PSI Chl-protein complexes co-migrating with CP43′ from iron-stressed cells than in PSI complexes from control cells where CP43′ is not present. This implies a carotenoid-binding role for the CP43′ protein which supports our previous suggestion for effective energy quenching and photoprotective role of CP43′ protein in cyanobacteria under iron stress.     

Iron deficiency in cyanobacteria causes monomerization of photosystem I trimers and reduces the capacity for state transitions and the effective absorption cross section of photosystem I in vivo

The induction of the isiA (CP43') protein in iron-stressed cyanobacteria is accompanied by the formation of a ring of 18 CP43' proteins around the photosystem I (PSI) trimer and is thought to increase the absorption cross section of PSI within the CP43'-PSI supercomplex. In contrast to these in vitro studies, our in vivo measurements failed to demonstrate any increase of the PSI absorption cross section in two strains (Synechococcus sp. PCC 7942 and Synechocystis sp. PCC 6803) of iron-stressed cells. We report that iron-stressed cells exhibited a reduced capacity for state transitions and limited dark reduction of the plastoquinone pool, which accounts for the increase in PSII-related 685 nm chlorophyll fluorescence under iron deficiency. This was accompanied by lower abundance of the NADP-dehydrogenase complex and the PSI-associated subunit PsaL, as well as a reduced amount of phosphatidylglycerol. Nondenaturating polyacrylamide gel electrophoresis separation of the chlorophyll-protein complexes indicated that the monomeric form of PSI is favored over the trimeric form of PSI under iron stress. Thus, we demonstrate that the induction of CP43' does not increase the PSI functional absorption cross section of whole cells in vivo, but rather, induces monomerization of PSI trimers and reduces the capacity for state transitions. We discuss the role of CP43' as an effective energy quencher to photoprotect PSII and PSI under unfavorable environmental conditions in cyanobacteria in vivo.     

Influence of thylakoid membrane lipids on the structure and function of the plant photosystem II core complex

Main conclusion

MGDG leads to a dimerization of isolated, monomeric PSII core complexes. SQDG and PG induce a detachment of CP43 from the PSII core, thereby disturbing the intrinsic PSII electron transport. The influence of the four thylakoid membrane lipids monogalactosyldiacylglycerol (MGDG), digalactosyldiacylglycerol (DGDG), sulfoquinovosyldiacylglycerol (SQDG) and phosphatidylglycerol (PG) on the structure and function of isolated monomeric photosystem (PS) II core complexes was investigated. Incubation with the negatively charged lipids SQDG and PG led to a loss of the long-wavelength 77 K fluorescence emission at 693 nm that is associated with the inner antenna proteins. The neutral galactolipids DGDG and MGDG had no or only minor effects on the fluorescence emission spectra of the PSII core complexes, respectively. Pigment analysis, absorption and 77 K fluorescence excitation spectroscopy showed that incubation with SQDG and PG led to an exposure of chlorophyll molecules to the surrounding medium followed by conversion to pheophytin under acidic conditions. Size-exclusion chromatography and polypeptide analysis corroborated the findings of the spectroscopic measurements and pigment analysis. They showed that the negatively charged lipid SQDG led to a dissociation of the inner antenna protein CP43 and the 27- and 25-kDa apoproteins of the light-harvesting complex II, that were also associated with a part of the PSII core complexes used in the present study. Incubation of PSII core complexes with MGDG, on the other hand, induced an almost complete dimerization of the monomeric PSII. Measurements of the fast PSII fluorescence induction demonstrated that MGDG and DGDG only had a minor influence on the reduction kinetics of plastoquinone Q_A and the artificial PSII electron acceptor 2,5-dimethyl-p-benzoquinone (DMBQ). SQDG and, to a lesser extent, PG perturbed the intrinsic PSII electron transport significantly.     

Digalactosyl-diacylglycerol deficiency impairs the capacity for photosynthetic intersystem electron transport and state transitions in Arabidopsis thaliana due to photosystem I acceptor-side limitations

Compared with wild type, the dgd1 mutant of Arabidopsis thaliana exhibited a lower amount of PSI-related Chl-protein complexes and lower abundance of the PSI-associated polypeptides, PsaA, PsaB, PsaC, PsaL and PsaH, with no changes in the levels of Lhca1-4. Functionally, the dgd1 mutant exhibited a significantly lower light-dependent, steady-state oxidation level of P700 (P700(+)) in vivo, a higher intersystem electron pool size, restricted linear electron transport and a higher rate of reduction of P700(+) in the dark, indicating an increased capacity for PSI cyclic electron transfer compared with the wild type. Concomitantly, the dgd1 mutant exhibited a higher sensitivity to and incomplete recovery of photoinhibition of PSI. Furthermore, dgd1 exhibited a lower capacity to undergo state transitions compared with the wild type, which was associated with a higher reduction state of the plastoquinone (PQ) pool. We conclude that digalactosyl-diacylglycerol (DGDG) deficiency results in PSI acceptor-side limitations that alter the flux of electrons through the photosynthetic electron chain and impair the regulation of distribution of excitation energy between the photosystems. These results are discussed in terms of thylakoid membrane domain reorganization in response to DGDG deficiency in A. thaliana.     

The action of lipases on chloroplast membranes. III. The effect of lipid hydrolysis on chlorophyll-protein complexes in thylakoid membranes

Bean thylakoid membranes treated with various lipolytic enzymes (bean galactolipase, phospholipases A₂, C, D) showed marked changes in their acyl lipid composition. As a consequence of acyl lipids hydrolysis, destruction of some chlorophyll a-protein complexes (CP1a, CP1, CPa) or monomerization of the oligomeric of light harvesting chlorophyll a/b protein complex (LHCP) was observed. It is concluded that galactolipids and phosphatidylcholine are responsible for the stability of CP1a, CP1 and CPa, respectively. Phosphatidylglycerol and to some extent monogalactosyldiacylglycerol are essential for the stabilization of oligomeric structures of light harvesting chlorophyll a/b protein complex.Abbreviations chl chlorophyll - CP1a, CP1 chl a-protein complexes, of PSI - CPa chl a-protein complex of PSII - DGDG diagalactosyldiacylglycerol - FC free chl - GL galactolipase - LHCP^1–3 light harvesting chl a/b protein complex - MGDG monogalactosyldiacylglycerol - PAGE polyacrylamide gel electrophoresis - PC phosphatidylcholine - PG phosphatidylglycerol - PLA₂ phospholipase A₂ - PL phospholipase C - PLD phospholipase D - PSI photosystem I - PSII photosystem II - SDS sodium dodecyl sulphate - SQDG sulfoquinovosyl-diacylglycerol - TCA trichloroacetic acid - Tricine N-tris-(hydroxymethyl)-methylglycine - Tris Tris-(hydroxymethyl)-aminomethan     

Time-resolved absorption and emission show that the CP43' antenna ring of iron-stressed synechocystis sp. PCC6803 is efficiently coupled to the photosystem I reaction center core

Excitation energy transfer and trapping processes in an iron stress-induced supercomplex of photosystem I from the cyanobacterium Synechocystis sp. PCC6803 were studied by time-resolved absorption and fluorescence spectroscopy on femtosecond and picosecond time scales. The data provide evidence that the energy transfer dynamics of the CP43'-PSI supercomplex are consistent with energy transfer processes that occur in the Chl a network of the PSI trimer antenna. The most significant absorbance changes in the CP43'-PSI supercomplex are observed within the first several picoseconds after the excitation into the spectral region of CP43' absorption (665 nm). The difference time-resolved spectra (DeltaDeltaA) resulting from subtraction of the PSI trimer kinetic data from the CP43'-PSI supercomplex data indicate three energy transfer processes with time constants of 0.2, 1.7, and 10 ps. The 0.2 ps kinetic phase is tentatively interpreted as arising from energy transfer processes originating within or between the CP43' complexes. The 1.7 ps phase is interpreted as possibly arising from energy transfer from the CP43' ring to the PSI trimer via closely located clusters of Chl a in CP43' and the PSI core, while the slower 10 ps process might reflect the overall excitation transfer from the CP43' ring to the PSI trimer. These three fast kinetic phases are followed by a 40 ps overall excitation decay in the supercomplex, in contrast to a 25 ps overall decay observed in the trimer complex without CP43'. Excitation of Chl a in both the CP43'-PSI antenna supercomplex and the PSI trimer completely decays within 100 ps, resulting in the formation of P700(+). The data indicate that there is a rapid and efficient energy transfer between the outer antenna ring and the PSI reaction center complex.     

The Effect of Light Intensity, Day Length, and Temperature on Fatty Acid Synthesis and Desaturation in Vicia faba L.

Some effects of light intensity, day length, and temperatureon the fatty acid composition of the major glycerolipids ofleaves of Vicia faba L. (cv. Giant Windsor) were observed. Increasinglight intensity caused an increase in the relative concentrationsof 16 : 1 in PG and 18 : 3 in MGDG and DGDG. Increasing daylength during growth (and continuous illumination of leaf tissue)had no effect on 16 : 1 in PG but caused a decrease in the 18: 3 content of PG, PC, MGDG, and DGDG. Since the quantitiesof these lipids increased under these conditions, the decreasewas not due to photodestruction but to the differences in therelative rates of biosynthesis and desaturation of fatty acids.Incubation of leaf tissue in the dark for 4 d had little effecton the fatty acid composition of MGDG, DGDG, and PG. Temperaturealso controls fatty acid synthesis and desaturation. Above theoptimum growth temperature (20 °C), the 18 : 3 content ofMGDG, DGDG, PG, and PC decreased. In mature leaf tissue, thedegree of unsaturation of MGDG may be modified upward in responseto temperature changes. When plants were grown at 30 °Cand transferred to 20 °C the level of 18 : 3 in MGDG ofthe leaf tissue increased to levels found in plants grown onlyat 20 °C. The level of 18 : 3 in MGDG does not decreaseas rapidly when plants grown at 20 °C were transferred to30 °C. This suggests that the lower temperature induceddesaturation of 18 : 2 to 18 : 3.     

Lipid composition and turnover in heterotrophic cell suspension cultures of Saccharum officinarum

Utilizing radioactively labelled precursors we found that fully heterotrophic sugarcane cells without carotenoids and chlorophyll and absolutely dependent on sucrose for growth were capable of incorporating galactose into both mono- and di-galactosyldiacylglycerol (MGDG and DGDG), sulfate and galactose into sulfolipid (SL), and phosphate into phosphatidylglycerol (PG). All above-mentioned lipids showed turnover allowing the calculation of their half-lifes: τ_0.5 = 28 h for MGDG. There is an initial increment in the labelling of DGDG (at the expense of MGDG) and then a decrement with τ_0.5 = 27 h. The SL shows a τ_0.5 = 30 h and τ_0.5 = 28 h for PG. It is evident that during differentiation changes in lipid metabolism occur allowing the cell not only to increase, but to localize preferentially the biosynthetic machinery of the above-mentioned lipids in the chloroplasts and to make the process light-dependent.     

Spectroscopic properties of PSI-IsiA supercomplexes from the cyanobacterium Synechococcus PCC 7942

The cyanobacterium Synechococcus PCC 7942 grown under iron starvation assembles a supercomplex consisting of a trimeric Photosystem I (PSI) complex encircled by a ring of 18 CP43' or IsiA light-harvesting complexes [Nature 412 (2001) 745]. Here we present a spectroscopic characterization by temperature-dependent absorption and fluorescence spectroscopy, site-selective fluorescence spectroscopy at 5 K, and circular dichroism of isolated PSI-IsiA, PSI and IsiA complexes from this cyanobacterium grown under iron starvation. The results suggest that the IsiA ring increases the absorption cross-section of PSI by about 100%. Each IsiA subunit binds about 16-17 chlorophyll a (Chl a) molecules and serves as an efficient antenna for PSI. Each of the monomers of the trimeric PSI complex contains two red chlorophylls, which presumably give rise to one exciton-coupled dimer and at 5 K absorb and fluoresce at 703 and 713 nm, respectively. The spectral properties of these C-703 chlorophylls are not affected by the presence of the IsiA antenna ring. The spectroscopic properties of the purified IsiA complexes are similar to those of the related CP43 complex from plants, except that the characteristic narrow absorption band of CP43 at 682.5 nm is missing in IsiA.     

Iron stress responses in the cyanobacterium Synechococcus sp. PCC7942

In the present study, we describe the sequential events by which the cyanobacterium Synechococcus sp. PCC 7942 adapts to iron deficiency. In doing so, we have tried to elucidate both short and long-term acclimation to low iron stress in order to understand how the photosynthetic apparatus adjusts to low iron conditions. Our results show that after an initial step, where CP43' is induced and where ferredoxin is partly replaced by flavodoxin, the photosynthetic unit starts to undergo major rearrangements. All measured components of Photosystem I (PSI), PSII and cytochrome (Cyt) ƒ decrease relative to chlorophyll (Chl) a . The photochemical efficiencies of the two photosystems also decline during this phase of acclimation. The well-known drop in phycobilisome content measured as phycocyanin (PC)/Chl was not due to an increased degradation, but rather to a decreased rate of synthesis. The largest effects of iron deficiency were observed on PSI, the most iron-rich structure of the photosynthetic apparatus. In the light of the recent discovery of an iron deficiency induced CP43' ring around PSI a possible dual function of this protein as both an antenna and a quencher is discussed. We also describe the time course of a blue shift in the low temperature Chl emission peak around 715 nm, which originates in PSI. The shift might reflect the disassembly and/or degradation of PSI during iron deficiency and, as a consequence, PSI might under these conditions be found predominantly in a monomeric form. We suggest that the observed functional and compositional alterations represent cellular acclimation enabling growth and development under iron deficiency, and that growth ceases when the acclimation capacity is exhausted. However, the cells remain viable even after growth has ceased, since they resumed growth once iron was added back to the culture.     

膜脂对菠菜细胞色素b6f复合体电子传递活性的影响

利用从菠菜(Spinacia oleracea L.)叶绿体分离、纯化出的缺失膜脂的细胞色素b6f蛋白复合体(Cyt b6f)制剂与从菠菜类囊体分离、纯化的膜脂进行体外重组,检测了不同膜脂对Cyt b6f催化电子传递活性的影响.结果表明:被检测的5种膜脂,即单半乳糖基甘油二酯(MGDG)、双半乳糖基甘油二酯(DGDG)、磷脂酰胆碱(PC)、磷脂酰甘油(PG)和硫代异鼠李糖基甘油二酯(SQDG)对Cyt b6f催化电子传递的活性均有明显的促进作用,但促进的程度各不相同,这可能与这些膜脂分子的带电性质密切相关.不带电荷的MGDG和DGDG及分子整体呈电中性的PC对促进Cyt b6f催化电子传递的活性非常有效,可分别使其活性提高89%、75%和77%;而带负电荷的PG和SQDG对活性的促进作用则相对较弱,仅可使其活性分别提高43%和26%.     

Plasma membrane lipid composition of the halophilic cyanobacterium Aphanothece halophytica

The plasma membrane from Aphanothece halophytica was isolated using both glycerol and sucrose gradient centrifugation. The isolated membrane was characterized for lipid content by TLC and isolated lipids were quantified by chemical analysis. The plasma membrane of A. halophytica was composed of MGDG, DGDG and PG. The sulfur containing lipid SQDG was not detected. The mole percent of each lipid in the plasma membrane varied with the external salinity of the media. MGDG was the most abundant lipid in the plasma membrane of cells grown at one molar external NaCl. At three molar external NaCl, PG was the most abundant lipid. The ratio of uncharged to charged lipids comprising the plasma membrane decreased as the external salinity increased. It is possible that the alteration in lipid composition is of major importance in the adaptation of A. halophytica to changing external salinity.Abbreviations TLC Thin-layer chromatography - MGDG momogalactosyldiacylglycerol - DGDG digaloctosyldiacylglycerol - PG phosphatidylglycerol - SQDG sulphoquinovosyldiacylglycerol     

Galactolipids and phospholipids of orange peel and juice chromoplasts

Chromoplasts from yellow orange (Citrus sinensis) fruit peel contain monogalactosyl diglycerides (MGDG), digalactosyl diglycerides (DGDG) and phosphatidyl glycerol (PG) in amounts similar to those found in chloroplasts from green fruit peel. Juice chromoplasts contain relatively little MGDG and no DGDG with high levels of phosphatidyl choline and phosphatidyl ethanolamine but no PG.     

Aluminum mediates compositional alterations of polar lipid classes in maize seedlings

Changes in lipid composition were investigated on maize roots and shoots under aluminum stress. After 4d exposure to 100 microM Al, root growth was inhibited while shoot growth was not affected. In roots, the decrease of the DBI (double bond index) of total fatty acids may signal a decrease in membrane fluidity. The total lipids (TL) decreased by 49%, but phospholipids (PL), phosphatidylcholine (PC) and phosphatidylinositol (PI) increased to approximately 3-fold. The MGDG increased to 2-fold but no significant change was found in the DGDG. The steryl lipids (SL) increased by 69%. The SL/PL ratio decreased from 2.64 to 1.52 and the MGDG/DGDG ratio increased from 0.45 to 1.06 in roots of Al-stressed plants. Al leads to oxidative stress in roots of treated plants as indicated by the increase of malondialdehyde (MDA) concentrations. In shoots, changes in fatty acid composition were associated with an increase of the DBI in all lipid classes except that of the DGDG decreased. The PG was the lipid class which shows the large variation of fatty acid composition. No significant changes were found either for TL, PL, SL or MDA concentrations in shoots of Al-treated plants. While PE levels did not show significant change, PI and PG increased and PC decreased. However, the Al caused 87% decrease in the GL levels. The MGDG and DGDG decreased to 19- and 8-fold, respectively. The deleterious effects of Al on polar lipids could be caused by a direct intervention of Al on plasma membrane and/or alteration of cell metabolism.     

The role of lipids in photosystem II

The thylakoid membranes of photosynthetic organisms, which are the sites of oxygenic photosynthesis, are composed of monogalactosyldiacylglycerol (MGDG), digalactosyldiacylglycerol (DGDG), sulfoquinovosyldiacylglycerol (SQDG), and phosphatidylglycerol (PG). The identification of many genes involved in the biosynthesis of each lipid class over the past decade has allowed the generation and isolation of mutants of various photosynthetic organisms incapable of synthesizing specific lipids. Numerous studies using such mutants have revealed that deficiency of these lipids primarily affects the structure and function of photosystem II (PSII) but not of photosystem I (PSI). Recent X-ray crystallographic analyses of PSII and PSI complexes from Thermosynechococcus elongatus revealed the presence of 25 and 4 lipid molecules per PSII and PSI monomer, respectively, indicating the enrichment of lipids in PSII. Therefore, lipid molecules bound to PSII may play special roles in the assembly and functional regulation of the PSII complex. This review summarizes our present understanding of the biochemical and physiological roles of lipids in photosynthesis, with a special focus on PSII. This article is part of a Special Issue entitled: Photosystem II.     

集胞藻Synechocystis sp.PCC 6803脂质组的分析

以集胞藻Synechocystis sp.PCC 6803为研究对象,研究建立了基于超高效液相色谱耦合串联质谱技术脂质组学分析方法.鸟枪法脂质组学通过电喷雾离子化有效分离油脂粗提物中所含单个脂质分子,在三重四极杆扫描碎片离子,能够利用特征片段离子鉴定光合甘油酯的种类和酰基组成,具有高效、灵敏度高和质量准确度高等优点.对...     

Effects of moderately enhanced levels of ozone on the acyl lipid composition of leaves of garden pea (Pisum sativum)

Plants of garden pea ( Pisum sativum L.) were exposed to charcoal-filtered air with or without addition of 65 ± 5 l⁻¹ ozone. Plants were harvested daily for 9 days and lipids were extracted from the second-oldest leaf. Visible injury of this leaf was evident from day 5 on, while the differences in lipids between ozone and control treatments were observed earlier. Ozone caused large decreases in the contents of monogalactosyldiacylglycerol (MGDG), digalactosyldiacylglycerol (DGDG) and sulfoquinovosyldiacylglycerol (SQDG), a slower decrease in the content of phosphatidylcholine (PC), but an increase in the content of phosphatidylethanolamine (PE) per leaf area, compared with exposure to charcoal-filtered air. The content of phosphatidylglycerol (PG) was unaffected by ozone. Compared with charcoal-filtered air, fumigation with ozone resulted in a decrease in the proportion of linolenic acid (18:3) of the total lipid extract, with a concomitant increase in the proportion of linoleic acid (18:2). For individual lipids, ozone caused a similar pattern of decreased 18:3 and increased 18:2 in MGDG, SQDG, PC and PE, while the fatty acid composition of DGDG was unaffected. In PG, ozone decreased the proportions of 18:3 and trans -Δ³-decenoic acid (16:1_trans), balanced by increased proportions of palmitic and oleic acids. The contents of chlorophylls and carotenoids were unaffected by ozone. Our results show that moderately elevated levels of ozone cause significant changes in the polar lipid composition of garden pea leaves and in the level of unsaturation of the lipid acyl groups and, furthermore, that ozone has different effects, which could be direct or indirect, on chloroplast lipids (MGDG, DGDG, SQDG, PG acylated with 16:1_trans) and cytosolic membrane lipids.     

Effect of high irradiance and high temperature on chloroplast composition and structure of <Emphasis Type="Italic">Dioscorea zingiberensis</Emphasis>

High irradiance (HI) and high temperature (HT) increased in chloroplasts the content of monogalactosyldiacylglycerol (MGDG) and decreased the contents of digalactosyldiacylglycerol (DGDG), sulfoquinovosyldiacylglycerol (SQDG), and phosphatidylinositol (PI). HI and HT accelerated the transformation of DGDG to MGDG. The contents of unsaturated fatty acids in chloroplasts increased, while those of saturated fatty acids decreased. The contents of total carotenoids, neoxanthin, violaxanthin, lutein, and β-carotene increased first, then decreased. The content of chlorophyll decreased. HI caused the unfolding of thylakoids that was not resumed after a 72-h recovery.     

Effect of Temperature on Growth of Bacillus sp. T-4, a Thermophilic Acidophilic Bacterium

The lipid distribution and function in the thylakoid membranes from a thermophilic cyanobacterium, Mastigocladus laminosus, were investigated. The thylakoid membranes were treated with digitonin and separated on a DEAE-cellulose column into fractions enriched in photosystem I or II complex. Lipid analyses showed a specific distribution of anionic lipids among the fractions. A mild delipidation of the membranes with cholate indicates that monogalactosyl diacylglycerol (MGDG) and sulfoquinovosyl diacylglycerol (SQDG) are released rapidly, while the major parts of digalactosyl diacylglycerol (DGDG) and phosphatidylglycerol (PG) are tightly associated with membranes, suggesting a different distribution between the two groups of lipids. Measurements of fluorescence of delipidated and reconstituted thylakoids showed the contribution of lipids to energy transfer. MGDG enhanced all the original fluorescence of thylakoids, while acidic PG and SQDG stimulated fluorescence of photosystem I and antena chlorophyll-protein complexes. DGDG was less effective under the conditions tested.