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71.
72.
Eira Kanervo Marjaana Suorsa Eva-Mari Aro 《Photochemical & photobiological sciences》2005,4(12):1072-1080
Light is an elusive substrate for the function of photosynthetic light reactions of photosynthesis in the thylakoid membrane. Therefore structural and functional dynamics, which occur in the timescale from seconds to several days, are required both at low and high light conditions. The best characterized short-time regulation mechanism at low light is a rapid state transition, resulting in higher absorption cross section of PSI at the expense of PSII. If the low light conditions continue, activation of the lhcb-genes and synthesis of the light-harvesting proteins will occur to optimize the functions of PSII and PSI. At high light, the transition to state 2 is completely inhibited, but the feedback de-excitation of absorbed energy as heat, known as the energy-dependent quenching (q(E)), is rapidly set up. It requires, at least, the DeltapH-dependent activation of violaxanthin de-epoxidase and involvement of the PsbS protein. Another crucial mechanism for protection against the high light stress is the PSII repair cycle. Furthermore, the water-water cycle, cyclic electron transfer around PSI and chlororespiration are important means induced under high irradiation, functioning mainly to avoid an excess production of reactive oxygen species. 相似文献
73.
Marko Boehm Jon Nield Pengpeng Zhang Eva-Mari Aro Josef Komenda Peter J. Nixon 《Journal of bacteriology》2009,191(20):6425-6435
Band 7 proteins, which encompass members of the stomatin, prohibitin, flotillin, and HflK/C protein families, are integral membrane proteins that play important physiological roles in eukaryotes but are poorly characterized in bacteria. We have studied the band 7 proteins encoded by the cyanobacterium Synechocystis sp. strain PCC 6803, with emphasis on their structure and proposed role in the assembly and maintenance of the photosynthetic apparatus. Mutagenesis revealed that none of the five band 7 proteins (Slr1106, Slr1128, Slr1768, Sll0815, and Sll1021) was essential for growth under a range of conditions (including high light, salt, oxidative, and temperature stresses), although motility was compromised in an Slr1768 inactivation mutant. Accumulation of the major photosynthetic complexes in the thylakoid membrane and repair of the photosystem II complex following light damage were similar in the wild type and a quadruple mutant. Cellular fractionation experiments indicated that three of the band 7 proteins (Slr1106, Slr1768, and Slr1128) were associated with the cytoplasmic membrane, whereas Slr1106, a prohibitin homologue, was also found in the thylakoid membrane fraction. Blue native gel electrophoresis indicated that these three proteins, plus Sll0815, formed large (>669-kDa) independent complexes. Slr1128, a stomatin homologue, has a ring-like structure with an approximate diameter of 16 nm when visualized by negative stain electron microscopy. No evidence for band 7/FtsH supercomplexes was found. Overall, our results indicate that the band 7 proteins form large homo-oligomeric complexes but do not play a crucial role in the biogenesis of the photosynthetic apparatus in Synechocystis sp. strain PCC 6803.Members of the band 7 superfamily of proteins are found throughout nature and are defined by a characteristic sequence motif, termed the SPFH domain, after the initials of the various subfamilies: the stomatins, the prohibitins, the flotillins (also known as “reggies”), and the HflK/C proteins (12, 49). The stomatins and prohibitins and to a lesser extent flotillins are highly conserved protein families and are found in a variety of organisms ranging from prokaryotes to higher eukaryotes (29, 34, 49), whereas HflK and HflC homologues are only present in bacteria.In eukaryotes band 7 proteins are linked with a variety of disease states consistent with important cellular functions (6). In general the eukaryotic band 7 proteins tend to be oligomeric and are involved in membrane-associated processes: for example, prohibitins are involved in modulating the activity of a membrane-bound FtsH protease (17, 46) and the assembly of mitochondrial respiratory complexes (30), stomatins are involved in ion channel function (47), and flotillins are involved in signal transduction and vesicle trafficking (25).In the case of prokaryotes, most work so far has focused on the roles of the HflK/C and YbbK (also known as QmcA, a stomatin homologue) band 7 proteins of Escherichia coli (7, 16, 17, 36) and the structure of a stomatin homologue in the archaeon Pyrococcus horikoshii (57). Much less is known about the structure, function, and physiological importance of band 7 proteins in other prokaryotes, especially the cyanobacteria (12).The unicellular cyanobacterium Synechocystis sp. strain PCC 6803 is a widely used model organism for studying various aspects of cyanobacterial physiology and, in particular, oxygenic photosynthesis. One of the main areas of our research is to understand the mechanism by which the oxygen-evolving photosystem II (PSII) complex found in the thylakoid membrane of Synechocystis sp. strain PCC 6803 is repaired following light damage. Recent work has identified an important role for FtsH proteases in PSII repair (19, 41). Given that FtsH is known to form large supercomplexes with HflK/C in E. coli (36) and with prohibitins in Saccharomyces cerevisiae mitochondria (46), we hypothesized that one or more band 7 proteins might interact with FtsH in cyanobacteria and play a role in the selective turnover of the D1 reaction center polypeptide during PSII repair and so provide resistance to high light stress (40). This idea was given early support by the detection of both FtsH and Slr1106, a prohibitin homologue, in a His-tagged PSII preparation isolated from Synechocystis sp. strain PCC 6803 (40) and the detection of Slr1128 (a stomatin homologue), Sll1021 (a possible flotillin homologue), and FtsH in a His-tagged preparation of ScpD, a small chlorophyll a/b-like-binding protein that associates with PSII (56). Recent mutagenesis experiments have also suggested a role for Slr1128 in maintaining growth at high light intensities (53).In this paper we have used targeted gene disruption mutagenesis and various biochemical approaches to investigate the structure and function of band 7 proteins in Synechocystis sp. strain PCC 6803, with particular emphasis on PSII function. We provide evidence that four predicted band 7 proteins in Synechocystis sp. strain PCC 6803 (Slr1106, Slr1768, Slr1128, and Sll8015) form large independent complexes, which in the case of Slr1128 forms a ring-like structure. No evidence was found for the formation of supercomplexes with FtsH. Importantly, single and multiple insertion mutants lacking up to four of the five band 7 proteins are able to grow as well as the wild type (WT) under a range of growth conditions, including high light stress. Our results suggest that band 7 proteins are not essential in Synechocystis sp. strain PCC 6803 and are not required for efficient PSII repair. Possible functions of the cyanobacterial band 7 proteins are discussed in the light of recent results from other systems. 相似文献
74.
Lundin B Nurmi M Rojas-Stuetz M Aro EM Adamska I Spetea C 《Photosynthesis research》2008,98(1-3):405-414
The extrinsic PsbO subunit of the water-oxidizing photosystem II (PSII) complex is represented by two isoforms in Arabidopsis thaliana, namely PsbO1 and PsbO2. Recent analyses of psbo1 and psbo2 knockout mutants have brought insights into their roles in photosynthesis and light stress. Here we analyzed the two psbo mutants in terms of PsbOs expression pattern, organization of PSII complexes and GTPase activity. Both PsbOs are present in wild-type plants, and their expression is mutually controlled in the mutants. Almost all PSII complexes are in the monomeric form not only in the psbo1 but also in the psbo2 mutant grown under high-light conditions. This results either from an enhanced susceptibility of PSII to photoinactivation or from malfunction of the repair cycle. Notably, the psbo1 mutant displays such problems even under growth-light conditions. These results together with the finding that PsbO2 has a threefold higher GTPase activity than PsbO1 have significance for the turnover of the PSII D1 subunit in Arabidopsis. 相似文献
75.
Marjaana Suorsa Michele Grieco Sari J?rvi Peter J. Gollan Saijaliisa Kangasj?rvi Mikko Tikkanen Eva-Mari Aro 《Plant signaling & behavior》2013,8(1)
In a plant’s natural environment, the intensity of light can change rapidly due to sunflecks, cloudiness and intermittent shading. Fluctuations between high and low illumination phases expose the photosynthetic machinery to rapidly changing signals that can be overlapping or contradictory, and accordingly plants have developed astute acclimation strategies to maintain optimal photosynthetic performance in these conditions. Continuous exposure to high light induces an array of protective mechanisms at anatomical, chemical and molecular levels, but when high light phases are short, such as under fluctuating light conditions, the protective strategies that afford protection to constant high light are not employed by plants. One mechanism that is engaged under both constant and fluctuating high light is the photosynthetic control of the Cyt b6f complex, which prevents hyper-reduction of the electron transfer chain in order to protect PSI from photodamage. The PGR5 protein was recently shown to play an indispensable role in this protective mechanism. This review revisits the findings of earlier studies into photosynthetic control and places PGR5 within the broader context of photoprotection and light acclimation strategies. 相似文献
76.
Irina Grouneva Peter J. Gollan Saijaliisa Kangasjärvi Marjaana Suorsa Mikko Tikkanen Eva-Mari Aro 《Planta》2013,237(2):399-412
The comparative study of photosynthetic regulation in the thylakoid membrane of different phylogenetic groups can yield valuable insights into mechanisms, genetic requirements and redundancy of regulatory processes. This review offers a brief summary on the current understanding of light harvesting and photosynthetic electron transport regulation in different photosynthetic eukaryotes, with a special focus on the comparison between higher plants and unicellular algae of secondary endosymbiotic origin. The foundations of thylakoid structure, light harvesting, reversible protein phosphorylation and PSI-mediated cyclic electron transport are traced not only from green algae to vascular plants but also at the branching point between the “green” and the “red” lineage of photosynthetic organisms. This approach was particularly valuable in revealing processes that (1) are highly conserved between phylogenetic groups, (2) serve a common physiological role but nevertheless originate in divergent genetic backgrounds or (3) are missing in one phylogenetic branch despite their unequivocal importance in another, necessitating a search for alternative regulatory mechanisms and interactions. 相似文献
77.
Trotta A Wrzaczek M Scharte J Tikkanen M Konert G Rahikainen M Holmström M Hiltunen HM Rips S Sipari N Mulo P Weis E von Schaewen A Aro EM Kangasjärvi S 《Plant physiology》2011,156(3):1464-1480
Light is an important environmental factor that modulates acclimation strategies and defense responses in plants. We explored the functional role of the regulatory subunit B'γ (B'γ) of protein phosphatase 2A (PP2A) in light-dependent stress responses of Arabidopsis (Arabidopsis thaliana). The predominant form of PP2A consists of catalytic subunit C, scaffold subunit A, and highly variable regulatory subunit B, which determines the substrate specificity of PP2A holoenzymes. Mutant leaves of knockdown pp2a-b'γ plants show disintegration of chloroplasts and premature yellowing conditionally under moderate light intensity. The cell-death phenotype is accompanied by the accumulation of hydrogen peroxide through a pathway that requires CONSTITUTIVE EXPRESSION OF PR GENES5 (CPR5). Moreover, the pp2a-b'γ cpr5 double mutant additionally displays growth suppression and malformed trichomes. Similar to cpr5, the pp2a-b'γ mutant shows constitutive activation of both salicylic acid- and jasmonic acid-dependent defense pathways. In contrast to cpr5, however, pp2a-b'γ leaves do not contain increased levels of salicylic acid or jasmonic acid. Rather, the constitutive defense response associates with hypomethylation of DNA and increased levels of methionine-salvage pathway components in pp2a-b'γ leaves. We suggest that the specific B'γ subunit of PP2A is functionally connected to CPR5 and operates in the basal repression of defense responses under low irradiance. 相似文献
78.
Chen G Allahverdiyeva Y Aro EM Styring S Mamedov F 《Biochimica et biophysica acta》2011,1807(2):205-215
Arabidopsis thaliana is widely used as a model organism in plant biology as its genome has been sequenced and transformation is known to be efficient. A large number of mutant lines and genomic resources are available for Arabidopsis. All this makes Arabidopsis a useful tool for studies of photosynthetic reactions in higher plants. In this study, photosystem II (PSII) enriched membranes were successfully isolated from thylakoids of Arabidopsis plants and for the first time the electron transfer cofactors in PSII were systematically studied using electron paramagnetic resonance (EPR) spectroscopy. EPR signals from both of the donor and acceptor sides of PSII, as well as from auxiliary electron donors were recorded. From the acceptor side of PSII, EPR signals from Q(A)- Fe2(+) and Phe- Q(A)- Fe2(+) as well as from the free Phe- radical were observed. The multiline EPR signals from the S?- and S?-states of CaMn?O(x)-cluster in the water oxidation complex were characterized. Moreover, split EPR signals, the interaction signals from Y(Z) and CaMn?O(x)-cluster in the S?-, S?-, S?-, and the S?-state were induced by illumination of the PSII membranes at 5K and characterized. In addition, EPR signals from auxiliary donors Y(D), Chl(+) and cytochrome b??? were observed. In total, we were able to detect about 20 different EPR signals covering all electron transfer components in PSII. Use of this spectroscopic platform opens a possibility to study PSII reactions in the library of mutants available in Arabidopsis. 相似文献
79.
The effect of copper on
photoinhibition of photosystem II in vivo was studied in
bean (Phaseolus vulgaris L. cv Dufrix). The plants were
grown hydroponically in the presence of various concentrations of
Cu2+ ranging from the optimum 0.3 μm
(control) to 15 μm. The copper concentration of leaves
varied according to the nutrient medium from a control value of 13 mg
kg−1 dry weight to 76 mg kg−1 dry weight.
Leaf samples were illuminated in the presence and absence of lincomycin
at different light intensities (500–1500 μmol photons
m−2 s−1). Lincomycin prevents the concurrent
repair of photoinhibitory damage by blocking chloroplast protein
synthesis. The photoinhibitory decrease in the light-saturated rate of
O2 evolution measured from thylakoids isolated from treated
leaves correlated well with the decrease in the ratio of variable to
maximum fluorescence measured from the leaf discs; therefore, the
fluorescence ratio was used as a routine measurement of photoinhibition
in vivo. Excess copper was found to affect the
equilibrium between photoinhibition and repair, resulting in a decrease
in the steady-state concentration of active photosystem II centers of
illuminated leaves. This shift in equilibrium apparently resulted from
an increase in the quantum yield of photoinhibition (ΦPI)
induced by excess copper. The kinetic pattern of photoinhibition and
the independence of ΦPI on photon flux density were not
affected by excess copper. An increase in ΦPI may
contribute substantially to Cu2+ toxicity in certain plant
species.Cu2+ is an essential micronutrient but in
excess is toxic for plants. It is a redox-active metal that functions
as an enzyme activator and is an important part of prosthetic groups of
many enzymes (for review, see Sandmann and Böger, 1983). Copper
concentrations in healthy plant tissues range from 5 to 20 mg
kg−1 dry weight. In
Cu2+-rich environments, accumulation of
Cu2+ in plant tissues depends on the species and
cultivar. Cu2+ seems to have several sites of
action, which vary among plant species. Toxic concentrations of
Cu2+ inhibit metabolic activity, which leads to
suppressed growth and slow development. Most Cu2+
ions are immobilized to the cell walls of roots or of mycorrhizal fungi
(Kahle, 1993).When the tolerance mechanisms in the root zone become overloaded,
Cu2+ is translocated by both the xylem and phloem
up to the leaves. Excess Cu2+ may replace other
metals in metalloproteins or may interact directly with SH groups of
proteins (Uribe and Stark, 1982). Cu2+-induced
free-radical formation may also cause protein damage (for review, see
Fernandes and Henriques, 1991; Weckx and Clijsters, 1996). High
concentrations of Cu2+ may catalyze the formation
of the hydroxyl radical from O2 and
H2O2. This
Cu2+-catalyzed Fenton-type reaction takes place
mainly in chloroplasts (Sandmann and Böger, 1980). The hydroxyl
radical may start the peroxidation of unsaturated membrane lipids and
chlorophyll (Sandmann and Böger, 1980), and these inhibitory
mechanisms might contribute to the observed inhibition of
photosynthetic electron transport by excess Cu2+
(Clijsters and Van Assche, 1985).The role of Cu2+ as an inhibitor of
photosynthetic electron transport has been studied in vitro. Both the
donor (Cedeno-Maldonado and Swader, 1972; Samuelsson and Öquist,
1980; Schröder et al., 1994) and acceptor (Mohanty et al., 1989;
Yruela et al., 1992, 1993, 1996a, 1996b; Jegerschöld et al.,
1995) sides of PSII have been proposed to be the most sensitive site
for Cu2+ action. On the donor side,
Cu2+ is thought to inhibit electron transport to
P680, the primary donor of PSII (Schröder et al., 1994). On the
acceptor side, Cu2+ interactions with the
pheophytin-QA-Fe2+-domain
or Cu2+-induced modifications in the amino acid
or lipid structure close to the QA- and
QB-binding sites have been suggested to cause the
inhibition of electron transport (Jegerschöld et al., 1995;
Yruela et al., 1996a, 1996b).Celeno-Maldonado and Swader (1972) noticed that preincubation of
chloroplasts in the light enhanced the
Cu2+-induced inhibition of electron transport,
and that PSII was more susceptible to this kind of inhibition than was
PSI. The hypothetical acceptor- and donor-side mechanisms of the
light-induced inhibition of electron transport, photoinhibition,
involve the same domains of attack as Cu2+. Both
acceptor- and donor-side photoinhibition trigger the D1 polypeptide of
the PSII reaction center for degradation (for review, see Aro et al.,
1993). The damaged D1 protein is degraded, and the recovery of PSII
activity needs de novo synthesis of D1 protein. Photoinhibition occurs
at all light intensities (Tyystjärvi and Aro, 1996); therefore,
the cycle of PSII photoinhibition, which is followed by degradation,
and, finally, resynthesis of the D1 protein, runs constantly in plant
cells in the light. If the photoinhibition-repair cycle is allowed to
run for some time at a constant light intensity, equilibrium is
reached. At equilibrium (steady state), all three reaction rates
(photoinhibition, D1 degradation, and D1 synthesis) are equal. Healthy
plants are often able to maintain a high steady-state concentration of
active PSII under widely varying light intensities. Even if the
concentration of active PSII is lowered by high light, the
concentration of D1 protein tends to stay fairly constant (Cleland et
al., 1990; Kettunen et al., 1991). In the bean (Phaseolus
vulgaris L.) plants used in this study the steady-state D1 protein
content remained almost constant even in the presence of excess
Cu2+.The effect of Cu2+ on photoinhibition in
vivo has been studied very little. Vavilin et al. (1995) suggest that
excess Cu2+ may slow the PSII repair cycle in the
green alga Chlorella pyrenoidosa, and Ouzounidou et al.
(1997) suggest that Cu2+ inhibits adaptation to
light in maize. In the current study we show that excess
Cu2+ induces a large increase in the rate
constant of photoinhibition in vivo in a higher plant. 相似文献
80.
The effect of copper on photoinhibition of photosystem II (PSII) in vitro was studied in bean ( Phaseolus vulgaris L. cv. Dufrix) and pumpkin ( Cucurbita pepo L.) thylakoids. The thylakoids were illuminated at 200–2 000 μmol photons m−2 s−1 in the presence of 70–1 830 added Cu2+ ions per PSII. Three lines of evidence show that the irreversible damage of PSII caused by illumination of thylakoids in the presence of Cu2+ was mainly due to donor-side photoinhibition resulting from inhibition of the PSII donor side by Cu2+ . First, addition of an artificial electron donor partially restored PSII activity of thylakoids that had been illuminated in the presence of Cu2+ . Second, already moderate light was enough to cause rapid inhibition of PSII, and the inhibition could be saturated by light. Third, the extrinsic polypeptides of the oxygen-evolving complex were found to become oxidized by the combined effect of Cu2+ and light. The presence of oxygen was not necessary for the copper-induced enhancement of photoinhibition of PSII. When the illumination was prolonged, copper caused a gradual collapse of the thylakoid structure by increasing degradation of thylakoid proteins. 相似文献