scholarly journals Involvement of the HtrA family of proteases in the protection of the cyanobacterium Synechocystis PCC 6803 from light stress and in the repair of photosystem II

2002 ◽  
Vol 357 (1426) ◽  
pp. 1461-1468 ◽  
Author(s):  
Paulo Silva ◽  
Young–Jun Choi ◽  
Hanadi A. G. Hassan ◽  
Peter J. Nixon
Keyword(s):  
Photosystem Ii ◽  
Light Stress ◽  
High Light ◽  
Triple Mutant ◽  
D1 Polypeptide ◽  
In The Wild ◽  
D1 Turnover ◽  
Major Target ◽  
Pcc 6803

Photosystem II (PSII) is prone to irreversible light–induced damage, with the D1 polypeptide a major target. Repair processes operate in the cell to replace a damaged D1 subunit within the complex with a newly synthesized copy. As yet, the molecular details of PSII repair are relatively obscure despite the critical importance of this process for maintaining PSII activity and cell viability. We are using the cyanobacterium Synechocystis sp. PCC 6803 to identify the various proteases and chaperones involved in D1 turnover in vivo . Two families of proteases are being studied: the FtsH family (four members) of Zn 2+ –activated nucleotide–dependent proteases; and the HtrA (or DegP) family (three members) of serine–type proteases. In this paper, we report the results of our studies on a triple mutant in which all three copies of the htrA gene family have been inactivated. Growth of the mutant on agar plates was inhibited at high light intensities, especially in the presence of glucose. Oxygen evolution measurements indicated that, under conditions of high light, the rate of synthesis of functional PSII was less in the mutant than in the wild–type. Immunoblotting experiments conducted on cells blocked in protein synthesis further indicated that degradation of D1 was slowed in the mutant. Overall, our observations indicate that the HtrA family of proteases are involved in the resistance of Synechocystis 6803 to light stress and play a part, either directly or indirectly, in the repair of PSII in vivo .

scholarly journals Replacement of α-Tocopherol by β-Tocopherol Enhances Resistance to Photooxidative Stress in a Xanthophyll-Deficient Strain of Chlamydomonas reinhardtii

2009 ◽  
Vol 8 (11) ◽  
pp. 1648-1657 ◽  
Author(s):  
Anchalee Sirikhachornkit ◽  
Jai W. Shin ◽  
Irene Baroli ◽  
Krishna K. Niyogi
Keyword(s):  
Vitamin E ◽  
Photosystem Ii ◽  
Chlamydomonas Reinhardtii ◽  
Antioxidant Activities ◽  
Lipid Peroxide ◽  
Experimental System ◽  
High Light ◽  
Photooxidative Stress ◽  
Triple Mutant

ABSTRACT Tocopherols (vitamin E) comprise a class of lipid-soluble antioxidants synthesized only in plants, algae, and some cyanobacteria. The majority of tocopherols in photosynthetic cells is in the α form, which has the highest vitamin E activity in humans, whereas the β, γ, and δ forms normally account for a small percentage of total tocopherols. The antioxidant activities of these forms of tocopherol differ depending on the experimental system, and their relative activities in vivo are unclear. In a screen for suppressors of the xanthophyll-deficient npq1 lor1 double mutant of Chlamydomonas reinhardtii, we isolated a vte3 mutant lacking α-tocopherol but instead accumulating β-tocopherol. The vte3 mutant contains a mutation in the homolog of a 2-methyl-6-phytyl-1,4-benzoquinone methyltransferase gene found in plants. The vte3 npq1 lor1 triple mutant with β-tocopherol survived better under photooxidative stress than did the npq1 lor1 mutant, but the vte3 mutant on its own did not have an obvious phenotype. Following transfer from low light to high light, the triple mutant showed a higher efficiency of photosystem II, a higher level of cell viability, and a lower level of lipid peroxide, a marker for oxidative stress, than did the npq1 lor1 mutant. After high-light transfer, the level of the photosystem II reaction center protein, D1, was also higher in the vte3 npq1 lor1 mutant, but the rate of D1 photodamage was not significantly different from that of the npq1 lor1 mutant. Taken together, these results suggest that the replacement of α-tocopherol by β-tocopherol in a xanthophyll-deficient strain of Chlamydomonas reinhardtii contributes to better survival under conditions of photooxidative stress.

scholarly journals Identification of hydroxy-plastochromanol in Arabidopsis leaves.

2010 ◽  
Vol 57 (1) ◽  
Author(s):  
Renata Szymańska ◽  
Jerzy Kruk
Keyword(s):  
Photosystem Ii ◽  
Singlet Oxygen ◽  
Light Stress ◽  
High Light ◽  
Low Light ◽  
High Light Stress ◽  
First Time

In the present study we have identified hydroxy-plastochromanol in plants for the first time. This compound was found both in low light and high light-grown Arabidopsis plants, however, under high light stress its level was considerably increased. Hydroxy-plastochromanol accumulated also during ageing of leaves of low light-grown plants, similarly as in the case of other prenyllipids. Our results indicate that hydroxy-plastochromanol found in leaves is probably formed as a result of plastochromanol oxidation by singlet oxygen generated in photosystem II during photosynthesis. These data also support the hypothesis that plastochromanol is an efficient antioxidant in vivo, similarly as tocopherols and plastoquinol.

scholarly journals Subunit composition of CP43-less photosystem II complexes of Synechocystis sp. PCC 6803: implications for the assembly and repair of photosystem II

2012 ◽  
Vol 367 (1608) ◽  
pp. 3444-3454 ◽  
Author(s):  
M. Boehm ◽  
J. Yu ◽  
V. Reisinger ◽  
M. Beckova ◽  
L. A. Eichacker ◽  
...  
Keyword(s):  
Photosystem Ii ◽  
Gel Electrophoresis ◽  
Photochemical Activity ◽  
Subunit Composition ◽  
Null Mutant ◽  
Trap Potential ◽  
Native Gel ◽  
Oxygen Evolving ◽  
Pcc 6803

Photosystem II (PSII) mutants are useful experimental tools to trap potential intermediates involved in the assembly of the oxygen-evolving PSII complex. Here, we focus on the subunit composition of the RC47 assembly complex that accumulates in a psbC null mutant of the cyanobacterium Synechocystis sp. PCC 6803 unable to make the CP43 apopolypeptide. By using native gel electrophoresis, we showed that RC47 is heterogeneous and mainly found as a monomer of 220 kDa. RC47 complexes co-purify with small Cab-like proteins (ScpC and/or ScpD) and with Psb28 and its homologue Psb28-2. Analysis of isolated His-tagged RC47 indicated the presence of D1, D2, the CP47 apopolypeptide, plus nine of the 13 low-molecular-mass (LMM) subunits found in the PSII holoenzyme, including PsbL, PsbM and PsbT, which lie at the interface between the two momomers in the dimeric holoenzyme. Not detected were the LMM subunits (PsbK, PsbZ, Psb30 and PsbJ) located in the vicinity of CP43 in the holoenzyme. The photochemical activity of isolated RC47-His complexes, including the rate of reduction of P680 + , was similar to that of PSII complexes lacking the Mn 4 CaO 5 cluster. The implications of our results for the assembly and repair of PSII in vivo are discussed.

Is the in vivo Photosystem I Function Resistant to Photoinhibition? An Answer from Photoacoustic and Far-Red Absorbance Measurements in Intact Leaves

1991 ◽  
Vol 46 (11-12) ◽  
pp. 1038-1044 ◽  
Author(s):  
Michel Havaux ◽  
Murielle Eyletters
Keyword(s):  
Light Stress ◽  
Red Light ◽  
Light Treatment ◽  
High Light ◽  
Saturation Curve ◽  
Strong Light ◽  
Ps Ii ◽  
Fluorescence Measurements ◽  
Ps I

Abstract Preillumination of intact pea leaves with a strong blue-green light of 400 W m-2 markedly inhibited both photoacoustically monitored O2-evolution activity and PS II photochemistry as estimated from chlorophyll fluorescence measurements. The aim of the present work was to examine, with the help of the photoacoustic technique, whether this high-light treatment deteriorated the in vivo PS I function too. High-frequency photoacoustic measurements indicated that photochemical conversion of far-red light energy in PS I was preserved (and even transiently stimulated) whereas photochemical energy storage monitored in light exciting both PS I and PS II was markedly diminished. Low-frequency photoacoustic measurements of the Emerson enhancement showed a spectacular change in the PS II/PS I activity balance in favor of PS I. It was also observed that the linear portion of the saturation curve of the far-red light effect in the Emerson enhancement was not changed by the light treatment. Those results lead to the conclusion that, in contrast to PS II, the in vivo PS I photofunctioning was resistant to strong light stress, thus confirming previous suggestions derived from in vitro studies. Estimation of the redox state of the PS I reaction center by leaf absorbance measurements at ca. 820 nm suggested that, under steady illumination, a considerably larger fraction of PS I centers were in the closed state in high-light pretreated leaves as compared to control leaves, presumably allowing passive adjustment of the macroscopic quantum yield of PS I photochemis­ try to the strongly reduced photochemical efficiency of photoinhibited PS II.

scholarly journals The role of inactive photosystem–II–mediated quenching in a last–ditch community defence against high light stress in vivo

2002 ◽  
Vol 357 (1426) ◽  
pp. 1441-1450 ◽  
Author(s):  
Wah Soon Chow ◽  
Hae–Youn Lee ◽  
Youn–Il Park ◽  
Yong–Mok Park ◽  
Yong–Nam Hong ◽  
...  
Keyword(s):  
Photosystem Ii ◽  
Light Stress ◽  
Extreme Environments ◽  
Photosynthetic Apparatus ◽  
Optimal Operation ◽  
Residual Fraction ◽  
Photosynthetic Membrane ◽  
Number Of Factors ◽  
Inactive Photosystem Ii

Photoinactivation of photosystem II (PSII), the light–induced loss of ability to evolve oxygen, is an inevitable event during normal photosynthesis, exacerbated by saturating light but counteracted by repair via new protein synthesis. The photoinactivation of PSII is dependent on the dosage of light: in the absence of repair, typically one PSII is photoinactivated per 10 7 photons, although the exact quantum yield of photoinactivation is modulated by a number of factors, and decreases as fewer active PSII targets are available. PSII complexes initially appear to be photoinactivated independently; however, when less than 30% functional PSII complexes remain, they seem to be protected by strongly dissipative PSII reaction centres in several plant species examined so far, a mechanism which we term ‘inactive PSII–mediated quenching‘. This mechanism appears to require a pH gradient across the photosynthetic membrane for its optimal operation. The residual fraction of functional PSII complexes may, in turn, aid in the recovery of photoinactivated PSII complexes when conditions become less severe. This mechanism may be important for the photosynthetic apparatus in extreme environments such as those experienced by over–wintering evergreen plants, desert plants exposed to drought and full sunlight and shade plants in sustained sunlight.

scholarly journals CpcM Posttranslationally Methylates Asparagine-71/72 of Phycobiliprotein Beta Subunits in Synechococcus sp. Strain PCC 7002 and Synechocystis sp. Strain PCC 6803

2008 ◽  
Vol 190 (14) ◽  
pp. 4808-4817 ◽  
Author(s):  
Gaozhong Shen ◽  
Heidi S. Leonard ◽  
Wendy M. Schluchter ◽  
Donald A. Bryant
Keyword(s):  
Light Stress ◽  
Fluorescence Emission ◽  
High Light ◽  
State Transitions ◽  
Comparative Genomic ◽  
Beta Subunits ◽  
Wild Type ◽  
Light Harvesting Complexes ◽  
Type Strains ◽  
Pcc 6803

ABSTRACT Cyanobacteria produce phycobilisomes, which are macromolecular light-harvesting complexes mostly assembled from phycobiliproteins. Phycobiliprotein beta subunits contain a highly conserved γ-N-methylasparagine residue, which results from the posttranslational modification of Asn71/72. Through comparative genomic analyses, we identified a gene, denoted cpcM, that (i) encodes a protein with sequence similarity to other S-adenosylmethionine-dependent methyltransferases, (ii) is found in all sequenced cyanobacterial genomes, and (iii) often occurs near genes encoding phycobiliproteins in cyanobacterial genomes. The cpcM genes of Synechococcus sp. strain PCC 7002 and Synechocystis sp. strain PCC 6803 were insertionally inactivated. Mass spectrometric analyses of phycobiliproteins isolated from the mutants confirmed that the CpcB, ApcB, and ApcF were 14 Da lighter than their wild-type counterparts. Trypsin digestion and mass analyses of phycobiliproteins isolated from the mutants showed that tryptic peptides from phycocyanin that included Asn72 were also 14 Da lighter than the equivalent peptides from wild-type strains. Thus, CpcM is the methyltransferase that modifies the amide nitrogen of Asn71/72 of CpcB, ApcB, and ApcF. When cells were grown at low light intensity, the cpcM mutants were phenotypically similar to the wild-type strains. However, the mutants were sensitive to high-light stress, and the cpcM mutant of Synechocystis sp. strain PCC 6803 was unable to grow at moderately high light intensities. Fluorescence emission measurements showed that the ability to perform state transitions was impaired in the cpcM mutants and suggested that energy transfer from phycobiliproteins to the photosystems was also less efficient. The possible functions of asparagine N methylation of phycobiliproteins are discussed.

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