The physiological significance of photosystem II heterogeneity in chloroplasts

Guenther, Jeanne E.; Melis, Anastasios

doi:10.1007/bf00030070

Cited by 162 publications

(82 citation statements)

References 18 publications

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“…Also in agreement with earlier studies (9,27), we found that photoinhibition adversely affected PSII,, whereas PSIIp appeared resistant to damage (Fig. 4) (17,18). A schematic depicting the role of this activation in the general PSII repair cycle is given in Figure 9.…”

Section: Discussionsupporting

confidence: 79%

Activation of a Reserve Pool of Photosystem II in Chlamydomonas reinhardtii Counteracts Photoinhibition

Neale¹,

Melis²

1990

Current Research in Photosynthesis

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The effect of strong irradiance (Q000 micromole photons per square meter per second) on PSII heterogeneity in intact cells of Chiamydomonas reinhardtii was investigated. Low light (LL,15 micromole photons per square meter per second) grown C. reinhardtii are photoinhibited upon exposure to strong irradiance, and the loss of photosynthetic functioning is due to damage to PSII. Under physiological growth conditions, PSII is distributed into two pools. The large antenna size (PSIIa) centers account for about 70% of all PSII in the thylakoid membrane and are responsible for plastoquinone reduction (OB-reducing centers). The smaller antenna (PSII) account for the remainder of PSII and exist in astate not yet able to photoreduce plastoquinone (0B-nonreducing centers). The exposure of C. reinhardtii cells to 60 minutes of strong irradiance disabled about half of the primary charge separation between P680 and pheophytin. The PSII,content remained the same or slightly increased during strong-irradiance treatment, whereas the photochemical activity of PSIIa decreased by 80%. Analysis of fluorescence induction transients displayed by intact cells indicated that strong irradiance led to a conversion of PSlI,6 from a 0.-nonreducing to a QO-reducing state. Parallel measurements of the rate of oxygen evolution revealed that photosynthetic electron transport was maintained at high rates, despite the loss of activity by a majority of PSIIa. The results suggest that PSlI, in C. reinhardtii may serve as a reserve pool of PSII that augments photosynthetic electron-transport rates during exposure to strong irradiance and partially compensates for the adverse effect of photoinhibition on PSII,. When isolated spinach thylakoids were illuminated with strong-irradiance (2500 Amol.m-2 s-') at 0C, both the QA2 (320 nm absorbance change) and Pheo (685 nm absorbance change) signal were lowered in parallel (8,9,12), suggesting inhibition of primary photochemistry. The PSII primary charge separation was also inhibited when intact cells of the green alga, Chiamydomonas reinhardtii, were exposed to strong irradiance (12). The rapid loss of the pheophytin photoreduction during photoinhibition has also been detected using EPR difference spectroscopy (46). These results indicated that photoinhibitory damage affected the ability of PSII to form the P680+ Pheo-charge separation.An alternative proposal (22, 37) is that photoinhibition results from light-dependent damage to the plastoquinone binding site, which is located on the 32 kD 'Dl' polypeptide of PSII. According to the latter model, only electron transfer from QA to the bound plastoquinone, QB, is disrupted, whereas no damage occurs to the water splitting enzyme or the reaction center. Support for this proposal was found in the rapid in vivo turnover of Dl in C. reinhardtii (22, 37). Subsequently, it has been accepted that the functional components of the PSII reaction center (Mn, Z, P680, Pheo, QA and QB) are all bound to the Dl/D2 heterodimer in analogy with the structure of the crys...

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Section: Discussionsupporting

confidence: 79%

Activation of a Reserve Pool of Photosystem II in Chlamydomonas reinhardtii Counteracts Photoinhibition

Neale¹,

Melis²

1990

Current Research in Photosynthesis

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“…As PSII in unstacked regions of the plant thylakoid may correspond to photosystems that are undergoing repair [33,34], the interchange between monomeric and dimeric PSII complexes in the membrane indeed may be rapid. However, if there are nascent PSII components that are stable in the membrane for several hours, then the interchange between monomers and dimers might not be that rapid for all PSII proteins.…”

Section: Turnover Of Psii and Psi Proteinsmentioning

confidence: 99%

Lifetimes of photosystem I and II proteins in the cyanobacterium Synechocystis sp. PCC 6803

2011

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Edited by Richard CogdellKeywords: Photosystem I Photosystem II Small Cab-like protein Protein turnover Half-life time a b s t r a c tThe half-life times of photosystem I and II proteins were determined using 15 N-labeling and mass spectrometry. The half-life times (30-75 h for photosystem I components and <1-11 h for the large photosystem II proteins) were similar when proteins were isolated from monomeric vs. oligomeric complexes on Blue-Native gels, suggesting that the two forms of both photosystems can interchange on a timescale of <1 h or that only one form of each photosystem exists in thylakoids in vivo. The half-life times of proteins associated with either photosystem generally were unaffected by the absence of Small Cab-like proteins.

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“…In intact cells of photosynthetic organisms, photoinhibition is a more complex phenomenon than it is in vitro because photodamaged PSII is rapidly repaired. The main feature of the repair process is the replacement of the D1 protein in the photodamaged PSII by newly synthesized D1 and reassembly of active PSII (Guenther and Melis, 1990;Kettunen et al, 1997; for review, see Mattoo et al, 1989;Aro et al, 1993;Andersson and Aro, 2001). Therefore, the extent of photoinhibition in vivo reflects the balance between the light-induced damage (photodamage) to PSII and the repair of the photodamaged PSII.…”

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confidence: 99%

Systematic Analysis of the Relation of Electron Transport and ATP Synthesis to the Photodamage and Repair of Photosystem II in Synechocystis

et al. 2005

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(I.S., N.M.) The photosynthetic machinery and, in particular, the photosystem II (PSII) complex are susceptible to strong light, and the effects of strong light are referred to as photodamage or photoinhibition. In living organisms, photodamaged PSII is rapidly repaired and, as a result, the extent of photoinhibition represents a balance between rates of photodamage and the repair of PSII. In this study, we examined the roles of electron transport and ATP synthesis in these two processes by monitoring them separately and systematically in the cyanobacterium Synechocystis sp. PCC 6803. We found that the rate of photodamage, which was proportional to light intensity, was unaffected by inhibition of the electron transport in PSII, by acceleration of electron transport in PSI, and by inhibition of ATP synthesis. By contrast, the rate of repair was reduced upon inhibition of the synthesis of ATP either via PSI or PSII. Northern blotting and radiolabeling analysis with [ 35 S]Met revealed that synthesis of the D1 protein was enhanced by the synthesis of ATP. Our observations suggest that ATP synthesis might regulate the repair of PSII, in particular, at the level of translation of the psbA genes for the precursor to the D1 protein, whereas neither electron transport nor the synthesis of ATP affects the extent of photodamage.

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The physiological significance of photosystem II heterogeneity in chloroplasts

Cited by 162 publications

References 18 publications

Activation of a Reserve Pool of Photosystem II in Chlamydomonas reinhardtii Counteracts Photoinhibition

Activation of a Reserve Pool of Photosystem II in Chlamydomonas reinhardtii Counteracts Photoinhibition

Lifetimes of photosystem I and II proteins in the cyanobacterium Synechocystis sp. PCC 6803

Systematic Analysis of the Relation of Electron Transport and ATP Synthesis to the Photodamage and Repair of Photosystem II in Synechocystis

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