Studies on reactions of illuminated chloroplasts

Mehler, Alan H.

doi:10.1016/0003-9861(51)90082-3

Cited by 739 publications

(104 citation statements)

References 11 publications

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“…If light energy perception exceeds the electron sink capacities of photosynthesis, increasing amounts of reactive oxygen species are formed (e.g. via the Mehler reaction) (24), and 2-Cys Prx gets overoxidized. Prx oligomerizes (Fig.…”

Section: Inactivation Occurs In Vivo Under Several Stress Conditionsmentioning

confidence: 99%

Reaction Mechanism of Plant 2-Cys Peroxiredoxin

König¹,

Lotte

Plessow

et al. 2003

Journal of Biological Chemistry

170

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Barley 2-cysteine peroxiredoxin (2-Cys Prx) was analyzed for peroxide reduction, quaternary structure, thylakoid attachment, and function as well as in vivo occurrence of the inactivated form, with emphasis on the role of specific amino acid residues. Data presented show the following. 1) 2-Cys Prx has a broad substrate specificity and reduces even complex lipid peroxides such as phosphatidylcholine dilineoyl hydroperoxide, although at low rates. 2) 2-Cys Prx partly becomes irreversibly oxidized by peroxide substrates during the catalytic cycle in a concentration-dependent manner, particularly by bulky hydroperoxides.

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Section: Inactivation Occurs In Vivo Under Several Stress Conditionsmentioning

confidence: 99%

Reaction Mechanism of Plant 2-Cys Peroxiredoxin

König¹,

Lotte

Plessow

et al. 2003

Journal of Biological Chemistry

170

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“…These electrons are transferred to oxygen by photosystem I (PSI) and result in the formation of superoxide radicals (O 2 . ) (5). A membrane-attached copper/zinc superoxide dismutase (Cu/ZnSOD) converts the superoxide radicals into hydrogen peroxide, and a membrane-bound ascorbate peroxidase (thylakoid-APX) converts the hydrogen peroxide back into water.…”

mentioning

confidence: 99%

The Water-Water Cycle Is Essential for Chloroplast Protection in the Absence of Stress

Rizhsky

Liang

Mittler

2003

Journal of Biological Chemistry

216

176

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Maintaining electron flow through the photosynthetic apparatus, even in the absence of a sufficient amount of NADP ؉ as an electron acceptor, is essential for chloroplast protection from photooxidative stress. At least two different pathways are thought to participate in this process, i.e. cyclic electron flow and the water-water cycle. Although the function of the water-water cycle was inferred from a number of biochemical and physiological studies, genetic evidence for the function of this cycle is very limited. Here we show that knockdown Arabidopsis plants with suppressed expression of the key water-water cycle enzyme, thylakoid-attached copper/zinc superoxide dismutase (KD-SOD), are suppressed in their growth and development. Chloroplast size, chlorophyll content, and photosynthetic activity were also reduced in KD-SOD plants. Microarray analysis of KD-SOD plants, grown under controlled conditions, revealed changes in transcript expression consistent with an acclimation response to light stress. Although a number of transcripts involved in the defense of plants from oxidative stress were induced in KD-SOD plants, and seedlings of KD-SOD plants were more tolerant to oxidative stress, these mechanisms were unable to compensate for the suppression of the water-water cycle in mature leaves. Thus, the localization of copper/zinc superoxide dismutase at the vicinity of photosystem I may be essential for its function. Our studies provide genetic evidence for the importance of the water-water cycle in protecting the photosynthetic apparatus of higher plants from photooxidative damage.Dissipation of excess energy absorbed by the photosynthetic apparatus is a fundamental process essential for the survival of almost all photosynthetic organisms. It prevents photooxidative damage that occurs when excited chlorophyll molecules improperly transfer their higher energy state to oxygen or neighboring molecules and convert them into reactive molecules or toxic radicals (1-3). This process is especially crucial when CO 2 fixation is limited because of environmental conditions such as cold or drought. Under these conditions, the energy absorbed by the photosynthetic apparatus cannot be channeled into the reduction of CO 2 , and photooxidative damage may occur (4). Maintaining electron flow through the photosynthetic membrane, even under stressful conditions, is therefore vital for preventing damage to plant cells (2). A number of different pathways are thought to cooperate in protecting the photosynthetic apparatus from photooxidative stress. These include the zeaxanthin cycle that directly protects the antenna molecules and the cyclic electron flow and the waterwater cycle that shunt electrons through the photosynthetic apparatus and maintain the pH gradient in the chloroplast, which is essential for the function of the zeaxanthin cycle (1, 2).The water-water cycle channels electrons obtained from the splitting of water molecules at photosystem II (PSII) 1 through the photosynthetic apparatus. These electrons are transferred ...

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“…Three plausible sites of oxygen radical formation were previously suggested : (1) oxygen reduction at the acceptor side of PS I [16] (Mehler reaction), (2) oxygen reduction at the acceptor side of PS II [17] and (3) water-oxidation at the donor side of PS II [18]. In the present study, we used a mutant of C. reinhardtii in which the oxygen evolving system is nonfunctional, making whole-chain electron transfer to PS I impossible.…”

Section: Discussionmentioning

confidence: 99%

Donor‐side photoinhibition in photosystem II from Chlamydomonas reinhardtii upon mutation of tyrosine‐Z in the D1 polypeptide to phenylalanine

et al. 1996

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When tyrosine-Z of the Dl-polypeptide of the photosystem II from Chlamydomonas reinhardtii was changed to phenylalanlne, the rapid donor to Pm+ was lost, and Pm+ accumulated on illumination. The rapid donation from tyroshte-Z was replaced by a slow electron transfer from an endogenous donor. Spectrophotometric measurements showed that carotenoids and chlorophylls were bleached by the Pa+ either directly or indirectly upon illumination. The carotenoid bleaching was inhibited in the presence of SOD or catalase, but the reaction did not require molecular oxygen as an electron acceptor. These observations led us to conclude that active oxygen radicals, possibly hydroxyl radicals, take part in the destruction of carotenoids in the Y161F mutant. Possible mechanisms for the destruction are discussed.

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Studies on reactions of illuminated chloroplasts

Cited by 739 publications

References 11 publications

Reaction Mechanism of Plant 2-Cys Peroxiredoxin

Reaction Mechanism of Plant 2-Cys Peroxiredoxin

The Water-Water Cycle Is Essential for Chloroplast Protection in the Absence of Stress

Donor‐side photoinhibition in photosystem II from Chlamydomonas reinhardtii upon mutation of tyrosine‐Z in the D1 polypeptide to phenylalanine

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