Molecular mechanisms behind light-induced inhibition of photosystem II electron transport and degradation of reaction centre polypeptides (original) (raw)
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Dynamic metabolism of photosystem II reaction center proteins and pigments
Physiologia Plantarum, 1999
synthetically active radiation stimulates D1/D2 heterodimer degradation in a synergistic manner. D1 undergoes several mary charge separation between P680, a chlorophyll a dimer, post-translational modifications including N-acetylation, phos-and the primary quinone acceptor Q A . This supramolecular protein complex consists of D1, D2, and subunits of phorylation, and palmitoylation. Light-dependent phosphorylation of D1 occurs in all flowering plants but not in the green cytochrome b 559 , the psbI gene product, and a few low molecular mass proteins. Ligated to this complex are pigments:
Photodamage to photosystem II - primary and secondary events
Journal of Photochemistry and Photobiology B: Biology, 1992
High light stress results in a reduction in the photosynthetic capacity of plants. This photoinhibition is targeted to photosystem II and seems to be an inevitable consequence of the complicated redox chemistry involved in the light-driven water-plastoquinone oxidoreduction reaction. Photoinactivation leads to irreversible damage of the reaction centre of photosystem II, in particular the Dl protein.
Planta, 1992
The obligate shade plant, Tradescantia albiflora Kunth grown at 50 ~tmol photons 9 m -2 s -1 and Pisum sativum L. acclimated to two photon fluence rates, 50 and 300 pmol. m -2. s -1, were exposed to photoinhibitory light conditions of 1700 pmol 9 m -2 9 s-1 for 4 h at 22 ~ C. Photosynthesis was assayed by measurement of CO2saturated Oz evolution, and photosystem II (PSII) was assayed using modulated chlorophyll fluorescence and flash-yield determinations of functional reaction centres. Tradescantia was most sensitive to photoinhibition, while pea grown at 300 ~tmol-m -2-s -~ was most resistant, with pea grown at 50 ~tmol 9 m-2. s-1 showing an intermediate sensitivity. A very good correlation was found between the decrease of functional PSII reaction centres and both the inhibition of photosynthesis and PSII photochemistry. Photoinhibition caused a decline in the maximum quantum yield for PSII electron transport as determined by the product of photochemical quenching (qp) and the yield of open PSII reaction centres as given by the steady-state fluorescence ratio, F'F~, according to Genty et al. (1989, Biochim. Biophys. Acta 990, 81-92). The decrease in the quantum yield for PSII electron transport was fully accounted for by a decrease in F'vF~, since qp at a given photon fluence rate was similar for photoinhibited and noninhibited plants. Under lightsaturating conditions, the quantum yield of PSII electron transport was similar in photoinhibited and noninhibited plants.
Role of the PSII-H Subunit in Photoprotection
Journal of Biological Chemistry, 2003
Photosystem I-less Synechocystis 6803 mutants carrying modified PsbH proteins, derived from different combinations of wild-type cyanobacterial and maize genes, were constructed. The mutants were analyzed in order to determine the relative importance of the intra-and extramembrane domains of the PsbH subunit in the functioning of photosystem (PS) II, by a combination of biochemical, biophysical, and physiological approaches. The results confirmed and extended previously published data showing that, besides D1, the whole PsbH protein is necessary to determine the correct structure of a Q B /herbicidebinding site. The different turnover of the D1 protein and chlorophyll photobleaching displayed by mutant cells in response to photoinhibitory treatment revealed for the first time the actual role of the PsbH subunit in photoprotection. A functional PsbH protein is necessary for (i) rapid degradation of photodamaged D1 molecules, which is essential to avoid further oxidative damage to the PSII core, and (ii) insertion of newly synthesized D1 molecules into the thylakoid membrane. PsbH is thus required for both initiation and completion of the repair cycle of the PSII complex in cyanobacteria.
Damage and repair of Photosystem II under exposure to UV radiation
Science Access, 2001
The ultraviolet component of sunlight is highly detrimental for the photosynthetic apparatus both in the UV-B (280-320 nm) and in the UV-A (320-400 nm) region. By characterizing the mechanism of UV-A induced damage in isolated spinach thylakoid preparations we have shown that it impairs electron transport mainly in the PSII complex, with much less effect on PSI activity. Within PSII, the main action site of UV-A is the Mn cluster of water oxidation with additional effects on the QB binding pocket. This damaging mechanism is basically the same as induced by UV-B. Under natural conditions the lower damaging efficiency of UV-A is compensated by its higher intensity leading to similar impact on photosynthesis as exerted by UV-B. By using 308 nm laser flashes to illuminate PSII centers which are synchronized to various oxidation states of the water-splitting complex, we have shown that the UV-B sensitivity of PSII depends on the redox state of the Mn cluster (low in S0 and S1, high in S2...
Keywords: Photodamage and PSII repair cycle STN8 kinase and PSII core proteins phosphorylation Proteases and D1 protein degradation Reactive oxygen species (ROS) Ultra-violet radiation a b s t r a c t Photosystem II (PSII) is vulnerable to high light (HL) illumination resulting in photoinhibition. In addition to photoprotection mechanisms, plants have developed an efficient PSII repair mechanism to save themselves from irreversible damage to PSII under abiotic stresses including HL illumination. The phosphorylation/dephosphorylation cycle along with subsequent degradation of photodamaged D1 protein to be replaced by the insertion of a newly synthesized copy of D1 into the PSII complex, is the core function of the PSII repair cycle. The exact mechanism of this process is still under discussion. We describe the recent progress in identifying the kinases, phosphatases and proteases, and in understanding their involvement in the maintenance of thylakoid structure and the quality control of proteins by PSII repair cycle during photoinhibition.
Light-induced degradation of D2 protein in isolated photosystem II reaction center complex
FEBS Letters, 1992
When isolated photosystem I1 reaction centers from spinach are exposed to photoinhibitory light in the presence of an electron aceeptor, breakdown products of the D2 protein at 28, 25, 23, 18, 9, 5 and 4.5 kDa are detected by immunoblotting with a monospeeifie anti-D2 polyelonal antibody. In a time-course experi~i~ent the 23 and 4.5 kDa fragments show a transient appearance, whilst the others are photoaceumulated. The regions of the D2 protein containing tl~e cleavage sites tbr the 28 and 18 kDa photoindueed fragments have been identified. Significant degradation of D2 takes place only in the presence: of an electron aeceptor, and breakdown of the protein is partially prevented by serine-type proteas¢ inhibitors.