Analysis of LhcSR3, a Protein Essential for Feedback De-Excitation in the Green Alga Chlamydomonas reinhardtii

To prevent photodamage by excess light, plants use different proteins to sense pH changes and to dissipate excited energy states. In green microalgae, however, the LhcSR3 gene product is able to perform both pH sensing and energy quenching functions

High Light Induced Disassembly of Photosystem II Supercomplexes in Arabidopsis Requires STN7-Dependent Phosphorylation of CP29

Photosynthetic oxidation of water and production of oxygen by photosystem II (PSII) in thylakoid membranes of plant chloroplasts is highly affected by changes in light intensities. To minimize damage imposed by excessive sunlight and sustain the photosynthetic activity PSII, organized in supercomplexes with its light harvesting antenna, undergoes conformational changes, disassembly and repair via not clearly understood mechanisms. We characterized the phosphoproteome of the thylakoid membranes from Arabidopsis thaliana wild type, stn7, stn8 and stn7stn8 mutant plants exposed to high light. The high light treatment of the wild type and stn8 caused specific increase in phosphorylation of Lhcb4.1 and Lhcb4.2 isoforms of the PSII linker protein CP29 at five different threonine residues. Phosphorylation of CP29 at four of these residues was not found in stn7 and stn7stn8 plants lacking the STN7 protein kinase. Blue native gel electrophoresis followed by immunological and mass spectrometric analyses of the membrane protein complexes revealed that the high light treatment of the wild type caused redistribution of CP29 from PSII supercomplexes to PSII dimers and monomers. A similar high-light-induced disassembly of the PSII supercomplexes occurred in stn8, but not in stn7 and stn7stn8. Transfer of the high-light-treated wild type plants to normal light relocated CP29 back to PSII supercomplexes. We postulate that disassembly of PSII supercomplexes in plants exposed to high light involves STN7-kinase-dependent phosphorylation of the linker protein CP29. Disruption of this adaptive mechanism can explain dramatically retarded growth of the stn7 and stn7stn8 mutants under fluctuating normal/high light conditions, as previously reported

Fine control of chlorophyll-carotenoid interactions defines the functionality of light-harvesting proteins in plants

V.B. and C.D.P.D. acknowledge the support from the Leverhulme Trust RPG-2015-337. This research utilized Queen Mary’s MidPlus computational facilities, supported by QMUL Research-IT and funded by EPSRC grant EP/K000128/1. W.P.B acknowledges support from the Photosynthetic Antenna Research Center (PARC), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award DE-SC0001035 for initial development of the TDC calculation code, as well as support from Army Research Office (ARO-MURI) Award W911NF1210420 for further development

Biological exposure index of styrene suggested by a physiologico-mathematical model

We used a physiologico-mathematical model to study the biological exposure index of styrene correlated to the Threshold Limit Value (TLV) suggested by the ACGIH for 1986-87. This model allows the solvent concentrations in blood, alveolar air, fat tissue, and in other biological media to be estimated and simultaneously the kinetics of its metabolites to be followed when a specific exposure is settled. The comparison between the results obtained from the mathematical model and the numerous research projects documented in the literature suggests a reciprocal validation. Moreover, some biological parameters (particularly the alveolar ventilation) can explain the variability of results obtained from studies concerning the solvent pollution of the factories, which used biological monitoring. The ranges of styrene concentrations in blood and alveolar air and the urinary concentrations of its metabolites (mandelic and phenylglioxylic acids) are discussed in connection with the exposure at 215 mg/m3. Important differences correlated to the definition of set-levels of TLV and Biological Exposure Index (BEI) have been found: particularly the TLVs lead to different solvent uptakes according to some biological parameters; the BEI can better explain the individual solvent uptake and body burden