title: Magnetic field protects plants against high light by slowing down production of singlet oxygen.
abstract: Recombination of the primary radical pair of photosystem II (PSII) of photosynthesis may produce the triplet state of the primary donor of PSII. Triplet formation is potentially harmful because chlorophyll triplets can react with molecular oxygen to produce the reactive singlet oxygen (¹O₂). The yield of ¹O₂ is expected to be directly proportional to the triplet yield and the triplet yield of charge recombination can be lowered with a magnetic field of 100-300 mT. In this study, we illuminated intact pumpkin leaves with strong light in the presence and absence of a magnetic field and found that the magnetic field protects against photoinhibition of PSII. The result suggests that radical pair recombination is responsible for significant part of ¹O₂ production in the chloroplast. The magnetic field effect vanished if leaves were illuminated in the presence of lincomycin, an inhibitor of chloroplast protein synthesis, or if isolated thylakoid membranes were exposed to light. These data, in turn, indicate that ¹O₂ produced by the recombination of the primary charge pair is not directly involved in photoinactivation of PSII but instead damages PSII by inhibiting the repair of photoinhibited PSII. We also found that an Arabidopsis thaliana mutant lacking α-tocopherol, a scavenger of ¹O₂, is more sensitive to photoinhibition than the wild-type in the absence but not in the presence of lincomycin, confirming that the target of ¹O₂ is the repair mechanism.
authors.affiliation: Molecular Plant Biology, Department of Biochemistry and Food Chemistry, University of Turku, FI-20014, Finland.
authors.forename: Marja
authors.initials: M
authors.lastname: Hakala-Yatkin
authors.forename: Päivi
authors.initials: P
authors.lastname: Sarvikas
authors.forename: Petriina
authors.initials: P
authors.lastname: Paturi
authors.forename: Mika
authors.initials: M
authors.lastname: Mäntysaari
authors.forename: Heta
authors.initials: H
authors.lastname: Mattila
authors.forename: Taina
authors.initials: T
authors.lastname: Tyystjärvi
authors.forename: Ladislav
authors.initials: L
authors.lastname: Nedbal
authors.forename: Esa
authors.initials: E
authors.lastname: Tyystjärvi
mesh_terms: D017360:Arabidopsis / Q000201:enzymology / Q000378:metabolism* / Q000528:radiation effects*; D028464:Cucurbita / Q000378:metabolism* / Q000528:radiation effects*; D019751:Intramolecular Transferases / Q000235:genetics; D007700:Kinetics; D008027:Light; D008280:Magnetics; D009154:Mutation / Q000235:genetics; D010100:Oxygen / Q000378:metabolism; D045332:Photosystem II Protein Complex / Q000378:metabolism; D018515:Plant Leaves / Q000378:metabolism / Q000528:radiation effects; D026082:Singlet Oxygen / Q000378:metabolism*; D024505:Tocopherols / Q000378:metabolism
chemical_list: D045332:Photosystem II Protein Complex; D026082:Singlet Oxygen; D019751:Intramolecular Transferases; C103397:tocopherol cyclase; D024505:Tocopherols; D010100:Oxygen