title: Imaging of NPQ and ROS formation in tobacco leaves: heat inactivation of the water-water cycle prevents down-regulation of PSII.
abstract: Non-photochemical chlorophyll fluorescence quenching (NPQ) plays a major role in the protection of the photosynthetic apparatus against damage by excess light, which is closely linked to the production of reactive oxygen species (ROS). The effect of a short heat treatment on NPQ and ROS production was studied with detached tobacco leaves by fluorescence imaging of chlorophyll and of the ROS sensor dye HO-1889NH. NPQ was stimulated >3-fold by 3 min pre-treatment at 44 degrees C, in parallel with suppression of CO(2) uptake, while no ROS formation could be detected. In contrast, after 3 min pre-treatment at 46 degrees C, NPQ was suppressed and ROS formation was indicated by quenching of HO-1889NH fluorescence. After 3 min pre-treatment at 46 degrees C and above, partial inactivation of ascorbate peroxidase and light-driven accumulation of H(2)O(2) was also observed. These data are discussed as evidence for a decisive role of the Mehler ascorbate peroxidase or water-water cycle in the formation of the NPQ that reflects down-regulation of PSII.
authors.affiliation: Institute of Plant Biology, Biological Research Center, Szeged, 6701 Hungary. ehideg@brc.hu
authors.forename: Eva
authors.initials: E
authors.lastname: Hideg
authors.forename: Péter B
authors.initials: PB
authors.lastname: Kós
authors.forename: Ulrich
authors.initials: U
authors.lastname: Schreiber
mesh_terms: D002245:Carbon Dioxide / Q000378:metabolism; D002734:Chlorophyll / Q000378:metabolism*; D005453:Fluorescence; D006358:Hot Temperature; D006861:Hydrogen Peroxide / Q000378:metabolism*; D010788:Photosynthesis; D045332:Photosystem II Protein Complex / Q000378:metabolism*; D018515:Plant Leaves / Q000378:metabolism*; D014026:Nicotiana / Q000378:metabolism*; D014867:Water / Q000378:metabolism
chemical_list: D045332:Photosystem II Protein Complex; D014867:Water; D002734:Chlorophyll; D002245:Carbon Dioxide; D006861:Hydrogen Peroxide