title: Repetitive short-pulse light mainly inactivates photosystem I in sunflower leaves.
abstract: Under field conditions, the leaves of plants are exposed to fluctuating light, as observed in sunfleck. The duration and frequency of sunfleck, which is caused by the canopy being blown by the wind, are in the ranges from 0.2 to 50 s, and from 0.004 to 1 Hz, respectively. Furthermore, >60% of the sunfleck duration ranges from 0.2 to 0.8 s. In the present research, we analyzed the effects of repetitive illumination by short-pulse (SP) light of sunflower leaves on the photosynthetic electron flow. The duration of SP light was set in the range from 10 to 300 ms. We found that repetitive illumination with SP light did not induce the oxidation of P700 in PSI, and mainly inactivated PSI. Increases in the intensity, duration and frequency of SP light enhanced PSI photoinhibition. PSI photoinhibition required the presence of O2. The inactivation of PSI suppressed the net CO2 assimilation. On the other hand, the increase in the oxidized state of P700 suppressed PSI inactivation. That is, PSI with a reduced reaction center would produce reactive oxygen species (ROS) by SP light, leading to PSI photodamage. This mechanism probably explains the PSI photodamage induced by constant light.
authors.affiliation: Department of Biological and Environmental Science, Faculty of Agriculture, Graduate School of Agricultural Science, Kobe University, 1-1 Rokkodai, Nada, Kobe, 657-8501 Japan.
authors.forename: Takehiro
authors.initials: T
authors.lastname: Sejima
authors.affiliation: Department of Biological and Environmental Science, Faculty of Agriculture, Graduate School of Agricultural Science, Kobe University, 1-1 Rokkodai, Nada, Kobe, 657-8501 Japan.
authors.forename: Daisuke
authors.initials: D
authors.lastname: Takagi
authors.affiliation: Department of Biological and Environmental Science, Faculty of Agriculture, Graduate School of Agricultural Science, Kobe University, 1-1 Rokkodai, Nada, Kobe, 657-8501 Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Fukayama
authors.affiliation: Department of Agriculture, Graduate School of Agricultural Science, Tohoku University, Tsutsumidori-Amamiyamachi, Aoba-ku, Sendai, 981-8555 JapanCREST, JST, 7 Gobancho, Chiyoda-ku, Tokyo, 102-0076 Japan.
authors.forename: Amane
authors.initials: A
authors.lastname: Makino
authors.affiliation: Department of Biological and Environmental Science, Faculty of Agriculture, Graduate School of Agricultural Science, Kobe University, 1-1 Rokkodai, Nada, Kobe, 657-8501 JapanCREST, JST, 7 Gobancho, Chiyoda-ku, Tokyo, 102-0076 Japan cmiyake@hawk.kobe-u.ac.jp.
authors.forename: Chikahiro
authors.initials: C
authors.lastname: Miyake
mesh_terms: D002245:Carbon Dioxide / Q000378:metabolism*; D002734:Chlorophyll / Q000378:metabolism; D004579:Electron Transport; D006368:Helianthus / Q000235:genetics / Q000502:physiology / Q000528:radiation effects*; D008027:Light; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism*; D010788:Photosynthesis / Q000502:physiology; D045331:Photosystem I Protein Complex / Q000235:genetics / Q000378:metabolism / Q000528:radiation effects*; D045332:Photosystem II Protein Complex / Q000235:genetics / Q000378:metabolism / Q000528:radiation effects; D018515:Plant Leaves / Q000235:genetics / Q000502:physiology / Q000528:radiation effects; D018526:Plant Transpiration; D017382:Reactive Oxygen Species / Q000378:metabolism*; D013997:Time Factors
chemical_list: D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D017382:Reactive Oxygen Species; D002734:Chlorophyll; D002245:Carbon Dioxide; D010100:Oxygen
keywords: Photoinhibition; Photosystem I; Reactive oxygen species (ROS); Water–Water Cycle (WWC)