title: Evidence for direct carotenoid involvement in the regulation of photosynthetic light harvesting.
abstract: Nonphotochemical quenching (NPQ) refers to a process that regulates photosynthetic light harvesting in plants as a response to changes in incident light intensity. By dissipating excess excitation energy of chlorophyll molecules as heat, NPQ balances the input and utilization of light energy in photosynthesis and protects the plant against photooxidative damage. To understand the physical mechanism of NPQ, we have performed femtosecond transient absorption experiments on intact thylakoid membranes isolated from spinach and transgenic Arabidopsis thaliana plants. These plants have well defined quenching capabilities and distinct contents of xanthophyll (Xan) cycle carotenoids. The kinetics probed in the spectral region of the S(1) --> S(n) transition of Xans (530-580 nm) were found to be significantly different under the quenched and unquenched conditions, corresponding to maximum and no NPQ, respectively. The lifetime and the spectral characteristics indicate that the kinetic difference originated from the involvement of the S(1) state of a specific Xan, zeaxanthin, in the quenched case.
authors.affiliation: Department of Chemistry, University of California, and Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
authors.forename: Ying-Zhong
authors.initials: YZ
authors.lastname: Ma
authors.forename: Nancy E
authors.initials: NE
authors.lastname: Holt
authors.forename: Xiao-Ping
authors.initials: XP
authors.lastname: Li
authors.forename: Krishna K
authors.initials: KK
authors.lastname: Niyogi
authors.forename: Graham R
authors.initials: GR
authors.lastname: Fleming
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism; D002338:Carotenoids / Q000378:metabolism*; D007700:Kinetics; D009154:Mutation; D010788:Photosynthesis / Q000502:physiology*; D030821:Plants, Genetically Modified; D013053:Spectrophotometry; D018724:Spinacia oleracea / Q000378:metabolism; D024341:Xanthophylls; D065146:Zeaxanthins; D019207:beta Carotene / Q000031:analogs & derivatives* / Q000378:metabolism
chemical_list: D024341:Xanthophylls; D065146:Zeaxanthins; D019207:beta Carotene; D002338:Carotenoids