title: Photosystem II fluorescence lifetime imaging in avocado leaves: contributions of the lutein-epoxide and violaxanthin cycles to fluorescence quenching.
abstract: Lifetime-resolved imaging measurements of chlorophyll a fluorescence were made on leaves of avocado plants to study whether rapidly reversible ΔpH-dependent (transthylakoid H(+) concentration gradient) thermal energy dissipation (qE) and slowly reversible ΔpH-independent fluorescence quenching (qI) are modulated by lutein-epoxide and violaxanthin cycles operating in parallel. Under normal conditions (without inhibitors), analysis of the chlorophyll a fluorescence lifetime data revealed two major lifetime pools (1.5 and 0.5 ns) for photosystem II during the ΔpH build-up under illumination. Formation of the 0.5-ns pool upon illumination was correlated with dark-retention of antheraxanthin and photo-converted lutein in leaves. Interconversion between the 1.5- and 0.5-ns lifetime pools took place during the slow part of the chlorophyll a fluorescence transient: first from 1.5 ns to 0.5 ns in the P-to-S phase, then back from 0.5 ns to 1.5 ns in the S-to-M phase. When linear electron transport and the resulting ΔpH build-up were inhibited by treatment with 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), the major fluorescence intensity was due to a 2.2-ns lifetime pool with a minor faster contribution of approximately 0.7 ns. In the presence of DCMU, neither the intensity nor the lifetimes of fluorescence were affected by antheraxanthin and photo-converted lutein. Thus, we conclude that both antheraxanthin and photo-converted lutein are able to enhance ΔpH-dependent qE processes that are associated with the 0.5-ns lifetime pool. However, unlike zeaxanthin, retention of antheraxanthin and photo-converted lutein may not by itself stabilize quenching or cause qI.
authors.affiliation: Institut für Pflanzenwissenschaften (IBG-2), Forschungszentrum Jülich, 52425 Jülich, Germany. s.matsubara@fz-juelich.de
authors.forename: Shizue
authors.initials: S
authors.lastname: Matsubara
authors.forename: Yi-Chun
authors.initials: YC
authors.lastname: Chen
authors.forename: Rosanna
authors.initials: R
authors.lastname: Caliandro
authors.lastname: Govindjee
authors.forename: Robert M
authors.initials: RM
authors.lastname: Clegg
mesh_terms: D004237:Diuron / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D008027:Light; D014975:Lutein / Q000737:chemistry*; D008856:Microscopy, Fluorescence; D027421:Persea / Q000201:enzymology*; D045332:Photosystem II Protein Complex / Q000737:chemistry* / Q000378:metabolism; D018515:Plant Leaves / Q000187:drug effects / Q000201:enzymology; D013997:Time Factors; D024341:Xanthophylls / Q000737:chemistry
chemical_list: D045332:Photosystem II Protein Complex; D024341:Xanthophylls; C005613:violaxanthin; D004237:Diuron; D014975:Lutein