title: On the regulation of photosynthesis by excitonic interactions between carotenoids and chlorophylls.
abstract: Selective 2-photon excitation (TPE) of carotenoid dark states, Car S(1), shows that in the major light-harvesting complex of photosystem II (LHCII), the extent of electronic interactions between carotenoid dark states (Car S(1)) and chlorophyll (Chl) states, phi(Coupling)(Car S(1)-Chl), correlates linearly with chlorophyll fluorescence quenching under different experimental conditions. Simultaneously, a linear correlation between both Chl fluorescence quenching and phi(Coupling)(Car S(1)-Chl) with the intensity of red-shifted bands in the Chl Q(y) and carotenoid absorption was also observed. These results suggest quenching excitonic Car S(1)-Chl states as origin for the observed effects. Furthermore, real time measurements of the light-dependent down- and up-regulation of the photosynthetic activity and phi(Coupling)(Car S(1)-Chl) in wild-type and mutant (npq1, npq2, npq4, lut2 and WT+PsbS) Arabidopsis thaliana plants reveal that also in vivo the quenching parameter NPQ correlates always linearly with the extent of electronic Car S(1)-Chl interactions in any adaptation status. Our in vivo measurements with Arabidopsis variants show that during high light illumination, phi(Coupling)(Car S(1)-Chl) depends on the presence of PsbS and zeaxanthin (Zea) in an almost identical way as NPQ. In summary, these results provide clear evidence for a very close link between electronic Car S(1)-Chl interactions and the regulation of photosynthesis. These findings support a photophysical mechanism in which short-living, low excitonic carotenoid-chlorophyll states serve as traps and dissipation valves for excess excitation energy.
authors.affiliation: Technische Universität Braunschweig, Institute for Physical and Theoretical Chemistry, Department for Biophysical Chemistry, Hans-Sommer-Strasse 10, 38106 Braunschweig, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Bode
authors.forename: Claudia C
authors.initials: CC
authors.lastname: Quentmeier
authors.forename: Pen-Nan
authors.initials: PN
authors.lastname: Liao
authors.forename: Nour
authors.initials: N
authors.lastname: Hafi
authors.forename: Tiago
authors.initials: T
authors.lastname: Barros
authors.forename: Laura
authors.initials: L
authors.lastname: Wilk
authors.forename: Florian
authors.initials: F
authors.lastname: Bittner
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Walla
mesh_terms: D000222:Adaptation, Physiological / Q000528:radiation effects; D017360:Arabidopsis / Q000378:metabolism / Q000502:physiology* / Q000528:radiation effects; D029681:Arabidopsis Proteins / Q000378:metabolism*; D002338:Carotenoids / Q000737:chemistry / Q000378:metabolism*; D002734:Chlorophyll / Q000737:chemistry / Q000378:metabolism*; D004735:Energy Transfer; D005453:Fluorescence; D007700:Kinetics; D008027:Light; D008954:Models, Biological; D017785:Photons; D010788:Photosynthesis / Q000502:physiology* / Q000528:radiation effects; D045332:Photosystem II Protein Complex / Q000378:metabolism*; D013053:Spectrophotometry
chemical_list: D029681:Arabidopsis Proteins; D045332:Photosystem II Protein Complex; D002734:Chlorophyll; D002338:Carotenoids