| 1. |
- Cisek, Richard, et al.
(författare)
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Optical microscopy in photosynthesis
- 2009
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Ingår i: Photosynthesis Research. - : Springer Science and Business Media LLC. - 0166-8595 .- 1573-5079. ; 102:2-3, s. 111-141
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Forskningsöversikt (refereegranskat)abstract
- Emerging as well as the most frequently used optical microscopy techniques are reviewed and image contrast generation methods in a microscope are presented, focusing on the nonlinear contrasts such as harmonic generation and multiphoton excitation fluorescence. Nonlinear microscopy presents numerous advantages over linear microscopy techniques including improved deep tissue imaging, optical sectioning, and imaging of live unstained samples. Nonetheless, with the exception of multiphoton excitation fluorescence, nonlinear microscopy is in its infancy, lacking protocols, users and applications; hence, this review focuses on the potential of nonlinear microscopy for studying photosynthetic organisms. Examples of nonlinear microscopic imaging are presented including isolated light-harvesting antenna complexes from higher plants, starch granules, chloroplasts, unicellular alga Chlamydomonas reinhardtii, and cyanobacteria Leptolyngbya sp. and Anabaena sp. While focusing on nonlinear microscopy techniques, second and third harmonic generation and multiphoton excitation fluorescence microscopy, other emerging nonlinear imaging modalities are described and several linear optical microscopy techniques are reviewed in order to clearly describe their capabilities and to highlight the advantages of nonlinear microscopy.
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| 2. |
- Polivka, Tomas, et al.
(författare)
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Energy transfer in the major intrinsic light-harvesting complex from Amphidinium carterae
- 2006
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Ingår i: Biochemistry. - : American Chemical Society (ACS). - 0006-2960 .- 1520-4995. ; 45:28, s. 8516-8526
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Tidskriftsartikel (refereegranskat)abstract
- Carbonyl carotenoids are important constituents of the antenna complexes of marine organisms. These carotenoids possess an excited state with a charge-transfer character ( intramolecular charge transfer state, ICT), but many details of the carotenoid to chlorophyll energy transfer mechanisms are as yet poorly understood. Here, we employ femtosecond transient absorption spectroscopy to study energy transfer pathways in the intrinsic light-harvesting complex (LHC) of dinoflagellates, which contains the carbonyl carotenoid peridinin. Carotenoid to chlorophyll energy transfer efficiency is about 90% in the 530-550 nm region, where the peridinin S-2 state transfers energy with an efficiency of 25-50%. The rest proceeds via the S-1/ICT channel, and the major S-1/ICT-mediated energy transfer pathway utilizes the relaxed S-1/ICT state and occurs with a time constant of 2.6 ps. Below 525 nm, the overall energy transfer efficiency drops because of light absorption by another carotenoid, diadinoxanthin, that contributes only marginally to energy transfer. Instead, its role is likely to be photoprotection. In addition to the peridinin-Chl-a energy transfer, it was shown that energy transfer also occurs between the two chlorophyll species in LHC, Chl-c(2), and Chl-a. The time constant characterizing the Chl-c2 to Chl-a energy transfer is 1.4 ps. The results demonstrate that the properties of the S1/ICT state specific for carbonyl carotenoids is the key to ensure the effective harvesting of photons in the 500-600 nm region, which is of vital importance to underwater organisms.
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| 3. |
- van Stokkum, Ivo H. M., et al.
(författare)
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Inter-pigment interactions in the peridinin chlorophyll protein studied by global and target analysis of time resolved absorption spectra
- 2009
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Ingår i: Chemical Physics. - : Elsevier BV. - 0301-0104. ; 357:1-3, s. 70-78
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Tidskriftsartikel (refereegranskat)abstract
- Inter-pigment interactions define the functioning of light-harvesting protein complexes. To describe the particularly complex molecular dynamics and interactions of peridinin and chlorophyll in the peridinin chlorophyll protein of Amphidinium carterae, we applied global and target analysis to a series of ultrafast transient absorption experiments. We have created and validated a model that consistently describes and characterizes the interactions and evolution of excited and ground-state populations after excitation in all different experiments. The series of energy transfer steps that follow excitation are described by our model of cascading populations and numerous rate constants that correspond to intra-molecular thermal relaxation, fast and slow peridinin-to-chlorophyll energy transfer steps, and chlorophyll excited-state annihilation. By analyzing the spectral response of ground-state peridinins to excited chlorophylls we have identified which specific peridinin molecule is most closely coupled to the chlorophylls. No evidence was found that the intra-molecular charge transfer (ICT) state of peridinin, identified in studies of peridinin in solution, is a separate entity in the protein. The peridinin that exhibited slow peridinin-to-chlorophyll energy transfer was characterized by a difference spectrum free from ICT features, consistent with the importance of coupled ICT and S, states for energy transfer. (c) 2008 Elsevier B.V. All rights reserved.
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