In-vivo_Bio-imaging_Seminar-Roland-Valcke_17032009

In-vivo_Bio-imaging_Seminar-Roland-Valcke_17032009 -...

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Fluores cence as a tool to communicate with plants: an example of vitality monitoring Roland Valcke Hasselt University, Diepenbeek UGent, 17/03/2009 Bio-imaging
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Fluores cence as a tool to communicate with plants Outline : - introduction : something about photosynthesis - fluorescence : Î what is it? Î where does it come from? Î what can you do with it Î fluorescence induction and quenching - fluores cence imaging : Î experimental set-up, prototypes Î ‘applications’, ‘combinations’, LIF (a selection) - some conclusions , potentialities and limitations
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Photosynthesis Life on earth is solar-powered. The chloroplasts of plants capture light energy that has traveled 160 million kilometers from the sun and convert it to chemical energy stored in sugar and other molecules. The process is called photosynthesis . Plants Cyanobacteria Photosynthetic bacteria h ν inorganic products organic products 6 CO 2 + 12 H 2 O Æ C 6 H 12 O 6 + 6 O 2 + 6 H 2 O
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Photosynthesis in higher plants, tissue most active in photosynthesis: leaf mesophyl cells: chloroplasts with chlorofyl + other pigments: carotenoïds light-energy used for: oxidation of water Î release of oxygen synthesis of carbon components, sugars (+ ……. .!!) light-reactions in thylakoïd membranes ( photosystems ): final products: ATP + NADPH carbon-fixation reactions: synthesis of sugars in stroma (Calvin-Benson cyclus)
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Photosynthesis Pathway of energy transduction is complex Î several physical and chemical mechanisms Î many components process initiated when light is absorbed by antenna pigment molecules Î transfer of energy ( = excitons) Î trapped at a reaction center Î chemically useful work: photochemistry Î dissipated as heat or re-emitted as light: fluorescence
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Photosynthesis Pigments : molecules characterised by ring structures and conjugated double bound systems limited rotations and vibrations probability of energy emission as light, not as heat pigments: chlorophyll , carotenoids
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Photosynthesis Chlorophyll: - chlorin macrocycles with 4-fold symmetry derived from porphyrin; - central Mg-atom: - is a ‘close shell’ divalent cation Î changes electron distribution - produces powerful excited states - planar head of four pyrrole rings, 1.5 x 1.5 nm + phytol group: 2 nm long - extended conjugated double bound system: - delocalized π -electrons - increase of area for photon capture - many redox levels for efficient energy capture and transfer - complex absorption/fluorescence spectrum
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Photosynthesis - chl a vs chl b : formyl (-CHO) group instead of methyl (-CH 3 ) group on ring B; Bchl: acetyl group instead of vinyl group on ring A and saturated ring B - molar extinction coefficient: 1.2 x 10 5 M -1 cm -1 (430nm) - a 10 -5 M solution absorbs 80% incident light - cross section: 3.8 x 10 -16 cm² - on a bright noon day with a photon flux of 2 x 10 -3 mol quanta m -2 sec -1 : a chl-molecule captures about 45 photons sec -1
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Photosynthesis 630nm 670nm The absorption spectrum of chlorophyll in organic solvents; 430 nm (Soret band) (B x , B y ) 630 nm: Q x , 670 nm: Q y x-axis: through N- of I and III; y-axis: II and IV
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Photosynthesis Absorption
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This note was uploaded on 05/28/2010 for the course WE BIOL000000 taught by Professor Laurychaerle during the Spring '10 term at Ghent University.

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In-vivo_Bio-imaging_Seminar-Roland-Valcke_17032009 -...

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