9 LIGHT ABSORPTION Photochemistry Antenna pigments PS II Photochemistry Antenna pigments PS II The absorbed light energy is funneled by excitation transfer into the RC’s, where energy conversion by charge separation takes place.
10 excited state ground state molecule absorbs photon photon Increasing energy LIGHT ABSORPTION
11 EXCITATION ENERGY TRANSFER Light Reaction Center Antenna Excitation transfer Electron transfer Donor Acceptor e-e- e-e-
12 PSII LHCII Cyt bfPSILHCI 2H 2 OO 2 + 4H + 2H + PQ PQH 2 2H + PC Fd NADP + H + NADPH H+H+ ATPase ADP + Pi ATP ELECTRON TRANSFER
20 Fv/Fm – MAXIMUM QUANTUM YIELD Quantum yield: Probability that the energy of a photon absorbed will be used for photosynthesis (i.e. enters in the e - - transport chain) Indicator of photosynthetic efficiency Maximum quantum yield : requires complete relaxation of the competing mechanisms with the photochemical energy conversion
21 Chondrus crispus Hanelt et al. (1992) Fv/Fm – Diurnal and spatial variation Depth (m) Macrocystis pyrifera Colombo-Pallotta (2007)
22 Littoral Sublittoral van de Poll et al. (2001) Fv/Fm – Comparison of stress responses between species
24 F/Fm’ – EFFECTIVE QUANTUM YIELD Used to describe the variation in the photochemical efficiency of PSII under illuminated conditions. Measurement of this parameter at certain irradiance value. Indicator of the ability of an organism to move electrons beyond PSII (ETR) F/Fm’ = (Fm’-F)/Fm’
25 ETR = Irradiance F/Fm’ 0,5 Absorptance (Genty et al. 1989) F/Fm’ = effective quantum yield (under light) 0,5 = Assumption that 50% of these quanta are absorbed by PSII Absorptance = fraction of incident light that is absorbed by the photosynthetic tissue. Not the same as absorbance (quantifies how much of the incident light is absorbed by an object). ELECTRON-TRANSPORT RATE (ETR)– CURVES
26 ELECTRON-TRANSPORT RATE (ETR)– CURVES ETR = Irradiance F/Fm’ 0,5 Absorptance Relative ETR = Irradiance F/Fm’ 0,5 (Ralph et al. 2002) -ETR: when absorption characteristics change between species, acclimations, seasons… - rel. ETR: use only when it is sure that there are no differences in the absorption characteristics
27 Macrocystis pyrifera Colombo-Pallotta et al. (2006) ETR– CURVES AS AN ANALOGUE TO P-E- CURVES
28 CHLOROPHYLL FLUORESCENCE EXTENSIVELY USE DUE TO: NON-DESTRUCTIVE NON-INVASIVE RAPID SENSITIVE IN REAL-TIME Since 1995 the number of articles published applying chlorophyll fluorescence on the analysis of the photosynthetic performance in macroalgae and seagrasses has increased more than five times.
29 The Chl fluorometer should be capable of measuring the fluorescence yield in a non-intrusive way: very low measuring light (i.e. exciting light) intensity for assessment of the fluorescence yield of a dark-adapted sample the detection system has to be very selective to distinguish between fluorescence excited by the measuring light and the much stronger signals caused by ambient and actinic light (full sun light, saturating light pulses for assessment of maximum fluorescence) fast time response to resolve the rapid changes in fluorescence yield upon dark-light and light-dark transitions PAM fluorometers: Pulse-Amplitude-Modulated fluorometers FLUOROMETERS
30 Allows measurement of fluorescence in the presence of actinic light (light absorbed by the photosynthetic apparatus to drive photosynthesis) How? – Measuring light is modulated and the fluorescence amplifier is highly selective for the modulated signal (yield of chlorophyll fluorescence) - pulse-modulated measuring light can be generated either by a light-emitting diode (LED; most PAM fluorometers) or a flash discharge lamp (i.e. XE-PAM) Pulse-Amplitude-Modulated Fluorometers Distinguish between fluorescence and ambient light