Resolution of the Photosystem I and Photosystem II contributions to chlorophyll fluorescence of intact leaves at room temperature (original) (raw)
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Plant and Cell Physiology, 2000
Parallel measurements of CO 2 assimilation, Chi fluorescence and 800 nm transmittance were carried out on intact leaves of wild type and cytochrome b 6 /f deficient transgenic tobacco grown at two different light intensities and temperatures, with the aim to diagnose processes limiting quantum yield of photosynthesis and investigate their adaptations to growth conditions. Relative optical crosssections of PSII and PSI antennae were calculated from measured gas exchange rates and fluorescence-related losses at PSII and P700 oxidation-related losses at PSI. In nonstress conditions (high light grown wild type and low light grown antisense type) optimal relative optical cross-section of PSII (fl n) was 0.48-0.51 and that of PSI («i) was 0.38-0.40, leaving a non-photosynthetic absorption cross-section (a 0) of 0.09-0.14 for nitrite assimilation and absorption in PSII/? and other photosynthetically inactive pigments. Stress conditions (low light grown wild type and high light grown antisense type, elevated growth temperatures) tend to increase a 0 and decrease PSII antenna crosssection more than that of PSI antenna, but this rule is reversed during senescence.
Photosynthesis Research, 2005
A method of partitioning the energy in a mixed population of active and photoinactivated Photosystem II (PS II) complexes based on chlorophyll fluorescence measurements is presented. There are four energy fluxes, each with its quantum efficiency: a flux associated with photochemical electron flow in active PS II reaction centres (J PS II ), thermal dissipation in photoinactivated, non-functional PS IIs (J NF ), light-regulated thermal dissipation in active PS IIs (J NPQ ) and a combined flux of fluorescence and constitutive, light-independent thermal dissipation (J f,D ). The four quantum efficiencies add up to 1.0, without the need to introduce an 'excess' term E, which in other studies has been claimed to be linearly correlated with the rate coefficient of photoinactivation of PS II (k pi ). We examined the correlation of k pi with various fluxes, and found that the combined flux (J NPQ + J f,D = J pi ) is as well correlated with k pi as is E. This combined flux arises from F s =F 0 m , the ratio of steady-state to maximum fluorescence during illumination, which represents the quantum efficiency of combined non-photochemical dissipation pathways in active PS IIs. Since F s =F 0 m or its equivalent, J pi , is a likely source of events leading to photoinactivation of PS II, we conclude that F s =F 0 m is a simple predictor of k pi .
Delayed chlorophyll fluorescence as a monitor for physiological state of photosynthetic apparatus
2009
Intact plants emit light quanta called delayed fluorescence (DF). DF is result of radiative deactivation of secondary excited chlorophyll molecules in Photosystem II (PS II) antennae complexes. The excitations are produced by backward electrontransfer reactions both in the donor and acceptor sides of PS II. The poly-exponential dark decay of DF in a time interval of tens of nanoseconds to tens of seconds reflects the kinetics of different forward and backward reactions of the photosynthetic electron transfer. The current work reviews the mechanisms of the DF light quanta generation and the methodical approaches that allow us to obtain quantitative information about the photosynthetic machinery state using the DF signal from native objects. We examine an approach for the simultaneous record of DF and prompt chlorophyll fluorescence during the transition of the photosynthetic machinery from dark-adapted to light-adapted state. A new device (Senior PEA) built by Hansatech (King's Lynn, UK) allows us to measure simultaneously the induction transients of prompt chlorophyll fluorescence, DF decaying in a time range 10 µs-240 ms, and the changes in transmission at 820 nm. The comparative analysis of the three types of signals and the application of a model-based description of the processes and reactions that determine the dynamics of the signals during the light-induced transitions (dynamic models and JIP-test) allow us to obtain, from a single few-seconds-long measurement, quantitative information for: a) energetic fluxes and efficiencies at different steps of energy transformation; b) rate constants of electron transfer in and between the two photosystems; c) energization of the thylakoid membrane. This illustrates that DF in combination with other optical and luminescent measurements is a highly informative method for investigation of the physiological state of the photosynthetic apparatus of plants in vivo and in situ, and is an indispensable tool for the purposes of the biophysical phenomics.
Chlorophyll fluorescence at 680 and 730 nm and leaf photosynthesis
Photosynthesis research, 2001
Chlorophyll fluorescence constitutes a simple, rapid, and non-invasive means to assess light utilization in Photosystem II (PS II). This study examines aspects relating to the accuracy and applicability of fluorescence for measurement of PS II photochemical quantum yield in intact leaves. A known source of error is fluorescence emission at 730 nm that arises from Photosystem I (PS I). We measured this PS I offset using a dual channel detection system that allows measurement of fluorescence yield in the red (660 nm < F < 710 nm) or far red (F > 710 nm) region of the fluorescence emission spectrum. The magnitude of the PS I offset was equivalent to 30% and 48% of the dark level fluorescence F(0) in the far red region for Helianthus annuus and Sorghum bicolor, respectively. The PS I offset was therefore subtracted from fluorescence yields measured in the far red spectral window prior to calculation of PS II quantum yield. Resulting values of PS II quantum yield were consistent...
Photosynthesis Research
Recently, the long-standing paradigm of variable chlorophyll (Chl) fluorescence (Fv) in vivo originating exclusively from PSII was challenged, based on measurements with green algae and cyanobacteria (Schreiber and Klughammer 2021, PRES 149, 213-231). Fv(I) was identified by comparing light-induced changes of Fv > 700 nm and Fv < 710 nm. The Fv(I) induced by strong light was about 1.5 × larger in Fv > 700 nm compared to Fv < 710 nm. In the present communication, concentrating on the model green alga Chlorella vulgaris, this work is extended by comparing the light-induced changes of long-wavelength fluorescence (> 765 nm) that is excited by either far-red light (720 nm, mostly absorbed in PSI) or visible light (540 nm, absorbed by PSI and PSII). Polyphasic rise curves of Fv induced by saturating 540 nm light are measured, which after normalization of the initial O-I1 rises, assumed to reflect Fv(II), display a 2 × higher I2-P transient with 720 nm excitation (720ex) co...
Rapid light curves: a new fluorescence method to assess the state of the photosynthetic apparatus
Photosynthesis Research, 1999
Photosynthetic electron transport rates (ETR), calculated from chlorophyll fluorescence parameters, were compared in long term light and dark adapted as well as photoinhibited Pisum sativum leaves using a novel chlorophyll fluorescence method and a new instrument: rapid light curves (RLC) generated with the MINI-PAM. RLCs are plots of ETRs versus actinic irradiances applied for 10 s. Large changes in maximum electron transport rates (ETR max ) were observed when leaves were shifted from dark to moderate light, or from dark to photoinhibitory light and vice versa. Maximum ETRs were very low following long term dark adaptation, but increased to maximum levels within 8 to 15 minutes of illumination. It took more than 3 hours, however, to return irradiance-exposed leaves to the fully dark adapted state. Quenching analysis of RLCs revealed large q E development in long-term dark adapted leaves accounting for the low ETRs. Leaves photoinhibited for 3 hours had similarly reduced ETRs. In these leaves, however, q I was largely responsible for this reduction. Actinic irradiance exposures and saturating flashes affected leaves with different irradiance histories differently.
Photosynthesis Research, 2000
We propose a simplified alternative method for quantifying the partitioning of excitation energy between photochemistry, fluorescence and thermal dissipation. This alternative technique uses existing well-defined quantum efficiencies such as F PS II , leaving no 'excess' efficiency unaccounted for, effectively separates regulated and constitutive thermal dissipation processes, does not require the use of F o and F 0 o measurements and gives very similar results to the method proposed by Kramer et al. [(2004) Photosynth Res 79: 209-218]. We demonstrate the use of the technique using chlorophyll fluorescence measurements in grapevine leaves and observe a high dependence on thermal dissipation processes (up to 75%) at both high light and low temperature. Abbreviations: DpH-trans-thylakoid pH gradient; P-mean total daily integrated sum; F f-quantum yield of fluorescence; F D-quantum yield of constitutive thermal energy dissipation; F NPQ-quantum yield of DpH-and xanthophyll-regulated thermal energy dissipation; F PS II-quantum yield of PS II photochemistry; F s , F m , F 0 m-relative fluorescence yield in steady-state illumination, relative maximum fluorescence yield in dark-adapted conditions or during illumination, respectively; I A-PAR absorbed by the leaf; J PS II , J NPQ and J f,D-energy flux via linear electron transport, regulated thermal processes and combined fluorescence and constitutive thermal processes, respectively; PAR-photosynthetically active radiation; q L-'lake' model photochemical quenching coefficient, q P-'puddle model' photochemical quenching coefficient; SE-standard error of the mean
Chlorophyll a fluorescence rise (FLR) measured in vivo in dark-adapted plant tissue immediately after the onset of high light continuous illumination shows complex O–K–J–I–P transient. The steps typically appear at about 400 ms (K), 2 ms (J), 30 ms (I), and 200 – 500 ms (P) and a transient decrease of fluorescence to local minima (dips D) can be observed after the K, J, and I steps. As the FLR reflects a function of photosystem II (PSII) and to more understand the FLR, a PSII reactions model was formulated comprising equilibrium of excited states among all light harvesting and reaction centre pigments and P680, reversible radical pair formation and the donor and acceptor side functions. Such a formulated model is the most detailed and complex model of PSII reactions used so far for simulations of the FLR. By varying of selected model parameters (rate constants and initial conditions) several conclusions can be made as for the origin of and changes in shape of the theoretical FLR and compare them with in-literature-reported results. For homogeneous population of PSII and using standard in-literature-reported values of the model parameters, the simulated FLR is characterized by reaching the minimal fluorescence F 0 at about 3 ns after the illumination is switched on lasting to about 1 ms, followed by fluorescence rise to a plateau located at about 2 ms and subsequent fluorescence rise to a global maximum that is reached at about 60 ms. Varying of the values of rate constants of fast processes that can compete for utilization of the excited states with fluorescence emission does not change qualitatively the shape of the FLR. However, primary photochemistry of PSII (the charge separation, recombination and stabilization), non-radiative loss of excited states in light harvesting antennae and excited states quenching by oxidized plastoquisnone (PQ) molecules from the PQ pool seem to be the main factors controlling the maximum quantum yield of PSII photochemistry as expressed by the F V /F M ratio. The appearance of the plateau at about 2 ms in the FLR is affected by several factors: the height of the plateau in the FLR increases when the fluorescence quenching by oxidized P680 + is not considered in the simulations or when the electron transfer from Q À A to Q ðÀÞ B is slowed down whereas the height of the plateau decreases and its position is shifted to shorter times when OEC is initially in higher S state. The plateau at about 2 ms is changed into the local fluorescence maximum followed by a dip when the fluorescence quenching by oxidized PQ molecules or the charge recombination between P680 + and Q À A is not considered in the simulations or when all OEC is initially in the S 0 state or when the S-state transitions of OEC are slowed down. Slowing down of the S-state transitions of OEC as well as of the electron transfer from Q À A to Q ðÀÞ B also causes a decrease n of maximal fluorescence level. In the case of full inhibition of the S-state transitions of OEC as well as in the case of full inhibition of the electron donation to P680 + by Y Z , the local fluorescence maximum becomes the global fluorescence maximum. Assuming homogeneous PSII population, theoretical FLR curve that only far resembles experimentally measured O–J–I–P transient at room temperature can be simulated when slowly reducing PQ pool is considered. Assuming heterogeneous PSII population (i.e. the a/b and the Q B-reducing/Q B-non-reducing heterogeneity and heterogeneity in size of the PQ pool and rate of its reduction) enables to simulate the FLR with two steps between minimal and maximal fluorescence whose relative heights are in agreement with the experiments but not their time positions. A cause of this discrepancy is discussed as well as different approaches to the definition of fluorescence signal during the FLR.