A simple method of a bicolor (multicolor), fast-Fourier, PAM chlorophyll fluorometry has been developed to obtain fluorescence induction curves. Quantum yields of PSII photochemistry were determined with blue and red simultaneously applied pulsed measuring lights for three subsequent 20-min periods of dark-, light-adaptation under actinic light and dark recovery. Measuring lights were cross-combined with blue and red actinic lights and saturation pulses. Coefficients of chromatic divergence were calculated as a ratio of the quantum yields obtained by red measuring light to that obtained by blue measuring light. Adaptation of Ficus benjamina and Hordeum vulgare leaves under blue (but not red) actinic light resulted in the sufficient increase of chromatic divergence. In addition, fraction of active, non(photo)inhibited, PSII centers was shown to be dependent on the color of measuring light. Thus, color of the light sources should be considered when reporting results of parameters evaluated from fluorescence induction curves., V. Lysenko, D. Lazár, T. Varduny., and Obsahuje bibliografii
Chlorophyll (Chl) α fluorescence induction (transient), measured by exposing dark-adapted samples to high light, shows a polyphasic rise, which has been the subject of extensive research over several decades. Several Chl fluorescence parameters based on this transient have been defined, the most widely used being the FV [= (FM-F0)]/FM ratio as a proxy for the maximum quantum yield of PSII photochemistry. However, considerable additional information may be derived from analysis of the shape of the fluorescence transient. In fact, several performance indices (PIs) have been defined, which are suggested to provide information on the structure and function of PSII, as well as on the efficiencies of specific electron transport reactions in the thylakoid membrane. Further, these PIs have been proposed to quantify plant tolerance to stress, such as by high light, drought, high (or low) temperature, or N-deficiency. This is an interesting idea, since the speed of the Chl α fluorescence transient measurement (<1 s) is very suitable for high-throughput phenotyping. In this review, we describe how PIs have been used in the assessment of photosynthetic tolerance to various abiotic stress factors. We synthesize these findings and draw conclusions on the suitability of several PIs in assessing stress responses. Finally, we highlight an alternative method to extract information from fluorescence transients, the Integrated Biomarker Response. This method has been developed to define multi-parametric indices in other scientific fields (e.g., ecology), and may be used to combine Chl α fluorescence data with other proxies characterizing CO2 assimilation, or even growth or grain yield, allowing a more holistic assessment of plant performance., A. Stirbet, D. Lazár, J. Kromdijk, Govindjee., and Obsahuje bibliografické odkazy
Chlorophyll a fluorescence induction measured by a fluorometer with a high temperature stressed plant material shows a new K step which is a clear peak due to fast fluorescence rise and subsequent decrease of fluorescence intensity. We focused on an explanation of the decrease of fluorescence after the K step using artificial electron acceptors and donors to photosystem 2 (PS2). Addition of the artificial electron acceptors or donors suppressed the decrease of fluorescence after the K step. We suggest that the decrease mainly reflects (by more than 81 %) an energy loss process in the reaction centre of PS2 which is most probably a nonradiative charge recombination between P680+ (oxidised primary electron donor in PS2) and a negative charge stored on either Pheo- or QA- (reduced primary electron acceptor of PS2 and reduced primary quinone electron acceptor of PS2, respectively). We suggest that the energy loss process is only possible when the inhibition of both the donor and the acceptor sides of PS2 occurs. and D. Lazár, P. Pospíšil, J. Nauš.
Oscillations in many of photosynthetic quantities with a period of about 1 min can be routinely measured with higher plant leaves after perturbation of the steady state by sudden change in gas phase. Among all hypotheses suggested so far to explain the oscillations, an effect of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) activation status to control the oscillations is highly probable, at least upon high temperature (HT) treatment when in vivo RuBPCO activity controlled by RuBPCO activase (RuBPCO-A) decreases. Therefore, we measured the oscillations in fluorescence signal coming from barley leaves (Hordeum vulgare L. cv. Akcent) after their exposure for various time intervals to different HTs in darkness. We also evaluated steady state fluorescence and CO2 exchange parameters to have an insight to functions of electron transport chain within thylakoid membrane and Calvin cycle before initiation of the oscillations. The changes in period of the oscillations induced by moderate HT (up to 43 °C) best correlated with changes in non-photochemical fluorescence quenching (qN) that in turn correlated with changes in gross photosynthetic rate (PG) and rate of RuBPCO activation (kact). Therefore, we suggest that changes in period of the oscillations caused by moderate HT are mainly controlled by RuBPCO activation status. For more severe HT (45 °C), the oscillations disappeared which was probably caused by an insufficient formation of NADPH by electron transport chain within thylakoid membrane as judged from a decrease in photochemical fluorescence quenching (qP). Suggestions made on the basis of experimental data were verified by theoretical simulations of the oscillations based on a model of Calvin cycle and by means of a control analysis of the model. and D. Lazár ... [et al.].
Theoretical modelling is often overlooked in photosynthesis research even if it can significantly help with understanding of explored system. A new model of light-induced photosynthetic reactions occurring in and around thylakoid membrane is introduced here and used for theoretical modelling of not only the light-induced chlorophyll (Chl) a fluorescence rise (FLR; the O-J-I-P transient), reflecting function of photosystem II (PSII), but also of the 820 nmtransmittance signal (I820), reflecting function of photosystem I (PSI) and plastocyanin (PC), paralleling the FLR. Correctness of the model was verified by successful simulations of the FLR and I820 signal as measured with the control (no treatment) sample but also as measured with 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone- (inhibits electron transport in cytochrome b 6/f) and methylviologen- (accepts electrons from iron-sulphur cluster of PSI) treated samples and with the control sample upon different intensities of excitation light. From the simulations performed for the control sample, contribution of the oxidised donor of PSI, P700, and oxidised PC to the I820 signal minimum (reflects maximal accumulations of the two components) was estimated to be 75% and 25%, respectively. Further in silico experiments showed that PC must be reduced in the dark, cyclic electron transport around PSI must be considered in the model and activation of ferredoxin-NADP+-oxidoreductase (FNR) also affects the FLR. Correct simulations of the FLR and I820 signal demonstrate robustness of the model, confirm that the electron transport reactions occurring beyond PSII affect the shape of the FLR, and show usefulness and perspective of theoretical approach in studying of the light-induced photosynthetic reactions.
We developed transgenic rice plants (Oryza sativa L. cv. Daeribbyeo) overproducing cytosolic glutathione reductase (GR) using a GR gene from Brassica campestris and studied their response to photo-oxidative stress in the presence of methyl viologen (MV, 10 and 50 μM concentrations) under room (25 °C) and moderately elevated (35 °C) temperature by analysis of chlorophyll (Chl) a fluorescence parameters (FV/FM, qN, and qP) and of Chl content. Elevated temperature enhanced and accelerated the photo-oxidative damage to photosynthetic apparatus expressed mainly by a fast decrease of qN. Higher temperature supported the protective reaction in transformed rice plants for lower MV concentration (10 μM) and eliminated the enhanced tolerance of photosystem 2 photochemistry to photooxidative stress for higher (50 μM) MV concentration. Different mechanisms and temperature dependence of oxidative and protective reactions explain the results. and R. Kouřil ... [et al.].
Parameters of the fast chlorophyll (Chl) fluorescence induction (the O-J-I-P curve) of plants of winter wheat grown in the field canopy were statistically tested for Gaussian distribution. Five different statistical methods showed that the obtained values did not obey the Gaussian distribution law. The presentation of the parameters with the help of the mean and standard deviation masks the information about statistical properties of the values. Thus, we recommend to present the parameters by means of median, quartiles, and minimum and maximum values rather than by means of the mean and standard deviation. and D. Lazár, J. Nauš.
Measurement of the chlorophyll (Chl) a fluorescence rise (FR) under higher exciting irradiance (EI), the O-J-I-P transient, or under lower irradiance, the O-I-P transient, is a routinely used method to access photosystem 2 function in thylakoid membranes of chloroplasts. Our measurements with a suspension of pea thylakoid membranes showed that the relative heights of the J and I steps in the FR depended not only on EI but also on the concentration and thickness of the sample. We explain this effect as a consequence of the gradient of EI within the sample. We tested this suggestion by theoretical simulations of the FR based on the model that was previously used for simulation of the FR considering in addition the gradient of EI within the sample. Our theoretical results correspond well with the experiments. The irradiance gradient effect may influence measured FR significantly and this fact should be taken into consideration in the interpretation of measured FRs. and P. Sušila ... [et al.].