The Steady State Chlorophyll a Fluorescence Exhibits in Vivo an Optimum as a Function of Light Intensity which Reflects the Physiological State of the Plant

Modulated (690 and 730 nm), as well as direct chlorophyll (Chl) a fluorescence and changes in the concentration of the oxidized P700 were measured under steady state conditions in leaves of higher plants adapted to different light intensities. All the leaf samples exhibit an optimum curve of steady state fluorescence yield (Fs) versus the light intensity but its position with respect to light intensity varies considerably from one species to another or from one sample to other even in the same plant or within the same leaf sample. However, the optimum level of Fs was always at a moderate light intensity. By using the modulated fluorescence technique, the system with all closed (Flm) or open reaction center (Flo) were measured in steady state conditions. Each experimentally measured fluorescence yield was separated into a fluorescence emission of open (Fopen = Flo,(1—Vs)) and closed (Fclosed = (Flm . Vs)) reaction center (RC) of photosystem II where Vs=(Fs - Flo)/(Flm - Flo) is the function of fraction of closed reaction centers. With increasing light intensity, the fraction of open RC decreased while the fraction of closed RC increased. Maximum quantum efficiency (ΦPo) and actual quantum efficiency (ΦP) decreased by increasing light intensity. An optimum level of Fs was observed, when the fraction of closed reaction centers Vs of each sample was about 0.2 showing a common quenching mechanism which determines the fluorescence properties under steady state condition. This explains the apparent phenomenological contradiction that the fluorescence yield under steady state conditions can increase or decrease upon an increase of actinic ligh

Photosynthetic electron transport activity in heat-treated barley leaves: The role of internal alternative electron donors to photosystem II

AbstractElectron transport processes were investigated in barley leaves in which the oxygen-evolution was fully inhibited by a heat pulse (48 °C, 40 s). Under these circumstances, the K peak (∼F400 μs) appears in the chl a fluorescence (OJIP) transient reflecting partial QA reduction, which is due to a stable charge separation resulting from the donation of one electron by tyrozine Z. Following the K peak additional fluorescence increase (indicating QA− accumulation) occurs in the 0.2–2 s time range. Using simultaneous chl a fluorescence and 820 nm transmission measurements it is demonstrated that this QA− accumulation is due to naturally occurring alternative electron sources that donate electrons to the donor side of photosystem II. Chl a fluorescence data obtained with 5-ms light pulses (double flashes spaced 2.3–500 ms apart, and trains of several hundred flashes spaced by 100 or 200 ms) show that the electron donation occurs from a large pool with t1/2 ∼30 ms. This alternative electron donor is most probably ascorbate

ATPase activity of thylakoid membranes in CTAB-hexanol-octane low water system

AbstractThylakoid membranes transferred into a low water system composed of n-octane, the cationic surfactant cetyltrimethylammonium bromide (CTAB), and 1-hexanol as cosurfactant, displayed protein- and substrate-dependent ATPase activities for more than 60 min. This activity was enhanced 7–10-fold and 3–4-fold with 28%-vol. of methanol and 21%-vol of tert-butanol present in the polar phase, respectively, in a fashion reminiscent of what occurs in aqueous media. Approximately 25% and 10% of control and methanol-enhanced ATPase activities found in buffer were detected in the low water system, respectively, and both activities showed a pronounced dependency on the amount of water present (between 2.5 and 15% of water (v/v)). 1H-Nuclear Magnetic Resonance (1H-NMR) studies revealed that the bound/free water ratio (a) increased with decreasing concentration of water in the reverse micellar phase and (b) slightly increased in the presence of methanol. The results altogether suggest that the amount and physical state of water significantly contribute to determine the ATPase activity in the low water system

Comparative measurements of membrane potentials with microelectrodes and voltage-sensitive dyes

The usefulness of a new voltage-sensitive fluorescent dye, the membrane permeant negatively charged oxonol dye diBA-C4-(3)−, was evaluated by measuring the membrane potentials of BICR/M1R-k and L cells with glass microelectrodes and simultaneously recording the fluorescence of the stained cells. The membrane potential of BICR/M1R-k cells was varied between −25 mV and −90 mV by changing the bicarbonate concentration in the medium or by voltage clamping. To avoid any interference by the inserted electrodes with the fluorescence measurement of the cytoplasm, the cells were fused by polyethyleneglycol to form giant cells (homokaryons). These homokaryons also allowed penetration by two glass microelectrodes without causing a serious leakage of the plasma membrane. The slow responding dye diBA-C4-(3)− had a fluorescence response of about 1% per mV. Mathematical analysis of the fluorescence changes after voltage clamping revealed a first-order reaction with a rate constant between 0.1 min−1 and 0.8 min−1, depending on the cell size which was determined by the number of nuclei per homokaryon. A model for the mechanism of the fluorescence changes is proposed

Analysis and use of neural networks as a tool for a rapid non-invasive estimation

Water deficit is one of the most important environmental factors limiting sustainable crop yields and it requires a reliable tool for fast and precise quantification. In this work we use simultaneously recorded signals of photoinduced prompt fluorescence (PF) and delayed fluorescence (DF) as well as modulated reflection (MR) of light at 820 nm for analysis of the changes in the photosynthetic activity in detached bean leaves during drying. Depending on the severity of the water deficit we identify different changes in the primary photosynthetic processes. When the relative water content (RWC) is decreased to 60% there is a parallel decrease in the ratio between the rate of excitation trapping in the Photosystem (PS) II reaction center and the rate of reoxidation of reduced PSII acceptors. A further decrease of RWC to 20% suppresses the electron transfer from the reduced plastoquinone pool to the PSI reaction center. At RWC below values 15%, the reoxidation of the photoreduced primary quinone acceptor of PSII, QA–, is inhibited and at less than 5%, the primary photochemical reactions in PSI and II are inactivated. Using the collected sets of PF, DF and MR signals, we construct and train an artificial neural network, capable of recognizing the RWC in a series of “unknown” samples with a correlation between calculated and gravimetrically determined RWC values of about R2 ≈ 0.98. Our results demonstrate that this is a reliable method for determination of RWC in detached leaves and after further development it could be used for quantifying of drought stress of crop plants in situ. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: from Natural to Artificial

Drought-induced modifications of photosynthetic electron transport in intact leaves: Analysis and use of neural networks as a tool for a rapid non-invasive estimation

AbstractWater deficit is one of the most important environmental factors limiting sustainable crop yields and it requires a reliable tool for fast and precise quantification. In this work we use simultaneously recorded signals of photoinduced prompt fluorescence (PF) and delayed fluorescence (DF) as well as modulated reflection (MR) of light at 820nm for analysis of the changes in the photosynthetic activity in detached bean leaves during drying. Depending on the severity of the water deficit we identify different changes in the primary photosynthetic processes. When the relative water content (RWC) is decreased to 60% there is a parallel decrease in the ratio between the rate of excitation trapping in the Photosystem (PS) II reaction center and the rate of reoxidation of reduced PSII acceptors. A further decrease of RWC to 20% suppresses the electron transfer from the reduced plastoquinone pool to the PSI reaction center. At RWC below values 15%, the reoxidation of the photoreduced primary quinone acceptor of PSII, QA–, is inhibited and at less than 5%, the primary photochemical reactions in PSI and II are inactivated. Using the collected sets of PF, DF and MR signals, we construct and train an artificial neural network, capable of recognizing the RWC in a series of “unknown” samples with a correlation between calculated and gravimetrically determined RWC values of about R2≈0.98. Our results demonstrate that this is a reliable method for determination of RWC in detached leaves and after further development it could be used for quantifying of drought stress of crop plants in situ. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: from Natural to Artificial

Collective intelligence as a Challenge to Approach Interdisciplinary Topics in Plant Biology

Strasser Reto J. Collective intelligence as a Challenge to Approach Interdisciplinary Topics in Plant Biology. In: Bulletin de la Classe des sciences, tome 14, n°7-12, 2003. pp. 261-263