A set-up for recording thermoluminescence emission together with the constant F0 fluorescence yield is described briefly. It is driven by a microcomputer through plugged-in cards.Practical aspects of the simulation of TL bands and of decomposition of complex TL signals are examined. A reproducible and linear temperature gradient and the use of photon counting for luminescence detection are important features for further analyzing the recorded signal. The simulation procedure used is a step-by-step calculation of the number of charge recombinations, which is then substracted from the number of remaining charge pairs able to produce luminescence. This procedure consists first of a graphical fitting, followed by a numerical minimization, with a maximum of five simulated components. The quality of the simulation is evaluated by the sum of squares of differences (signal-simulation), related to the signal area. Equivalent decomposition patterns may be found for the same recording and additional information is needed for interpretation of TL data. Averaging signals is feasible, provided that maximum temperatures Tm of averaged bands are sufficiently similar (±3°C). Simultaneous measurement of the antenna fluorescence yield F0, using an ultra-weak pulsed blue LED, gives an estimate of the luminescence yield. This has to be taken into account in the analysis of the Q band and of high temperature (>40°C) bands.The simulation parameters appear to be dependent on plant growth conditions. Quantitative analysis of thermoluminescence emission could be useful in the study of the effects of climatic factors on the photosynthetic apparatus in plants.

The crosslinking of poly(vinyl alcohol) (PVA) films under ultraviolet irradiation for between 1 and 4 h was studied in air at 25 °C in the presence of sodium benzoate by Fourier‐transform infrared spectroscopy (FTIR) using the attenuated total reflectance technique (ATR). Principal component analysis (PCA) is a mathematical procedure that allows treatment of the entire infrared spectrum and is very appropriate for analysing the chemical modifications initiated by sodium benzoate which occur in PVA upon UV irradiation. By PCA it was possible to clarify the mechanism of crosslinking of PVA. From this FTIR–PCA study, it is suggested that a free radical arising from the photolysis of sensitizer would abstract a tertiary hydrogen atom from the polymer chain to yield a polymeric radical. This radical reacts with OH groups, leading to the formation of ether bonds between the polymeric chains and hence to crosslinking and insolubilization of the PVA. © 2001 Society of Chemical Industry

-Mutations in the secondary quinone electron acceptor (Q.) pocket of the D, protein conferring a modification on the donor side of photosystem II (PSII) have been characterized by gene cloning and sequencing i n two metribuzin-resistant mutants of Synechorystis PCC 6714. l h e mutations induce different herbicide resistances: i n M , , , a point mutation at the codon 248, isoleucine to threonine, results in resistance only to metribuzin; i n M , , , a single mutation, Alaz5'Val, confers metribuzin, atrazine, and ioxynil resistance. As with other herbicide-resistant mutants, M30 and M35 present modifications i n the electron transfer between the primary quinone electron acceptor (QA) and Qs. In addition, they have a modified oscillatory pattern of oxygen emission: after dark adaptation, the maximum oscillation i s shifted by one flash. Both mutants have a higher concentration of the redox state in the darkadapted state than the wild type. l h e mutations render the oxygenevolving system more accessible to cell reductants. The mutation AlaZs1Val also confers to PSll an increased sensitivity to high light. We have already demonstrated that under light stress a double mutant, AzV (Alaz5'Val, Phe'l'Ser), lost the ability to recover the PSll activity sooner than the wild type. Here, we confirm that the modification of the alanine-251 is responsible for this specific sensitivity to high light. We conclude that specific mutations of the Q. pocket modify the behavior of the cells under light stress and have an effect on the structure of the D1 protein in the other side of the membrane.PSII is the site of water oxidation and plastoquinone reduction (for recent reviews, see Babcock, 1987; Rutherford, 1989; Vermaas, 1991; Debus, 1992). The D1 protein, one of the proteins at the core of PSII, is involved in both reactions; it contains the binding niche of the plastoquinone molecules, which serve as QB, and it also provides some of the ligands of the manganese cluster involved in the oxygen-evolving mechanism.The plastoquinone molecule, which binds to a niche formed by a large hydrophilic loop connecting helices IV and V of D1 on the luminal side of the membrane, receives two electrons as a result of two separate photochemical events. After primary charge separation, a very rapid reduction of the QA occurs, and then the electron is transferred to Q B . This reaction is reversible and gives rise to an equilibrium between the states Q A -Q~ and QAQB-. After a second charge separation, Q B receives a second electron and leaves its site as QBH2.

Thermoluminescence experiments have been carried out to study the effect of a transmembrane proton gradient on the recombination properties of the S2 and S3 states of the oxygen evolving complex with QA (-) and QB (-), the reduced electron acceptors of Photosystem II. We first determined the properties of the S2QA (-) (Q band), S2QB (-) and S3QB (-) (B bands) recombinations in the pH range 5.5 to 9.0, using uncoupled thylakoids. The, a proton gradient was created in the dark, using the ATP-hydrolase function of ATPases, in coupled unfrozen thylakoids. A shift towards low temperature of both Q and B bands was observed to increase with the magnitude of the proton gradient measured by the fluorescence quenching of 9-aminoacridine. This downshift was larger for S3QB (-) than for S2QB (-) and it was suppressed by nigericin, but not by valinomycin. Similar results were obtained when a proton gradient was formed by photosystem I photochemistry. When Photosystem II electron transfer was induced by a flash sequence, the reduction of the plastoquinone pool also contributed to the downshift in the absence of an electron acceptor. In leaves submitted to a flash sequence above 0°C, a downshift was also observed, which was supressed by nigericin infiltration. Thus, thermoluminescence provides direct evidence on the enhancing effect of lumen acidification on the S3→S2 and S2→S1 reverse-transitions. Both reduction of the plastoquinone pool and lumen acidification induce a shift of the Q and B bands to lower temperature, with a predominance of lumen acidification in non-freezing, moderate light conditions.