Surface Chemistry Studies of Photosystem II

The monolayer systems of PS II membranes, PS II core complex particles, and the mixture of monogalactosyldiacylglycerol (MGDG) with PS II core complex particles were constructed by means of the Langmuir technique. The surface pressure and surface potential properties of these systems were analyzed. The apparent particle sizes were determined from surface pressure–area isotherms, which were 200 nm2 for PS II membranes and 320 nm2 for PS II core complex particles. The surface pressure isotherm analysis of the mixed monolayer of MGDG and PSII core complex particles shows that the mixed monolayer has good miscibility at all surface pressures

Étude de l’activité photosynthétique à l’aide de la spectroscopic photoacoustique: applications potentielles en écotoxicologie

Résumé La spectroscopic photoacoustique permet la détection de la chaleur émise lors de désactivations thermiques suite à l’absorption, par un échantillon, de la lumière monochromatique modulée. En faisant varier la longueur d’onde du faisceau d’analyse, nous obtenons un spectre comparable à celui obtenu par la spectroscopic d’absorption. La spectroscopic photoacoustique possède l’avantage d’être applicable aux échantillons dont les propriétés optiques ne se prêtent pas aux techniques spectroscopiques conventionnelles, par exemple dans le cas des algues unicellulaires. Cette technique permet, en plus de l’analyse spectrale, la mesure de l’activité photosynthétique d’échantillons sains ou soumis à divers agents environnementaux (polluants, chaleur, …). Des résultats obtenus avec Anacystis nidulans, Phaeodactylum tricornutum et Pisum sativum sont présentés dans le présent travail. Nous croyons que les possibilités de la spectroscopic photoacoustique sont suffisantes pour susciter l’intérêt des chercheurs dans le domaine de la toxicologie et en particulier dans l’évaluation des dangers environnementaux reliés à l’utilisation des substances toxiques

Qualitative changes in the fluorescence spectra of intact pea leaves after photoinhibition

In high light (1400 W m−2) treated, intact pea leaves, a decrease in the ratio of fluorescence emission at 685 to 730 nm and an increase in fluorescence intensity between 500 and 600 nm were observed. Furthermore, photoacoustically monitored heat emission increased slightly, and O2 evolution decreased significantly. These findings are interpreted as effects of a photoprotective mechanism separating the carotenoid pool from the chlorophylls. This is supported by fluorescence excitation measurements and the results of a study on the reversibility of the process.Key words: chlorophyll fluorescence, carotenoid fluorescence, photoinhibition, photosynthesis, energy transfer

Photoacoustic Study of Changes in the Energy Storage of Photosystems I and II during State 1-State 2 Transitions

Using photoacoustic spectroscopy, state 1-state 2 transitions were demonstrated in vivo in intact sugar maple leaves (Acer saccharum Marsh.) by following the changes in energy storage of photosystems (PS) I and II. Energy storage measured with 650 nm modulated light (light 2) in the presence of background white light indicated the total energy stored by both photosystems (ES(t)), and in the presence of background far-red light showed the energy stored by PSI (ES(psi)). The difference between ES(t) and ES(psi) gave the energy stored by PSII (ES(psii)). While ES(t) remained nearly constant during state transitions, both ES(psi) and ES(psii) changed considerably. The ratio of ES(psii) to ES(psi), an indicator of the energy distribution between the two photosystems, decreased or increased during transition to state 2 or state 1, respectively. State transitions were completed in about 20 min and were fully reversible. During transition from state 1 to state 2, the fraction of excitation energy gained by PSI was nearly equal to that lost by PSII. This fraction of excitation energy transferred from PSII to PSI accounted for about 5% of the absorbed light (fluorescence is not considered), 19% of ES(t), 34% of ES(psii), and 43% of ES(psi) in state 2. NaF treatment inhibited the transition to state 1. Data in the present study confirm the concept of changes in absorption cross-section of photosystems during state transitions

Emission of Sulfur Dioxide from Sulfite-Treated Birch Leaves

In the present paper, we report the emission of S02 from 10 mM sulfite-treated birch ( Betula papyrifera Marsh) leaves both in light and in the dark. The emission reaches maximum at around 60 min during treatment. In some leaves, maximum emission is noticed even after 5 to 10 min of initiation of sulfitetreatment. It is also observed in the presence of 3{3,4-dichlorophenyl)-1-1 dimethylurea (DCMU). However, the emission rates are higher in light than in the dark or in the presence of DCMU. This emission is not observed with sulfate-treated leaves

SO(2) Effect on Photosynthetic Activities of Intact Sugar Maple Leaves as Detected by Photoacoustic Spectroscopy

Short-term (4 hours) effect of different concentrations of SO(2) fumigation on in vivo photochemical activities of sugar maple (Acer saccharum Marsh.) leaves was investigated using photoacoustic spectroscopy. The relative quantum yield of O(2) evolution (ratio of O(2) signal to the photothermal signal) and photochemical energy storage are increased by 0.05 microliter per liter of SO(2). This increase is more pronounced in 5 to 7 year old saplings than in 3 month old seedlings. Both oxygen-relative quantum yield and energy storage of seedlings are inhibited by increased concentrations of SO(2) and the inhibition is concentration dependent. The inhibition is greater in seedlings than in saplings at 2 microliters per liter of SO(2), indicating the more susceptible nature of seedlings. The present study indicates a concentration dependent differential effect of SO(2) on photochemical activities of sugar maple leaves