Protoplasts prepared from the wild type tobacco N. tabacum var. John William’s Broadleaf ex­ hibit photosynthetic oxygen-evolution if the suspension medium is supplemented with bicarbonate. In the absence of bicarbonate no steady state oxygen-evolution is observed with such prepara­ tions. Instead, an appreciable uptake which is mainly insensitive to DCMU and which persists over hours, and ther...

A quinone-mediated two-electron gate is shared by Photosystem II (PS II) and the photosystem of purple bacteria. In the bacterial reaction center, electron transfer from the reduced primary quinone acceptor, QA, to the secondary quinone, QB, as well as the sensitivity of this electron transfer step to inhibition by terbutryn, are regulated by the H subunit of the reaction center. Sequential rem...

Fluorescence imaging represents a non-invasive tool for revealing and understanding spatial heterogeneity in leaf performance caused by external factors, such as abiotic stress. Sun (Rosa meillandina and Chrysanthemum morifolium) and shade (Spathiphyllum wallisii) plants were used to study their tolerance to heat and high illumination. Fluorescence yield, effective PSII quantum yield and non-ph...

Neither Dunaliella cells grown with 5% CO(2) nor their isolated chloroplasts had a CO(2) concentrating mechanism. These cells primarily utilized CO(2) from the medium because the K((0.5)) (HCO(3) (-)) increase from 57 micromolar at pH 7.0 to 1489 micromolar at pH 8.5, where as the K((0.5)) CO(2) was about 12 micromolar over the pH range. After air adaptation for 24 hours in light, a CO(2) conce...

Photoreduction of the artificial electron acceptor, cytochrome c, by isolated spinach chloroplasts in the absence of added catalyst has been found to be resistant to inhibition by 10 mM salicyl­ aldoxime. This contrasts with the pronounced inhibition of the photoreduction of both 2,6-dichlorophenolindophenol and ferricyanide over a range of electron flow rates, and indicates an inhibition on th...

Thylakoid membranes contain the redox active complexes catalyzing the light-dependent reactions of photosynthesis in cyanobacteria, algae and plants. Crude thylakoid membranes or purified photosystems from different organisms have previously been utilized for generation of electrical power and/or fuels. Here we investigate the electron transferability from thylakoid preparations from plants or ...

The effects of natural, overwintering conditions on photosystem I and photosystem II activity were examined in isolated thylakoids of periwinkle (Vinca minor L.), an endemic, cold-tolerant, herbaceous evergreen. DCMU-Insensitive photosystem I activity (ascorbate/dichlorophenolindophenol --> methylviologen) exhibited a twofold increase in light-saturated rates upon exposure to low temperature an...

Recent evidence has indicated the presence of novel plastoquinone-binding sites, QC and QD, in photosystem II (PSII). Here, we investigated the potential involvement of loosely bound plastosemiquinones in superoxide anion radical (O2-) formation in spinach PSII membranes using electron paramagnetic resonance (EPR) spin-trapping spectroscopy. Illumination of PSII membranes in the presence of the...

BACKGROUND Currently, hydrogen fuel is derived mainly from fossil fuels, but there is an increasing interest in clean and sustainable technologies for hydrogen production. In this context, the ability of some photosynthetic microorganisms, particularly cyanobacteria and microalgae, to produce hydrogen is a promising alternative for renewable, clean-energy production. Among a diverse array of ph...

Lifetime-resolved imaging measurements of chlorophyll a fluorescence were made on leaves of avocado plants to study whether rapidly reversible ΔpH-dependent (transthylakoid H(+) concentration gradient) thermal energy dissipation (qE) and slowly reversible ΔpH-independent fluorescence quenching (qI) are modulated by lutein-epoxide and violaxanthin cycles operating in parallel. Under normal condi...