Photosynthetic organisms protect themselves from high-light stress by dissipating excess absorbed energy as heat in a process called non-photochemical quenching (NPQ). Zeaxanthin is essential for the full development of NPQ, but its role remains debated. The main discussion revolves around two points: where does zeaxanthin bind and does it quench? To answer these questions we have followed the ...

The PsbS protein of photosystem II functions in the regulation of photosynthetic light harvesting. Along with a low thylakoid lumen pH and the presence of de-epoxidized xanthophylls, PsbS is necessary for photoprotective thermal dissipation (qE) of excess absorbed light energy in plants, measured as non-photochemical quenching of chlorophyll fluorescence. What is known about PsbS in relation to...

Photosynthetic bacteria contain bacteriochlorophyll (BChl) that absorbs light and delivers the resulting singlet excitation energy to photochemical reaction centers.' The reaction centers, which have been isolated in a form free of lightharvesting BChl,'-3 contain a photochemically specialized BChl which in Rhodopseudomonas spheroides is called P870 after its absorption maximum near 870 nm. Exc...

High light poses a threat to oxygenic photosynthetic organisms. Similar to eukaryotes, cyanobacteria evolved a photoprotective mechanism, non-photochemical quenching (NPQ), which dissipates excess absorbed energy as heat. An orange carotenoid protein (OCP) has been implicated as a blue-green light sensor that induces NPQ in cyanobacteria. Discovered in vitro, this process involves a light-induc...

Plants and algae have a love/hate relationship with light. As oxygenic photoautotrophic organisms, they require light for life; however, too much light can lead to increased production of damaging reactive oxygen species as byproducts of photosynthesis. In extreme cases, photooxidative damage can cause pigment bleaching and death, a phenomenon all too familiar to anyone who has tried to move a ...

Photocycloaddition, Thymine, Azetidine, Cyclobutane Adducts Photochemical reactions of thymine linked to hypoxanthine or imidazole by a trimethylene chain were studied in aqueous solution. Irradiation (A = 254 nm) of thymine-hypoxanthine pair yielded two internal cycloadducts with azetidine and cyclobutane part structures. Sensitization and quenching experiments suggested that the excited singl...

Growth of two species of marine microalgae, namely Nannochloropsis gaditana Lubián (Eustigmatophyceae) and Nannochloris maculata Butcher (Chlorophyceae), was investigated in cultures submitted to three different concentrations of dissolved inorganic carbon (DIC). Cultures of N. gaditana grown in the absence of DIC in the medium and aerated with less than 0.0001% (v/v) CO2 in air (low DIC condit...