Stefania Viola

Bioscience and biotechnology Institute of Aix-Marseille, CEA Cadarache

In plants, algae, and some photosynthetic bacteria, the ElectroChromic Shift (ECS) of photosynthetic pigments, which senses the electric field across photosynthetic membranes, is widely used to quantify the activity of the photosynthetic chain. In cyanobacteria, ECS signals have never been used for physiological studies, although they can provide a...

Significance Far-red photosystem II (FR-PSII) contains a small number of FR-chlorophylls (- f or - d ) with the rest (∼85%) being chlorophyll- a molecules. Here ultrafast studies on FR-PSII support a model in which the primary electron donor is a FR-chlorophyll (P 720 , likely in the Chl D1 position), while the second electron donor is chlorophyll-...

Chloroplasts of land plants characteristically contain grana, cylindrical stacks of thylakoid membranes. A granum consists of a core of appressed membranes, two stroma-exposed end membranes, and margins, which connect pairs of grana membranes at their lumenal sides. Multiple forces contribute to grana stacking, but it is not known how the extreme c...

The cyanobacterium Synechocystis sp. PCC 6803 is widely used for research on photosynthesis and circadian rhythms, and also finds application in sustainable biotechnologies. Synechocystis is naturally transformable and undergoes homologous recombination, which enables the development of a variety of tools for genetic and genomic manipulations. To g...

In Chlamydomonas reinhardtii, chloroplast gene expression is tightly regulated post‐transcriptionally by gene‐specific trans‐acting protein factors. Here we report the molecular identification of an OctotricoPeptide Repeat (OPR) protein, MDA1, which governs the maturation and accumulation of the atpA transcript, encoding subunit α of the chloroplas...

Low-temperature, metastable electrochromism has been used as a tool to assign pigments in Photosystem I (PS I) from Thermosynechococcus vulcanus and both the white light (WL) and far-red light (FRL) forms of Chroococcidiopsis thermalis. We find a minimum of seven pigments is required to satisfactorily model the electrochromism of PS I. Using our mo...

Photosystem II (PSII) uses the energy from red light to split water and reduce quinone, an energy-demanding process based on chlorophyll a (Chl-a) photochemistry. Two types of cyanobacterial PSII can use chlorophyll d (Chl-d) and chlorophyll f (Chl-f) to perform the same reactions using lower energy, far-red light. PSII from Acaryochloris marina ha...

Flash-induced absorption changes in the Soret region arising from the [P D1 P D2 ] ⁺ state, the chlorophyll cation radical formed upon excitation of Photosystem II (PSII), were obtained using Mn-depleted PSII cores at pH 8.6. Under these conditions, Tyr D is reduced before the first flash but oxidised before subsequent flashes. When Tyr D • is pres...

Photosystem II (PSII) uses the energy from red light to split water and reduce quinone, an energy-demanding process based on chlorophyll a (Chl-a) photochemistry. Two kinds of cyanobacterial PSII can use Chl-d and Chl-f to perform the same reactions using lower energy, far-red light. PSII from Acaryochloris marina has Chl-d replacing all but one of...

Many cyanobacteria species can use both plastocyanin and cytochrome c6 as lumenal electron carriers to shuttle electrons from the cytochrome b6f to either photosystem I or the respiratory cytochrome c oxidase. In Synechocystis sp. PCC6803 placed in darkness, about 60% of the active PSI centres are bound to a reduced electron donor which is responsi...

Photosynthesis occurs in thylakoids, a highly specialized membrane system. In the cyanobacterium Synechocystis sp. PCC 6803 (hereafter Synechocystis 6803), the thylakoids are arranged parallel to the plasma membrane and occasionally converge towards it to form biogenesis centers. The initial steps in photosystem II (PSII) assembly are thought to ta...

The chloroplast ATP synthase/ATPase (cpATPase) couples ATP synthesis to the light-driven electrochemical proton gradient. The cpATPase is a multi-protein complex and consists of a membrane-spanning protein channel (comprising subunit types a, b, b' and c) and a peripheral domain (subunits α, β, γ, δ and ε). We report the characterization of the Ara...