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Plants and algae often absorb too much light-more than they can actually use in photosynthesis. To prevent photo-oxidative damage and to acclimate to changes in their environment, photosynthetic organisms have evolved direct and indirect mechanisms for sensing and responding to excess light. Photoreceptors such as phototropin, neochrome, and cryptochrome(More)
The glutathione peroxidase homologous gene (Gpxh gene) in Chlamydomonas reinhardtii is up-regulated under oxidative stress conditions. The Gpxh gene showed a remarkably strong and fast induction by the singlet oxygen-generating photosensitizers neutral red, methylene blue and rose Bengal. The Gpxh mRNA levels strongly increased, albeit much more slowly,(More)
SIGNIFICANCE In photosynthetic organisms, excited chlorophylls (Chl) can stimulate the formation of singlet oxygen ((1)O(2)), a highly toxic molecule that acts in addition to its damaging nature as an important signaling molecule. Thus, due to this dual role of (1)O(2), its production and detoxification have to be strictly controlled. RECENT ADVANCES(More)
High light illumination of photosynthetic organisms stimulates the production of singlet oxygen by photosystem II and causes photooxidative stress. In Chlamydomonas reinhardtii, singlet oxygen also induces the expression of the nuclear-encoded glutathione peroxidase homologous gene GPXH. We provide evidence that singlet oxygen stimulates GPXH expression by(More)
Different substrate conditions, such as varying CO(2) concentrations or the presence of acetate, strongly influence the efficiency of photosynthesis in Chlamydomonas reinhardtii. Altered photosynthetic efficiencies affect the susceptibility of algae to the deleterious effects of high light stress, such as the production of reactive oxygen species (ROS) and(More)
Acclimation of Chlamydomonas reinhardtii cells to low levels of singlet oxygen, produced either by photoreactive chemicals or high light treatment, induces a specific genetic response that strongly increases the tolerance of the algae to subsequent exposure to normally lethal singlet oxygen-producing conditions. The genetic response includes the increased(More)
When exposed to strong sunlight, photosynthetic organisms encounter photooxidative stress by the increased production of reactive oxygen species causing harmful damages to proteins and membranes. Consequently, a fast and specific induction of defense mechanisms is required to protect the organism from cell death. In Chlamydomonas reinhardtii, the(More)
Thiol/selenol peroxidases are ubiquitous nonheme peroxidases. They are divided into two major subfamilies: peroxiredoxins (PRXs) and glutathione peroxidases (GPXs). PRXs are present in diverse subcellular compartments and divided into four types: 2-cys PRX, 1-cys PRX, PRX-Q, and type II PRX (PRXII). In mammals, most GPXs are selenoenzymes containing a(More)
Excess light can impose severe oxidative stress on photosynthetic organisms. We have characterized high-light responses in wild-type Chlamydomonas reinhardtii and in the npq1 lor1 double mutant. The npq1 lor1 strain lacks two photoprotective carotenoids, lutein and zeaxanthin, and experiences acute photo-oxidative stress upon exposure to excess light. To(More)
The expression of the glutathione peroxidase homologous gene Gpxh, known to be specifically induced by the formation of singlet oxygen (1O2), was analyzed in cells of Chlamydomonas reinhardtii exposed to environmental conditions causing photoinhibition. Illumination with high light intensities, leading to an increased formation of 1O2 in photosystem II,(More)