Regulatory subunit B'gamma of protein phosphatase 2A prevents unnecessary defense reactions under low light in Arabidopsis

Peer reviewe

An investigation of the PsbS protein isolated from spinach chloroplast membranes.

Dissipation of excess light energy in plant photosynthetic membranes plays an important role in the response of plants to the environment, providing short-term balancing between the intensity of sunlight and photosynthetic capacity. The carotenoid zeaxanthin and the photosystem Il subunit PsbS play vital roles in this process, but the mechanism of their action is largely unexplained. This thesis reports a novel procedure for the extraction of the PsbS protein from spinach thylakoids, including a detailed account of the developmental process and characterisation of the isolated protein. The ability of the PsbS protein to bind xanthophyll cycle carotenoids in vitro was assessed, leading to the observation that the isolated protein was able to bind exogenous zeaxanthin, the binding resulting in a strong red shift in the absorption spectrum, and the appearance of characteristic features in the resonance Raman spectrum and a distinct circular dichroism spectrum, indicating pigment-protein, as well as specific pigmentpigment, interaction. A strong shift in the absorption spectrum of PsbS phenylalanine residues after zeaxanthin binding was observed. It is concluded that zeaxanthin binding to PsbS is the origin of the well known energy dissipation-related 535-nm absorption change. The ability of this PsbS-zeaxanthin complex to affect the rate of chlorophyll fluorescence quenching of the major LHcn antenna protein is detailed, revealing an increase in the rate of quenching, whilst the magnitude of quenching remained constant. The altered properties of zeaxanthin and PsbS after in vitro reconstitution and their subsequent effect on LHCnb provide the first direct indication about how they regulate energy dissipation

Photosynthesis

Among the myriads of volumes dedicated to various aspects of photosynthesis, the current one is singular in integrating an update of the most recent insights on this most important biological process in the biosphere. While photosynthesis fuels all the life supporting processes and activities of all living creatures on Earth, from bacteria though mankind, it also created in the first place, our life supporting oxygenic atmosphere, and keeps maintaining it. This volume is organized in four sections: I) Mechanisms, II) Stress effects, III) Methods, and IV) Applications

Differential Gene Expression in a Louisiana Strain of Microalgae

Considerable interest in alternative energy has stimulated research in biofuels, particularly microalgal biofuels. In particular, strains of algae that accumulate lipids to be used for biofuels must be adapted to outdoor growth and resistant to invasive species. Differential gene expression in a Louisiana algae/cyanobacteria co-culture consisting of approximately 97% Chlorella vulgaris and 3% Leptolyngbya sp. possessing these traits was examined. Possible reasons for the enhanced growth of the co-culture relative to a Chlorella monoculture were reviewed, including cyanobacterial symbiosis and chemicals produced by cyanobacteria or bacteria that could influence the growth of Chlorella. The co-culture and Chlorella monoculture were cultivated at scalar irradiance levels of 180 and 400 µmol/m2-sec and nitrate levels corresponding to 50% and 100% of the nitrate levels of Bold’s Basal Medium. Dry biomass and cell counts were measured for the cultures initially, in the early exponential phase, in the late exponential phase, and at the end of the growth period. Lipid content was measured in the late exponential phase and at the end of the growth period. Total RNA was extracted and suppression subtractive hybridization was performed. Expressed sequence tags corresponding to putatively differentially expressed genes were sequenced, yielding one-hundred and five putatively differentially expressed genes. Quantitative PCR was performed on nine genes to compare gene expression in Chlorella in the co-culture and monoculture. All nine genes showed statistically significant expression level differences between the Chlorella vulgaris in the co-culture and in the monoculture for cultures grown at the same irradiance and nitrate levels. Evidence from the gene expression experiments, combined with observations in the literature, suggest the possible effect of a cyanobacteria-produced substance such as microcystins by the Leptolyngbya sp. Second, two Photosystem II genes were upregulated in the Chlorella monocultures, and one Photosystem I gene was upregulated in the co-cultures. Finally, the upregulation of a gene for an oil globule associated protein was found in the co-culture Chlorella. A homologous protein has been found in similar green algae, and further study of it in Chlorella is expected