Phosphoglycolate phosphatases (PGPases) catalyze the first step of the photorespiratory cycle in cyanobacteria, algae and plants, which salvages the toxic intermediate 2-phosphoglycolate. This process is essential to support photosynthesis in an oxygen-rich atmosphere. Preliminary studies showed that the cyanobacterial model strain _{Synechocystis} sp. PCC 6803 encodes up to four putative PGPases, which however differ from the respective plant enzyme in structure and phylogeny. To investigate if these PGPase candidate proteins can really function in the photorespiratory cycle, they were expressed after fusion with a transit peptide for chloroplast import in Arabidopsis antisense lines with reduced PGPase activity, which can only grow in the presence of elevated CO₂ amounts. For the project, 14 independent transgenic Arabidopsis lines expressing specific cyanobacterial PGPase genes with five to ten individuals each have been studied during this Master thesis. The phenotype, photosynthesis by gas exchange and fluorescence, protein expression by Western-blotting, and metabolite composition by LC-MS were studied using plants that were first cultivated under high CO₂ conditions (1% CO₂) and then shifted to ambient air. After comprehensive pre-investigations it was eventually achieved to identify seven Arabidopsis lines which showed significantly lowered 2-phosphoglycolate contents after expressing the cyanobacterial PGPases Slr0458, Slr0586 or Sll1349, respectively, compared to AtPGPase antisense control line. Thus, the partial complementation of the Arabidopsis antisense lines seems to support the functionality of cyanobacterial PGPases in the photorespiratory cycle.

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Stefan Lucius conducted this work at the Institute for Biosciences, Department for Plant Physiology in the working group of Prof. Dr. Martin Hegemann and was supervised by Prof. Martin Hagemann/Dr. Stefan Timm.