Photorespiration in Arabidopsis thaliana : natürliche Evolution und gentechnologische Modifikation

The bi-functional enzyme RUBISCO, the key enzyme of photosynthesis, catalyzes not only the carboxylation of ribulose-1,5-bisphosphate but also the oxygenation of this substrate. This reaction leads to the formation of the toxic compound glycolate. Glycolate cannot be used by the plant and has to be recycled by the energy consuming photorespiratory pathway. The first step of photorespiration is the oxidation of glycolate to glyoxylate. Land plants and charophycean green algae oxidize glycolate inside the peroxisome. This reaction is catalyzed by a glycolate oxidase that uses oxygen as a cofactor. Chlorophycean Green algae use a mitochondrial glycolate dehydrogenase with organic co-factors for this reaction. The glyoxylate produced is transaminated to glycine which is converted to glycerate in further reactions. Through the reactions of photorespiration, part of the afore fixed carbon can be salvaged. However, there is also a substantial loss of CO2 and NH3 from organic compounds. Previous studies had shown that Arabidopsis thaliana, a higher plant contains a mitochondrial glycolate dehydrogenase (AtGDH). This supported the hypothesis of an evolutionary linkage between peroxisomal and mitochondrial glycolate metabolism. In the first part of this work the importance of mitochondrial glycolate metabolism was analyzed with respect to photorespiration. The reduction of the photorespiratory parameters PIB (post illumination CO2 burst) and glycine/serine-ratio in AtGDH mutants indicated a participation of this pathway in photorespiration. Reduced CO2 release from AtGDH mutant mitochondria in radioactive labeling studies supported these results. Additionally, two putative alanine:glyoxylate-aminotransferase were identified by radioactive labeling and fluorescence localization studies that may play a role in the mitochondrial glycolate metabolism. In the course of these studies several results indicated that glycolate oxidation does not only take place in mitochondria and peroxisomes but also in chloroplasts of Arabidopsis thaliana. Enzymatic assay of isolated chloroplasts and “dual-targeting” experiments suggested that the responsible enzyme was AtGDH. In the second part of this work, the influence of a transgenic photorespiratory bypass on photosynthesis, photorespiration, and plant growth was studied. The Blueprint for this bypass is the catabolic Escherichia coli glycerate pathway. This pathway had been introduced before into the chloroplasts of Arabidopsis thaliana resulting in enhanced CO2 concentration in the vicinity of RUBISCO, improved CO2 assimilation rates and consequently enhanced growth. In this study, a combined transcriptome and metabolome analysis of plants overexpressing the relevant genes was performed. The results indicated little disturbance of the basal metabolism of transgenic lines, but specifically higher leaf sugar concentrations under photorespiratory conditions. These data together suggest that the photorespiratory bypass enables an efficient detoxification of glycolate, a higher rate of photosynthesis and higher leaf sugar concentrations which together ends in a higher biomass production.

Grantor dc:publisher

Publikationsserver der RWTH Aachen University

Year dc:date

2009

Author dc:creator

• Nießen, Markus

Contributors dc:contributor

• Peterhänsel, Christoph

• info:eu-repo/classification/ddc/570
• Photosynthese
• Alanin-Aminotransferase
• Gentechnologie
• Biomasse
• Biowissenschaften, Biologie
• photorespiration
• aminotransferase
• photosynthesis
• genetic engineering
• biomass

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

ger

Identifier

https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-113615%22

OAI record oai:identifier

https://publications.rwth-aachen.de/oai2d?verb=GetRecord&metadataPrefix=oai_dc&identifier=oai%3Apublications.rwth-aachen.de%3A51309