JXB Advance Access originally published online on June 26, 2007
Journal of Experimental Botany 2007 58(10):2709-2715; doi:10.1093/jxb/erm131
RESEARCH PAPER |
Mitochondrial glycolate oxidation contributes to photorespiration in higher plants
RWTH Aachen, Institute of Biology I, Worringer Weg 1, D-52056 Aachen, Germany
* To whom correspondence should be addressed. E-mail: cp{at}bio1.rwth-aachen.de
The oxidation of glycolate to glyoxylate is an important reaction step in photorespiration. Land plants and charophycean green algae oxidize glycolate in the peroxisome using oxygen as a co-factor, whereas chlorophycean green algae use a mitochondrial glycolate dehydrogenase (GDH) with organic co-factors. Previous analyses revealed the existence of a GDH in the mitochondria of Arabidopsis thaliana (AtGDH). In this study, the contribution of AtGDH to photorespiration was characterized. Both RNA abundance and mitochondrial GDH activity were up-regulated under photorespiratory growth conditions. Labelling experiments indicated that glycolate oxidation in mitochondrial extracts is coupled to CO2 release. This effect could be enhanced by adding co-factors for aminotransferases, but is inhibited by the addition of glycine. T-DNA insertion lines for AtGDH show a drastic reduction in mitochondrial GDH activity and CO2 release from glycolate. Furthermore, photorespiration is reduced in these mutant lines compared with the wild type, as revealed by determination of the post-illumination CO2 burst and the glycine/serine ratio under photorespiratory growth conditions. The data show that mitochondrial glycolate oxidation contributes to photorespiration in higher plants. This indicates the conservation of chlorophycean photorespiration in streptophytes despite the evolution of leaf-type peroxisomes.
Key words: Glycolate dehydrogenase, photorespiration, plant evolution, streptophytes
Received 30 April 2007; Revised 21 May 2007 Accepted 22 May 2007
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