Evidence for18O labeling of photorespiratory CO2in photoautotrophic cell cultures of higher plants illuminated in the presence of18O2

✍ Scribed by Laurent Cournac; Bernard Dimon; Gilles Peltier

• Publisher: Springer-Verlag
• Year: 1993
• Tongue: English
• Weight: 795 KB
• Volume: 190
• Category: Article
• ISSN: 0032-0935
• DOI: 10.1007/bf00196970

✦ Synopsis

The 180-enrichment of CO 2 produced in the light or during the post-illumination burst was measured by mass spectrometry when a photoautotrophic cell suspension of Euphorbia characias L. was placed in photorespiratory conditions in the presence of molecular 180 2. The only tSO-labeled species produced was C180160; no C180180 could be detected. Production of C180160 ceased after addition of two inhibitors of the photosynthetic carbon-oxidation cycle, aminooxyacetate or aminoacetonitrile, and was inhibited by high levels of CO2. The average enrichment during the post-illumination burst was estimated to be 46-t-15% of the enrichment of the 02 present during the preceding light period. Addition of exogenous carbonic anhydrase, by catalyzing the exchange between CO2 and H20, drastically diminished the 180-enrichment of the produced CO2. The very low carbonio-anhydrase level of the photoautotrophic cell suspension probably explains why the 180 labeling of photorespiratory CO2 could be observed for the first time. These data allow the establishment of a direct link between 02 consumption and CO 2 production in the light, and the conclusion that CO 2 produced in the light results, at least partially, from the mitochondrial decarboxylation of the glycine pool synthesized through the photosynthetic carbon-oxidation cycle. Analysis of the CL80160 and CO 2 kinetics provides a direct and reliable way to assess in vivo the real contribution of photorespiratory metabolism to CO2 production in the light.