Mass-spectrometric determination of O2and CO2gas exchange in illuminated higher-plant cells

✍ Scribed by Marie-Hélène Avelange; Jean M. Thiéry; Frédéric Sarrey; Pierre Gans; Fabrice Rébeillé

• Publisher: Springer-Verlag
• Year: 1991
• Tongue: English
• Weight: 737 KB
• Volume: 183
• Category: Article
• ISSN: 0032-0935
• DOI: 10.1007/bf00197782

✦ Synopsis

In order to estimate photosynthetic and respiratory rates in illuminated photoautotrophic cells of carnation (Dianthus caryophyllus L.), simultaneous measurements of CO2 and 02 gas exchange were performed using 1802, 13CO2 and a mass-spectrometry technique. This method allowed the determination, and thus the comparison, of unidirectional fluxes of 02 and CO2. In optimum photosynthetic conditions (i.e. in the presence of high light and a saturating level of CO2), the rate of CO 2 influx represented 75+5% of the rate of gross O2 evolution. After a dark-to-light transition, the rate of CO2 efflux was inhibited by 50% whereas the O2-uptake rate was little affected. The effect of a recycling of respiratory CO2 through photosynthesis on the exchange of CO2 gas was investigated using a mathematical model. The confliction of the experimental data with the simulated gas-exchange rates strongly supported the view that CO2 recycling was a minor event in these cells and could not be responsible for the observed inhibition of CO2 efflux. On the basis of this assumption it was concluded that illumination of carnation cells resulted in a decrease of substrate decarboxylations, and that CO2 efflux and O2 uptake were not as tightly coupled in the light as in the dark. Furthermore, it could be calculated from the rate of gross photosynthesis that the chloroplastic electron-transport chain produced enough ATP in the light to account for the measured CO2-uptake rate without involving cyclic transfer of electrons around PSI or mitochondrial supplementation.