Ratio between carboxylation and oxygenation (Vc/Vo) activities of RuBisCO

Range in Low Light (LL) plants 3.5:1 in high light acclimated (HL-ACC) plants 2.3:1 unitless
Organism Thale cress Arabidopsis thaliana
Reference Ma F, Jazmin LJ, Young JD, Allen DK. Isotopically nonstationary 13C flux analysis of changes in Arabidopsis thaliana leaf metabolism due to high light acclimation. Proc Natl Acad Sci U S A. 2014 Nov 25 111(47):16967-72. doi: 10.1073/pnas.1319485111. abstract and p.16970 left column 4th paragraphPubMed ID25368168
Method Abstract: "[Investigators] performed in vivo isotopic labeling of Arabidopsis thaliana rosettes with (13)CO2 and estimated fluxes throughout leaf photosynthetic metabolism by INST-MFA [Isotopically nonstationary metabolic flux analysis]. Plants grown at 200 µmol m^(-2)s^(-1) light were compared with plants acclimated for 9 d at an irradiance of 500 µmol⋅m^(-2)⋅s^(-1)."
Comments Abstract: "Despite a doubling in the carboxylation rate, the photorespiratory flux increased from 17 to 28% of net CO2 assimilation with high-light acclimation (Vc/Vo: 3.5:1 vs. 2.3:1, respectively)." P.16970 left column 4th paragraph: "Absolute fluxes (µmol metabolite/gFW/hr) obtained from the best-fit models were subsequently normalized by the net assimilation rate to enable direct comparisons of carbon partitioning between LL and HL-ACC conditions (Fig. 3). Both the carboxylation and oxygenation activities of RuBisCO were established through the modeling process, resulting in a ratio of Vc/Vo that dropped from 3.5:1 in LL plants to 2.3:1 in HL-ACC plants. The change in this ratio reflected an absolute increase in photorespiratory flux from 19 to 60 µmol CO2 released/gFW/hr, whereas carboxylation changed from 135 to 278 µmol CO2 fixed/gFW/hr. As a result, photorespiratory fluxes were 17 and 28% of net assimilation, respectively. The additional carbon lost to photorespiration in the HL-ACC condition was offset primarily by decreases in the relative flux to starch accumulation (from 33 to 24% of net assimilation)."
Entered by Uri M
ID 113455