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Isotopically nonstationary ¹³C flux analysis of changes in Arabidopsis thaliana leaf metabolism due to high light acclimation

Ma, Fangfang, Jazmin, Lara J., Young, Jamey D., Allen, Doug K.
Proceedings of the National Academy of Sciences of the United States of America 2014 v.111 no.47 pp. 16967-16972
Arabidopsis thaliana, acclimation, biomass production, carbon, carbon dioxide, carboxylation, environmental factors, ions, isotope labeling, leaves, light intensity, metabolic engineering, metabolites, phenotype, photosynthesis, plant physiology, stable isotopes
Improving plant productivity is an important aim for metabolic engineering. There are few comprehensive methods that quantitatively describe leaf metabolism, although such information would be valuable for increasing photosynthetic capacity, enhancing biomass production, and rerouting carbon flux toward desirable end products. Isotopically nonstationary metabolic flux analysis (INST-MFA) has been previously applied to map carbon fluxes in photoautotrophic bacteria, which involves model-based regression of transient ¹³C-labeling patterns of intracellular metabolites. However, experimental and computational difficulties have hindered its application to terrestrial plant systems. We performed in vivo isotopic labeling of Arabidopsis thaliana rosettes with ¹³CO ₂ and estimated fluxes throughout leaf photosynthetic metabolism by INST-MFA. Plants grown at 200 µmol m ⁻²s ⁻¹ light were compared with plants acclimated for 9 d at an irradiance of 500 µmol⋅m ⁻²⋅s ⁻¹. Approximately 1,400 independent mass isotopomer measurements obtained from analysis of 37 metabolite fragment ions were regressed to estimate 136 total fluxes (54 free fluxes) under each condition. The results provide a comprehensive description of changes in carbon partitioning and overall photosynthetic flux after long-term developmental acclimation of leaves to high light. Despite a doubling in the carboxylation rate, the photorespiratory flux increased from 17 to 28% of net CO ₂ assimilation with high-light acclimation (Vc/Vo: 3.5:1 vs. 2.3:1, respectively). This study highlights the potential of ¹³C INST-MFA to describe emergent flux phenotypes that respond to environmental conditions or plant physiology and cannot be obtained by other complementary approaches.