Summary
The 12CO2- and 14CO2-exchange of illuminated corn leaf discs were measured at normal (21%) and low (1%) oxygen. After periods of exposure to 14CO2 or to 14CO2 followed by 12CO2, the discs were killed and the specific activities of some metabolites were determined. At both O2 concentrations the specific activity of 3-PGA increased and decreased rapidly during the first 5 min of 14CO2-feeding or 12CO2-flushing but did not equilibrate with that of the CO2 in the assimilation chamber even after 15 min. The specific activity of aspartic acid also showed bimodal kinetics during both feeding and flushing. The specific activities of 3-phosphoglyceric acid (3-PGA), aspartic acid and alanine were higher at 1% O2 than at 21% O2, but glycine and serine were lower in specific activity at 1% O2. The results are in agreement with the proposed initial fixation of CO2 into C4-dicarboxylic acids and subsequent transfer of this carbon to 3-PGA. Indirect evidence supports the idea that at 21% O2, CO2 was produced by the corn leaf discs in the light and was refixed into C4-dicarboxylic acids. At 1% O2, the photorespiratory process could also have been active although the flux of carbon through the glycolate pathway was probably smaller than at 21% O2.
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Abbreviations
- PEP:
-
phosphoenolpyruvate
- 3-PGA:
-
3-phosphoglyceric acid
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Mahon, J.D., Fock, H., Höhler, T. et al. Changes in specific radioactivities of corn-leaf metabolites during photosynthesis in 14CO2 and 12CO2 at normal and low oxygen. Planta 120, 113–123 (1974). https://doi.org/10.1007/BF00384921
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DOI: https://doi.org/10.1007/BF00384921