Partitioning of Transfer and Carboxylation Components of Intracellular Resistance to Photosynthetic CO2 Fixation: A Critical Analysis of the Methods Used

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Abstract
The partitioning of intracellular resistance to CO2 transfer in two components: mesophyll (rm.) and carboxylation (rx) resistances, is based upon the combination of two sub-models: one encompassing transfer processes and the second, the carboxylation system. All the determinations derived from this method yield a high rm/rx ratio. it is demonstrated in low oxygen conditions, whatever the model used, that this conclusion is highly-dependent upon the form of the equation used at the carboxylation level. The possible influence of O2 concentration on the rm/rx ratio is discussed. Starting from a Rabinowitch model (rectangular hyperbola), some of the conditions necessary to yield lower rm/rx ratio are considered. It is shown that the most relevant factor when modelling the Calvin cycle is the number of limiting pools (enzymes or cofactors) rather than the number of limiting reactions.