Quantum yields for CO2 uptake in some diploid and tetraploid plant species

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Abstract
Quantum (photon) yields for CO2 uptake on an absorbed photon fluence rate (PFR) basis (φa) were determined for a number of diploid and tetraploid species under a range of experimental conditions. Little variation in φa was found either between species or across ploidy levels, which suggests that there are no intrinsic differences in the kinetics of CO2 fixation. Variations in photosynthetic rate or quantum yield expressed on an incident PFR basis (φj) were found to be largely due to differences in leaf absorptance. On this basis these results do not support the biochemical evidence showing ploidy‐related differences in the Km (CO2) of ribulose ‐1,5‐bisphosphate carboxylase/oxygenase. However, there are obvious difficulties in relating in vitro enzyme kinetic data to in vivo studies and these problems are discussed.