Is there scope for improving balance between RuBP-regeneration and carboxylation capacities in wheat at elevated CO2?

Carboxylation and RuBP-regeneration capacities, which determine light-satur ated photosynthetic rate, were analysed in leaves of spring wheat (Triticum aestivum L, cv, Minaret) grown under different atmospheric CO2 partial pre ssure (pC(a)) and N supply regimes. Capacities were estimated from a large number of gas exchange, Rubisco and ATP-synthase content measurements, and from these, the pC(a) at which the two capacities are equal was derived, to allow direct comparison with growth pC(a). Acclimation of the balance betw een the two capacities to growth at elevated pC(a) in wheat was only partia l and appears to occur mostly in older flag leaves and at low N, However, i n contrast to conclusions drawn from previous analyses of these data, there was evidence of a specific effect of growth at 70 Pa pC(a), where carboxyl ation capacity is reduced more than RuBP-regeneration capacity for a given leaf N content. A model was used to estimate the effects of fluctuations in PPFD and temperature in the growth environment on the optimal balance betw een these capacities, This showed that the observed balance between carboxy lation and RuBP-regeneration capacities in young wheat leaves could be cons istent with adaptation to the current, or even the preindustrial pC(a).