ACCLIMATION OF PHOTOSYNTHETIC PROTEINS TO RISING ATMOSPHERIC CO2

In this review we discuss how the photosynthetic apparatus, particular ly Rubisco, acclimates to rising atmospheric CO2 concentrations (c(a)) . Elevated c(a) alters the control exerted by different enzymes of the Calvin cycle on the overall rate of photosynthetic CO2 assimilation, so altering the requirement for different functional proteins. A decre ased flux of carbon through the photorespiratory pathway will decrease requirements for these enzymes. From modeling of the response of CO2 uptake (A) to intracellular CO2 concentration (c(i)) it is shown that the requirement for Rubisco is decreased at elevated c(a), whilst that for proteins limiting ribulose 1,5 bisphosphate regeneration may be i ncreased. This balance may be altered by other interactions, in partic ular plasticity of sinks for photoassimilate and nitrogen supply; hypo theses on these interactions are presented. It is speculated that incr eased accumulation of carbohydrate in leaves developed at elevated c(a ) may signal the 'down regulation' of Rubisco. The molecular basis of this 'down regulation' is discussed in terms of the repression of phot osynthetic gene expression by the elevated carbohydrate concentrations . This molecular model is then used to predict patterns of acclimation of perennials to long term growth in elevated c(a).