Quantitative Assessment of the Degree to Which Ribulosebisphosphate Carboxylase/Oxygenase Determines the Steady-State Rate of Photosynthesis During Sun-Shade Acclimation in Helianthus annuus L

Abstract

The degree to which ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) determines or limits the steady state rate of CO₂ assimilation during sun-shade acclimation in sunflower (Helianthus annuus) was examined and expressed as a 'flux control coefficient'. The coefficients were calculated according to the procedure developed by Woodrow et al. (1987) [In: Proc. Congress on Rubisco, (Ed. R. G. Jensen.) (Tucson: U.S.A.)] an outline of which is presented in this paper. The analysis shows that the Rubisco control coefficient, and therefore the degree of flux control exerted by this enzyme, increases with increasing light intensity until, at saturating light, Rubisco is the principal determinant of the photosynthetic rate. There was however a marked difference in the range of light intensities over which changes in flux control occurred between the plants at various stages of acclimation.