Kinetics of Rubisco Activation as Determined from Gas-exchange Measurements in Antisense Plants of Arabidopsis thaliana Containing Reduced Levels of Rubisco Activase

Abstract

The kinetics of the increase in photosynthesis rate following an increase in PFD were determined in wildtype Arabidopsis thaliana plants and in two antisense plants that contained reduced levels of Rubisco activase. Experiments were conducted over a range of intercellular CO₂ mole fractions (c_i). The rate at which photosynthesis approached steady-state following an increase in PFD was similar for wildtype and transformed plants at low values of c_i. At higher values of c_i, however, wildtype plants approached steady state more rapidly than did the antisense plants. Photosynthesis time courses were used to calculate Rubisco activation rates for the three types of plants, and Rubisco activation rate was found to be proportional to activase content at a c_i of 280 µmol mol^-1. These data are discussed in the context of proposed mechanisms for Rubisco activase in the activation of Rubisco.