KINETICS OF RUBISCO ACTIVATION AS DETERMINED FROM GAS-EXCHANGE MEASUREMENTS IN ANTISENSE PLANTS OF ARABIDOPSIS-THALIANA CONTAINING REDUCED LEVELS OF RUBISCO ACTIVASE

The kinetics of the increase in photosynthesis rate following an incre ase in PFD were determined in wildtype Arabidopsis thaliana plants and in two antisense plants that contained reduced levels of Rubisco acti vase. Experiments were conducted over a range of intercellular CO2 mol e fractions (c(i)). The rate at which photosynthesis approached steady -state following an increase in PFD was similar for wildtype and trans formed plants at low values of c(i). At higher values of c(i), however , wildtype plants approached steady state more rapidly than did the an tisense plants. Photosynthesis time courses were used to calculate Rub isco activation rates for the three types of plants, and Rubisco activ ation rate was found to be proportional to activase content at a c(i) of 280 mu mol mol(-1). These data are discussed in the context of prop osed mechanisms for Rubisco activase in the activation of Rubisco.