KINETIC CHARACTERISTICS OF RIBULOSE-1,5-BISPHOSPHATE CARBOXYLASE IN-VIVO .1. NUMERICAL ESTIMATION BASED ON A MODEL OF CO2 EXCHANGE OF THE PHOTOSYNTHESIZING LEAF

The present paper describes a method for measuring kinetic characteristics of rubisco in leaves of C3 plants in vivo. The method is based on analysis of leaf CO2 exchange dynamics after disconnection of light and the segment of the momentary carbon dioxide curve of photosynthesis corresponding to low CO2 concentrations. The analysis uses a model of CO2 exchange dynamics under non-steady-state conditions of light-dark transition that takes into account the effect of reassimilation. The procedure cites the experimental dependency of the rate of the rubisco-catalyzed carboxylation reaction on concentration of the substrates CO2 and ribulose- 1,5-bisphosphate (RuBP) within a wide interval of variation of these concentrations. Changes of CO2 and RuBP concentration in carboxylation sites are achieved by varying CO2 concentration in the gas delivered to the leaf and by varying the intensity of leaf illumination. Determination of the Michaelis constant of rubisco for RuBP in vivo by the given method is fairly difficult to accomplish because nonsaturation of the carboxylation reaction with respect to RuBP is possible for a number of plants. The error of determining the Michaelis constant of rubisco for CO2 is 30%.