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 characteris tics of rubisco in leaves of C3 plants in vivo. The method is based on analysis of leaf CO2 exchange dynamics after disconnection of light a nd 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 C O2 and ribulose- 1,5-bisphosphate (RuBP) within a wide interval of var iation of these concentrations. Changes of CO2 and RuBP concentration in carboxylation sites are achieved by varying CO2 concentration in th e gas delivered to the leaf and by varying the intensity of leaf illum ination. Determination of the Michaelis constant of rubisco for RuBP i n vivo by the given method is fairly difficult to accomplish because n onsaturation of the carboxylation reaction with respect to RuBP is pos sible for a number of plants. The error of determining the Michaelis c onstant of rubisco for CO2 is 30%.