We examined the effects of leaf temperature on the estimation of maximal Rubisco capacity (Vcmax ) from gas exchange measurements of wheat leaves using a C3 photosynthesis model. Cultivars of spring wheat (Triticum aestivum (L)) and triticale (X Triticosecale Wittmack) were grown in a greenhouse or in the field and measured at a range of temperatures under controlled conditions in a growth cabinet (2 and 21% O2 ) or in the field using natural diurnal variation in temperature, respectively. Published Rubisco kinetic constants for tobacco did not describe the observed CO2 response curves well as temperature varied. By assuming values for the Rubisco Michaelis-Menten constants for CO2 (Kc ) and O2 (Ko ) at 25 °C derived from tobacco and the activation energies of Vcmax from wheat and respiration in the light, Rd , from tobacco, we derived activation energies for Kc and Ko (93.7 and 33.6 kJ mol-1 , respectively) that considerably improved the fit of the model to observed data. We confirmed that temperature dependence of dark respiration for wheat was well described by the activation energy for Rd from tobacco. The new parameters improved the estimation of Vcmax under field conditions, where temperatures increased through the day.
Keywords: CO2 compensation point; CO2 response curves; Michaelis-Menten kinetic constants; Rubisco; Triticum aestivum; activation energy; respiration.
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