The effect of temperature on C4-type leaf photosynthesis parameters

C-4-type photosynthesis is known to vary with growth and measurement temperatures. In an attempt to quantify its variability with measurement temperature, the photosynthetic parameters - the maximum catalytic rate of the enzyme ribulose 1-5-bisphosphate carboxylase/oxygenase (Rubisco) (V-max), the maximum catalytic rate of the enzyme phosphoenolpyruvate carboxylase (PEPC) (V-pmax) and the maximum electron transport rate (J(max)) - were examined. Maize plants were grown in climatic-controlled phytotrons, and the curves of net photosynthesis (A.) versus intercellular air space CO2 concentrations (C-i), and A. versus photosynthetic photon flux density (PPFD) were determined over a temperature range of 15-40 degrees C. Values of V-max, V-pmax and J(max) were computed by inversion of the von Caemmerer & Furbank photosynthesis model. Values of V-pmax and J(max) obtained at 25 degrees C conform to values found in the literature. Parameters for an Arrhenius equation that best fits the calculated values of V-cmax, V-pmax and J(max) are then proposed. These parameters should be further tested with C-4 plants for validation. Other model key parameters such as the mesophyll cell conductance to CO2] (g(i)), the bundle sheath cells conductance to CO2 (90 and Michaelis-Menten constants for CO2 and 02 (K-c, K-p and K-o) also vary with temperature and should be better parameterized.