Temperature response of in vivoRubisco kinetics and mesophyll conductance in Arabidopsis thaliana: Comparisons to Nicotiana tabacum

Biochemical models of photosynthesis use the temperature dependency of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) kinetics and mesophyll conductance to CO ₂ (g _m). However, the in vivo temperature response of Rubisco kinetics and g _m has only been measured in the warm adapted Nicotiana tabacum; therefore, we determined these parameters in the cool-adapted Arabidopsis thaliana to see how species-dependent differences impact modeled rates of photosynthesis. While the individual Rubisco kinetic parameters in N. tabacum and A. thaliana were similar across temperatures, they collectively resulted in significantly different modeled rates of photosynthesis. Additionally, g _m increased with temperature in N. tabacum but not in A. thaliana. Commentary: New challenges in modeling photosynthesis: temperature dependencies of Rubisco kinetics Biochemical models are used to predict and understand the response of photosynthesis to rising temperatures and CO₂ partial pressures. These models require the temperature dependency of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) kinetics and mesophyll conductance to CO₂ (g_m). However, it is not known how the temperature response of Rubisco kinetics differs between species, and comprehensive in vivo Rubisco kinetics that include g_m have only been determined in the warm-adapted Nicotiana tabacum. Here, we measured the temperature response of Rubisco kinetics and g_m in N. tabacum and the cold-adapted Arabidopsis thaliana using gas exchange and ¹³CO₂ isotopic discrimination on plants with genetically reduced levels of Rubisco. While the individual Rubisco kinetic parameters in N. tabacum and A. thaliana were similar across temperatures, they collectively resulted in significantly different modelled rates of photosynthesis. Additionally, g_m increased with temperature in N. tabacum but not in A. thaliana. These findings highlight the importance of considering species-dependent differences in Rubisco kinetics and g_m when modelling the temperature response of photosynthesis.