Temperature dependence of in vitro Rubisco kinetics in species of Flaveria with different photosynthetic mechanisms.

There is general consensus in the literature that plants with different photosynthetic mechanisms (i.e. C3 vs. C4) have Rubiscos characterised by different kinetic performances. However, potential differences in the temperature dependencies of Rubisco kinetic parameters between C3 and C4 plants are uncertain. Accordingly, six species of Flaveria with contrasting photosynthetic mechanisms (C3, C3/C4 and C4) were selected and their Rubisco Michaelis-Menten constants for CO2 and RuBP (K c and K RuBP), carboxylase catalytic turnover rate ([Formula: see text]) and CO2/O2 specificity factor (S c/o) were measured between 10 and 40 °C. The results confirmed different Rubisco characteristics between C3 and C4 plants. Rubisco from the C3 species had higher E a for K c and [Formula: see text] than that from C4 species, which were translated into differences in the temperature response of the carboxylase catalytic efficiency ([Formula: see text]/K c). However, E a did not differ for S c/o or K RuBP. Although a mechanism remains uncertain, it appears that the Asp/Glu-149-Ala and Met-309-Ile substitutions lead to differences in the temperature responses of catalysis between C3 and C4 Rubiscos in Flaveria. Therefore, the above observations are consistent with the fact that C3 species have a higher photosynthetic efficiency and ecological dominance in cool environments, with respect to C4 species in temperate environments.