Rubisco Catalytic Properties and Temperature Response in Crops

Abstract

Rubisco catalytic traits and their thermal dependence are two major factors limiting the CO2 assimilation potential of plants. In this study, we present the profile of Rubisco kinetics for 20 crop species at three different temperatures. The results largely confirmed the existence of significant variation in the Rubisco kinetics among species. Although some of the species tended to present Rubisco with higher thermal sensitivity (e.g. Oryza sativa) than others (e.g. Lactuca sativa), interspecific differences depended on the kinetic parameter. Comparing the temperature response of the different kinetic parameters, the Rubisco Km for CO2 presented higher energy of activation than the maximum carboxylation rate and the CO2 compensation point in the absence of mitochondrial respiration. The analysis of the Rubisco large subunit sequence revealed the existence of some sites under adaptive evolution in branches with specific kinetic traits. Because Rubisco kinetics and their temperature dependency were species specific, they largely affected the assimilation potential of Rubisco from the different crops, especially under those conditions (i.e. low CO2 availability at the site of carboxylation and high temperature) inducing Rubisco-limited photosynthesis. As an example, at 25°C, Rubisco from Hordeum vulgare and Glycine max presented, respectively, the highest and lowest potential for CO2 assimilation at both high and low chloroplastic CO2 concentrations. In our opinion, this information is relevant to improve photosynthesis models and should be considered in future attempts to design more efficient Rubiscos.

Figure 1.

Relationship of k_cat^c with K_c (A) and the S_c/o (B). Black symbols correspond to C₃ species at 15°C (triangles), 25°C (circles), and 35°C (inverted triangles); white symbols correspond to C₄ species at 15°C (triangles), 25°C (circles), and 35°C (inverted triangles). Each symbol represents the average value of a single species per temperature interaction.

Figure 2.

Simulated A_Rubisco for C₃ and C₄ species at 15°C, 25°C, and 35°C and at C_c values of 250 μbar (A) and 150 μbar (B). Equations used to calculate A_Rubisco were those described in the biochemical model of C₃ photosynthesis (Farquhar et al., 1980), as explained in “Materials and Methods.” Bars represent minimum values of A_c- and A_j-limited A_Rubisco. Asterisks beside the bars indicate A_c-limited A_Rubisco, and the absence of asterisks indicates A_j-limited A_Rubisco. The rates of electron transport were 60, 150, and 212 μmol m⁻² s⁻¹ at 15°C, 25°C, and 35°C, respectively. The concentration of active Rubisco sites was assumed to be invariable at 25 μmol m⁻² for all species and environmental conditions. The values used for the Rubisco kinetic parameters (k_cat^c, Γ*, and K_c^air) are those shown in Table I and Supplemental Table S1.