Effect of temperature on the CO2/O2 specificity of ribulose-1,5-bisphosphate carboxylase/oxygenase and the rate of respiration in the light

Abstract

Responses of the rate of net CO2 assimilation (A) to the intercellular partial pressure of CO2 (p i ) were measured on intact spinach (Spinacia oleracea L.) leaves at different irradiances. These responses were analysed to find the value of p i at which the rate of photosynthetic CO2 uptake equalled that of photorespiratory CO2 evolution. At this CO2 partial pressure (denoted Г), net rate of CO2 assimilation was negative, indicating that there was non-photorespiratory CO2 evolution in the light. Hence Г was lower than the CO2 compensation point, Γ. Estimates of Г were obtained at leaf temperatures from 15 to 30°C, and the CO2/O2 specificity of ribulose 1,5-bisphosphate (RuBP) carboxylase/oxygenase (E.C. 4.1.1.39) was calculated from these data, taking into account changes in CO2 and O2 solubilities with temperature. The CO2/O2 specificity decreased with increasing temperature. Therefore we concluded that temperature effects on the ratio of photorespiration to photosynthesis were not solely the consequence of differential effects of temperature on the solubilities of CO2 and O2. Our estimates of the CO2/O2 specificity of RuBP carboxylase/oxygenase are compared with in-vitro measurements by other authors. The rate of nonphotorespiratory CO2 evolution in the light (R d ) was obtained from the value of A at Г. At this low CO2 partial pressure, R d was always less than the rate of CO2 evolution in darkness and appeared to decrease with increasing irradiance. The decline was most marked up to about 100 μmol quanta m(-2) s(-1) and less marked at higher irradiances. At one particular irradiance, however, R d as a proportion of the rate of CO2 evolution in darkness was similar in different leaves and this proportion was unaffected by leaf temperature or by [O2] (ambient and greater). After conditions of high [CO2] and high irradiance for several hours, the rate of CO2 evolution in darkness increased and R d also increased.

Modelling the impacts of weather and climate variability on crop productivity over a large area: A new process-based model development, optimization, and uncertainties analysis

“…Parameters t, k o , and k c are kinetic parameters with a Q 10 dependence on temperature (Brooks and Farquhar, 1985;Collatz et al, 1991). An appropriate simplification of the model (with different values for a and a and saturating p i ) is applied for plants with C 4 physiology (Haxeltine and Prentice, 1996a).…”

Recruitment of pre-existing networks during the evolution of C 4 photosynthesis

“…2-PG is toxic and so is rapidly metabolized to prevent its accumulation [7]. The metabolism of PG is known as photorespiration and is energetically costly, especially at high temperatures when rates of oxygenation increase [8]. It has been proposed that high rates of oxygenation by RuBisCO led to the evolution of increased specificity for CO 2 , but also that an inescapable trade-off between specificity and the rate of catalysis led to a lower turnover rate [9].…”

An analytical model of non‐photorespiratory CO2 release in the light and dark in leaves of C3 species based on stoichiometric flux balance

“…For example, non-photorespiratory CO2 efflux, Rc, continues in the light but typically at a lower rate than in the dark (Brooks & Farquhar 1985;Kirschbaum & Farquhar 1987;Bloom et al 1989;Villar, Held & Merino 1995). Several explanations for reduced Rc in the light have been proposed, most of which involve photosynthesis to some degree:(1) ExcessATP or redox equivalents generated by the light reactions of photosynthesis can help satisfy cellular ATP demand, permitting a reduced rate of respiratory substrate oxidation.…”

“…Early experiments found no Kok effect in low oxygen, suggesting a role for photorespiration (Cornic & Jarvis 1972;Ishii & Murata 1978), but later, experiments at high CO2 found the effect, arguing against such a role (Sharp, Matthews & Boyer 1984;Kirschbaum & Farquhar 1987).The current consensus is that the Kok effect results from a partial inhibition of Rc at very low light (Sharp et al 1984;Kirschbaum & Farquhar 1987). It remains unclear why this inhibition is relieved so sharply at irradiances c. 10-20 mmol m -2 s -1 , given that Rc continues to decline as irradiance increases up to 200 mmol m -2 s -1 or more (Brooks & Farquhar 1985; Atkin et al 2000).…”