Moderately High Temperatures Inhibit Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase (Rubisco) Activase-Mediated Activation of Rubisco1

Abstract

We tested the hypothesis that light activation of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) is inhibited by moderately elevated temperature through an effect on Rubisco activase. When cotton (Gossypium hirsutum L.) or wheat (Triticum aestivum L.) leaf tissue was exposed to increasing temperatures in the light, activation of Rubisco was inhibited above 35 and 30°C, respectively, and the relative inhibition was greater for wheat than for cotton. The temperature-induced inhibition of Rubisco activation was fully reversible at temperatures below 40°C. In contrast to activation state, total Rubisco activity was not affected by temperatures as high as 45°C. Nonphotochemical fluorescence quenching increased at temperatures that inhibited Rubisco activation, consistent with inhibition of Calvin cycle activity. Initial and maximal chlorophyll fluorescence were not significantly altered until temperatures exceeded 40°C. Thus, electron transport, as measured by Chl fluorescence, appeared to be more stable to moderately elevated temperatures than Rubisco activation. Western-blot analysis revealed the formation of high-molecular-weight aggregates of activase at temperatures above 40°C for both wheat and cotton when inhibition of Rubisco activation was irreversible. Physical perturbation of other soluble stromal enzymes, including Rubisco, phosphoribulokinase, and glutamine synthetase, was not detected at the elevated temperatures. Our evidence indicates that moderately elevated temperatures inhibit light activation of Rubisco via a direct effect on Rubisco activase.

Rubisco activase constrains the photosynthetic potential of leaves at high temperature and CO 2

“…This effect of temperature on Rubisco activation has been reported previously (10,11,(16)(17)(18)28) and includes evidence from gas exchange measurements, which showed that the maximum carboxylation rate, calculated from gas exchange parameters, decreased at high temperature (35). The effects of high CO 2 and low O 2 on Rubisco activation also have been reported previously (12)(13)(14), but an effect of CO 2 is not always observed (15), possibly because of differences in experimental technique.…”

“…In fact, intrinsic f luorescence measurements indicated that the decrease in ATPase activity that occurred at moderately high temperatures was associated with a change in the quaternary structure of activase from the more active associated state to the less active dissociation state (37). Also, the distribution of activase changed from soluble to insoluble in cotton leaves that were heated above 40°C, suggesting that the ability of activase to self-associate in planta was altered at temperatures below the temperature optimum for ATPase activity (17). Because ATP hydrolysis is required for but is not tightly coupled to Rubisco activation (27,31), changes in the quaternary structure of activase could affect its ability to physically interact with Rubisco somewhat independent of the effect on ATP hydrolysis.…”

“…Consequently, changes in photosynthesis in response to changing environmental conditions seldom are attributed to changes in Rubisco activation. Two exceptions are when photosynthesis is inhibited by moderate heat stress (10,11,(16)(17)(18) and when photosynthesis is not in steady state after an increase in light intensity (19).…”

“…Consequently, changes in photosynthesis in response to changing environmental conditions seldom are attributed to changes in Rubisco activation. Two exceptions are when photosynthesis is inhibited by moderate heat stress (10,11,(16)(17)(18) and when photosynthesis is not in steady state after an increase in light intensity (19).For a Rubisco active site to be catalytically competent, it must be carbamylated by CO 2 and free of inhibitory sugar phosphates (20). Active sites that are not carbamylated bind RuBP very tightly to form a dead-end complex that carbamylates only after the very slow dissociation of RuBP (21).…”

Extreme climatic events: impacts of drought and high temperature on physiological processes in agronomically important plants

“…Rubisco remains functional at temperatures above 50 • C. However, high temperature causes a more rapid inactivation which is reverted in an ATP-dependent reaction (carbamylation) catalyzed by Rubisco activase (CraftsBrandner and Salvucci, 2004;Kim and Portis, 2006). Since Rubisco activase is highly heat-sensitive, this enzyme becomes a key player for the rate of photosynthesis at elevated temperature (Feller et al, 1998;Salvucci et al, 2001;Yamori et al, 2012). Depending on the plant species, Rubisco activase activity is negatively affected by temperatures above 30 • C ).…”