Rubisco, Rubisco activase, and global climate change

Abstract

Global warming and the rise in atmospheric CO(2) will increase the operating temperature of leaves in coming decades, often well above the thermal optimum for photosynthesis. Presently, there is controversy over the limiting processes controlling photosynthesis at elevated temperature. Leading models propose that the reduction in photosynthesis at elevated temperature is a function of either declining capacity of electron transport to regenerate RuBP, or reductions in the capacity of Rubisco activase to maintain Rubisco in an active configuration. Identifying which of these processes is the principal limitation at elevated temperature is complicated because each may be regulated in response to a limitation in the other. Biochemical and gas exchange assessments can disentangle these photosynthetic limitations; however, comprehensive assessments are often difficult and, for many species, virtually impossible. It is proposed that measurement of the initial slope of the CO(2) response of photosynthesis (the A/C(i) response) can be a useful means to screen for Rubisco activase limitations. This is because a reduction in the Rubisco activation state should be most apparent at low CO(2) when Rubisco capacity is generally limiting. In sweet potato, spinach, and tobacco, the initial slope of the A/C(i) response shows no evidence of activase limitations at high temperature, as the slope can be accurately modelled using the kinetic parameters of fully activated Rubisco. In black spruce (Picea mariana), a reduction in the initial slope above 30 degrees C cannot be explained by the known kinetics of fully activated Rubisco, indicating that activase may be limiting at high temperatures. Because black spruce is the dominant species in the boreal forest of North America, Rubisco activase may be an unusually important factor determining the response of the boreal biome to climate change.

The Costs of Photorespiration to Food Production Now and in the Future

“…The activation state also decreased with temperature above the thermal optimum at each measurement of carbon dioxide concentration in these experiments, likely because of the limited thermotolerance of Rubisco activase, a vital chaperone for Rubisco activity (66). Despite this relationship between Rubisco activation state and temperature, it is still debated whether this results directly in the decrease in photosynthetic rate at elevated temperature or leads to other limitations becoming more dominant (65,66). Changes in Rubisco quantity or activation state affect absolute rates of V o but have only a slight impact on the V o /V c ratio under identical atmospheric carbon dioxide concentrations.…”

Systems-Wide Analysis of Acclimation Responses to Long-Term Heat Stress and Recovery in the Photosynthetic Model OrganismChlamydomonas reinhardtii

“…It was suggested previously that the deactivation of Rubisco under HS might be a regulated response to a limitation elsewhere in the photosynthetic apparatus (Sharkey, 2005;Sage et al, 2008). As discussed above, the demand for de novo biosynthesized saturated FAs for the remodeling of membrane lipids during the first hours of HS potentially represents a significant sink for ATP and NADPH.…”

“…Rubisco activase catalyzes the release from the Rubisco active site of ribulose-1,5-bisphosphate and other sugar phosphates that, when bound to Rubisco prior to its carbamylation and Mg 2+ binding, inactivate the enzyme (Jensen, 2000). The question is whether the inactivation of thermolabile Rubisco activase by HS is an undesired effect, or rather a mechanism implemented specifically as part of a regulated response to moderate HS, as suggested previously (Sharkey, 2005;Sage et al, 2008;Sharkey and Zhang, 2010).…”

Leaf-Level Gas Exchange and Foliar Chemistry of Common Old-Field Species Responding to Warming and Precipitation Treatments

“…Even slight warming may cause some plant species to exceed their metabolic optima, reducing photosynthetic output and decreasing plant survival (Niu et al 2006;Sage et al 2008). Warming can also suppress photosynthetic rates as a result of warming-induced soil moisture stress (De Valpine and Harte 2001).…”