Submitted to: Plant Physiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/1/2003
Publication Date: 1/1/2004
Citation: Salvucci, M.E., Crafts-Brandner, S.J. 2004. Relationship between the heat tolerance of photosynthesis and the thermal stability of rubisco activase in plants from contrasting thermal environments. Plant Physiology. 134: 1460-1470 Interpretive Summary: In the process of photosynthesis, plants convert light into chemical energy. The energy produced by photosynthesis is then used to synthesize sugars and other foodstuffs. Heat stress inhibits photosynthesis, reducing the overall yield of the plant. Previous research from this research group identified an enzyme called Rubisco activase as the component of photosynthesis that is most sensitive to inhibition by heat. Rubisco activase is a regulatory enzyme that controls the activity of the major carbon dioxide-fixing enzyme in plants. In this manuscript, we examine the inhibition of photosynthesis by moderate heat stress in plants from contrasting thermal environments. The results provide strong evidence for a universal role for Rubisco activase in limiting photosynthesis at high temperature in higher plants. In particular, the data show that activase from desert species was considerably more stable to heat than activase from cold environment species. The data, especially information on the primary structure of activase from these different species, can eventually be used to make changes that improve the activity and stability of Rubisco activase in order to improve the efficiency of photosynthesis under heat stress.
Technical Abstract: Inactivation of Rubisco has been proposed as the mechanism for inhibition of photosynthesis by moderate heat stress. To investigate this proposal, the temperature response of net photosynthesis, Rubisco activation, chlorophyll fluorescence and Rubisco and Rubisco activase activities were examined in plants from contrasting environments. The activation state of Rubisco in the Antarctic hairgrass, Deschampsia antarctica, and the desert shrub, Larrea tridentata, correlated precisely with net photosynthesis at optimal and supraoptimal but not at suboptimal temperatures. Non-photochemical quenching (NPQ) and the potential yield of PSII (FV/FM) were more sensitive to temperature in D. antarctica and two other species endemic to cold regions (i.e., Lysipomia pumila and spinach) compared with species from warm regions (i.e., L. tridentata, Simmondsia chinensis, tobacco and cotton). For all species, NPQ was the more sensitive parameter. The temperature response of activity and the rate of catalytic inactivation were similar for Rubisco from L. tridentata and D. antarctica, whereas the optimum for ATP hydrolysis by recombinant L. tridentata, cotton, and tobacco activase was almost 8ºC higher than for D. antarctica and spinach activase. Thus, the properties of activase in plants from contrasting thermal environments were consistent with a role for this enzyme in limiting photosynthesis at high temperature.