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Characterization of Rubisco activase from thermally contrasting genotypes of Acer rubrum (Aceraceae)¹

Oak Ridge National Laboratory, Environmental Sciences Division, Oak Ridge, Tennessee 37831-6422 USA; Clemson University, Department of Horticulture, Poole Agriculture Center, Box 340319, Clemson, South Carolina 29634-0319 USA; Clemson University, Department of Forestry and Natural Resources, Lehotsky Hall, Clemson, South Carolina 29634-0319; Clemson University, Department of Genetics and Biochemistry, 100 Jordan Hall, Clemson, South Carolina 29634-0318 USA; and ⁶Clemson University, Institute of Environmental Toxicology, P.O. Box 709, Pendleton, South Carolina 29670-0709 USA

ABSTRACT

The lability of Rubisco activase function is thought to have a major role in the decline of leaf photosynthesis under moderate heat (<35°C). To investigate this further, we characterized Rubisco activase and explored its role in the previously demonstrated thermal acclimation and inhibition of two genotypes of Acer rubrum originally collected from Florida (FL) and Minnesota (MN). When plants were grown at 33/25°C (day/night) for 21 d, the FL genotype compared to the MN genotype maintained about a two-fold increase in leaf photosynthetic rates at 33–42°C and had a 22% increase in the maximal rate of Rubisco carboxylation (V_cmax) at 33°C under nonphotorespiratory conditions. Both genotypes had two leaf Rca transcripts, likely from equivalent alternative splicing events. The RCA1 and RCA2 proteins increased modestly in FL plants under warmer temperature, while only RCA2 protein increased in MN plants. Rubisco large subunit (RbsL) protein abundance was relatively unaffected in either genotype by temperature. These results support the idea that Rubisco activase, particularly the ratio of Rubisco activase to Rubisco, may play a role in the photosynthetic heat acclimation in A. rubrum and may have adaptive significance. This mechanism alone is not likely to entirely explain the thermotolerance in the FL genotype, and future research on adaptive mechanisms to high temperatures should consider activase function in a multipathway framework.

Key Words: heat stress • photosynthesis • red maple • Rubisco activase • Rubisco large subunit • warming

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				W. L. Bauerle, J. D. Bowden, and G. G. Wang The influence of temperature on within-canopy acclimation and variation in leaf photosynthesis: spatial acclimation to microclimate gradients among climatically divergent Acer rubrum L. genotypes J. Exp. Bot., September 4, 2007; (2007) erm177v1. [Abstract] [Full Text] [PDF]