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

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.