Low photorespiratory capacity is sufficient to block photosynthetic capacity acclimation in high light

The induction of high photosynthetic capacity (i.e., the CO2- and light-saturated maximum photosynthetic rate) in HL is a shared response among many herbaceous dicot plants. The increase in photosynthetic capacity following a shift to growth in high light (HL) was measured across a large panel of Arabidopsis thaliana ecotypes revealing substantial ecotypic variation in photosynthetic capacity acclimation to HL. Metabolomic data quantified during the HL shift for a strongly acclimating ecotype and a weakly acclimating ecotype identified differences between the ecotypes in primary nitrogen (N) assimilation, photorespiration, and triose-phosphate utilization pathways after the HL shift. Based on these results, rates of N assimilation and photorespiration were measured using metabolic indicators for these pathways across the full ecotype panel. N assimilation and photorespiration rates early in the HL shift were found to positively correlate with the magnitude of induction of photosynthetic capacity later in HL shift. Shifting ecotypes into HL growth conditions under non-photorespiratory conditions was sufficient to convert non-acclimating ecotypes and also photorespiratory mutants into strongly acclimating ecotypes. This work supports a model where high photorespiratory capacity, and thus the ability to maintain high photorespiration rates, prevents a negative photorespiration-dependent signal that blocks the induction of high photosynthetic capacity in HL.