Temperature effects on photosynthetic acclimation and carbon accumulation
Three Arabidopsis genotypes, Col-0, C24, and fum2 were grown at a control temperature of 20 °C for 8 weeks. Plants were then either kept at 20 °C or transferred to 5, 10, 15, 25 or 30 °C for 7 days. Maximum photosynthetic capacity (Pmax ) was measured at 20 °C and under light- and CO2-saturating conditions on the 1st (Fig. S4) and 7th (Fig. 2a) day of treatment. Pmax provides an indication of the acclimation state of the photosynthetic apparatus.Pmax did not change on the 1stday of temperature treatments nor did it vary significantly between genotypes (Fig. S4). However, after one week of treatment, Col-0 showed a significant change in Pmax in response to the 5, 10, and 30 °C treatments (Fig. 2a). Similarly, the C24 accession showed a change in Pmax at 5 and 30 °C . The fum2 mutant, which lacks cytosolic fumarase, does not show a consistent trend in altering its Pmax in response to the temperature treatments. The 5 °C treatment is hereafter referred to as cold treatment whilst the 30 °C treatment is referred to as a warm treatment.
CO2 fixation under growth conditions was evaluated on the 1st and 7th day of cold (Fig. 2b) and warm treatments (Fig. 2c). In plants transferred to cold, CO2 fixation was initially reduced in all three genotypes. However, in Col-0 and C24 plants, photosynthesis recovered after one week of acclimation, reaching the same rate of rate as seen in plants maintained at 20 °C. In contrast, the fum2 mutant failed to recover its rate of photosynthesis in response to cold. Under warm treatment, Col-0 plants showed lower rates of photosynthesis after one week, whereas C24 and fum2 plants maintain a constant rate of photosynthesis for the duration of the treatment (Fig. 3c). Rates of respiration show a similar trend to those of photosynthesis in response to cold (Fig. S1a). In the warm treatment, only the fum2 mutant shows a sustained decrease in respiration after one week (Fig. S1b).