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).