Fig. 3

Assimilation of ¹³C during time course labeling assays of wild-type Arabidopsis as determined by elemental analysis-isotope ratio mass spectrometry (EA-IRMS). a plants were equilibrated in a dynamic flow cuvette under standard conditions (see “Methods and materials” for details) in a natural atmosphere until a photosynthetic steady state was attained, then labeled with 400 μL L^{−1 13}CO₂ before flash freezing in liquid nitrogen. Aliquots of ground, lyophilized tissue were analyzed by EA-IRMS. Naturally occurring isotope abundance was subtracted using the y-intercept of the raw data, which was identical to the natural abundance detected in unlabeled controls. Data points indicate net ¹³C isotope assimilated (A₁₃) by individual plants during the labeling experiment. Between 14 and 19 plants were used for each time point as follow: 6 min, n = 15; 9 min, n = 16; 12 min, n = 15; 15 min, n = 15; 18 min, n = 16; 21 min, n = 16; 24 min, n = 19; 30 min, n = 16; 36 min, n = 16; 42 min, n = 14. Error bars show standard deviation. b Light intensity was varied to assess the ability of this method to quantitatively describe carbon assimilation under different environmental conditions. Each point represents an individual plant. Time course labeling series were performed on plants cultivated and labeled under low (80 PAR, n = 10), medium (140 PAR, n = 10), or high light conditions (500 PAR, n = 6). Standard conditions were maintained for all other variables. c Alternative representation of data in a as ¹³C/¹²C isotope ratios where δ¹³C = (R_sample/R_PDB − 1) × 1000, R_sample is the ¹³C/¹²C ratio of the sample, and RPDB is the same ratio of the PeeDee Belemnite reference material (0.0112372). The y-intercept value (− 36.16 ‰, see inset) can be used to infer the ¹³C discrimination in Arabidopsis and closely matches values obtained for unlabeled control plants, which is within the normal range for a C3 plant