Table II.

Gas exchange, CA activity, Δ18O, and isotopic equilibrium measurements

Net CO2 assimilation rate (A), the pCO2 at the site of CO2-H2O oxygen exchange in the mesophyll cytosol (pm), the ratio of mesophyll cytosolic to ambient CO2 partial pressure (pm/pa), the residence time of CO2 in the aqueous phase within the leaf (τ), stomatal conductance (gs), leaf CA activity (CAleaf), online Δ18O discrimination, and proportion of chloroplast CO2 in isotopic equilibrium with chloroplast water (θ) determined from online Δ18O measurements (Eq. 7) and predicted from in vitro CA assays and gas exchange (Eq. 9) in F. bidentis and tobacco measured at various irradiances (μmol quanta m−2 s−1) and the F. bidentis with reduced levels of Rubisco (anti-SSU) and wild-type Z. mays measured at 2,000 (μmol quanta m−2 s−1). Other conditions are as described in the legend to Figure 1. gw = 10 mol m−2 s−1 Pa−1 for all plants except tobacco where gw = 5 mol m−2 s−1 Pa−1. n = 3 to 5.

PlantIrradianceAgsCAleafΔ18OMeasuredPredicted
μmol m−2 s−1μmol m−2 s−1pmpm/paτmol m−2 s−1μmol m−2 s−1θθ
F. bidentis wild type1506.2 ± 0.2410 ± 190.77 ± 0.0311.5 ± 1.60.12 ± 0.032,855 ± 602182 ± 381.06 ± 0.041.00 ± 0.01
30012.2 ± 0.2363 ± 320.70 ± 0.067 ± 10.21 ± 0.072,558 ± 652103 ± 290.89 ± 0.021.00 ± 0.01
80025.9 ± 0.9283 ± 280.59 ± 0.063.8 ± 0.40.33 ± 0.092,000 ± 53243 ± 100.65 ± 0.040.99 ± 0.01
1,40033.7 ± 1.3252 ± 250.56 ± 0.052.8 ± 0.20.41 ± 0.071,844 ± 26231 ± 50.54 ± 0.040.99 ± 0.01
2,00037.6 ± 1.2234 ± 150.53 ± 0.032.6 ± 0.10.42 ± 0.041,868 ± 18023 ± 20.45 ± 0.040.99 ± 0.01
Tobacco30015.9 ± 0.9161 ± 140.45 ± 0.045.0 ± 0.30.18 ± 0.031,197 ± 19437 ± 40.89 ± 0.080.99 ± 0.01
50021.1 ± 1.5142 ± 130.41 ± 0.043.6 ± 0.20.25 ± 0.041,060 ± 18229 ± 20.81 ± 0.100.99 ± 0.01
80024.7 ± 1.9130 ± 110.39 ± 0.042.9 ± 0.20.30 ± 0.06976 ± 18323 ± 10.67 ± 0.040.99 ± 0.01
F. bidentis anti-SSu2,00023.6 ± 3.1323 ± 50.68 ± 0.024.0 ± 0.70.40 ± 0.092,285 ± 23151 ± 30.63 ± 0.020.99 ± 0.01
Z. mays2,00033.9 ± 1.586 ± 80.19 ± 0.021.9 ± 0.10.18 ± 0.01296 ± 3213 ± 10.62 ± 0.100.88 ± 0.03