Table I.

Gas exchange and leaf characteristics of wild-type A. edulis and PEPC mutants

Net CO₂ assimilation rate (A), the ratio of intercellular to ambient CO₂ partial pressures (p_i/p_a), stomatal conductance (g_s), carbon isotope discrimination (Δ¹³C), oxygen isotope discrimination (Δ¹⁸O), PEPC and Rubisco activity, the rate constant of leaf CA (k_CA mol m⁻² s⁻¹ bar⁻¹), leaf CA activity (CA_leaf), the extent of isotopic equilibrium, leaf mass per area (LMA), and total leaf nitrogen per area in wild-type (WT) and heterozygous (Pp) and homozygous (pp) mutant A. edulis plants. Gas-exchange measurements were made at a pCO₂ of 531 μbar, a pO₂ of 48 mbar, irradiance of 2,000 μmol quanta m⁻² s⁻¹, and a leaf temperature of 30°C. Calculations of θ were made with g_m = 1 mol m⁻² s⁻¹ bar⁻¹. Shown are the means ± se of measurements made on three to five leaves from separate plants. nd indicates measurements were not determined. Statistical analysis was conducted using an ANOVA and different letters indicate significant differences between plants at P < 0.05. *, CA _leaf = k_CAp_m and p_m was calculated from A and p_i using a conductance of CO₂ from the intercellular air space to the site of PEPC carboxylation equal to 1 mol m⁻² s⁻¹ bar⁻¹.

Measurements	WT	Pp	pp
Photosynthetic parameters
A (μmol m−2 s−1)	40.9 ± 1.6a	32.1 ± 1.7b	4.1 ± 0.4c
pi/pa	0.39 ± 0.06a	0.45 ± 0.07a	0.82 ± 0.02b
gs (mol m−2 s−1)	0.28 ± 0.04a	0.25 ± 0.06a	0.09 ± 0.01b
Δ13C ‰	3.3 ± 0.4a	3.0 ± 0.5a	16.2 ± 3.0b
Δ18O ‰	16.8 ± 1.8a	20.9 ± 3.1a	207.4 ± 50.8b
Enzyme activities
PEPC (μmol m−2 s−1)	144.9 ± 8.8a	61.0 ± 4.6b	3.8 ± 0.4c
Rubisco (μmol m−2 s−1)	44.2 ± 3.2a	nd	48.1 ± 3.2a
kCA (mol m−2 s−1 bar−1)	6.1 ± 0.4a	5.3 ± 0.7a	6.4 ± 1.0a
CAleaf* (μmol m−2 s−1)	783 ± 153a	831 ± 113a	2818 ± 64b
Isotopic equilibrium (θ)
Predicted (Eq. 12)	0.98 ± 0.01a	0.98 ± 0.01a	1.00 ± 0.00a
Measured (Eq. 11)	0.62 ± 0.02a	0.62 ± 0.07a	0.91 ± 0.05b
Leaf parameters
Total leaf N (mmol m−2)	132 ± 23a	120 ± 10a	130 ± 4a
LMA (g m−2)	34.0 ± 2.9a	38.5 ± 3.2a	30.8 ± 1.6a