Table 2. Estimates of Plasmodesmal Flux between Mesophyll and Bundle Sheath Cells in Leaves of C₃ and C₄ Species.

Species	CO2 Assimilation Rate per Leaf Area (µmol CO2 m−2 s−1)	Mean Sb (m2 m−2)	CO2 Assimilation Rate per Bundle Sheath Surface Area (µmol CO2 m−2 s−1)	CO2 Assimilation Rate per PD (×10−18 mol CO2 s−1)	Sucrose Flux per PD (×10−18 mol Sucrose s−1)
Rice, C3	27.1 ± 0.96a	1.1 ± 0.06a	24.7 ± 0.87a	24.7 ± 0.87a	2.1 ± 0.07a
Wheat, C3	35.0 ± 1.48b	1.2 ± 0.17a	29.8 ± 1.26b	11.5 ± 0.49b	1.0 ± 0.04b
S. viridis, C4	29.5 ± 1.50a	1.6 ± 0.04b	18.1 ± 0.92c	1.9 ± 0.10c	NA
Maize, C4	38.6 ± 1.14b	2.0 ± 0.08c	19.5 ± 0.58c	2.6 ± 0.08d	NA

For the “CO₂ Assimilation Rate per PD” column, assuming that in C₄ species the minimum flux of C₄ acids through the PD needs to be equal to or greater than the CO₂ assimilation rate. For C₃ species, the numbers indicate the fluxes required if a C₄ photosynthetic pathway were installed without anatomical changes. For the “Sucrose Flux per PD” column, assuming sucrose must pass from mesophyll to bundle sheath cells for phloem loading in C₃ monocot leaves at a rate in equilibrium with CO₂ assimilation rates. Statistical differences according to MATLAB two-sample t test at P value < 0.05 are indicated by letters. Values indicated by the same letter within a column are not statistically different. NA, not applicable.