Cell wall properties in Oryza sativa influence mesophyll CO2 conductance

Diffusion of CO2 from the leaf intercellular air space to the site of carboxylation (g(m)) is a potential trait for increasing net rates of CO2 assimilation (A(net)), photosynthetic efficiency, and crop productivity. Leaf anatomy plays a key role in this process; however, there are few investigations into how cell wall properties impact g(m) and A(net). Online carbon isotope discrimination was used to determine g(m) and A(net) in Oryza sativa wild-type (WT) plants and mutants with disruptions in cell wall mixed-linkage glucan (MLG) production (Cs/F6 knockouts) under high- and low-light growth conditions. Cell wall thickness (T-cw), surface area of chloroplast exposed to intercellular air spaces (S-c), leaf dry mass per area (LMA), effective porosity, and other leaf anatomical traits were also analyzed. The g(m) of Cs/F6 mutants decreased by 83% relative to the WT, with c.28% of the reduction in g(m) explained by S-c. Although A(net)/LMA and A(net)/Chl partially explained differences in A(net) between genotypes, the change in cell wall properties influenced the diffusivity and availability of CO2. The data presented here indicate that the loss of MLG in Cs/F6 plants had an impact on g(m) and demonstrate the importance of cell wall effective porosity and liquid path length on g(m).