Leaf cell wall properties and stomatal density influence oxygen isotope enrichment of leaf water

Oxygen isotopic composition (Δ 18 O LW ) of leaf water can help improve our understanding of how anatomy interacts with physiology to influence leaf water transport. Leaf water isotope models of Δ 18 O LW such as the Péclet effect model have been developed to predict Δ 18 O LW , and it incorporates transpiration rate ( E ) and the mixing length between unenriched xylem water and enriched mesophyll water, which can occur in the mesophyll ( L m ) or veins ( L v ). Here we used two cell wall composition mutants grown under two light intensities and RH to evaluate the effect of cell wall composition on Δ 18 O LW . In maize ( Zea mays ), the compromised ultrastructure of the suberin lamellae in the bundle sheath of the ALIPHATIC SUBERIN FERULOYL TRANSFERASE mutant ( Zmasft ) reduced barriers to apoplastic water movement, resulting in higher E and L v and, consequently, lower Δ 18 O LW . In cellulose synthase-like F6 ( Cslf6 ) mutants and wildtype of rice ( Oryza sativa ), the difference in Δ 18 O LW in plants grown under high and low growth light intensity co-varied with their differences in stomatal density. These results show that cell wall composition and stomatal density influence Δ 18 O LW by altering the Péclet effect and that stable isotopes can facilitate the development of a physiologically and anatomically explicit water transport model.