CO2 diffusion in tobacco: a link between mesophyll conductance and leaf anatomy (Interface Focus)

Three key factors affect a plant’s ability to fix carbon: enzymatic activity of Rubisco, stomatal conductance, and the journey from sub-stomatal cavity to Rubisco, also known as mesophyll conductance (g_m). This latter is the focus of this new work by Clarke et al. They delightfully compare this journey to that of Princess Leia from Star Wars (see the adjoining illustration; the CO₂ molecule works surprisingly well as her head and hair). Here, the authors address how leaf age and leaf position in the canopy affect g_m, with the objective of improving models of photosynthesis. To do this, they measured carbon isotope discrimination, gas exchange, Rubisco activity, and leaf anatomy. They found that g_m decreases with leaf age, which can largely be attributed to a corresponding increase in cell wall thickness and a decrease in exposure of chloroplasts to intercellular airspace. (Summary by Mary Williams @PlantTeaching) Interface Focus 10.1098/rsfs.2020.0040