Maximum CO₂diffusion inside leaves is limited by the scaling of cell size and genome size

Abstract

SummaryMaintaining high rates of photosynthesis in leaves requires efficient movement of CO2 from the atmosphere to the chloroplasts inside the leaf where it is converted into sugar. Throughout the evolution of vascular plants, CO2 diffusion across the leaf surface was maximized by reducing the sizes of the guard cells that form stomatal pores in the leaf epidermis1,2. Once inside the leaf, CO2 must diffuse through the intercellular airspace and into the mesophyll cells where photosynthesis occurs3,4. However, the diffusive interface defined by the mesophyll cells and the airspace and its coordinated evolution with other leaf traits are not well described5. Here we show that among vascular plants variation in the total amount of mesophyll surface area per unit mesophyll volume is driven primarily by cell size, the lower limit of which is defined by genome size. The higher surface area enabled by smaller cells allows for more efficient CO2 diffusion into photosynthetic mesophyll cells. Our results demonstrate that genome downsizing among the flowering plants6 was critical to restructuring the entire pathway of CO2 diffusion, facilitating high rates of CO2 supply to the leaf mesophyll cells despite declining atmospheric CO2 levels during the Cretaceous.

The 3D construction of leaves is coordinated with water use efficiency in conifers

“…A similar variance meta-analysis, including post hoc Tukey's honest significant differences, was employed to compare the studied conifer species with other gymnosperms, along with angiosperms and ferns. Data for comparisons across plant groups was obtained from a recently published study Supplementary Dataset 2 23 (available on request). Supplementary Text 1.…”

Digitally deconstructing leaves in 3D using X‐ray microcomputed tomography and machine learning

“…To conclude, this segmentation framework allowed us to generate a considerable amount of segmented leaves over a wide array of species (see Théroux-Rancourt et al, 2020a). It has the potential to empower researchers to broaden sampling, to ask new questions about the 3D structure of leaves, and to derive new and meaningful metrics for biological structures.…”

Maximum CO2diffusion inside leaves is limited by the scaling of cell size and genome size

“…Segmented microCT images are available on Zenodo at doi:10.5281/zenodo.3606064 (https://zenodo.org/record/3606064). A preprint version of this work is available [63].…”