Journal
PROCEEDINGS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES
Volume 288, Issue 1945, Pages -Publisher
ROYAL SOC
DOI: 10.1098/rspb.2020.3145
Keywords
vascular plants; leaf mesophyll; intercellular airspace; gas diffusion
Categories
Funding
- Katherine Esau Fellowship
- Austrian Science Fund (FWF) [M2245, P30275]
- US NSF [DEB-1838327]
- Office of Science, Office of Basic Energy Sciences, of the US Department of Energy [DE-AC02-05CH11231]
- Austrian Science Fund (FWF) [P30275, M2245] Funding Source: Austrian Science Fund (FWF)
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Genome size plays a crucial role in determining the sizes and packing densities of cells in leaf tissues, which in turn affect CO2 diffusion. Smaller cells enable more mesophyll surface area to be packed into the leaf volume, facilitating higher CO2 diffusion. Additionally, the spongy mesophyll layer facilitates gaseous phase diffusion while the palisade mesophyll layer facilitates liquid-phase diffusion.
Maintaining high rates of photosynthesis in leaves requires efficient movement of CO2 from the atmosphere to the mesophyll cells inside the leaf where CO2 is converted into sugar. CO2 diffusion inside the leaf depends directly on the structure of the mesophyll cells and their surrounding airspace, which have been difficult to characterize because of their inherently three-dimensional organization. Yet faster CO2 diffusion inside the leaf was probably critical in elevating rates of photosynthesis that occurred among angiosperm lineages. Here we characterize the three-dimensional surface area of the leaf mesophyll across vascular plants. We show that genome size determines the sizes and packing densities of cells in all leaf tissues and that smaller cells enable more mesophyll surface area to be packed into the leaf volume, facilitating higher CO2 diffusion. Measurements and modelling revealed that the spongy mesophyll layer better facilitates gaseous phase diffusion while the palisade mesophyll layer better facilitates liquid-phase diffusion. Our results demonstrate that genome downsizing among the angiosperms was critical to restructuring the entire pathway of CO2 diffusion into and through the leaf, maintaining high rates of CO2 supply to the leaf mesophyll despite declining atmospheric CO2 levels during the Cretaceous.
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