Photosynthetic processes in terrestrial plants annually incorporate 140 billion net tons of carbon dioxide from the atmosphere into plant metabolism. The prodigious capacity for carbon sequestration through biomass production offers a potential mitigation strategy to the climatological effects of atmospheric carbon. Prior to photosynthetic assimilation, carbon dioxide molecules must pass through the mesophyll, a spongy tissue within the leaf at the interface to the atmosphere. Carbon assimilation and mesophyll conductance are found experimentally to vary with temperature, with carbon assimilation doubling over temperature ranges found in greenhouse conditions. Leveraging recent simulation advances and lipidomics, we develop molecular models for carbon dioxide permeation through mesophyll membranes for model plant systems Arabidopsis thaliana and Nicotiana tabacum with unparalleled spatial and temporal resolution. Analyzing carbon dioxide membrane crossings at varying temperatures, we find that the membrane permeability increases at the same rate as experimental measures for carbon assimilation in vivo. This suggests that passive membrane permeability for carbon dioxide is rate limiting for photosynthetic processes. Replica exchange umbrella sampling simulations highlight small energetic barriers to membrane entry at the membrane-water interface. Using the inhomogeneous solubility diffusion model, we estimate carbon dioxide permeability across the plant plasma membrane to be substantially faster than prior fluorescence-based measures. Together with ongoing experimental work, these simulations highlight a role for unfacilitated passive permeation processes within carbon fixation.

Quantifying temperature dependent mesophyll conductance within leaf plasma membranes

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