Size matters for single-cell C$_4$ photosynthesis in $\textit{Bienertia}$

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Jurić, I 
González-Pérez, V 
Hibberd, JM 
Edwards, G 
Burroughs, NJ 

Bienertia cycloptera belongs to a diverse set of plants, recently discovered to perform C4 photosynthesis within individual mesophyll cells. How these plants accomplish high photosynthetic efficiency without adopting Kranz anatomy remains unanswered. By modelling the processes of diffusion, capture, and release of carbon dioxide and oxygen inside a typical Bienertia mesophyll cell geometry, we show that a spatial separation as low as 10 μm between the primary and the secondary carboxylases, can, on its own, provide enough diffusive resistance to sustain a viable C4 pathway at 20 °C, with a CO2 leakage <35%. This critical separation corresponds to a cell diameter of 50 μm, consistent with the observed range where Bienertia’s mesophyll cells start to develop their characteristic mature anatomy. Our results are robust to significant alterations in model assumptions and environmental conditions, their applicability extending even to aquatic plants.

Bienertia, C$_4$ photosynthesis, carbon fixation, photon cost, photosynthetic efficiency, single-cell C$_4$, spatial modelling.
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Journal of Experimental Botany
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Oxford University Press
Biotechnology and Biological Sciences Research Council (BB/M011356/1)
Biotechnology and Biological Sciences Research Council (BB/I024445/1)
This research was supported by the BBSRC project grant BB/M011291/1 and the NSF grants MCB-1359634 and MCB-1146928.