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Increased bundle sheath leakiness of <scp> CO <sub>2</sub> </scp> during photosynthetic induction shows a lack of coordination between the <scp> C <sub>4</sub> </scp> and <scp> C <sub>3</sub> </scp> cycles

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  • Yu Wang
  • Samantha S. Stutz
  • Carl J. Bernacchi
  • Ryan A. Boyd
  • Donald R. Ort
  • Stephen P. Long
<mark>Journal publication date</mark>31/12/2022
<mark>Journal</mark>New Phytologist
Issue number5
Number of pages15
Pages (from-to)1661-1675
Publication StatusPublished
<mark>Original language</mark>English


Use of a complete dynamic model of NADP-malic enzyme C 4 photosynthesis indicated that, during transitions from dark or shade to high light, induction of the C 4 pathway was more rapid than that of C 3 , resulting in a predicted transient increase in bundle-sheath CO 2 leakiness (ϕ). Previously, ϕ has been measured at steady state; here we developed a new method, coupling a tunable diode laser absorption spectroscope with a gas-exchange system to track ϕ in sorghum and maize through the nonsteady-state condition of photosynthetic induction. In both species, ϕ showed a transient increase to > 0.35 before declining to a steady state of 0.2 by 1500 s after illumination. Average ϕ was 60% higher than at steady state over the first 600 s of induction and 30% higher over the first 1500 s. The transient increase in ϕ, which was consistent with model prediction, indicated that capacity to assimilate CO 2 into the C 3 cycle in the bundle sheath failed to keep pace with the rate of dicarboxylate delivery by the C 4 cycle. Because nonsteady-state light conditions are the norm in field canopies, the results suggest that ϕ in these major crops in the field is significantly higher and energy conversion efficiency lower than previous measured values under steady-state conditions.