Effects of reduced carbonic anhydrase activity on CO2assimilation rates inSetaria viridis: a transgenic analysis Article Swipe
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· 2016
· Open Access
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· DOI: https://doi.org/10.1093/jxb/erw357
· OA: W2529286203
In C<sub>4</sub> species, the major β-carbonic anhydrase (β-CA) localized in the mesophyll cytosol catalyses the hydration of CO<sub>2</sub> to HCO<sub>3</sub><sup>-</sup>, which phosphoenolpyruvate carboxylase uses in the first step of C<sub>4</sub> photosynthesis. To address the role of CA in C<sub>4</sub> photosynthesis, we generated transgenic Setaria viridis depleted in β-CA. Independent lines were identified with as little as 13% of wild-type CA. No photosynthetic defect was observed in the transformed lines at ambient CO<sub>2</sub> partial pressure (pCO<sub>2</sub>). At low pCO<sub>2</sub>, a strong correlation between CO<sub>2</sub> assimilation rates and CA hydration rates was observed. C<sup>18</sup>O<sup>16</sup>O isotope discrimination was used to estimate the mesophyll conductance to CO<sub>2</sub> diffusion from the intercellular air space to the mesophyll cytosol (g<sub>m</sub>) in control plants, which allowed us to calculate CA activities in the mesophyll cytosol (C<sub>m</sub>). This revealed a strong relationship between the initial slope of the response of the CO<sub>2</sub> assimilation rate to cytosolic pCO<sub>2</sub> (AC<sub>m</sub>) and cytosolic CA activity. However, the relationship between the initial slope of the response of CO<sub>2</sub> assimilation to intercellular pCO<sub>2</sub> (AC<sub>i</sub>) and cytosolic CA activity was curvilinear. This indicated that in S. viridis, mesophyll conductance may be a contributing limiting factor alongside CA activity to CO<sub>2</sub> assimilation rates at low pCO<sub>2</sub>.
