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Effects of instantaneous and growth CO2 levels and abscisic acid on stomatal and mesophyll conductances

Mizokami, Yusuke, Noguchi, Ko, Kojima, Mikiko, Sakakibara, Hitoshi, Terashima, Ichiro
Plant, cell and environment 2019 v.42 no.4 pp. 1257-1269
Arabidopsis thaliana, C3 photosynthesis, abscisic acid, carbon dioxide, diffusivity, leaves, mesophyll, mutants, stomata, stomatal movement
C₃ photosynthesis is often limited by CO₂ diffusivity or stomatal (gₛ) and mesophyll (gₘ) conductances. To characterize effects of stomatal closure induced by either high CO₂ or abscisic acid (ABA) application on gₘ, we examined gₛ and gₘ in the wild type (Col‐0) and ost1 and slac1‐2 mutants of Arabidopsis thaliana grown at 390 or 780 μmol mol⁻¹ CO₂. Stomata of these mutants were reported to be insensitive to both high CO₂ and ABA. When the ambient CO₂ increased instantaneously, gₘ decreased in all these plants, whereas gₛ in ost1 and slac1‐2 was unchanged. Therefore, the decrease in gₘ in response to high CO₂ occurred irrespective of the responses of gₛ. gₘ was mainly determined by the instantaneous CO₂ concentration during the measurement and not markedly by the CO₂ concentration during the growth. Exogenous application of ABA to Col‐0 caused the decrease in the intercellular CO₂ concentration (Cᵢ). With the decrease in Cᵢ, gₘ did not increase but decreased, indicating that the response of gₘ to CO₂ and that to ABA are differently regulated and that ABA content in the leaves plays an important role in the regulation of gₘ.