To protect against water loss, land plants have developed the cuticle; however, the cuticle strongly restricts CO2 uptake for photosynthesis. Controlling this trade-off relationship is an important strategy for plant survival, but the extent to which the changes in cuticle affects this relationship is not clear. To evaluate this, we measured CO2 assimilation rate and transpiration rate together in the Arabidopsis thaliana mutant excessive transpiration1 (extra1), which exhibited marked evaporative water loss due to an increased cuticle permeability caused by a new allele of ACETYL-COA CARBOXYLASE 1 (ACC1). Under high humidity (85%) conditions, the extra1 mutant exhibited higher CO2 assimilation rate in exchange for decreasing water use efficiency by one-third compared to the slow anion channel-associated 1 (slac1) mutant, whose stomata are continuously open. Our results indicate that the increased cuticle permeability in extra1 affects transpiration rate more than CO2 assimilation rate, but the effect on CO2 assimilation rate is larger than the effect of open stomata in slac1, suggesting that the cuticle permeability is an important parameter for the trade-off relationship between drought tolerance and CO2 uptake in land plants.
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