Cuticle permeability is an important parameter for the trade-off strategy between drought tolerance and CO₂ uptake in land plants

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.