Low relative air humidity and increased stomatal density independently hamper growth in young Arabidopsis.

Stomatal pores in plant leaves mediate CO uptake for photosynthesis and water loss via transpiration. Altered stomatal density can affect plant photosynthetic capacity, water use efficiency, and growth, potentially providing either benefits or drawbacks depending on the environment. Here we explore, at different air humidity regimes, gas exchange, stomatal anatomy, and growth of Arabidopsis lines designed to combine increased stomatal density (epf1, epf2) with high stomatal sensitivity (ht1-2, cyp707a1/a3).

Stomatal CO2 responses at sub- and above-ambient CO2 levels employ different pathways in Arabidopsis.

Stomatal pores that control plant CO2 uptake and water loss affect global carbon and water cycles. In the era of increasing atmospheric CO2 levels and vapor pressure deficit (VPD), it is essential to understand how these stimuli affect stomatal behavior. Whether stomatal responses to sub-ambient and above-ambient CO2 levels are governed by the same regulators and depend on VPD remains unknown.

Mitogen-activated protein kinases MPK4 and MPK12 are key components mediating CO -induced stomatal movements.

Respiration in leaves and the continued elevation in the atmospheric CO concentration cause CO -mediated reduction in stomatal pore apertures. Several mutants have been isolated for which stomatal responses to both abscisic acid (ABA) and CO are simultaneously defective. However, there are only few mutations that impair the stomatal response to elevated CO , but not to ABA.