Ozone inhibits guard cell K(+) channels implicated in stomatal opening

Ozone (O(3)) deleteriously affects organisms ranging from humans to crop plants, yet little is understood regarding the underlying mechanisms. In plants, O(3) decreases CO(2) assimilation, but whether this could result from direct O(3) action on guard cells remained unknown. Potassium flux causes osmotically driven changes in guard cell volume that regulate apertures of associated microscopic pores through which CO(2) is supplied to the photosynthetic mesophyll tissue. We show in Vicia faba that O(3) inhibits (i) guard cell K(+) channels that mediate K(+) uptake that drives stomatal opening; (ii) stomatal opening in isolated epidermes; and (iii) stomatal opening in leaves, such that CO(2) assimilation is reduced without direct effects of O(3) on photosynthetic capacity. Direct O(3) effects on guard cells may have ecological and agronomic implications for plant productivity and for response to other environmental stressors including drought.