X-ray micro-CT imaging to study foliar water uptake mechanisms in plants with contrasting leaf topography.

Formation of an aqueous continuum from the leaf surface to the sub-stomatal cavity is a key process, affecting the foliar entry of solutes, particles, and pathogens. However, the factors controlling the transition from a water droplet to the formation of a continuous water film remain poorly understood. To address current limitations in state-of-the-art bioimaging methods, we developed an X-ray micro-CT technique that enables nondestructive, time-resolved visualization of water films on live barley (Hordeum vulgare) and potato (Solanum tuberosum) plants under controlled environmental conditions. We compare droplet behavior, leaf wetting, and the formation of foliar water films on two important crop plants, potato and barley, which differ markedly in their leaf surface characteristics, in terms of hydrophobicity of the cuticle, as well as stomatal topography and trichome morphology and density. We show that continuous water films, from the cuticle into stomata, may form within a few hours, and that a given set of environmental conditions may trigger hydraulic activation of stomata in one crop but not in another, depending largely on the physicochemical properties of the liquid and leaf surface morphological features.