Abstract

Capparis odoratissima is a tree species native to semi-arid environments of the northern coast of South America where low soil water availability coexists with frequent nighttime fog. A previous study showed that water applied to leaf surfaces enhanced leaf hydration, photosynthesis, and growth, but the mechanisms of foliar water uptake are unknown. Here we combine detailed anatomical evaluations with water and dye uptake experiments in the laboratory, and use immunolocalization of pectin and arabinogalactan protein epitopes to characterize water uptake pathways in leaves. Abaxially, the leaves of C. odoratissima are covered with peltate hairs, while the adaxial surfaces are glabrous. Both surfaces are able to absorb condensed water, but the lower surface has higher rates of water uptake. Numerous idioblasts connect the adaxial leaf surface and the abaxial peltate hairs, both of which contain hygroscopic substances such as arabinogalactan proteins and pectins. The highly specialized anatomy of the leaves of C odoratissima fulfills the dual function of minimizing water loss when stomata are closed, while maintaining the ability to absorb liquid water. Cell-wall related hygroscopic compounds in the peltate hairs and idioblasts create a network of microchannels that maintain leaf hydration and promote water uptake.