5 CONCLUSIONS
Leaf water absorption has been widely studied in the major groups of angiosperms, including magnoliids (eight genera), monocots (seven genera), and eudicots (67 genera) (reviewed by Berry et al., 2019, and by Dawson & Goldsmith, 2018), pointing to foliar water uptake as a key factor affecting plant function in most ecosystems (Weathers et al., 2019). However, the effect of foliar hydration in the overall plant physiology is stronger in dry or semi-dry environments (Schreel et al., 2019), such as the dryland tropical areas where C. odoratissimagrows, where the water in the soil is often a limiting resource, and aerial water may become pivotal for plant growth and survival.
Our data strongly suggest that the pathway for water uptake inCapparis odoratissima is mediated by the interconnected idioblasts and peltate hairs. We propose a model (Figure 8) that involves apertures of the leaves toward the adaxial surface, which are involved in water uptake, but may facilitate evapotranspiration. Hygroscopic materials belonging to arabinogalactan proteins serve to draw water into the lumen of the idioblasts, while pectins in the mesophyll and the epidermis may further facilitate the incorporation of water into leaf tissues. We believe that this cascade of biochemical and physical events underlies the ability of Capparis odoratissimatrees to utilize atmospheric water resources.