Chemical and structural heterogeneity of olive leaves and their trichomes.

Many biological surfaces have hairs, known as trichomes in plants. Here, the wettability and macro- and micro-scale features of olive leaves are analyzed. The upper leaf side has few trichomes, while the lower side has a high trichome density. By combining different techniques including electron and atomic force microscopy, trichome surfaces are found to be chemically (hydrophilic-hydrophobic) heterogeneous at the nano-scale. Both olive leaf surfaces are wettable by water, having a high water contact angle hysteresis and great drop adhesion. The ultra-structural pattern observed for epidermal pavement cells differs from the reticulate cuticle structure of trichomes which shows that leaf surface areas may be substantially different despite being located nearby. Our study provides evidence for the nano-scale chemical heterogeneity of a trichome which may influence the functional properties of biological surfaces, such as water and solute permeability or water capture as discussed here for plants.