Differential composition of epicuticular waxes in wild and domesticated barley affects leaf physiology and plant-Herbivore interactions

Barley (Hordeum vulgare) is an important agricultural cereal crop, however due to extensive breeding, domesticated cultivars are characterized with altered physiology and partial/complete loss of stress tolerance. Herein, we investigated whether differential compositions of epicuticular waxes (EW) in wild and domesticated barely affect leaf physiology and interactions with herbivores. Metabolite profiling of the two cultivars for their EW compositions via Gas Chromatography-Mass Spectrometry (GC-MS) revealed that wild barley leaves accumulate ~33% more waxes compared to leaves of the domesticated cultivar, as also inferred by Scanning Electron Microscopy (SEM) of leaf surfaces. It seems that the higher wax loads detected in wild barley are attributed to higher levels of primary alcohols, the predominant wax constituents of barely leaves. EW are known to minimize water loss through transpiration, yet measurements suggested that wild barley transpire at higher rates, likely as its leaves are ~20% more densely covered by stomata. Photosynthetic evaluations performed by Li-COR indicated that domesticated barley exhibit higher rates of carbon assimilation and stomatal conductance in response to increased light intensities. Finally, barley EW were previously suggested as important determinants of plant-herbivore interactions, and thus, we fed tobacco cutworm (Spodoptera litura) larva with leaves belonging to the two cultivars. These demonstrated that ~42% more surface areas of domesticated leaves were eaten compared to wild leaves, suggesting that higher EW loads and density apparently interfere with the feeding process of larva. Altogether, our findings provide insight to the importance of EW in leaf physiology and interactions with the environment.