UPLC-QTof-MSE Metabolomics Reveals Changes in Leaf Primary and Secondary Metabolism of Hop (Humulus lupulus L.) Plants under Drought Stress

The hop (Humulus lupulus L.) is an important specialty crop used in beer production. Untargeted UPLC-QTof-MSE metabolomics was used to determine metabolite changes in the leaves of hop plants under varying degrees of drought stress. Principal component analysis revealed that drought treatments produced qualitatively distinct changes in the overall chemical composition of three out of four genotypes tested (i.e., Cascade, Sultana, and a wild var. neomexicanus accession but not Aurora), although differences among treatments were smaller than differences among genotypes. A total of 14 compounds consistently increased or decreased in response to drought stress, and this effect was generally progressive as the severity of drought increased. A total of 10 of these marker compounds were tentatively identified as follows: five glycerolipids, glutaric acid, pheophorbide A, abscisic acid, roseoside, and dihydromyricetin. Some of the observed metabolite changes likely occur across all plants under drought conditions, while others may be specific to hops or to the type of drought treatments performed.