The Expression of Genes Involved in Synthesis of Bitter Acids and Xanthohumol and the Content of These Compounds in Aroma and Bitter Hop under Reduced Nitrogen Fertilisation

Abstract

Hop (Humulus lupulus) is cultivated for industrial purposes, primarily for brewing, but also for pharmaceutical and cosmetic applications. The hop cones are valued for their secondary metabolites, including bitter acids and prenylflavonoids. The objective of the presented study was to investigate the impact of reducing nitrogen fertilisation on the activity of genes involved in the production of bitter acids and xanthohumol in cultivars Lubelski (aroma) and Magnat (bitter) grown in the field. Furthermore, the content of these compounds was determined. The results demonstrated that the majority of studied genes were expressed at a similar level despite the reduction in the nitrogen dose by 25–30%. Nitrogen dose influenced the activity of genes BCAT2, HS1, and PAL. Moreover, the differences in gene expression were observed between cultivars and developmental stages. The reduction in nitrogen dose did not result in a reduction in secondary metabolite content. The content of alpha and beta acids in Magnat was approximately 14.8% and 3.2%, respectively, while in Lubelski it was approximately 7.7% and 5.8%, respectively. The content of xanthohumol in both cultivars was approximately 0.7%.