Dr Jacobsen is internationally renowned for his contributions to plant science in the field of hormonal action in plant cells. In his analysis of the a-amylase gene in barley aleurone cells, he showed that gibberellin action involved new protein and mRNA synthesis. At the gene level, he identified elements in the a-amylase promoter which mediate gibberellin control. He identified a transcription factor, GAMYB, which binds to the a-amylase promoter to control transcription. This protein/DNA interaction is a major component of the gibberellin signal transduction pathway. Jacobsen has applied this knowledge to genetically engineer barley to improve malting quality.