Rosmarinic acid accumulation in Melissa officinalis shoot cultures is mediated by ABA

Abstract

Plant responses to elicitors are the result of a series of highly modulated consecutive changes in hormones or reactive oxygen species (ROS). Abscisic acid (ABA) is a stress hormone that coordinates the complex networks of stress responses and its content is rapidly changed in response to stresses. This study evaluated the effects of application of ABA (0, 5, 25, 50, and 100 µM) to shoot cultures of lemon balm (Melissa officinalis L.) in Murashige and Skoog (MS) liquid medium on growth, H2O2 production, rosmarinic acid (RA) content, total phenolic compound accumulation, phenylalanine-ammonia lyase (PAL) gene expression, and PAL activity. Our results showed that all the applied concentrations of ABA decreased the growth rate of shoots. Moreover, the expression of PAL, tyrosine aminotransferase (TAT), and rosmarinic acid synthase (RAS) genes, PAL activity, and the accumulation of total phenolic compound as well as RA were increased in the ABA-treated shoots. The highest content of RA was detected in the shoots treated with 100 µM ABA. The results suggested that both the PAL- and TAT-derived pathways were induced by ABA to increase RA accumulation in the shoot cultures of lemon balm. The results revealed that application of ABA led to up-regulation of respiratory burst oxidase homolog (RBOH) expression, which was correlated with the production of H2O2 in the shoots cultures. In addition, the cis epoxy carotenoid dioxygenase (NCED) gene, which encodes key enzyme involved in ABA biosynthesis was up-regulated. These results demonstrated that ABA treatment enhanced endogenous ABA content and rosmarinic acid synthesis in the shoot cultures of lemon balm.