Melatonin enhances biomass, phenolic accumulation, and bioactivities of rosemary (Rosmarinus officinalis) in vitro shoots under UV‐B stress

Abstract

Melatonin is a stress‐related hormone that plays a critical role in triggering the plant defence system and regulating secondary metabolism when plants are exposed to stress. To explore the potential roles of melatonin in response to Ultraviolet‐B (UV‐B) radiation, we examined the effects of exogenous melatonin on rosemary in vitro shoots under UV‐B stress. The application of melatonin (50 μM) alleviated the adverse effects of UV‐B stress on the biomass, photosynthetic pigment contents, and membrane lipids of the rosemary in vitro shoots. Melatonin significantly increased superoxide dismutase (1.15.1.1, SOD), peroxidase (1.11.1.7, POD), and catalase (1.11.1.6, CAT) activities by 62%, 99%, and 53%, respectively. The contents of total phenols, rosmarinic acid, and carnosic acid increased under UV‐B stress, and they further increased by the melatonin treatment by 41%, 68%, and 67%, respectively, compared with the control group. Under UV‐B stress, the increased total phenol content in melatonin‐pretreated plants could be attributed to the activation of phenylalanine ammonia‐lyase (4.3.1.5, PAL) and tyrosine aminotransferase (2.6.1.5, TAT). In addition, melatonin enhanced the antioxidant and antibacterial activities of the rosemary in vitro shoots under UV‐B stress. These results suggest that melatonin can alleviate the damage caused by UV‐B stress and also enhance the secondary metabolism and bioactivity of rosemary in vitro shoots.

Impact of Exogenous Melatonin Application on Photosynthetic Machinery under Abiotic Stress Conditions

“…Similar to this, melatonin-treated Arabidopsis subjected to UV-B stress demonstrated increased GR, APX, and SOD activity as well as lower lipid peroxidation levels and higher Fv/Fm values [ 109 ]. The melatonin application reduced the negative effects of UV-B stress on the biomass, photosynthetic pigment levels, and membrane lipids of the rosemary in vitro shoots increasing the activity of antioxidant enzymes and accumulation of total phenols ([ 110 ], Table 6 ). Figure 3 exhibits how plants generally react when exogenous melatonin is applied to them in a stressful environment.…”

Expression Patterns and Functional Analysis of Three SmTAT Genes Encoding Tyrosine Aminotransferases in Salvia miltiorrhiza

“…Phenolic acids, especially rosmarinic acid (RA) and salvianolic acid B (SalB), have strong scavenging ability for free radicals and hypolipidemic, anti-inflammatory, and analgesic effects [3]. Identifying genes involved in the biosynthesis and regulation of phenolic acids in S. miltiorrhiza has attracted increasing attention recently [4]. As far as we know, 29 genes involved in the biosynthesis of SalB have been identified in the S. miltiorrhiza genome, including three SmTATs [5].…”

“…The enzyme catalyzes the reversible transamination between tyrosine and 4-hydroxyphenylpyruvate (4-HPP) [7]. In plants, 4-HPP serves as a precursor for the biosynthesis of various tyrosine-derived plant natural products such as tocopherols, RA, plastoquinone, cyanogenic glycosides, and benzylisoquinoline alkaloids [8][9][10].…”