Plant Perception of Light: The role of indoleamines in Scutellaria species

Abstract

Light mediates plant growth through diverse mechanisms and signaling networks including plant growth regulators (PGRs). We hypothesized that a novel class of PGRs, the indoleamines, are plant signaling molecules that perceive changes in light composition and initiate a cascade of metabolic responses. We used three Scutellaria model species (skullcap): S. lateriflora, S. galericulata and S. racemosa that produce high levels of melatonin and serotonin to investigate this hypothesis. Axenic Scutellaria cultures were exposed to red, blue, green or full spectrum white light spectra provided by light emitting diode (LED) lighting systems, or daylight fluorescent bulbs. Melatonin (MEL), serotonin (5HT), abscisic acid (ABA), auxin (IAA), and jasmonic acid (JA), were quantified by liquid chromatography with tandem mass spectrometry. Melatonin was detected consistently in plants grown under blue light in all species of Scutellaria. In S. galericulata, significant quantities of ABA were detected in plants grown under white light but not detected in plants grown under other light spectra. In timeline studies of S. racemosa plants exposed to limited red or blue light spectra had significantly reduced levels of tryptamine (TRM), 5HT and MEL in the shoots initially but melatonin was detected after 12 hours and quantifiable amounts of 5HT were detected after 7 days. Supplementation of the culture medium with MEL or 5HT did not change the pattern of MEL in blue light grown cultures but did change patterns of 5HT accumulation. 5HT was highest in plants grown under red light immediately after culture and decreased over 7 days. These data indicate that the relative amounts of MEL and 5HT are responsive to light spectra and redirect metabolic resources to enable plant adaptations to changing environments.

Serotonin and Melatonin Biosynthesis in Plants: Genome-Wide Identification of the Genes and Their Expression Reveal a Conserved Role in Stress and Development

“…Exposure to red light leads to immediate accumulation of Ser in Scutellaria, which decreases over 7 days. In contrast, Mel is detected in plants grown under blue light [60]. Using a short-day flowering plant, Chenopodium rubrum, Kolářet al [61] showed that light suppresses Mel biosynthesis in plants.…”

Melatonin: One molecule one- medicine for many diseases, coronavirus (SARS-CoV-2) disease (Covid19); Function in plants

“…In one of the study it was reported that 3 months of red light exposure led to increased melatonin levels in Glycyrrhiza uralensis (licorice) plants than those grown under blue or white light (Afreen et al, 2006). A similar effect was found in Scutellaria racemosa where short time exposure to blue light initially led to increased melatonin levels but long term red exposure resulted in increased endogenous melatonin concentrations (Forsyth et al, 2020). Overall, there is a strong relationship between light and melatonin whose mechanism has yet to be described thoroughly (Forsyth, In one of the study, relation between the different melatonin content of two cultivars of Nicotiana tabacum and its susceptibility to ozone has been suggested (Dubbels et al, 1995;Hattori et al, 1995).…”

Salt stress in Arabidopsis thaliana seedlings: Role of indoleamines in stress alleviation

“…Moreover, Ser showed strong antioxidant effect but less influence on ABA related gene upregulation. Both Mel and Ser can act as antioxidants, exhibit wide ranging effects in plant development under normal and stress conditions, and are known to improve survival of plants in response to biotic and abiotic stresses (21,(59)(60)(61)(62)(63). In addition to antioxidation, these stress survival mechanisms may include altered biosynthesis, redistribution, interconversions and feedback mechanisms in the indoleamines pathway (23).…”