Melatonin improves bioreductant capacity and silver nanoparticles synthesis using Catharanthus roseus leaves

Melatonin is a natural hormone found in a variety of living organisms, including plants, and possesses the potential to act as a growth promoter and stress alleviator. The present study aims in understanding the effect of melatonin in Catharanthus roseus (C. roseus; medicinal plant used in anticancer therapy) leaf extracts for enhanced silver nanoparticle synthesis. Our results indicated that the supplementation of 300 mu M melatonin to C. roseus leaves improves silver nanoparticles (AgNPs) synthesis. The phytosynthesized AgNPs were characterized using UV-Vis spectroscopy, FE-TEM, Zetasizer, XRD, AAS and FTIR spectroscopy. Moreover, the AgNPs were found to be smaller in size (ranging from 10-25 nm) with potent antibacterial activity (MIC and MBC values against the most prevalent urinary tract pathogens, Escherichia coli and Staphylococcus aureus, being 15.6 +/- 0.0 mg mL(-1) and 31.25 +/- 0.0 mg mL(-1) respectively). Furthermore, LC-MS/MS analysis of the melatonin treated C. roseus leaf extracts indicated the presence of significant biomolecules; 6-acetyl morphine (used as an analgesic), rauwolscine and fisetin (anticancer compounds). Melatonin treatment of C. roseus leaves also enhanced its antioxidant potential and total chlorophyll content. Thus, melatonin serves as a potential agent to improve C. roseus growth and therapeutic potential.