Secondary metabolites and the antimicrobial potential of five different Coleus species in response to salinity stress

Abstract Salinity is one of the major abiotic stresses that affects the growth and productivity of plants. The presence of soluble salts at high concentration near the root system restricts the uptake of water by plants. Plants grown under saline conditions possess higher amounts of secondary metabolites compared with those grown under normal conditions. The use of traditional medicine to treat infectious diseases is increasing day by day throughout the world. Developing novel drugs with antimicrobial potential from the source of medicinal plants is receiving attention to replace the use of synthetic drugs and to combat the growth of multi-drug resistant strains. Thus screening of medicinal plant extracts is carried out to evaluate their antimicrobial potency. The present study aimed at determining the secondary metabolites and antimicrobial potential of leaf, stem and root ethanol and chloroform extracts of five different Coleus species; C.aromaticus, C.amboinicus, Cbarbatus, C.forskohlii and C.zeylanicus subjected to salinity stress. The up regulation in the content of plant bioactive compounds along with the antimicrobial activities of ethanol and chloroform extracts under the influence of salinity stress have been observed during the study in Coleus. The leaf, stem and root extracts of all the five Coleus species showed good antimicrobial activity against the tested pathogenic strains. The leaf extracts of Coleus showed higher inhibitory activity compared to the stem and root extracts. Ethanol extracts showed higher anti-microbial activity ranging from 1.5-100 mg/ml compared with the chloroform extracts ranging from 0.97-250 mg/ml respectively. The study revealed that the increased antimicrobial activity with increasing salinity might be due to the up regulation of secondary metabolites. The leaf, stem and root extracts of Coleus showed effective antimicrobial activity against the pathogenic strains even under saline conditions is due to the up regulation of secondary metabolites which provides a scope of developing novel drugs to treat infectious diseases.