Study of heavy metal induced changes in some selected medicinal plants

Abstract

Heavy metal pollution has increasingly become an environmental issue associated with the accelerated process of industrialization and has proven to be harmful to plant productive capacity and human health. Medicinal plants, which are used in the preparation of medicines, have especially become threatened as they have largely been grown in polluted sites. The aim of the current study was to assess the impact of certain heavy metals influencing the germination, development, physiological, antioxidant, and bioactive substance production of three medicinal plants, Andrographis paniculata, Emilia sonchifolia, and Tridax procumbens. The experimental study entailed the controlled treatment of seeds and seedlings with varying concentrations of copper (Cu), chromium (Cr), and zinc (Zn). The parameters considered in detecting the early growth responses, in addition to the biochemical analysis, aimed at determining the activity of the antioxidants and the total phenolic, included germination percentage, root, shoot, vigour index, and phytotoxicity. The measurement of bioactive compounds, andrographolide, and quercetin by using the principle of high performance liquid chromatography (HPLC) was also done. The outcome revealed that high metal stress had significant effects on germination and growth, and these were dose- and species-specific. Lesser concentrations of Cu and Zn had stimulatory effects on growth and the production of secondary metabolites, while high concentrations and Cr treatment had significant inhibitory effects on growth and caused phytotoxicity. Among the test plants, Tridax procumbens had been found to be relatively tolerant to high metal stress, while Emilia sonchifolia had been found to be highly sensitive. The increased accumulation of antioxidants in response to low metal stress had been found to be an adaptive measure against oxidative stress. This study concludes that there can be significant impacts of heavy metals on the physiological and phytochemical properties of medicinal plants. The results of the analysis have provided important information that can be used to monitor the growing conditions, especially with respect to heavy metal impact, and shed light on the physiology of plant stress and tolerance to heavy metals