Effect of heavy metals on physiology and anatomy of Artemisia Nilagirica Clarke pamp

Abstract

Artemisia nilagirica (Clarke) Pamp., commonly known as Indian wormwood, is a tall aromatic perennial shrub belonging to the family Asteraceae and is widely recognized for its therapeutic properties. The present study investigates heavy metal-induced stress responses and tolerance mechanisms in 4. nilagirica following exposure to aluminium (80 pM), chromium (70 pM), copper (50 pM), iron (70 puM) and mercury (10 pM) under Hoagland nutrient conditions. Roots, stems and leaves were analysed to assess morphological, anatomical, biochemical and metabolic alterations associated with metal toxicity. Metal exposure resulted in significant reductions in root and shoot length and leaf arca compared to control plants. Plants treated with mercury exhibited increased stomatal density and wider stomatal apertures, indicating an adaptive response likely facilitating mercury phytovolatilization. Copper exposure induced the development of glandular and non-glandular trichomes on both leaf surfaces, suggesting a sequestration-based detoxification strategy. Anatomical analyses revealed increased cell wall thickness as a key tolerance mechanism for immobilizing toxic metal ions and preventing cytoplasmic damage. Structural abnormalities, including disrupted epidermal layers and altered xylem vessel diameter, were observed in plants exposed to chromium, copper, iron and mercury, whereas aluminium treatment caused minimal anatomical alterations, indicating comparatively lower toxicity at the tested concentration. Biochemical analyses demonstrated a significant decline in tolerance index across all metal treatments. Chlorophyll content decreased, while carotenoid levels increased, reflecting a protective response against photooxidative stress. Elevated levels of proteins, phenolics, proline, malondialdehyde, and enhanced activities of antioxidant enzymes such as catalase and superoxide dismutase confirmed the induction of oxidative stress and activation of antioxidant defence mechanisms. SEM and SEM-EDX analyses revealed ultrastructural changes and confirmed the localization and accumulation of metal ions within plant tissues, while ICP-OES analysis validated metal bioaccumulation. GC-MS profiling revealed substantial alterations in the composition of bioactive secondary metabolites under heavy metal stress, including the emergence of compounds potentially involved in metal detoxification, alongside a reduction in metabolites associated with medicinal efficacy. FTIR analysis further demonstrated metal-specific modifications in functional groups of proteins and polysaccharides, indicating significant metabolic perturbations. Cytotoxicity studies using Dalton’s lymphoma ascites (DLA) cells showed that metal contamination significantly influenced the anticancer activity of 4. nilagirica leaf extracts; although cytotoxicity increased with extract concentration, overall anticancer efficacy was attenuated due to metal-bioactive compound interactions. Collectively, this study elucidates the complex physiological, biochemical, and molecular responses of A. nilagirica to heavy metal stress, highlighting its adaptive tolerance mechanisms, potential role as a bioindicator of metal pollution, and the need for careful evaluation of metal contamination in medicinal and therapeutic applications.