Toxicity, physiological, and morphological alterations of Indian camphorweed (Pluchea indica) in response to excess copper.

Abstract

Indian camphorweed (Pluchea indica (L.) Less.) is used as herbal tea due to the presence of volatile aromatic oils and several phytochemical compounds. The aim of this study was to assess the impact of copper (Cu) contamination on the physiology and morphology of P. indica, and the health risks associated with its consumption as tea. The cuttings of P. indica were subjected to 0mM (control), 5mM (low Cu), and 20mM (excess Cu) of CuSO4 treatments for 1, 2, and 4weeks. Thereafter, Cu contamination as well as physiological and morphological parameters were assessed. Cu accumulation was higher in the root tissues of plants (25.8 folds higher as compared to the leaves) grown under 20mM CuSO4 for 4weeks. This increased Cu accumulation resulted in the inhibition of root length, root fresh weight, and root dry weight. Cu concentration was found maximum (1.36μgg-1 DW) in the leaf tissues under 20mM Cu exposure for 4weeks, with the highest target hazard quotient (THQ = 1.85), whereas Cu was not detected in control. Under exposure to 20mM Cu treatment for 4weeks, leaf greenness, maximum quantum yield of photosystem II, and photon yield of photosystem II diminished by 21.4%, 16.1%, and 22.4%, respectively, as compared to the control. Leaf temperature was increased by 2.5°C, and the crop stress index (CSI) exceeded 0.6 when exposed to 20mM Cu treatment for 2 and 4weeks; however, the control had a CSI below 0.5. This led to a reduced transpiration rate and stomatal conductance. In addition, the net photosynthetic rate was also found sensitive to Cu treatment, which resulted in decreased shoot and root growth. Based on the key results, it can be suggested that P. indica herbal tea derived from the foliage of plants grown under a 5mM Cu level (0.75μgg-1 DW) with a target hazard quotient below one aligns with the recommended dietary intake of Cu in leafy vegetables. The study recommends choosing cuttings from plants with a small canopy as plant material in the greenhouse microclimates to validate the growth performance in the Cu-contaminated soil and simulate the natural shrub architecture and life cycle.