Copper (Cu) is a toxic metal that accumulates in soil due to agricultural and industrial activities, potentially impacting plant growth and productivity. Our study examined the phytotoxic effects of Cu on Vigna radiata L. by exposing plants to a series of Cu concentrations (1, 4 and 7 mM) under controlled conditions. Growth parameters, photosynthetic performance, biochemical traits, and oxidative stress indicators were analyzed in 21-day-old Cu-treated plants and compared with control plants. The results demonstrated a concentration-dependent decline in shoot and root biomass, relative water content (RWC), pigment content, photosynthetic efficiency, carbohydrates, and lipid content. Conversely, oxidative stress markers such as malondialdehyde (MDA), electrolyte leakage, superoxide dismutase (SOD) and ascorbate peroxidase (APX) activity and proline accumulation increased significantly with increasing Cu concentrations, indicating cellular damage. Notably, protein levels increased with increased Cu concentrations, which may contribute to their tolerance to metal stress, however, it was insufficient to mitigate stress. Further research is needed to validate these findings and explore the mechanisms underlying copper stress tolerance.

This study evaluated the physiological responses, hormonal signaling, osmotic and nutrient levels, as well as the performance of essential oils, antioxidant enzymes, and secondary metabolites in Lavender plants subjected to chromium and fluoride toxicity and biochar application. The findings indicated that the administration of raw and especially multiple-chemical engineered biochars decreased fluoride (about 16-40%) and chromium (39-60%) levels in Lavender leaves, whereas raised CEC and soil pH, nitrogen (10-37%), potassium (20-47%), phosphorus (10-60%), magnesium (30-49%), calcium (20-50%), zinc (39-240%), iron (40-120%), plant biomass, and photosynthetic pigments of Lavender plant leaves under toxic fluoride and chromium conditions. The treatments with multiple-chemical engineered biochars decreased the osmotic stress and osmolyte concentration (carbohydrates, soluble proteins, and proline) in the leaves of Lavender plants. Both raw and multiple-chemical engineered biochars significantly enhanced the water content of plant leaves, reaching up to 10% under toxic circumstances. Moreover, these treatments decreased the synthesis of stress hormones such as jasmonic acid (4-17%), salicylic acid (29-49%), and abscisic acid (30-66%), while increasing the production of Indole-3-acetic acid (IAA) (15-29%) in Lavender plants subjected to chromium and fluoride stress. The use of multiple-chemical engineered biochars showed notable efficacy in enhancing antioxidant enzyme's activity against oxidative damage induced by metal toxicity and decreasing proline accumulation. Maximum concentrations of linalyl acetate, borneol, camphor, and linalool were achieved under fluoride and chromium stress conditions by metaphosphoric acid-engineered biochar. Multiple-chemical engineered biochars application can be inferred as valuable approach to enhance both the quality and quantity of lavender essential oil under conditions of fluoride and chromium-induced stress.