Assessing lead toxicity induced alterations in expression of transmembrane metal transporter OsHMA9 and physio-biochemical activities of canola

Abstract

Rapid industrialization has accelerated heavy metal contamination of agricultural, posing severe risk to ecosystem, food safety, human and animal health. In the present study, we examined the physiological and biochemical responses of four canola (Brassica napus L.) varieties; CON-II, Super Raya, Dunkeld and Super Canola, to lead (Pb) stress (600 mg kg⁻¹ soil). Pb exposure markedly suppressed growth and morphological traits across all varieties; however, Super Raya exhibited comparatively superior performance, maintaining higher plant height, root and shoot biomass (fresh and dry), and root length. The accumulation of Pb in roots and leaves of canola plants posed a toxic effect to biochemical activities thus enhancing malondialdehyde concentration and electrolyte leakage. The disturbance in metabolism of canola plants under Pb stress resulted into depletion in chlorophyll concentration while the activities of antioxidants involving glutathione reduce (GSH), superoxide dismutase (SOD), ascorbic acid (ASA), peroxidase (POD), ascorbate peroxidase (APX), catalase (CAT) and total antioxidant activity were significantly enhanced in order to detoxify its deleterious effects. The translocation factor indicated that Super Raya retained maximum Pb in its roots rather than to translocate in its leaves. Furthermore, b exposure significantly induced OsHMA9 expression in all varieties, with the highest induction observed in Super Raya. The results demonstrate that although Pb stress impairs physio-biochemical functions in canola, Super Raya possesses comparatively stronger tolerance mechanisms, including restricted Pb translocation and enhanced antioxidant defense.