Phytoremediation potential of Brazilian sunflower cultivars under lead-induced stress: bioaccumulation, enzymatic activity and physiological responses

Sunflower plants (Helianthus annuus) are recognized for their potential in soil decontamination due to their high capacity for biomass production and ion accumulation, making them promising candidates for phytoremediation of heavy metals. This study aimed to evaluate the tolerance of Brazilian sunflower cultivars BRS415 and BRS323 to 150, 180, 240, 300, 900, and 4400 mg kg− 1 of Pb(NO3)2 in artificially contaminated soil. To evaluate the phytoremediation potential, we investigated the physiological and chemical parameters of the plants, and analyzed the oxidative enzyme activity. The cultivars were assessed for physiological parameters, chlorophyll content, ATP concentration, heavy metal tolerance, and antioxidant potential after a 30-day cultivation period. The plant showed excellent structural development with 900 mg kg⁻¹ of lead compared to the lower concentrations and demonstrated a strong ability to transfer the contaminant to its structures, primarily retaining it in the roots. Chlorophyll a content at Pb900 was close to that of the control, and ATP levels increased by 62% (Pb150) and 77% (Pb900) compared to the control. The cultivar also exhibited strong activation of its antioxidant defense system, with catalase (CAT) and ascorbate peroxidase (APX) showing elevated enzymatic activity in all plant parts at Pb900. Guaiacol peroxidase (G-POX) was also highly active, contributing to the formation of structural and functional barriers that reduced metal translocation within the plant. These findings demonstrate that the Brazilian hybrid BRS323 possesses a significant ability to thrive under lead stress, supported by a complex and efficient biochemical defense network throughout the phytoremediation process. .