Mitigating Cd and drought stresses through 24-Epibrassinolide seed priming in basil ( Ocimum Basilicum L.): impacts on antioxidant capacity and secondary metabolite profiles

This study investigates the effects of 24-epibrassinolide (BR) on the biochemical and physiological responses of basil (Ocimum basilicum L. cv purpurascens Benth) under cadmium (Cd) and drought stress. Under extreme conditions (25% field capacity (FC) + 30 mg kg–1 Cd), BR priming resulted in reinforced antioxidative response, with catalase (CAT), and ascorbate peroxidase (APX) activities increasing by 42% and 29%, respectively, compared to unprimed plants. Despite a drastic reduction in flavonoid content (41%) and unchanged phenylalanine ammonia lyase (PAL) enzymatic activity and total phenolic content, individual phenolic compounds, including apigenin (116%), rutin (110%), cinnamic acid (80%), and caffeic acid (40%), were significantly increased. Concurrently, BR enhanced the accumulation of methyleugenol (81%), trans-β-farnesene (31%), and caryophyllene (20%), while markedly reducing the uptake of metals, such as Cd by 89%, and iron (Fe) by 87%. These findings demonstrate that BR seed priming serves as an adaptive strategy to strengthen basil's physiological defenses under stress.