Aluminum tolerance in Pfaffia glomerata is associated with antioxidant defense, osmolyte accumulation, and pathway-specific transcriptional regulation

Abstract Aluminum (Al) contamination in acidic soils severely limits plant growth and development. This study investigated the mechanisms and timing of Al toxicity in Pfaffia glomerata , a medicinal species of growing pharmacological interest. Based on the hypothesis that P. glomerata mitigates Al toxicity through tissue-specific adjustments in redox metabolism, accumulation of protective metabolites, and regulation of genes involved in cell wall structure and 20-hydroxyecdysone biosynthesis, plantlets were grown in vitro for 40 days under five Al concentrations (0, 200, 400, 600, and 800 μM). Concentrations above 600 μM significantly impaired plant growth. Aluminum accumulated in both roots and leaves, indicating active translocation throughout the plant. Plants exposed to 600 μM Al exhibited increased levels of glucose and fructose, and to a lesser extent, sucrose and starch. Additionally, starch, proline, malate, and fumarate levels rose in response to Al stress, suggesting metabolic adjustments for stress mitigation. Elevated antioxidant enzyme activity and malondialdehyde accumulation in the roots indicated oxidative stress. At the molecular level, the expression of genes related to 20-hydroxyecdysone biosynthesis ( PgSpook and PgPhantom ) was downregulated in the roots, while genes involved in cell wall biosynthesis ( PgCCR , PgCAD , PgC4H ) were upregulated in the leaves and downregulated in the roots. These findings show that P. glomerata tolerates moderate Al stress via a multifaceted response involving morphological adjustments, redox regulation, metabolite accumulation, and differential gene expression. This is the first evidence of Al-induced downregulation of 20-hydroxyecdysone biosynthesis in a medicinal species and identifies novel molecular targets for enhancing stress tolerance in non-model plants.