Nano-Molybdenum Disulfide Enhances Antioxidant Defense and Aroma Formation in Fragrant Rice Under Cadmium Stress via Modulation of 2-Acetyl-1-Pyrroline Biosynthesis

2-acetyl-1-pyrroline (2-AP), the key volatile compound responsible for aroma in aromatic rice, is highly susceptible to abiotic stresses such as cadmium (Cd) toxicity. However, the potential role of molybdenum disulfide nanoflakes (MoS2FL) in regulating antioxidant defense and 2-AP biosynthesis under Cd stress remains largely unexplored. In this study, a pot experiment was conducted to evaluate the effects of foliar MoS2FL application on antioxidant defense, aroma formation, and Cd-stress mitigation in two fragrant rice cultivars, Meixiangzhan-2 and Basmati, grown in Cd-contaminated soil (50 mg kg−1). Cadmium stress significantly reduced key enzymes and precursors involved during 2-AP biosynthesis, including Δ1-pyrroline-5-carboxylate synthetase (P5CS), Δ1-pyrroline, pyrroline-5-carboxylic acid (P5C), diamine oxidase (DAO) and proline dehydrogenase (PRODH), along with downregulation of their associated genes. In contrast, foliar application of MoS2FL was associated with reduced Cd-induced oxidative stress, as indicated by increased antioxidant enzyme activities (SOD, POD, and CAT) and decreased malondialdehyde (MDA) accumulation. Moreover, MoS2FL increased precursor accumulation, enzymatic activities, and transcript abundance of genes associated with 2-AP biosynthesis, whereas gamma-aminobutyric acid (GABA) content, betaine aldehyde dehydrogenase (BADH) activity, and BADH2 gene expression were significantly reduced. Consequently, MoS2FL application significantly increased 2-AP content by 44.47% in Meixiangzhan-2 and 39.94% in Basmati under Cd stress. These findings suggest that MoS2 nanoflakes may serve as a promising nano-enabled strategy to enhance antioxidant defense, improve aroma quality, and mitigate cadmium stress in fragrant rice, potentially through changes associated with the 2-AP biosynthesis pathway. This study highlights the potential application of nanomaterials in improving crop quality and stress resilience in sustainable agricultural systems.