Nitrogen-doped carbon quantum dots enhance rice seedlings growth and antioxidant defense system under arsenic stress

Arsenic (As) toxicity severely restricts rice growth, particularly in flooded paddies, while carbon quantum dots (CQDs) have recently gained increasing attention for their ability to improve plant tolerance against variety of stressors. Here, we investigated nitrogen-doped CQDs (N-CQDs) as a nano-enabled strategy to mitigate As toxicity in aromatic Basmati rice. Four Basmati rice cultivars were seed-primed with hydrothermally synthesized N-CQDs at 0, 100, 200 and 300 ppm. Cultivar B-515 showed highest increase in germination (14 %) at 100 ppm as compared to non-stressed seedlings. Subsequently, B-515 seedlings were subjected to pot experiment at varying concentrations of N-CQDs against As-contaminated soil (30-60 ppm). Under As toxicity, N-CQDs at 100 ppm significantly enhanced plant height (17 %), dry weight (29 %), chlorophyll contents (59 %), relative water contents (31 %), and membrane stability index (25 %), while reducing leaf As accumulation by 58 %. Antioxidant enzymes viz. superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and proline levels rose significantly, suggesting improved antioxidant defense mechanism against As stress. The significant increase in proline, a direct biochemical precursor of 2-acetyl-1-pyrroline (2-AP), provides a strong rationale to hypothesize that N-CQDs could enhance grain aroma in mature Basmati plants, a promising direction for future validation at the reproductive stage. Overall, these findings highlight N-CQDs potential as an effective, dose-sensitive approach to alleviate As toxicity and improve stress resilience in rice. Future field-scale studies should assess its long-term soil impacts and effects on 2-AP biosynthetic pathways.