Negatively but Not Positively Charged Nanoceria Promoted Lateral Root Growth via Modulating the Distribution of Reactive Oxygen Species Rather than Auxin

Lateral root (LR) formation is important for plant growth. ROS (reactive oxygen species)play an important role in LR formation. While how nanomaterials affect ROS distribution to promote LR formation and the role of ROS in primordia in LR formation are rarely known. Cerium oxide nanoparticles (nanoceria), as a potent ROS scavenger, are widely used in plants. This study investigates the effects of poly (acrylic acid) nanoceria (PNC, 6.5 nm, -36 mV), aminated nanoceria (ANC, 6.9 nm, 30 mV), and bulk nanoceria (BNC, 84.9 nm, -5.5 mV) on LR formation in <i>Arabidopsis</i>. Only PNC increased LR numbers by 73.5%, reducing root H₂O₂ levels by up to 90.44% and altering O₂^•- distribution in LR primordia (LRP). Furthermore, DPI (diphenyleneiodonium, O₂^•- inhibitor) decreased LR numbers by 18.9%, while PNC treatment reversed this inhibition (12.25 ± 0.53 vs 8.38 ± 0.52). Transcriptome analysis shows PNC regulated ROS metabolism via genes like peroxiredoxins and peroxidases, promoting LR formation. Interestingly, PNC does not affect auxin distribution (confirmed by DR5pro::GFP lines) or alleviate NPA-induced (N-1-naphthylphthalamic acid, an auxin transport inhibitor) LR inhibition. These findings suggest that PNC enhances LR formation through ROS modulation rather than auxin signaling.