Pre-spraying nitrogen-doped carbon dots prior to stress enhance rice tolerance by improving metabolism, antioxidant, and cell wall.

In this study, a nitrogen-doped CDs (N-CDs) was developed and found to enhance the growth and stress tolerance of rice seedlings by pre-spraying in hydroponics. A preliminary experiment determined an effective dose of N-CDs at 100 μg/mL for rice growth by foliar spraying once a day for two weeks. Then, pre-spraying of N-CDs at 100 μg/mL for one week significantly enhanced the tolerance of rice seedlings to salt (NaCl at 100 mM), cadmium (1 mg/L), and 2,4-dichlorophenoxyacetic acid (5 mg/L) stress without N-CDs exposure, with 12.77-205.03 % increase in root and leaf parameters compared to those without N-CDs pre-treatment. Transcriptomics demonstrated that pre-spraying of N-CDs reprogrammed the phytohormones and MAPK signaling pathways of rice seedlings and up-regulated genes involved in metabolism, antioxidant activity, cytoskeleton, and cell replication. Metabolomics revealed higher metabolism, energy metabolism, and cytoskeleton development of rice seedlings pre-sprayed with N-CDs. Physiological and phenotypic investigations confirmed that rice seedlings pre-sprayed with N-CDs showed an increase in root vitality, cytoplasmic content, and Ca, Mg, and Mn concentrations in by 115.09 %, 39.52 %, 9.37 %, 13.07 %, and 19.29 % respectively, and peroxidase activity by 160.74 %. N-CDs also increased the cell wall thickness and root lignocellulose content of rice seedlings. Therefore, it was concluded that pre-spraying of N-CDs mediated signaling pathways to enhance the defense mechanism of rice seedlings against stress by improving metabolism, antioxidants, and cell wall development. This study underscored the potential of pre-spraying of N-CDs as a promising strategy to enhance plant stress tolerance in the face of increasing environmental challenges.