Carbon dots promote cotton growth and development by enhancing photosynthesis and antioxidant enzyme activities

Carbon dots (CDs), an emerging class of nanomaterials, have shown great potential to modulate plant growth and development. However, the underlying molecular mechanisms and gene regulatory networks through which CDs influence physiological processes remain largely unexplored, limiting their application in agriculture. In this study, citric acid was used to synthesis CDs by microwave-assisted method. Here, we treat cotton leaves with different concentrations of CDs to study their effects on cotton growth and development. The findings demonstrated that, at appropriate doses, CDs could enhance cotton biomass accumulation, with concurrent increases in fresh and dry weights. At 100 mg·L− 1, cotton exhibited optimal morphological performance: the aboveground biomass showed increases of 67.69% and 42.89% in fresh and dry weight, respectively. In addition, the belowground biomass displayed 34.48% and 46.65% increments, respectively. CDs-mediated increases in chlorophyll content and photosynthetic enzyme activities, together with improvements in photosystem performance, suggest that CDs likely enhance photosynthetic efficiency in cotton and thereby promote growth. Moreover, CDs strengthened the antioxidant defense system primarily by enhancing the activities of key enzymes (SOD and POD), despite a concurrent decrease in CAT activity. To elucidate the molecular basis underlying the observed physiological responses, RNA-sequencing (RNA-seq) was performed to provide deeper insights into the gene expression profiles associated with CD-mediated growth. In summary, transcriptomic analysis revealed that CDs significantly enriched the ‘photosynthesis-antenna proteins’ pathway, where Lhcb1 (light-harvesting complex II chlorophyll a/b binding protein 1), Lhcb2 (light-harvesting complex II chlorophyll a/b binding protein 2) and Lhcb3 (light-harvesting complex II chlorophyll a/b binding protein 3) were significantly up-regulated, and the ‘flavone and flavonol biosynthesis’ pathway, involving the up-regulation of F3′5′H (flavonoid 3’,5’-hydroxylase). These molecular findings are highly consistent with the physiological data, demonstrating that CDs promote cotton growth by enhancing light-harvesting efficiency and antioxidant defense systems. By integrating transcriptomic profiling with physiological measurements, this study elucidates the molecular pathways by which citric acid–based CDs enhance photosynthesis and antioxidant capacity in cotton. Our findings provide a mechanistic basis for the use of CDs to optimize crop production.