# Seed Nanopriming with Spirulina-Derived Carbon Dots Enhances Rice (Oryza sativa L.) Germination, Crop Establishment, and Seedling Metabolic Performance

## TL;DR

Spirulina-derived carbon dots improve rice seed germination and seedling growth by enhancing metabolic activity and resource mobilization.

## Contribution

Demonstrates that Spirulina-derived carbon dots act as effective nanobiostimulants for rice seed nanopriming.

## Key findings

- Nanopriming with Spirulina CDs increased germination rate by 25% and root length by 37%.
- Seedlings showed higher starch (24%) and phenolics (20%) accumulation with no oxidative stress.
- Proteomic analysis revealed metabolic reprogramming favoring growth over defense mechanisms.

## Abstract

Biogenic carbon dots (CDs) are emerging as promising plant biostimulants, yet their effects during early crop establishment remain underexplored. Here, we synthesized and characterized Spirulina-derived CDs and evaluated their efficacy as seed nanopriming agents in rice (Oryza sativa L.). CDs exhibited nanoscale size, abundant surface functionalities, and a highly negative ζ-potential, indicative of stable aqueous dispersions. Spectroscopic characterization (Raman and FTIR) confirmed a graphitic–amorphous carbon structure. Near-infrared spectroscopy coupled to principal component analysis revealed time-dependent metabolic changes during imbibition, identifying 8–12 h as the optimal priming window. Nanopriming with Spirulina CDs (0.2 mg mL−1 for 12 h) increased the seed germination rate (25%), the germination speed index (17%), vigor index I (22%), and root length (37%) compared to hydropriming. Biochemically, the nanoprimed seedlings accumulated higher levels of starch (24%), total carbohydrates (8%), and total phenolics (20%), without evidence of oxidative imbalance, based on antioxidant capacity measurements and proteomic profiling. Proteomic analysis revealed coordinated metabolic reprogramming, characterized by increased abundance of proteins involved in translation, energy metabolism, and ion/nutrient homeostasis, alongside reduced abundance of proteins associated with defense and catabolic processes. This shift from stress-preparation to growth-oriented metabolism supports improved seedling establishment. Overall, Spirulina-derived CDs function as effective nanobiostimulants that promote early metabolic activation and resource mobilization, offering a sustainable strategy to enhance rice seedling establishment.