1H Nuclear Magnetic Resonance and Liquid Chromatography Coupled with Mass Spectrometry-Based Metabolomics Reveal Enhancement of Growth-Promoting Metabolites in Onion Seedlings Treated with Green-Synthesized Nanomaterials

Seed priming is a promising approach to improve germination, emergence, and seedling growth by triggering pre-germinative metabolism and enhancing seedling vigor. Recently, nanopriming gained importance in seed improvement as a result of the small size and unique physicochemical characteristics of nanomaterials. In the present study, silver and gold nanoparticles were synthesized using onion extracts as the reducing agent. Similarly, the agro-food industrial byproducts citrus seed oil and curcumin-removed turmeric oleoresin were used for the preparation of nanoemulsions. For seed priming, these green-synthesized nanomaterials were incubated with seeds of two onion (Allium cepa L.) cultivars (Legend and 50147) for 72 h, and then the plants were grown in a greenhouse for 3 weeks. Seed priming with these nanomaterials increased seed germination and seedling emergence. One-dimensional 1H nuclear magnetic resonance and liquid chromatography coupled with mass spectrometry metabolomics studies showed that different nanopriming treatments distinctly altered the metabolome of onion seedlings. Seed priming treatments significantly inhibited plant hormones and growth regulators, such as abscisic acid and cis-(+)-12-oxo-phytodienoic acid, and enhanced germination stimulators, such as γ-aminobutyric acid and zeatin, in onion seeds and seedlings. Therefore, these priming treatments have positive impact on improving seed performance and plant growth.