N-Acetyl-D-Glucosamine—Zinc Oxide Nanoconjugates: An Eco-Friendly Approach for Soybean Growth Enhancement

In the contemporary era, nanotechnology has emerged as a transformative tool across multiple sectors, including agriculture, with the potential to support sustainable food production. Among metallic nanoparticles (NPs), zinc oxide nanoparticles (ZnO NPs) play a crucial role in supplying zinc, an essential micronutrient required for crop growth and development. Soybean (Glycine max (L.) Merr.) is a globally important legume cultivated to meet increasing food and nutritional demands, and adequate zinc availability is vital for optimizing its growth and yield. Although conventional zinc fertilizers can enhance crop productivity, excessive application may exert phytotoxic effects, particularly within the rhizosphere environment. To mitigate these limitations, ZnO NPs are increasingly synthesized via biogenic approaches or conjugated with organic compounds to improve their environmental compatibility and reduce adverse impacts on plants and soil ecosystems. N-Acetyl-D-glucosamine (GlcNAc), an amino sugar and a monomer of chitin and chitosan, is known for its diverse commercial applications, including the stimulation of beneficial soil microbial communities. The present study investigates the growth-promoting potential of GlcNAc-conjugated ZnO NPs (GlcNAc–ZnO NPs) in soybean. The results demonstrate that GlcNAc–ZnO NPs exert a pronounced, concentration-dependent effect on soybean growth, physiology, and molecular regulation. Notably, an optimal dose of 75 mg/L GlcNAc–ZnO NPs significantly enhanced plant growth promotion compared with unmodified ZnO NPs and untreated controls, highlighting the importance of surface conjugation of organic compounds in improving plant growth performance.