Prunella vulgaris-derived biostimulant enhances copper tolerance in rice by mitigating oxidative damage and regulating ion homeostasis

Overabundance of soil copper may adversely affect natural and agricultural systems. In growing plants, excess copper severely impairs nutrient absorption and metabolic activity in roots. Here, we show that Prunella vulgaris (Pv) extract can alleviate copper toxicity in rice seedlings. First, we found that copper stress has inhibitory effects on growth and biomass of rice seedlings. After exposure to high levels of copper, plants exhibited high copper contents, elevated lipid peroxidation biomarker (Malondialdehyde - MDA) levels, and increased numbers of inviable cells. Interestingly, treatment with 0.25% (w/v) Pv extract robustly rescued the growth of plants exposed to copper stress. Transcriptomic analysis suggested that Pv extract might regulate cell wall properties under copper stress. Furthermore, Pv extract significantly upregulated several genes involved in biosynthesis of proline, deoxymugineic acid, metalloproteins, vacuolar and efflux transporters. These findings suggest that Pv-induced cellular defense responses might help to combat copper-associated oxidative stress. Additionally, LC/MS analysis of Pv extract revealed the presence of diverse bioactive compounds such as caffeic acid, rosmarinic acid, and melatonin. Taken together, these findings reveal mechanisms by which Pv extract attenuates copper toxicity and suggest a means of improving agricultural production.