Green Synthesis of Hypericum perforatum-Mediated Silver Nanoparticles and Their Dose-Dependent Effects on Growth and Oxidative Stress in Mentha piperita

This study explores the synthesis of silver nanoparticles derived from Hypericum perforatum L. and their impact on peppermint growth and physiology, aiming to understand their mechanisms and potential in sustainable agriculture. Synthesis of silver nanoparticles via reaction with AgNO3 at 37°C was done. The formation was confirmed by color change, UV-Vis analysis, dynamic light scattering (DLS), and scanning electron microscopy. A completely randomized design experiment with four replicates was carried out to examine the impact of different concentrations of silver nanoparticles (0, 10, 40, and 80 mg/L) on growth parameters and morpho-physiological characteristics of Mentha piperita L. The absorbance peak between 400–500 nm confirmed silver nanoparticle formation. The average particle size was 11.9 ± 0.7 nm, ranging from 11.2 to 12.6 nm, indicating a uniform size distribution, determined via DLS. At a concentration of 40 mg/L, these nanoparticles improved peppermint growth and reduced oxidative stress, evidenced by decreased levels of malondialdehyde and ion leakage, markers of oxidative damage and increased the chlorophyll a to chlorophyll b ratio. Conversely, at 80 mg/L, they failed to promote growth and exacerbated oxidative stress in peppermint. H2O2 content, SOD and catalase enzyme activity was induced at 80 mg/L concentration of H. perforatum silver nanoparticles. the results indicated low concentration of H. perforatum silver nanoparticles had positive effect on growth of peppermint and may enhance defense mechanisms for higher-level stress with important implications for interactions, and evolution future studies should investigate the bioactivity of H. perforatum silver nanoparticles and their potential applications in medical sciences, including comparisons with raw plant extracts.