Unveiling the protective role of silicon dioxide nanoparticles against copper-induced oxidative damage in soybean plants through altered proline metabolism and antioxidants

Copper (Cu) is an essential micronutrient for plant growth and development. However, excessive Cu from diverse anthropogenic sources leads to the significant loss of crop production. On the other hand, low dose of silicon dioxide nanoparticles (SiO₂-NPs) showed promising response to various abiotic stresses. This study was conducted to explore the response of SiO₂-NPs in soybean plants exposed to elevated levels of Cu and uncover the efficacy of SiO₂-NPs to alleviate the Cu induced toxicity by regulating proline metabolism and antioxidant system. A low level (25 μM) of Cu in the presence of SiO₂-NPs (50 ppm) significantly increased growth performance, photosynthetic efficiency, and altered proline metabolism. However, higher levels (50, and 100 μM) of Cu alone showed inhibitory effects in concentration dependent manner through increased oxidative stress (electrolyte leakage, H₂O₂ content, and lipid peroxidation). The follow-up application of SiO₂-NPs to the Cu-stressed plants improved growth, water relations, photosynthesis, decreased leaf Cu accumulation and simultaneously enhanced the various antioxidant enzymes viz. catalase, peroxidase and superoxide dismutase with the improved RuBisCO activity and excess proline accumulation along with altered ProDH and P5CS activities. These findings suggested that SiO₂-NPs played a dual role through improved growth and photosynthetic performance of soybean plants in the presence of low dose of Cu and concurrently provide resilience to the soybean plants under higher concentrations of Cu through altered proline metabolism and elevated levels of antioxidant enzymes and proline accumulation resulting in improved growth, water relations and photosynthesis.