Effect of SiO₂ and TiO₂ nanoparticles through foliar and root dipping treatments: a comprehensive comparison of growth, photosynthesis, secondary metabolites, redox status and enzyme responses in Ocimum sanctum

Nanotechnology shows potential to promote sustainable and productive agriculture and address the growing population and food demand worldwide. Recently, there has been an increase in interest in using nanoparticles (NPs) in agriculture. The current investigation aimed to examine the effects of two different NPs, SiO₂ or TiO₂ as foliar spray or root dipping treatment on tulsi (Ocimum sanctum L.) to identify the optimal concentration of SiO₂ and TiO₂ NPs that influence the growth, physiology, and biochemical processes of tulsi. The findings suggest that the treatment of SiO₂ or TiO₂ NPs led to an increase in peltate glandular trichomes (PGTs) density and diameter, chlorophyll content, photosynthesis, gas exchange traits, and elemental status; which led to enhancement of shoot and root length, fresh and dry mass of shoot and root, leaf area and leaf per plant. The application of SiO₂ or TiO₂ NPs led to the stimulation of enzyme activity responsible for maintaining carboxylation/decarboxylation homeostasis (carbonic anhydrase), nitrogen metabolism (nitrate reductase), Calvin cycle (RuBisCo), and TCA cycle (succinate dehydrogenase and fumarase). In addition, SiO₂ or TiO₂ NPs also played a crucial role in preserving a balance between reactive oxygen species (ROS) and the scavenging system by maintaining elevated activities of antioxidant enzymes involved in ROS detoxification. In the comparison between the two modes of treatment foliar treatment exhibited a more promising response compared to root dipping. SiO₂ and TiO₂ NPs increased Ocimum sanctum growth, physiology, and biochemical traits, with foliar application showing superior effects over root dipping. These NPs improve photosynthesis, enzyme activity, and antioxidant defense, making them promising for sustainable agriculture. Future studies should focus on long-term impacts, optimal dosages, and environmental safety to ensure their effective use in crop production.