Unravelling the role of silica nanoparticles in alleviating chromium heavy metal stress in Mexican marigold (Tagetes erecta L.).

This study investigates the potential of silica nanoparticles (SiO2 NPs) to alleviate chromium (Cr) stress in Tagetes erecta L. (Mexican marigold). For the purpose, their effects on plant growth, biochemical traits, and physiological responses were assessed. A completely randomized design (CRD) was employed using three replicates per treatment across nine treatment groups; T1 = Control, T2 = Cr-I (CrCl3; 50 mg kg-1), T3 = Cr-II (CrCl3; 100 mg kg-1), T4 = NPs-I (SiO2 NPs; 100 mg L-1), T5 = NPs-II (SiO2 NPs; 200 mg L-1), T6 = Cr-I + NPs-I, T7 = Cr-I + NPs-II, T8 = Cr-II + NPs-I, and T9 = Cr-II + NPs-II. Results showed that Cr stress significantly reduced shoot and root length, fresh and dry biomass, and photosynthetic pigment content. Beside this Cr stress increased proline, hydrogen peroxide (H2O2), malondialdehyde (MDA), and membrane permeability which indicate oxidative damage in T. erecta plants. In contrast, the exogenous application of SiO2 NPs reduced H2O2, MDA, and membrane permeability. These treatments while improved chlorophyll a, chlorophyll b, carotenoids, and plant growth parameters thus indicating alleviation of Cr induced negative effects on T. erecta plants. SiO2 NPs also elevated antioxidant enzyme activities and improved the uptake of essential nutrients such as calcium (Ca2+) and potassium (K+), thereby strengthening the plant's defense mechanisms under metal stress. Collectively, these results demonstrate that SiO2 NPs can effectively modulate stress responses and enhance antioxidant defense, offering a promising strategy to alleviate the adverse impacts of heavy metal stress in plants.