Fabrication of salicylic acid nanosphere for long-term induced immunity performance

Abstract

We synthesised a silicon dioxide nanosphere with a novel nanostructure by loading salicylic acid (SA) as a plant disease resistance inductor to prolong plant life. The SA nanosphere was evaluated by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, N₂ adsorption method, enzyme activity test and pot experiments. The results demonstrated that the SA nanosphere induced the activities of polyphenol oxidase, phenylalanine ammonia-lyase, peroxidase, and chitinase to enhance plant immunity to inhibit Phytophthora nicotianae. Its SA loading capacity reached approximately 80%. The SA nanospheres exhibited a sustained release and maintained its resistance effect at 84.79% after 15 days. Thus, the SA nanospheres could gradually release SA to enhance inhibitive enzyme activity in diseased plants. Furthermore, finite element method was used to establish different nanosphere models and analyse the SA releasing process. SA concentration sharply increased near the nanospheres, and SA was slowly released to the solution. This SA nanosphere will have a great potential in future environmental-friendly practical application.

Fig. 1. Schematic representation of the synthesis of the SA nanospheres.

Fig. 2. (a) FE-SEM and (b) TEM images of the MSNs.

Fig. 3. (a) Zeta potential distribution of silica nanoparticle emulsion and (b) particle size distribution of MSNs in water.

Fig. 4. (a) N₂ adsorption–desorption isotherm and (b) BJH pore size distribution of MSNs.

Fig. 5. Mass loss curves of MSNs, SA nanospheres and SA under air atmosphere from 20 °C to 600 °C.

Fig. 6. Efficiency of different treatments on PPO (a), PAL (b), POD (c) and CHI (d) at different days.

Fig. 7. Effects of different treatments on P. nicotianae in the pot experiment. SA nanosphere (a₁, a₂, a₃, a₄), SA solution (b₁, b₂, b₃, b₄), and water (c₁, c₂, c₃, c₄) treatments after 3, 7, 10 and 15 days, respectively.

Fig. 8. TEM morphologies of leaves and roots with different treatments. Blank root (a₁) and leaf samples (a₂–a₄); fungus-infected root (b₁ and b₁₁) and leaf samples (b₂–b₄) and SA-treated root (c₁) and leaf samples (c₂–c₄). CH: chloroplast, M: mitochondrion, V: vacuole, PM: plasma membrane, P: protein, N: nucleus, CW: cell wall, S: starch grain.

Fig. 9. 2-D geometries of one nanosphere (a), two nanosphere (b) and four nanosphere model (c). The calculated data along red dashed lines were used for FEM analysis. Dimension: nanometre. Calculated SA concentrations along red dashed lines with different immersion time for one nanosphere (d), two nanosphere (e) and four nanosphere model (f).

Fig. 10. FEM calculated SA concentration distributions of one, two and four nanospheres for 0 (a), 100 (b), 300 (c) and 600 s (d), respectively.

Fig. 11. FEM calculated SA concentration distributions of one nanosphere (a₁, a₂, a₃, a₄), two nanospheres (b₁, b₂, b₃, b₄) and four nanospheres (c₁, c₂, c₃, c₄) for 0, 5, 100 and 600 s releasing time, respectively. Dimension: nanometre.