Seed Nanopriming with ZnO and SiO2 Enhances Germination, Seedling Vigor, and Antioxidant Defense Under Drought Stress

Abstract

Drought stress is one of the main factors limiting seed germination and seedling establishment in field crops such as jalapeño peppers (Capsicum annuum L.). Nanopriming, a seed improvement technique using nanoparticle suspensions, has emerged as a sustainable approach to improving water use efficiency during the early stages of development. This study evaluated the effects of zinc oxide (ZnO, 100 mg·L^-1), silicon dioxide (SiO₂, 10 mg·L^-1), and their combination (ZnO + SiO₂), stabilized with chitosan, on the germination yield and drought tolerance of jalapeño seeds under mannitol-induced water stress (0%, 15%, and 30%). Compared to the hydroprimed control (T1), nanoparticle treatments consistently improved seed yield. Priming with ZnO (T2) increased the germination percentage by up to 25%, priming with SiO₂ (T3) improved the germination rate by 34%, and the combined treatment (T4: ZnO + SiO₂) improved the fresh weight of the seedlings by 40%. Proline accumulation increased 7.5 times, antioxidant capacity (DPPH) increased 6.5 times, and total phenol content increased 4.8 times in the combined treatment. Flavonoid levels also showed notable increases, suggesting enhanced antioxidant defense. These results clearly demonstrate the superior efficacy of nanoparticle pretreatment compared to conventional hydraulic pretreatment, especially under drought conditions. Multivariate analysis further highlighted the synergistic role of ZnO and SiO₂ in improving osmolite accumulation, antioxidant activity, and water use efficiency. Nanopriming with ZnO and SiO₂ offers a promising, economical, and scalable strategy to improve germination, early growth, and drought resistance in jalapeño pepper cultivation under semi-arid conditions.

Keywords: SiO2; ZnO; drought stress; germination; jalapeño pepper; nanopriming; seedling.

Figure 1

The morphological response of four varieties under nanopriming and drought stress. Panels (A–L) show shoot length, root length, stem diameter, and fresh weight in four jalapeño varieties (Mixteco, Ideal, Imperial and Forajido) under three drought levels (0%, 15% and 30%) and four treatments: T1 (Hydropriming), T2 (ZnO + Q), T3 (SiO₂ + Q), and T4 (ZnO + SiO₂ + Q). Bars represent the mean ± SD. Different letters indicate significant differences (Tukey HSD, p ≤ 0.05).

Figure 2

The morphological response of four varieties under nanopriming and drought stress. Panels (A–I) show the shoot–root ratio, Vigor Index I, and Vigor Index II in four jalapeño varieties (Mixteco, Ideal, Imperial and Forajido) under three drought levels (0%, 15%, and 30%) and four treatments: T1 (Hydropriming), T2 (ZnO + Q), T3 (SiO_{2 +} Q), and T4 (ZnO + SiO₂ + Q). Bars represent the mean ± SD. Different letters indicate significant differences (Tukey HSD, p ≤ 0.05).

Figure 3

The effect of nanopriming treatments and drought stress levels on the photosynthetic pigments and soluble sugar composition of four jalapeño pepper varieties. Panels (A–G) display the response in the varieties Mixteco, Ideal, Imperial, and Forajido under three drought stress levels (0%, 15%, and 30%) and four nanopriming treatments: T1 (Hydropriming), T2 (ZnO + Q), T3 (SiO₂ + Q), and T4 (ZnO + SiO₂ + Q). The variables assessed were (A) chlorophyll (a); (B) chlorophyll (b); (C) total chlorophyll; (D) glucose; (E) fructose; (F) sucrose. Each data point represents the mean ± standard deviation. Different letters indicate statistically significant differences (Tukey HSD, p ≤ 0.05). Under 15% water stress, MT215 (Mixteco + ZnO) improved germination dynamics by reducing the average germination time by 26% and increasing the germination rate by 34% compared to IMT115. Several treatments, such as MT115, IT315, and IT415, maintained 100% germination even under water stress.

Figure 3

The effect of nanopriming treatments and drought stress levels on the photosynthetic pigments and soluble sugar composition of four jalapeño pepper varieties. Panels (A–G) display the response in the varieties Mixteco, Ideal, Imperial, and Forajido under three drought stress levels (0%, 15%, and 30%) and four nanopriming treatments: T1 (Hydropriming), T2 (ZnO + Q), T3 (SiO₂ + Q), and T4 (ZnO + SiO₂ + Q). The variables assessed were (A) chlorophyll (a); (B) chlorophyll (b); (C) total chlorophyll; (D) glucose; (E) fructose; (F) sucrose. Each data point represents the mean ± standard deviation. Different letters indicate statistically significant differences (Tukey HSD, p ≤ 0.05). Under 15% water stress, MT215 (Mixteco + ZnO) improved germination dynamics by reducing the average germination time by 26% and increasing the germination rate by 34% compared to IMT115. Several treatments, such as MT115, IT315, and IT415, maintained 100% germination even under water stress.

Figure 4

Biochemical responses in four jalapeño pepper varieties under different nanopriming treatments and drought stress levels. The panels show (A) free proline content (μg g⁻¹ FW), (B) total phenolic content (mg GAE g⁻¹ FW), (C) total flavonoid content (mg QE g⁻¹ FW), and (D) DPPH radical scavenging activity (mg TE g⁻¹ FW). Bars represent the mean ± standard deviation for each variable. The treatments applied were T1 (Hydropriming), T2 (ZnO + Q), T3 (SiO₂ + Q), and T4 (ZnO + SiO₂ + Q) across three drought stress levels (0%, 15%, and 30%) in the varieties Mixteco, Ideal, Imperial, and Forajido. Letters above the bars indicate significant differences between treatments according to a Tukey HSD test (p ≤ 0.05).

Figure 5

Principal component analysis (PCA) and Pearson correlation heatmaps under different water stress levels. Panels (A), (C), and (E) represent the PCA biplots of morphophysiological and biochemical traits evaluated in four jalapeño pepper varieties (MIXTECO, IDEAL, IMPERIAL, and FORAJIDO) under 0%, 15%, and 30% water stress conditions, respectively. The ellipses represent the distribution and clustering of each variety based on the first two principal components. Panels (B), (D), and (F) show the corresponding Pearson correlation heatmaps for the same variables and stress levels. Positive correlations are shown in red and negative in blue, with the intensity indicating the strength of the correlation. These analyses highlight the multivariate relationships and changes in trait associations as water stress intensifies.

Figure 6

A radar chart comparing ZnO (green), SiO₂ (red), and ZnO + SiO₂ (blue) nanopriming in jalapeño under 0%, 15%, and 30% drought stress. Fifteen variables were evaluated. ZnO+SiO₂ showed the best overall performance under 30% stress, while SiO₂ stood out under 15%. Combined treatments improved both growth and antioxidant responses under drought.

Figure 7

Morphology of samples using transmission electron microscopy (TEM): (A) ZnO; (B) SiO₂.

Figure 8

The experimental design with a 4 × 4 × 3 factorial arrangement, evaluating four varieties of jalapeño pepper, four priming treatments, and three levels of induced water stress.

Figure 9

Germination radicle length of 1 to 2 mm (Binocular stereo microscope with VE-S4 zoom system (Velab Co., Pharr, TX, USA)).