Metabolomic Response of Early-Stage Wheat (Triticum aestivum) to Surfactant-Aided Foliar Application of Copper Hydroxide and Molybdenum Trioxide Nanoparticles

Abstract

Surfactants are commonly used in foliar applications to enhance interactions of active ingredients with plant leaves. We employed metabolomics to understand the effects of Triton^TM X-100 surfactant (SA) and nanomaterials (NMs) on wheat (Triticum aestivum) at the molecular level. Leaves of three-week-old wheat seedlings were exposed to deionized water (DI), surfactant solution (SA), NMs-surfactant suspensions (Cu(OH)₂ NMs and MoO₃ NMs), and ionic-surfactant solutions (Cu IONs and Mo IONs). Wheat leaves and roots were evaluated via physiological, nutrient distribution, and targeted metabolomics analyses. SA had no impact on plant physiological parameters, however, 30+ dysregulated metabolites and 15+ perturbed metabolomic pathways were identified in wheat leaves and roots. Cu(OH)₂ NMs resulted in an accumulation of 649.8 μg/g Cu in leaves; even with minimal Cu translocation, levels of 27 metabolites were significantly changed in roots. Due to the low dissolution of Cu(OH)₂ NMs in SA, the low concentration of Cu IONs induced minimal plant response. In contrast, given the substantial dissolution of MoO₃ NMs (35.8%), the corresponding high levels of Mo IONs resulted in significant metabolite reprogramming (30+ metabolites dysregulated). Aspartic acid, proline, chlorogenic acid, adenosine, ascorbic acid, phenylalanine, and lysine were significantly upregulated for MoO₃ NMs, yet downregulated under Mo IONs condition. Surprisingly, Cu(OH)₂ NMs stimulated wheat plant tissues more than MoO₃ NMs. The glyoxylate/dicarboxylate metabolism (in leaves) and valine/leucine/isoleucine biosynthesis (in roots) uniquely responded to Cu(OH)₂ NMs. Findings from this study provide novel insights on the use of surfactants to enhance the foliar application of nanoagrochemicals.

Keywords: metabolomics; nanoagrochemicals; nanomaterials; surfactants; wheat.

Figure 1

Metal ions released from (A) 100 mg/L Cu(OH)₂ NMs and (B) 100 mg/L MoO₃ NMs in DI water (DI) and surfactant containing suspensions (SA). PLS-DA score plots of overall metabolites in wheat (C) leaves and (D) roots after one-week foliar exposure to DI and SA solutions. Three replicates were used under each condition.

Figure 2

Significant metabolic pathway changes in wheat after one-week foliar exposure to surfactant solution. The color scale indicates the fold changes compared with DI water. The border of the box indicates whether the metabolite changes happened in wheat leaves (green) or roots (red).

Figure 3

Comparison of significantly changed metabolites (/log2(fold change)/>1) in wheat leaves exposed to (A) Cu(OH)₂ NMs; (B) MoO₃ NMs; (C) Cu IONs; and (D) Mo IONs. Experimental conditions: SA—200 mg/L Triton^TM X-100 solution; Cu(OH)₂ NMs—100 mg/L Cu(OH)₂ NMs (as Cu content) in SA; Cu IONs—0.1 mg/L CuSO₄·5H₂O (as Cu content) in SA; MoO₃ NMs—100 mg/L MoO₃ NMs (as Mo content) in SA; and Mo IONs—35 mg/L Na₂MoO₄ 2H₂O (as Mo content) in SA. The numbers in the pie chart represent the significantly changed metabolites from each metabolite category. The color of the numbers in the outer circular ring indicates fold changes of the significantly dysregulated metabolites: red (fold change > 5), orange (2 < fold change < 5), blue (0.2 < fold change < 0.5), and purple (fold change < 0.2). Three replicates were used under each condition.

Figure 4

Comparison of significantly changed metabolites (/log2(fold change)/>1) in wheat roots exposed to (A) Cu(OH)₂ NMs; (B) MoO₃ NMs; (C) Cu IONs; and (D) Mo IONs. Experimental conditions: SA—200 mg/L Triton^TM X-100 solution; Cu(OH)₂ NMs—100 mg/L Cu(OH)₂ NMs (as Cu content) in SA; Cu IONs—0.1 mg/L CuSO₄·5H₂O (as Cu content) in SA; MoO₃ NMs—100 mg/L MoO₃ NMs (as Mo content) in SA; and Mo IONs—35 mg/L Na₂MoO₄·2H₂O (as Mo content) in SA. The numbers in the pie chart represent the significantly changed metabolites from each metabolite category. The color of the numbers in the outer circular ring indicates fold changes of the significantly dysregulated metabolites: red (fold change > 5), orange (2 < fold change < 5), blue (0.2 < fold change < 0.5), and purple (fold change < 0.2). Three replicates under each condition.

Figure 5

Venn diagram of (A) dysregulated metabolites and (B) perturbed metabolic pathways in wheat after one-week foliar exposure to NMs suspensions. Legend: wheat leaves exposed to Cu(OH)₂ NMs; wheat leaves exposed to MoO₃ NMs; wheat roots exposed to Cu(OH)₂ NMs; wheat roots exposed to MoO₃ NMs.