Biogenic ZnO Nanoparticles Synthesized Using a Novel Plant Extract: Application to Enhance Physiological and Biochemical Traits in Maize

Abstract

The need to increase crop productivity and resistance directs interest in nanotechnology. Indeed, biogenic metal oxide nanoparticles can promote beneficial effects in plants, while their synthesis avoids the environmental impacts of conventional synthetic procedures. In this context, this research aimed to synthesize biogenic zinc oxide nanoparticles (ZnO-NPs) using, for the first time, an extract of a wild and spontaneous aquatic species, Lemna minor (duckweed). The effectiveness of this biogenic synthesis was evidenced for comparison with non-biogenic ZnO-NPs (obtained without using the plant extract), which have been synthesized in this research. XRD (X-ray diffraction), FE-SEM (field emission gun electron scanning microscopy), EDX (energy dispersive x-ray spectroscopy), TEM (transmission electron microscope) and UV-vis (ultraviolet-visible spectrophotometry) showed the biogenic approach effectiveness. The duckweed extract was subjected to UHPLC-ESI/QTOF-MS (ultra high-pressure liquid chromatography quadrupole time of flight mass spectrometry) phenolic profiling. This untargeted characterization highlighted a high and chemically diverse content in the duckweed extract of compounds potentially implicated in nanoparticulation. From an application standpoint, the effect of biogenic nanoparticles was investigated on some traits of maize subjected to seed priming with a wide range of biogenic ZnO-NPs concentrations. Inductive effects on the shoot and root biomass development were ascertained concerning the applied dosage. Furthermore, the biogenic ZnO-NPs stimulated the content of chlorophylls, carotenoids, and anthocyanin. Finally, the study of malondialdehyde content (MDA) as a marker of the oxidative status further highlighted the beneficial and positive action of the biogenic ZnO-NPs on maize.

Keywords: antioxidant activity; biogenic nanoparticles; duckweed; phytochemicals; plant stimulation.

Figure 1

XRPD (a) and UV-vis (b) patterns of biogenic and non-biogenic ZnO-NPs.

Figure 2

FE-SEM and TEM images of samples non-biogenic (a,a’) and biogenic (b,b’) ZnO-NPs.

Figure 3

EDX elemental mapping of samples non-biogenic (a) and biogenic (b) ZnO-NPs.

Figure 4

Abundance of phenolic compounds (mg 100 g⁻¹) in the duckweed. Compounds have been screened by untargeted metabolomics, and cumulative abundance per each class quantified against a representative compound per each class.

Figure 5

Shoot (a) and root (b) length recorded at 14 days after the treatments in maize seedlings subjected to the treatments with biogenic ZnO-NPs (T25, T50, T100 and T200) compared to the untreated control samples. Letters in the figure, when different, indicate statistically significant differences for p < 0.05 between treatments.

Figure 6

The figure shows the content of chlorophyll a and b (a) and on carotenoids and anthocyanin (b) recorded 14 days after the treatments with biogenic ZnO-NPs (T25, T50, T100 and T200) compared to the untreated control samples. Letters in the figure, when different, indicate statistically significant differences for p < 0.05 between treatments.

Figure 7

The figure shows the amount of MDA found 14 days after the treatments with biogenic ZnO-NPs (T25, T50, T100 and T200) compared to the untreated control samples. Letters in the figure, when different, indicate statistically significant differences for p < 0.05 between treatments.

Figure 8

The proposed mechanism for ZnO-NPs formation.

Figure 9

Summary of the positive effects of biogenic ZnO-NPs, obtained using duckweed extracts, in maize.