Biogenic copper nanoparticles from Avicennia marina leaves: Impact on seed germination, detoxification enzymes, chlorophyll content and uptake by wheat seedlings

Abstract

Biogenic copper nanoparticles (Cu NPs) were synthesized using the aqueous crude extract of mangrove leaves, Avicennia marina (CE). GC-MS metabolite profiling of CE showed that their carbohydrates are mainly composed of D-mannose (29.21%), D-fructose, (18.51%), L-sorbose (12.91%), D-galactose (5.47%) and D-Talose (5.21%). Ultra-fine nanoparticles of 11.60 ±4.65 nm comprising Cu2O and Cu(OH)2 species were obtained with a carbohydrate and phenolic content of 35.6±3.2% and 3.13±0.05 mgGA/g, respectively. The impact of the biogenic Cu NPs on wheat seedling growth was dose-dependent. Upon treatment with 0.06 mg/mL of Cu NPs, the growth was promoted by 172.78 ± 23.11 and 215.94 ± 37.76% for wheat root and shoot, respectively. However, the lowest relative growth % of 81.94 ± 11.70 and 72.46 ± 18.78% were recorded for wheat root and shoot, respectively when applying 0.43 mg/mL of Cu NPs. At this concentration, peroxidase activity (POX) of the germinated wheat seeds also decreased, while ascorbic acid oxidase (AAO) and polyphenol oxidase (PPO) activities increased. Higher uptake of copper was observed in the root relative to the shoot implying the accumulation of the nanoparticles in the former. The uptake was also higher than that of the commercial Cu NPs, which showed an insignificant effect on the seedling growth. By treating the wheat leaves in foliar application with 0.06 mg/mL of Cu NPs, their contents of Chlorophyll a, Chlorophyll b, and total chlorophyll were enhanced after 21 days of application. Meanwhile, the high concentration (0.43 mg/mL) of Cu NPs was the most effective in reducing the leaf content of chlorophyll (a, b, and total) after the same time of application. The findings of this study manifest the potential of utilizing controlled doses of the prepared biogenic Cu NPs for inhibition or stimulation of seedling growth.

Fig 1. Schematic outline of the work conducted in this study.

FTIR: Fourier Transform Infrared Spectroscopy, GC-MS: Gas Chromatography-Mass Spectrometry, XRD: X-ray Diffraction, EDX: Energy-dispersive X-ray spectroscopy, TEM: Transmission Electron Microscopy, SEM: Scanning Electron Microscopy, UV-Vis: Ultraviolet-Visible spectrophotometry, Carb: Carbohydrates, TPC: Total Phenolic Content.

Fig 2. Schematic outline of the pot cultivation.

Physical and chemical characteristics of the soil used in this study as well as the procedure used for Chlorophyll extraction and estimation of chlorophyll a, b and total chlorophyll contents were previously reported by Essa et al. [20].

Fig 3

UV-Vis spectra of the biogenic and commercial Cu NPs (a), together with the FTIR spectra of the CE, biogenic and commercial Cu NPs (b).

Fig 4

TEM image (a), XRD pattern (b), SEM image (c), EDX analysis (d) and of the biogenic Cu NPs.

Fig 5

Root (a) and shoot lengths (b) of the germinated wheat seeds after their incubation in CE, biogenic and commercial Cu NPs.

Fig 6

Effect of CE, biogenic and commercial Cu NPs on % relative growth of root (a) and shoot lengths (b) and germination index of wheat seeds (c).

Fig 7

Effect of CE and Cu NPs on CAT (a), POX (b), PPO (c) and AAO (d) activities in wheat germinated seeds (μg/g fresh wt min^-1) at the 4^th day of germination.

Fig 8

Cu uptake in wheat seedlings (a) and Translocation factor of wheat seedlings (b).

Fig 9. Chlorophyll a, b and total chlorophyll contents upon exposure to CE and Cu NPs.