Nano-Formulations of Copper Species Coated with Sulfated Polysaccharide Extracts and Assessment of Their Phytotoxicity on Wheat (Triticum aestivum L.) Seedlings in Seed Germination, Foliar and Soil Applications

Copper nanoparticles were synthesized via a bioreduction using sulfated polysaccharides (SPs) extracted from Avicennia marina mangrove leaves and their phytotoxicity effect on wheat (Triticum aestivum L.) seedlings was assessed. As analyzed by high-performance liquid chromatography (HPLC), SPs extract constituted mainly 49.3% glucose, 24.6% galactose and 20.5% glucouronic acid by mol. A nanoformulation of ultrafine Cu2O/Cu(OH)2 nanoparticles coated with SPs (Cu NPs) was prepared with an average particle size of 2.11 ± 0.64 nm and a slightly negatively-charged zeta potential of 11 ± 0.46 mV. Applying high concentrations of Cu NPs on wheat seeds inhibited the respective shoot and root relative growth percentages, yielding 13.22 ± 9.91 and 36.72 ± 18.51% at 0.06 mg/mL of the nanoformulation. Comparable values were obtained when the seeds were subjected to 0.06 mg/L of SPs extract applied in the free form. In a foliar application, 0.06 mg/mL of Cu NPs reduced the respective total chlorophyll and carotenoids contents by 17.4% and 24.3% relative to the control while the treatment with SPs reduced them by slightly higher values of 27.9% and 32.6%, respectively, after 14 days of application. Therefore, Cu NPs show a comparable inhibition effect to that of the free SPs extract but offer the additional advantages of nanoformulations. In soil applications, however, Cu NPs stimulated the growth of wheat seedlings in contrary to SPs and increased the total chlorophyll and carotenoids by 49.76% and 70%, respectively. This gives an additional merit to the nanoformulation that can potentially be used as an effective biostimulant in soil.