The Effect of Green Zinc Oxide Nanoparticles on the Physicochemical Properties of Ganoderma lucidum Mushroom

Nanotechnology is an emerging technology which can revolutionize various scientific fields such as agriculture. Zinc oxide nanoparticles (ZnONPs) are one of the metal oxide nanoparticles that are biocompatible and environmentally friendly. Zinc is an active element and a strong reducing agent. Ganoderma lucidum is a parasite fungus which has been used as a popular food and also to treat of various diseases. The medicinal value of strains of this fungus are related to their biologically active compounds such as proteins, flavonoids, antioxidants, vitamins, and minerals. Different issues have been reported for chemical synthesis of ZnONPs such as high cost and toxicity of chemicals, therefore, nowadays green synthesis method is widely used to synthesize metal nanoparticles due to its environmental friendliness, lower toxicity rate and more safety. Various natural components such as plants, algae, fungi and bacteria are used to synthesize zinc oxide nanoparticles which among them, green synthesis by plant extracts has attracted special attention for the synthesis of various metal nanoparticles. The purposes of the current study were to evaluate the possibility of using Foeniculum vulgare seed extract to synthesize green ZnONPs and the influence of ZnONPs and ZnO treatments on different characteristics of G. lucidum strains.   

In this study, the aqueous extract of vulgare L. seeds was used to synthesize green ZnONPs. G. lucidum strains (Gl01 and Gl16) were obtained from the forests of Mazandaran province and were used after verification of their nature. The formation of nanoparticles was confirmed by dynamic light scattering (DLS) and transmission electron microscopy (TEM). The effect of different concentrations of ZnONPs and ZnO (0, 4, 6 and 8 mM) on total phenolic content, flavonoids, antioxidant capacity, carbohydrates, ascorbic acid, beta-carotene and lycopene, and the activity of antioxidant enzymes including polyphenol oxidase (PPO), ascorbate peroxidase (APX), glutathione peroxidase (GPX) and glutathione reductase (GR) of two wild strains of G. lucidum were studied in submerged culture. The study was conducted as a factorial experiment based on completely randomized design with three replications. Analysis of variance was performed using SAS v.19 software and mean comparisons were conducted based on SNK method.

The results indicated that the shape of ZnONPs was spherical and they had a uniform distribution, with an average particle size of 13 to 25 nm. Bulk ZnO and ZnONPs significantly affected the biochemical properties of lucidum strains. The flavonoid content of both G. lucidum strains increased with increasing the concentration of bulk ZnO and ZnONPs. The results showed that ascorbic acid content of G. lucidum significantly increased in response to different concentrations of bulk ZnO and ZnONPs. The results clearly revealed a significant difference between treatments in terms of β-carotene and lycopene content, so that β-carotene and lycopene content increased with increasing the concentration of bulk ZnO and ZnONPs to 6 mM, but increasing the concentration until 8 mM, led to a significant decrease in these traits. Also, the results indicated a significant difference between treatments in terms of the activity of antioxidant enzymes including GPX, APX, PPO and GR. Based on results, the antioxidant enzymes activity increased with increasing the concentration of bulk ZnO and ZnONPs to 6 mM, and then, decreased at concentration of 8 mM. Also in both strains, the activity of antioxidant enzymes on 8th day was higher than on 4th day. The stress caused by heavy metals induces the biosynthesis of antioxidant compounds in plant cells. Studies have shown that application of ZnOPNs leads to increasing total phenol content resulting in enhancing antioxidant capacity of treated crops. Also, based on reports enhancing the antioxidant enzymes activity and increasing flavonoids and ascorbic acid content caused by ZnONPs application lead to lower reactive oxygen species in plant cells under stress conditions leading to lower cellular damages.   

Our study determined the appropriate concentrations of ZnONPs and ZnO based on positive effects on content and activity of antioxidant agents in lucidum strains. Among treatments, ZnONPs had a greater positive effect on mycelium antioxidant characteristics than bulk ZnO and also, the effects in Gl01 strain were more pronounced than in Gl16.