Graphene oxide composited with nano-Fe3O4 for enhancing root reducibility in ryegrass (Lolium perenne L.)

Graphene derivatives are the fastest developing nanomaterials of the 21st century. Graphene oxide (GO) is versatile and is usually used in the form of composite materials and is inevitably introduced into the environment. However, studies on the potential effects on plant physiological parameters and metabolism, particularly concentration-dependent effects, remain limited. In this study, four concentrations (0, 10.0, 100, and 500 mg L⁻¹) of GO/Fe₃O₄ (a laboratory-made graphene oxide and nano ferroferric oxide composite) were added to hydroponic ryegrass (Lolium perenne L.) via root application to investigate the impact on physiological parameters. Scanning electron microscopy, elemental mapping, and dynamic light scattering (DLS) revealed that GO/Fe₃O₄ is highly aggregated and negatively charged, making it difficult for the composite to enter plant cells. Results showed that GO/Fe₃O₄ at low and medium concentrations (10.0 mg L⁻¹ and 100 mg L⁻¹) increased ryegrass root reducibility and catalyzed H₂O₂ reduction. Transmission electron microscopy (TEM) images and the Fe content of ryegrass roots indicated that GO/Fe₃O₄ facilitated root accumulation of Fe in a concentration-dependent manner. Reverse transcription-qPCR results demonstrated that an appropriate concentration of GO/Fe₃O₄ significantly down-regulated the expression of genes associated with proline synthesis and up-regulated LpGCLC, LpGR, LpGST6, and LpDHAR in the glutathione–ascorbic acid (GSH–ASA) cycle. These findings provide a basis for the use of GO/Fe₃O₄ in modulating physiological processes in ryegrass.