Evaluation of concentration and application time of Nanographene oxide on photosynthetic and antioxidant performance of cucumber in greenhouse conditions

Plants life has been affected by carbon cycle. The discovery of new forms of carbon in recent years has raised the question of how these forms affect plants. One of these new forms of graphene is the nanosized form caused by the mechanical breakdown of graphite materials. In this study, the effect of different concentrations of nanographene oxide (NGO) on plant growth, photosynthesis and antioxidant enzymes activity of cucumber plants in hydroponic culture was investigated. The seedlings root were treated with different concentrations of NGO including 0.4, 0.8, 1.2, 1.6 and 2 mg ml-1 graphene oxide for 30 and 60 minutes before transferring to culture medium. The results showed that NGO at lower concentrations (1.2 mg ml-1) can increase plant growth characteristics such as root and shoot dry weight as well as increase chlorophyll content and maximum photosynthetic yield. Maximum chlorophyll content (41.18) and photosynthetic efficiency (0.42) were observed at 1.2 mg ml-1. The maximum activity of peroxidase and superoxide dismutase enzymes was observed at concentrations of 1.2 and 1.6 mg ml-1 respectively. Malondialdehyde content decreased by 58 (30 min) and 23 (60 min) percent at 1.2 mg ml-1 concentration compared to control. The NGO also increased the concentration of nitrogen, potassium and iron and decreased the concentration of calcium compared to the control, but no significant difference was observed in the concentration of phosphorus and zinc. In fact, optimal concentrations of NGO can be used as a regulator and stimulant of cucumber plants growth. However, further studies are needed to investigate the effect of these emerging nanoparticles on plants.