Abstract
The spent engine oil (SEO) is a major source of pollution and impacts the soil quality and plant growth. Phytoremediation is an environmentally friendly technique for soil remediation. The aim of this study was to assess how the phytoremediation ability and stress resistance of okra (Abelmoschus esculentus (L.) could be improved with the use of exogenous melatonin (MT). P. Moench) cultivated in a soil contaminated with SEO. Four concentrations of SEO (0, 100, 200 and 300 μM) and three MT levels (0, 100 and 200 μM) were investigated in a 4×3 factorial pot experiment. SEO stress had significant effects on plant growth, plant physiological activity and biochemical activity. MT application dose-dependently however mitigated these negative effects. Seedling exposure to MT resulted in up to 11.51%, 15.85% and 32.71% increase in shoot length, root length and number of leaves, respectively, as compared to the stressed control. Physiological parameters also enhanced, including photosynthetic rate (13.12%), chlorophyll content (26.32%), stomatal conductance (26.41%) and transpiration rate (31.62%). The maximum improvement was with the total amino acid content (107.78) in severe stress. Moreover, it is important to point out that the removal efficiency of anthracene has risen from XX% (SEO-only treatment) to XX% (SEO + 200 μM MT) showing an improvement of the phytodegradation efficiency. Two-way ANOVA showed that there were significant (p < 0.05) differences among the various SEO, MT and SEO x MT for all parameters. These results indicate that the use of exogenous melatonin in the field of phytoremediation with A. esculentus in soils contaminated with SEO could be a good option for sustainable remediation.