Morphophysiological and Redox Modulation of Abelmoschus esculentus Under Graded Crude Oil Soil Contamination

This study evaluated the morphophysiological and biochemical responses of Abelmoschus esculentus to graded crude oil contamination under a controlled pot experiment. Five treatments were established: 0% (control), 0.1%, 0.2%, 0.3% and 0.4% v/w contamination, arranged in a completely randomised design with five replicates. Growth dynamics over seven weeks showed progressive increases in plant height and stem girth across treatments; however, higher contamination levels (0.3–0.4% v/w) significantly reduced final height (≈32 cm) relative to the control (≈36 cm). Stem girth followed a similar trend, with reduced thickening at higher contamination by week 7. Relative water content declined dose-dependently from 92% in the control to 51% at 0.4% v/w, indicating substantial impairment of plant water status. Biochemical analyses revealed tissue-specific modulation of oxidative stress markers and antioxidants. Malondialdehyde (MDA) concentrations ranged from 0.0034–0.0051 µmol g⁻¹ FW (leaf), 0.0098–0.0121 µmol g⁻¹ FW (stem) and 0.0020–0.0089 µmol g⁻¹ FW (root), reflecting variable lipid peroxidation across treatments. Conversely, Vitamin C increased progressively with contamination, reaching 94 µmol g⁻¹ FW (leaf), 271 µmol g⁻¹ FW (stem) and 336 µmol g⁻¹ FW (root). Reduced glutathione (GSH) also exhibited substantial induction, particularly in roots at 0.2% v/w (20.4 µmol g⁻¹ FW) and stems at 0.4% v/w (15.3 µmol g⁻¹ FW). Overall, crude oil contamination induced dose-dependent growth inhibition and water deficit, accompanied by activation of antioxidant defence systems. The findings demonstrate that A. esculentus exhibits measurable redox plasticity and moderate tolerance to petroleum stress, although higher contamination levels compromise morphophysiological performance.