Diesel effects on root hydraulic conductivity and morphological changes of the vascular cylinder in Medicago sativa

• Root anatomy and hydraulic conductivity modifications by diesel were assessed.
• Diesel-stress caused root anatomical alterations and loss of hydraulic conductivity.
• Arrangement of vascular cylinder changed from tetrarch to triarch due to diesel.
• Number but not size of metaxylem vessels increased due to diesel.
• Accumulation of superoxide and peroxide in cell roots is enhanced by diesel-stress.

The effects petroleum hydrocarbons (PH) on the morphological and physiological responses of roots have not been well studied. This research evaluated the root hydraulic responses of Medicago sativa seedlings exposed to diesel. Seeds were germinated in test tubes with 1% water-agar contaminated with diesel (3000, 6000, 9000, 12 000, 15 000, 18 000 and 21 000 μL L−1), and uncontaminated test tubes were used as controls (0 μL L−1). Ten days-old roots were detached to determine root anatomy, hydraulic conductivity (Kh), specific hydraulic conductivity (Ks), percentage of loss conductivity (PLC), and leaf water potential (Ψlw). Root morphological changes were related to the loss of tetrarch arrangement; however, the number of metaxylem vessels increased in response to diesel. Increasing diesel concentrations resulted in diminished Kh and Ks values, as well as enhanced PLC values. Diesel contamination resulted in the accumulation of superoxide and hydrogen peroxide in root cells, as determined by confocal microscopy.