FIGURE 4.

Detection of ${\mathrm{O}}_{\mathrm{2}}^{\mathrm{•–}}$ in leaf disks of 24-day-old pea plants grown from the control (C), hydroprimed (H), and hydroprimed with an aqueous solution of 50 μM melatonin (H-MEL50) or 200 μM melatonin (H-MEL200) seeds. Photographs were taken at T₀ (before PQ treatment) and after 2, 4, 6, 24, and 48 h of disk incubation in 75 μM PQ solution. Red arrows indicate dark spots of formazan derived from NBT oxidized by ${\mathrm{O}}_{\mathrm{2}}^{\mathrm{•–}}$.