DAB and NBT staining
The accumulation of H2O2 and active oxygen species (Papageorgiou et al.) were assessed by staining the leaves, root or stems of pepper or N. benthamiana plants with 1 mg ml-1 diaminobenzidine (DAB) or Nitrotetrazolium Blue chloride (NBT). After overnight treatment with DAB and NBT, the stained leaves were cleared by boiling in [lactic: glycerol: absolute ethanol (1: 1: 3, V: V: V)] and then destained overnight in absolute ethanol.