Potato Virus X (PVX) Elimination as Short and Long Term Effects of Hydrogen Peroxide and Salicylic Acid Is differentially Mediated by Oxidative Stress in Synergism with Thermotherapy

Short and long term effects of hydrogen peroxide (H2O2) and salicylic acid (SA) were examined in: thermotolerance, virus X (PVX)-free microplants obtained by in vitro thermotherapy, catalase activity (CAT) and H2O2 concentration. Short term effects (STE) were tested as follows: (a) nodal explants were cultivated 30 d on MS medium containing SA 10(-5) or 10(-6) M; and (b) nodal explants were waterlogged for 1 h in 1 or 5 mM H2O2 solution and subsequently cultured in MS for 30 d. Long term effects were tested as follows (LTE): the experimental regime was identical to STE but SA and H2O2 treated plants were subcultured for an additional 30 d period on MS. All treatments were followed by thermotherapy (32-42 C) for 35 d. Results showed SA and H2O2 induced thermotolerance during thermotherapy. The percentage of PVX-free plants obtained in H2O2 was significantly higher than in SA in STE and LTE by 3-and 4 fold respectively. CAT activity was differentially mediated by SA and H2O2.