Induction of thermotolerance in potato microplants by acetylsalicylic acid and H2O2

Potato microplants propagated as nodal explants were subjected to heat treatments in vitro similar to those employed in the thermotherapy step of virus eradication procedures. Low concentrations (10(-6)-10(-5) WI) of acetylsalicylic acid (ASA) in the culture medium improved (by 3.7-fold) tolerance of a 9-week high-temperature (35 degrees C) treatment. Furthermore, tissues subcultured on to ASA-free medium following several weeks of growth on ASA were more thermotolerant (by 3.8-fold) of a 7 week 35 degrees C treatment, and (by 38-fold) of a 15 h 42 degrees C heat-shock. Stems of microplants grown on ASA contained significantly less catalase activity and higher levels of H2O2 than controls. Explanting and heat treatment, however, reduced catalase activity to similar levels in ASA-treated and control microplant tissues. To investigate whether H2O2 could be involved in signal transduction during the induction of thermotolerance, nodal explants were incubated for 1 h in H2O2 (0.1-50 mM), and then cultured under standard conditions. The microplants that grew from the H2O2-treated explants showed concentration-dependent decreases in stem height, but were significantly more thermotolerant than controls, more than 1 month after the H2O2 treatment. Thus, thermotolerance induced in these conditions was extremely stable. It is concluded that both salicylate and H2O2 treatments can induce thermotolerance in this system.