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 st ep 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) treatme nt. Furthermore, tissues subcultured on to ASA-free medium following s everal weeks of growth on ASA were more thermotolerant (by 3.8-fold) o f a 7 week 35 degrees C treatment, and (by 38-fold) of a 15 h 42 degre es C heat-shock. Stems of microplants grown on ASA contained significa ntly less catalase activity and higher levels of H2O2 than controls. E xplanting and heat treatment, however, reduced catalase activity to si milar levels in ASA-treated and control microplant tissues. To investi gate 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 mi croplants that grew from the H2O2-treated explants showed concentratio n-dependent decreases in stem height, but were significantly more ther motolerant 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.