Induction of thermotolerance in potato microplants by acetylsalicylic acid and H2O2

Potato microplants propagated as nodal explants were subjected to heattreatments in vitro similar to those employed in thethermotherapy step of virus eradication procedures. Low concentrations(10^-6-10^-5 M) ofacetylsalicylic acid (ASA) in the culture medium improved (by 3.7-fold)tolerance of a 5-week high-temperature (35C)treatment. Furthermore, tissues subcultured on to ASA-free medium followingseveral weeks of growth on ASA were more thermotolerant (by 3.8-fold) of a7 week 35C treatment, and (by 38-fold) of a15 h 42°C heat-shock. Stems of microplants grown on ASA containedsignificantly less catalase activity and higher levels of H2O2 thancontrols. Explanting and heat treatment, however, reduced catalase activityto similar levels in ASA-treated and control microplant tissues. Toinvestigate whether H2O2 could be involved in signal transduction duringthe induction of thermotolerance, nodal explants were incubated for 1 h inH2O2 (0.1-50 mM), and then cultured under standard conditions. Themicroplants that grew from the H2O2-treated explants showedconcentration-dependent decreases in stem height, but were significantlymore thermotolerant than controls, more than 1 month after the H2O2treatment. Thus, thermotolerance induced in these conditions was extremelystable. It is concluded that both salicylate and H2O2 treatments caninduced thermotolerance in this system.Keywords:Acetylsalicylic acid, heat-shock, hydrogen peroxide, potato,microplant, thermotolerance.