Induction of Freezing Tolerance by the Application of Hydrogen Peroxide and Salicylic Acid as Tuber-Dip or Canopy Spraying in Solanum tuberosum L. Plants

Abstract

Low temperature stress is a current challenge to plants that is associated with climate change. In plants, exposure to extreme temperatures is followed by the accumulation of reactive oxygen species, such as hydrogen peroxide (H2O2), leading to oxidative stress. Salicylic acid (SA) and H2O2 mediate the tolerance responses to stress and have been reported to induce freezing tolerance in potato microplants. The objectives of the present investigation were (1) to evaluate the short- and long-term effects of H2O2 and SA treatments on freezing tolerance in potato (Solanum tuberosum L.) plants grown from tubers and (2) to analyse the relationship between catalase (CAT) activity and H2O2 concentration associated with freezing tolerance responses. We observed the lowest freezing survival rates in 45-day-old potato plants (cv. Granate) compared to younger plants. The two treatments consisted of (1) the tuber-dip (long-term) treatment in which sprouted minitubers were saturated for 1 h in SA 10−5 M or H2O2 1 mM and planted in soil under greenhouse conditions and (2) the crop-spray (short-term) treatment in which plants 5–8 cm high were sprayed twice a week with SA 10−5 M or H2O2 1 mM until 45 days of age. In all treatments, 45-day-old plants were then exposed to − 6 ± 1 °C for 4 h. The survival rate was measured 15 days after freezing. CAT and H2O2 measurements were performed 1 h before and after the freezing treatment. The results showed that SA and H2O2 induced freezing tolerance in both the short- and long-term treatments. Survival was significantly higher in SA- and H2O2-treated plants than in control plants. In both the long- and short-term treatments this higher survival was associated with lower internal H2O2 concentrations after freezing compared with control plants and decreasing oxidative stress. SA and H2O2 induced different levels of CAT activity after freezing compared to that found in the control plants in the long- and the short-term treatments. These results suggest the SA and H2O2 function in independent pathways in terms of their induction of freezing tolerance that depends on the method the treatment was applied, by spraying the canopy or by immersion of the sprouted seed tuber.