Acclimation of sunflower plants to salt stress with hydrogen peroxide

Abstract

This study aimed to test the hypothesis that hydrogen peroxide (H2O2) can increases the tolerance of sunflower plants to salt stress, using different strategies of application. In the first experiment, a selection of the treatments of H2O2 priming with greater dry mass production was carried out. For this purpose, before of salt stress application, seed of sunflower were primed at four concentrations of H2O2 associated to three exposure periods for selection of the better treatments, during 35 days after soaking (DAS). The second experiment was performed using greater treatments selected from the experiment previous. In this experiment, every 7 days, the physiological and biochemical parameters of plants were monitored. In the third experiment, the selection of the treatments of H2O2 priming via leaf spraying with greater dry mass production was carried out. In this experiment, four concentrations of H2O2 (via leaf spraying) were associated at three numbers of application during 35 days after soaking (DAS). The fourth experiment was performed using greater treatments selected from the experiment previous. In this experiment, every 7 days, the physiological and biochemical parameters of plants were monitored. The fifth experiment aimed to evaluate the effect of different methods of applying hydrogen peroxide (H2O2) via seed and/or via leaf spraying in sunflower plants under salt stress. In this experiment, five treatments were tested: control (absence of NaCl and absence of H2O2); salt control (presence of 100 mM NaCl and absence of H2O2); 1 mM H2O2 via seed (in the presence of 100 mM NaCl); 1 mM H2O2 via leaf spraying (in the presence of 100 mM NaCl); and 1 mM H2O2 via seed + 1 mM H2O2 via leaf spraying (in the presence of 100 mM NaCl). At 20 DAS dry masses of plants were quantified. In general, for all experiments, the salt stress promoted a strong reduction of plant growth, in relation to control treatment. However, this reduction was less pronounced in some treatment H2O2-primed, confirming the hypothesis that H2O2 is able to attenuate the negative effect of salinity, increasing the tolerance of plants Our results showed that the priming of seed or plants with H2O2 can increase photosynthetic efficiency, reduce Na+ and Cltransport to leaves and increase antioxidant enzyme activity, mainly catalase, contributing to increased salt tolerance. But we also verified that, application of H2O2 leaf spraying (after salt stress) is not able to attenuate the negative effectcaused by salt in sunflower plants.