Seed-priming with H2O2 alleviates subsequent salt stress by preventing ROS production and amplifying antioxidant defense in cauliflower seeds and seedlings

In the present study, we examined the impact of three seed priming agents; H2O2, GA(3) and NaCl on the oxidative stress status in primed seed germination dynamics and growth establishment of cauliflower seedlings subsequently grown under salt stress. Results showed beneficial effect of all priming agents in improving plant responses to salinity. However, specific differences, depending on development stage, organ and priming type were recorded. At the germination stage, GA(3) was the most advantageous agent to accelerate seedling emergence. At the seedling stage, seedlings obtained from redried H2O2-primed seeds showed the highest level of seed superoxide anion (5-fold) and H2O2 (4-fold), resulting in higher MDA content (2.4-fold). At the same time, priming seeds with H2O2 triggered the overall seedling antioxidant defense, including enzymatic (SOD, CAT, GPX and APX) and non-enzymatic systems (AsA, GSH and proline). Salinity restricted the growth of both leaves (43%) and roots (60%) of cauliflower seedlings issued from unprimed seeds. Under primed conditions, the relative contribution of GA(3) and NaCl was more associated with growth establishment and osmotic adjustment. However, H2O2 role was greatly correlated with the antioxidant defense. Indeed, salt-treated seedlings issued from H2O2-primed seeds showed the lowest levels of superoxide anion, H2O2 and MDA, resulting in the highest activities of the entire antioxidant systems. These findings support the hypothesis that cauliflower plants, when exposed to salt stress benefit from H2O2 seed priming, as a pre-germination stimulus, to prevent itself from subsequent oxidative injuries, which supports the hypothesis of "stress memory" of subsequent salt stress.