The Synergistic Priming Effect of Exogenous Salicylic Acid and H2O2 on Chilling Tolerance Enhancement during Maize (Zea mays L.) Seed Germination

Abstract

Chilling stress is an important constraint for maize seedling establishment in the field. To examine the role of salicylic acid (SA) and hydrogen peroxide (H₂O₂) in response to chilling stress, we investigated the effects of seed priming with SA, H₂O₂, and SA+H₂O₂ combination on maize resistance under chilling stress (13°C). Priming with SA, H₂O₂, and especially SA+H₂O₂ shortened seed germination time and enhanced seed vigor and seedling growth as compared with hydropriming and non-priming treatments under low temperature. Meanwhile, SA+H₂O₂ priming notably increased the endogenous H₂O₂ and SA content, antioxidant enzymes activities and their corresponding genes <i>ZmPAL, ZmSOD4, ZmAPX2, ZmCAT2</i>, and <i>ZmGR</i> expression levels. The α-amylase activity was enhanced to mobilize starch to supply metabolites such as soluble sugar and energy for seed germination under chilling stress. In addition, the SA+H₂O₂ combination positively up-regulated expressions of gibberellic acid (GA) biosynthesis genes <i>ZmGA20ox1</i> and <i>ZmGA3ox2</i>, and down-regulated GA catabolism gene <i>ZmGA2ox1</i> expression; while it promoted GA signaling transduction genes expressions of <i>ZmGID1</i> and <i>ZmGID2</i> and decreased the level of seed germination inhibitor gene <i>ZmRGL2</i>. The abscisic acid (ABA) catabolism gene <i>ZmCYP707A2</i> and the expressions of <i>ZmCPK11</i> and <i>ZmSnRK2.1</i> encoding response receptors in ABA signaling pathway were all up-regulated. These results strongly suggested that priming with SA and H₂O₂ synergistically promoted hormones metabolism and signal transduction, and enhanced energy supply and antioxidant enzymes activities under chilling stress, which were closely relevant with chilling injury alleviation and chilling-tolerance improvement in maize seed. <b>Highlights:</b>Seed germination and seedling growth were significantly improved under chilling stress by priming with SA+H₂O₂ combination, which was closely relevant with the change of reactive oxygen species, metabolites and energy supply, hormones metabolism and regulation.