The Synergistic Priming Effect of Exogenous Salicylic Acid and H 2 O 2 on Chilling Tolerance Enhancement during Maize ( Zea mays L.) Seed Germination.

Chilling stress is an important constraint for maize seedling establishment in the field. To examine the role of salicylic acid (SA) and hydrogen peroxide (H ₂ O ₂ ) in response to chilling stress, we investigated the effects of seed priming with SA, H ₂ O ₂ , and SA+H ₂ O ₂ combination on maize resistance under chilling stress (13°C). Priming with SA, H ₂ O ₂ , and especially SA+H ₂ O ₂ shortened seed germination time and enhanced seed vigor and seedling growth as compared with hydropriming and non-priming treatments under low temperature. Meanwhile, SA+H ₂ O ₂ priming notably increased the endogenous H ₂ O ₂ and SA content, antioxidant enzymes activities and their corresponding genes ZmPAL, ZmSOD4, ZmAPX2, ZmCAT2 , and ZmGR 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+H ₂ O ₂ combination positively up-regulated expressions of gibberellic acid (GA) biosynthesis genes ZmGA20ox1 and ZmGA3ox2 , and down-regulated GA catabolism gene ZmGA2ox1 expression; while it promoted GA signaling transduction genes expressions of ZmGID1 and ZmGID2 and decreased the level of seed germination inhibitor gene ZmRGL2 . The abscisic acid (ABA) catabolism gene ZmCYP707A2 and the expressions of ZmCPK11 and ZmSnRK2.1 encoding response receptors in ABA signaling pathway were all up-regulated. These results strongly suggested that priming with SA and H ₂ O ₂ 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. Highlights: Seed germination and seedling growth were significantly improved under chilling stress by priming with SA+H ₂ O ₂ combination, which was closely relevant with the change of reactive oxygen species, metabolites and energy supply, hormones metabolism and regulation.