Involvement of salicylic acid in cold priming-induced freezing tolerance in wheat plants

Freezing is one of the most damaging abiotic stress factors. Cold priming has been shown to enhance freezing tolerance in wheat. However, the underlying mechanisms are unclear. Salicylic acid (SA) is an important signal molecule involved in plant responses to abiotic and biotic stresses. This study aims to investigate the role of SA in cold priming-induced freezing tolerance in wheat plants. The results showed that the expression of gene encoding phenylalanine ammonia-lyase (PAL, a key enzyme involved in SA biosynthesis) and the level of endogenous SA (both free and conjugated) were significantly up-regulated following cold priming treatment. The role of SA in cold priming-induced freezing tolerance was further explored using the donor and inhibitor of endogenous SA. l-α-aminooxy-β-phenylpropionic acid (AOPP, a specific inhibitor of PAL) pretreatment reversed the increment of SA level induced by cold priming treatment, attenuated the positive effects of cold priming on antioxidant capacity (as indicated by the contents of MDA, ASA and GSH, and the activities of APX, GR, DHAR and MDHAR) and cold-responsive genes expression (such as AOX1a, IRI2 and HSP70) under the later freezing stress as well as the freezing tolerance (as indicated by the photochemical activity, electrolyte leakage and biomass). The application of exogenous SA could obviously counteract the negative effects of AOPP. Findings of the present study suggested that the roles of SA in cold priming-induced freezing tolerance in wheat might involve regulation of antioxidant capacity and cold-responsive gene expression.