Salicylic acid and cold priming induce late-spring freezing tolerance by maintaining cellular redox homeostasis and protecting photosynthetic apparatus in wheat

An increasing number of studies provide evidence that priming (pre-exposure of plants to moderate stress or chemical stimulus) can confer plant tolerance to a later occurring severe stress. The main objective of this study was to explore and compare the physiological mechanisms of salicylic acid (SA) and cold priming to enhance freezing tolerance. Wheat plants were firstly primed with SA (100 mu M) or cold temperature (day/night temperature of 6 degrees C/2 degrees C), and then grown without any treatment for 8 days, and subsequently subjected to a freezing stress (day/night temperature of 2 degrees C/0 degrees C on the first day and - 2 degrees C/- 4 degrees C on the second day) at the jointing stage. The results showed that primed plants up-regulated the expression level of WRKY gene (WRKY19), heat shock transcription factor (HSF3), mitochondrial alternative oxidase (AOX1a), and heat shock protein (HSP70) under freezing stress, which contribute to increase of antioxidant capacity and protection of photosystem in parallel with lower malonaldehyde content, superoxide radical production and higher photochemistry efficiency of photosystem II under freezing stress as compared with non-primed plants. Furthermore, primed plants had a better photosynthesis performance and higher biomass production during the recovery period, and higher grain yield at maturity as compared with non-primed plants. Collectively, these results indicated that SA and cold priming effectively upregulated the expression of cold-responsive genes under freezing stress, resulting in increased antioxidant activity and cyanide-resistant respiration capacity and molecular chaperones level, maintaining cellular redox homeostasis and protecting photosynthetic apparatus, thereby conferring tolerance to freezing stress in wheat plants.