Ethylene enhances tolerance to chilling stress in tomato fruit partially through the synergistic regulation between antioxidant enzymes and ATP synthases

Gaseous plant hormone ethylene plays a pivotal role during adaptive responses of crop growth and ripening, the mechanisms by which regulates tomato fruit response to chilling stress, however, remain limited. Our results showed that the expression of ACS2, ETR3, EIN2 and ERF2 and the protein content of EIL3 changed rapidly when tomato fruit exposed to 4 °C. Compared with storage at 25 °C, ethylene content and maturity of tomato fruit were inhibited at 4 °C. These results indicated that ethylene signaling might respond to chilling stress. In addition, take advantage of ethephon (ETH) or 1-Methylcyclopropene (1-MCP) treatment, we found that the severity of cold injury in tomato fruit was reduced or intensified, respectively. ETH-treated fruit displayed lower levels of ion leakage, malondialdehyde (MDA), H2O2 and O2.-, but higher activities of antioxidant enzymes including ascorbate peroxidase (APX), peroxidase (POD), superoxide dismutase (SOD) and catalase (CAT), as well as higher expression levels of SlICE1 and SlCBF1 than control (WT) and 1-MCP-treated fruit. Furthermore, ETH treatment attenuated chilling stress by ensuring a higher adenosine triphosphate (ATP) content, which was accompanied with higher activities of energy metabolism enzyme including H+-ATPase, Ca2+-ATPase, succinic dehydrogenase (SDH) and cytochrome C oxidase (CCO) than control and 1-MCP treatment. Correlation analysis showed that ETH treatment increased the correlation of ATP and SOD (r = 0.91), H+-ATP and POD (r = 0.94), H+-ATP and SOD (r = 0.97), while 1-MCP treatment inhibited their correlation. These findings reveal a new regulatory pathway that ethylene enhances tolerance to chilling stress in tomato fruit partially through the synergistic regulation between antioxidant enzymes and ATP synthases.