Effects of 1-MCP on proline, polyamine, and nitric oxide metabolism in postharvest peach fruit under chilling stress

Peach (Prunus persica Batsch 'Yuhualu') fruit are sensitive to chilling injury (CI). Proline, polyamine (PA), and nitric oxide (NO) are important small regulators of various metabolic pathways under chilling stress that mitigate CI. Ethylene is known to promote senescence and CI, while 1-methylcyclopropene (1-MCP) is an antagonist that inhibits the effects of ethylene. However, how 1-MCP and ethylene affect proline, PA, and NO levels under chilling stress remains unclear. To address these questions, 1-MCP (1 mu L center dot L-1) and ethylene (1 mu L center dot L-1) treatments were applied to peach fruit. Fruit were stored at 4 degrees C for 28 d, then moved to 25 degrees C for 3 d immediately after cold storage. Peach fruit exhibited CI symptoms after 7 d of cold storage with enhanced electrolyte leakage and malondialdehyde contents. The 1-MCP treatment significantly (P < 0.05) restrained peach CI, and fruit did not exhibit CI symptoms until 14 d of cold storage. Proline and PAs in peach under chilling stress were mostly synthesized from glutamate and arginine, which were catalyzed by Delta 1-pyrroline-5-carboxylate synthetase and arginine decarboxylase, respectively. 1-MCP-treated fruit exhibited higher proline and PA contents and enhanced chilling tolerance compared to the control, while ethylene-treated fruit had lower proline and PA contents and reduced chilling tolerance. Ethylene-treated fruit, which exhibited more severe CI symptoms compared to the control, had significantly (P < 0.05) lower NO contents and NO synthase activities. However, NO may not be a direct acting factor in 1-MCP-induced chilling tolerance, as 1-MCP-treated fruit had lower NO contents and NO synthase activities compared to the control. In conclusion, proline and PA clearly played direct and important roles in 1-MCP-induced peach chilling tolerance, while NO may not be actively involved.