Regulation of cold resistance by the polyamine biosynthetic gene SlSPDS2 via modulating the antioxidant enzyme system and osmotic regulatory substances in Solanum lycopersicum

The essential role of polyamine in cold stress resistance in tomato has been widely studied. However, the involvement of Spermidine synthase (SPDS) in the regulation of cold stress and their relationship with the antioxidant enzyme system and osmotic regulatory substances in tomato are not well characterized. In the current study, we found that cold stress induced the expression of polyamine biosynthetic genes and the accumulation of polyamine. The overexpression of SlSPDS2 (SlSPDS2-OE), a key Spermidine biosynthetic gene, significantly improved seedlings growth and increased seedlings index as well as alleviated the cold stress injury with decreased O2∙−, H2O2 and malondialdehyde contents. In SlSPDS2 overexpression lines, the contents of free polyamine, free salicylic acid, chlorophyll, proline and soluble sugar were increased compared with wild type (WT) under cold stress. The antioxidant enzyme activities and their coding genes expression were increased compared with WT under cold stress. SlSPDS2 silencing seedlings with weakened cold resistance showed oxidative damage and inhibition of growth. These results indicated that SlSPDS2 plays a positive role in tomato cold tolerance by regulating polyamine metabolism, antioxidants, and osmolytes.