Polyamine metabolism and biosynthetic genes expression in tomato (Lycopersicon esculentum Mill.) seedlings during cold acclimation

To elucidate the possible involvement of polyamines (PAs) in the chilling tolerance of tomato, we have investigated the metabolism of PAs, physiological features including levels of compatible solutes (soluble sugar, soluble protein, proline) and the malondialdehyde (MDA) content in the leaves of two tomato cultivar seedlings differing in chilling tolerance during cold acclimation. Putrescine (Put) has been shown to accumulate in leaves of both cultivars but to be higher in cv. Mawa (chilling-tolerant) than in cv. Moneymaker (chilling-sensitive) during cold acclimation. Arginine decarboxylase (ADC) activities increased in both cultivars in response to cold acclimation; however, almost no changes of ornithine decarboxylase (ODC) activities were observed in both cultivars. Furthermore, we found LeADC and LeODC expressions enhanced partly, but the LeADC1 expression did not improve in two cultivars under cold acclimation. Activity levels of diamine oxidase (DAO), polyamine oxidase (PAO), soluble sugar and soluble protein contents were higher in cv. Mawa than those in cv. Moneymaker under cold acclimation. PAs catabolism might influence proline accumulation in tomato leaves under cold acclimation. MDA content did not obviously increase in both cultivars except when the Put accumulation was reduced. Furthermore, we found that the chilling tolerances of tomato seedlings were reduced by exogenous D-arginine (D-Arg) application, but by adding back Put, the chilling tolerances were enhanced. Hence, the results suggest that Put plays an important role in tomato chilling tolerance.