Effect of putrescine application on maintenance of zucchini fruit quality during cold storage: Contribution of GABA shunt and other related nitrogen metabolites

• Putrescine treatment improves the response to low temperature of zucchini fruit.
• The GABA shunt participates in the adaptation of zucchini fruit to cold storage.
• Putrescine treatment increases the energy of zucchini fruit in chilling.
• Betaine and proline accumulation improve adaptation to chilling.

Polyamine metabolism has been suggested to be a crucial factor in the response of plants to several abiotic stresses, including low temperature. Zucchini fruit is susceptible to develop chilling injury when stored at low temperature. In this study, the effects of putrescine, spermidine and spermine treatment (1 mM) on the physiological behavior of zucchini fruit during cold storage were investigated, focusing on the changes in polyamine metabolism and in alterations of polyamine-related nitrogen metabolites and hormones. Among the polyamines used, exogenous application of putrescine was found to be the best treatment to improve postharvest cold tolerance. Treated fruit were of better quality, and in general after cold storage they showed reduced weight loss, chilling injury, and malondialdehyde and hydrogen peroxide contents. Putrescine treatment induced betaine and proline accumulation, fatty acid desaturase expression, and also changes in the biochemical GABA shunt pathway during cold storage. These responses may contribute to increased energy production in fruit treated with putrescine. In general, the putrescine treatment induced different pathways that are considered stress defense mechanisms, and we hypothesize that they could contribute to improve postharvest quality of zucchini fruit after storage at 4 °C.