Polyamines (PAs) are related closely with many abiotic stresses. However, conjugated PA functions are not clear in alleviating chilling injury in fruit. The contents of free PAs in plum flesh cell and conjugated PAs in plasma membrane (PM), the activities of S-adenosylmethionine decarboxylase (SAMDC) and transglutaminase (TGase), and the degree of chilling injury were investigated in harvested plum (Prunus salicina L.) fruit pre-treated with exogenous melatonin. Chilling treatment resulted in the injury of plasma membrane (PM), as judged by the increased PM permeability, chilling injury index and malondialdehyde (MDA) content, and the decreased sulfhydryl group contents. Exogenous melatonin alleviated chilling injury, in parallel with the increased levels of free spermidine (Spd) and spermine (Spm) in cell, conjugated non-covalently (CNC) Spd and Spm, and conjugated covalently (CC) Put and Spd in PM, resulting from the increased activities of SAMDC and TGase. The results of the additional experiments with two inhibitors, methylglyoxyl-bis (guanylhydrazone) (MGBG) and phenanthrolin, which inhibit the activities of SAMDC and TGase, respectively, were complementary evidences for our research. MGBG and TGase treatment decreased the level of CNC PAs (Spd and Spm) and CC PAs (Put and Spd), respectively, coupled with aggravating the chilling injury. From these above mentioned-results, it could be suggested that exogenous melatonin alleviated chilling injury by elevating the levels of CNC Spd, CNC Spm, CC Put and CC Spd in PM.

多胺（PAs）与许多非生物胁迫密切相关。然而，共轭的PA功能在减轻水果的冷害方面尚不清楚。研究了李子（Prunus salicina）中李肉细胞中游离PA的含量以及质膜（PM）中结合的PA的含量，S-腺苷甲硫氨酸脱羧酶（SAMDC）和转谷氨酰胺酶（TGase）的活性以及冷害程度。L.）用外源褪黑素预处理的水果。冷藏处理导致质膜（PM）的损伤，这可以通过PM渗透性的提高，冷害指数和丙二醛（MDA）含量的降低以及巯基基团含量的降低来判断。外源性褪黑激素减轻了冷害，同时细胞中的游离亚精胺（Spd）和亚精胺（Spm）含量增加，非共价（CNC）Spd和Spm共轭，共价（CC）Put和Spd共轭于PM，从SAMDC和TGase的活动增加。两种抑制剂分别抑制SAMDC和TGase活性的另外两种抑制剂分别为甲基乙醛双（胍基hydr）（MGBG）和菲咯啉的实验结果是本研究的补充证据。MGBG和TGase处理分别降低了CNC PA（Spd和Spm）和CC PA（Put和Spd）的水平，并加重了冷害。根据上述结果，可以认为外源性褪黑激素可通过提高PM中CNC Spd，CNC Spm，CC Put和CC Spd的含量减轻冷害。