Putrescine Improves the Resistance of Peach Fruit to Cold Stress via Elevating the Polyamines Conjugated to Plasma Membranes and Maintaining Membrane Conformation.

Exogenous polyamines can enhance postharvest fruit cold resistance and alleviate cold injury. However, the mechanism underlying polyamine-mediated cold resistance remains to be eluciated. Therefore, in this research, polyamines conjugated to plasma membrane (PLM) and membrane conformation were detected in the putrescine pretreated peach fruits under cold condition. The results showed that cold stress resulted in the changes in the PLM conformation and cause the cold injury as judged by the increased plasma membrane permeability and the decreased sulphydryl content. Pretreatment with putrescine mitigated the cold injury of the fruits and resulted in the stabilization of PLM, coupled with the increased contents of non-covalently (NC)-conjugated spermidine (Spd) and spermine (Spm), and covalently-conjugated (C) putrescine (Put) and Spd in PLM. From the results, it could be inferred that polyamines conjugated to PLM and membrane conformation stabilization might be involved in the putrescine-mediated resistance of the harvested peach fruits to cold stress. This inference was confirmed by the complementary experiments with methylglyoxal-bis(guanylhydrazone) (MGBG) and phenanthroline, which inhibited S-adenosylmethionine decarboxylase and transglutaminase activities, respectively. MGBG restrained the putrescine-induced increases in NC-conjugated Spd and Spm and phenanthroline declined the increases in C-conjugated putrescine in PLM induced by exogenous putrescine. Furthermore, both MGBG and phenanthroline reversed the mitigation effects of putrescine on fruit cold injury, in parallel with the decrease of membrane conformation stabilization. Collectively, we could conclude that putrescine-mediated fruit cold resistance involved in the increases in the polyamines conjugated to PLM and the maintenance of membrane conformation. The relationship between the conjugated polyamines and membrane conformation stabilization was discussed in the research. [ABSTRACT FROM AUTHOR]