Regulation of nitric oxide on lipoxygenase in peach fruit during cold storage

Nitric oxide (NO) has become a new messenger in plant biology with an important role in a plethora of physiological processes. In order to investigate the regulation of NO on the lipoxygenase (LOX) in 'Feicheng' peach fruit during cold storage, peaches at physiological maturity were treated with 5, 15 and 30 μmol L^‑1 NO solution, respectively. The activity of LOX in peach fruit was inhibited by NO during cold storage, especially at 15 μmol L^‑1 NO. The expression level of PpLOX family genes in fruit decreased during cold storage. The expression of PpLOX1, PpLOX2 and PpLOX3 was first promoted and then inhibited over a week by NO; by contrast, the gene expression of PpLOX4 was inhibited and then promoted over two weeks by NO. The effects of 15 μmol L^‑1 NO was more obvious than those of 5 and 30 μmol L^‑1 NO. Isobaric tags for relative and absolute quantitation (iTRAQ) technology was used to analyze LOX protein in peaches. Compared with control, the protein contents of LOX-1, LOX-3 and LOX-4 were downregulated by NO during cold storage, while LOX-2 was upregulated. Density functional theory (DFT) B3LYP method was used to simulate the interaction between NO concentration and LOX protein. The results showed that NO could bind to the active site of LOX protein via hydrogen bonding, and tended to undergo S-nitrosylation reaction. It can be concluded that NO can control the activity of LOX by regulating the gene expression of PpLOX in peach fruit, and then affect the storage quality of peach fruit.