Effects of hot air and methyl jasmonate treatment on the metabolism of soluble sugars in peach fruit during cold storage

Soluble sugar metabolism affects the quality and chilling resistance of postharvest peach fruit. Although hot air (HA) and methyl jasmonate (MeJA) treatments are often effective in reducing chilling injury (CI), little is known about the relationship between sugar metabolism and HA or MeJA treatments in peach fruit. In this study, peach fruit was treated with hot air at 37 °C for 3 days or MeJA vapor at 10 μmol/L for 24 h before storage at 5 °C. Soluble sugar content, gene expression and enzyme activities associated with sugar metabolism were measured. Both treatments resulted in an initial increase, then a decrease in sucrose content over the course of storage time. Sucrose levels at every time point, but one, throughout the experiment were significantly higher than in control fruit, paralleled by higher gene expression and activity of SPS (sucrose phosphate synthase) and lower expression and activity of AI (acid invertase). HA-treated fruit had the highest sucrose content at the end of storage and the mildest CI symptoms. All treated fruit had higher sorbitol content and lower levels of SDH (sorbitol dehydrogenase) gene expression than control fruit. After 21 days in cold storage, sucrose content had decreased sharply in the control group, hexose content was not markedly affected, perhaps due to the increased expression of PFK (phosphofructokinase), resulting in more glucose entering the Embden–Meyerhof–Parnas pathway (EMP). These results suggest that the increase in sucrose observed during cold storage, associated with higher SPS and lower AI levels, enhances the chilling tolerance observed in HA- and MeJA-treated fruit.