Retardation of postharvest softening of blueberry fruit by methyl jasmonate is correlated with altered cell wall modification and energy metabolism

The effects of methyl jasmonate (MeJA) on fruit firmness, cell wall modification and energy metabolism on postharvest blueberry were investigated. Results showed that MeJA delayed softening of blueberry. Compared with the control, MeJA-treated fruit exhibited higher levels of chelate-soluble pectin, sodium carbonate-soluble pectin, hemicellulose and cellulose and lower level of water-soluble pectin. Moreover, the activity and transcript level of cell wall degrading enzymes were markedly inhibited by MeJA treatment, including carboxymethyl cellulase, polygalacturonase, pectin methylesterase and β-galactosidase. Levels of adenosine triphosphate, adenosine diphosphate and energy charge in MeJA-treated fruit were significantly higher than those in control fruit. Activities and expression levels of the enzymes involved in energy metabolism, including H+-adenosine triphosphatase, Ca2+-adenosine triphosphatase, cytochrome C oxidase and succinic dehydrogenase, were elevated in MeJA-treated blueberry. These results suggest that MeJA delays the softening of postharvest blueberry by restraining the degradation of cell wall materials and maintaining energy metabolism.