Organic acids metabolism and GABA shunt involved in maintaining quality of Malus domestica by methyl jasmonate treatment.

Apples (cv. Golden Delicious) were used as the materials to investigate methyl jasmonate (MeJA) dipping on quality parameters, organic acids metabolism and GABA shunt during storage at 21 ± 1 °C and 75 ± 5 % relative humidity. Results demonstrated that MeJA treatment reduced mass loss, respiratory intensity and ethylene release, and maintained higher flesh firmness and soluble solid content of apples. MeJA also decreased malic acid content, increased succinic and tartaric acids contents, and inhibited cytoplasmic aconitase (Cyt-ACO), NADP-malate (NADP-ME), phosphoenolpyruvate dehydrogenase (PEPC), mitochondrial citrate synthase (Mit-CS), glutamate dehydrogenase (GAD), and GABA transferase (GABA-T) activities in apples. NADP-isocitrate dehydrogenase (NADP-IDH), mitochondrial cis-aconitase (Mit-ACO), and cytoplasmic NAD-malate dehydrogenase (CytNAD-MDH) activities in apples were also enhanced by MeJA dipping. Moreover, MeJA dipping enhanced MdCytNAD-MDH and MdNADP-IDH expressions, and down-regulated MdGAD, MdGABA-T, MdNADP-ME, MdPEPC, MdCyt-ACO and MdMit-CS expressions in apples. These results suggest that MeJA dipping can maintain storage quality of "Golden Delicious" apples by regulating organic acids metabolism and GABA shunt.

Postharvest melatonin dipping maintains quality of apples by mediating sucrose metabolism.

Senescence is a pivotal factor that causes quality breakdown and economic loss of fruit after harvest. In this study, 'Golden Delicious' apples were used as the materials to investigate the effect of melatonin dipping on quality parameters and sucrose metabolism during room temperature storage. Postharvest melatonin treatment inhibited respiratory intensity and ethylene release, increased flesh firmness, soluble sugar, ascorbic acid, and soluble solid contents, and titratable acid in apples. Furthermore, melatonin treatment inhibited acid invertase and neutral invertase activities, increased sucrose synthase and sucrose phosphate synthase activities, and repressed the activities of sorbitol dehydrogenase, sorbitol oxidase and sucrose synthase cleavage in apple fruit. All these findings suggest that exogenous application of melatonin could maintain quality of 'Golden Delicious' apples by mediating the enzyme activity in sucrose metabolism.