Study On Mechanism Of Meja Treatment On Chilling Injury And Disease Of Loquat After Harvest

Loquat is a subtropical fruit of high commercial value on the international market. But they generally have a short shelf life because they are susceptible to microbial decay, mechanical damage, moisture and nutritional losses. Low temperature storage is commonly used to inhibit decay incidence and extend loquat storage periods, but it increases the severity of flesh leatheriness. Therefore, it is crucial to study the regulation and mechanism of quality deterioration of loquat fruit after harvest for transportation and storage. It has been reported that treatment with10μmol/L MeJA can extend the shelf life of loquat fruit for markedly reducing chilling injury and inhibited anthracnose rot of loquat fruit. In this paper, loquat fruit of Jiefangzhong were also treated with10μmol/L MeJA. Then the possible mechanisms of MeJA treatment on chilling injury and disease of loquat fruit after harvest were investigated from AsA and GSH metabolism, proline and GABA metabolism and PAs and energy stastus, expecting to give theoretical bases for the application of MeJA on loquat fruit. The results were as follows:1. AsA and GSH contents and change of some related enzymes in loquat fruit treated with MeJA were investigated. The results showed that during the chilling development manifested as firmness, extractable juice and internal browning index of cold-stored loquat fruit, the levels of AsA reduced and GSH decreased, accompanying with the accumulation of DHA and GSSG. Application of MeJA to loquat fruit inhibited the development of chilling injury and increased AsA and GSH contents due to the inhibition of AO activity and enhancement of MDHAR, DHAR and GR activities. Meanwhile, MeJA also enhanced activities of APX, GSH-POD and GST. Our results suggested that MeJA can regulate the ascorbate and glutathione metabolism and has important roles in alleviating oxidative damage and enhancing chilling tolerance in loquat fruit.2. The effect of MeJA treatment on the contents of proline and GABA and change of some related enzymes in loquat fruit was investigated. The control fruit exhibited severe flesh leatheriness, the specific CI symptom in loquat fruit, after21days of storage at1℃, which was reduced in MeJA-treated fruit. During the development of CI in loquat fruit, proline and GAB A accumulated with the storage time, MeJA treatment markedly enhanced the increases in proline and GABA contents. Meanwhile, the MeJA-treated fruit exhibited significantly higher activities of P5CS, OAT and GAD, and lower activity in PDH than control during the storage, which resulted in the higher contents of proline and GABA in those fruit. These results suggest that the reduction in CI in loquat fruit by MeJA may be due to the increased proline and GABA contents.3. The effect of MeJA on change of polyamines content and energy status and their relation to disease resistance were studied. Treatment of loquat fruit with MeJA resulted in significantly lower disease incidence rate and smaller lesion diameter compared with the control fruit. The treated fruit manifested higher content of polyamines such as Put, Spd and Spm than control during storage, which can be oxidised to yield H2O2. Meanwhile, MeJA treatment maintained higher level of ATP, but inhibited the increase in AMP content in loquat fruit. MeJA treatment could effectively inhibit anthracnose rot by increasing polyamines contents and maintaining energy status.