| Summary: | 碩士 === 國立臺灣大學 === 園藝學研究所 === 99 === ‘Jen-Ju Bar’guava (Psidium guajava L.) is an important economical fruit crop in Taiwan. In order to expand the overseas market, both quarantine treatment (14 days at 0℃) and long-term transportation have been associated with low temperature storage for guava fruits. However, since guava fruit is a chilling-sensitive produce, low temperature storage often causes chilling injury (CI) symptoms, such as browning and pitting, on guava fruits, reducing the quality and marketability. To reduce the development of CI symptoms, methyl jasmonate (MeJA) has been utilized in the form of fumigation. But the fumigation treatment of MeJA demands an airtight space and long period of time (16 hours), which is time-consuming and hence decreasing the practicability of this method. Therefore, the objective of this study is to develop an effective treatment to reduce the CI by using MeJA and jasmonic acid (JA) for both immersion and pressure infiltration. For immersion treatment, fruits were first dipped in solution of 0.05~1 mM MeJA and 0.05~0.2 mM JA , and then stored at 0℃ for 14 days followed by 3 days at 20℃. CI index, electrolyte leakage and maximum quantum efficiency of PSII photochemistry (Fv / Fm) were used to estimate the level of CI. Result showed that, the CI index of treatment with 0.1 mM JA for 10 minutes was 2.5, which is significantly lower than that of control group, 3.5. And the percentage of electrolyte leakage of treated group is 42%, while that of control group is 55%. Furthermore, JA treatment delayed the decrease in the Fv / Fm value guava fruits. In contrast, the treatment of 0.05~1 mM MeJA showed no effect on CI development. For pressure infiltration treatment, fruit were pressure infiltrated at 400、500、600、650、700 mmHg for 1 or 5 min in 0.1 mM JA or MeJA solution. However, comparing with control fruits, all fruits showed serious CI symptoms after pressure infiltration treatment. To study the mechanism of JA on reducing the CI of guava fruits, the enzyme activity of catalase, superoxide dismutase, and glutathione reductase were analyzed. Results showed that the activity of catalase decreased during storage, while the activity of superoxide dismutase, glutathione reductase, and AsA in treated fruits were significantly higher than control group at the 14th day of storage and under 20℃. And the DPPH percentage of treated fruits increased during the later stage of storage. It could be inferred that JA alleviate CI symptoms on guava fruits possibly via increasing the antioxidant system and the ability of scavenging reactive oxygen species (ROS) therefore reducing the oxidative stress.
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