Active Oxygen And Cell Wall Metabolism In Aril Of Longan Fruit Inoculated With Lasiodiplodia Theobromae (pat.) Griff. & Maubl

Longan (Dimocarpus longan Lour.) is a famous subtropical fruit species in the South of China. It's rich in nutritional value, medicinal value and health value. Since longan fruit mature during the hot and humid August/September in China, the fruit deteriorate rapidly after harvest due to pericarp browning, aril breakdown and decay, the fruit have a very short postharvest life of a week at ambient temperature. This short postharvest period limits its long-distance transportation, marketing and consumption. One of the main reasons that the longan fruit deteriorate rapidly is aril breakdown. Aril breakdown seriously affect the eating quality and commodity value. The study of the relationship between aril breakdown and post-harvest disease are rarely reported. The dominant factor lead to aril breakdown of postharvest longan fruit has not yet verdicted.The black-rotten disease caused by Lasiodiplodia theobromae (Pat.) Griff. &Maubl is the main disease of postharvest longan fruit in Fujian Province of China. The materials of this experiment were fruits of longan (Dimocarpus longan Lour. cv. Lidongben), which were inoculated with Lasiodiplodia theobromae (Pat.)Griff. &Maubl. In this experiment, we researched the changes of active oxygen species and cell wall metabolism in aril of longan inoculated with Lasiodiplodia theobromae (Pat.) Griff. &Maubl.. The possible mechanism on aril breakdown of postharvest longan fruit after pathogen infection was also hypothesized. The results were as follows:1. Aril breakdown of longan fruit after inoculation with Lasiodiplodia theobromae (Pat.)Griff. &Maubl. was extremely serious compared with the controlled longan. Aril breakdown rate accelerated obviously and aril breakdown index was remarkable higher (P<0.01) than the controlled longan.2. The changes of active oxygen species metabolism in aril of longan inoculated with Lasiodiplodia theobromae (Pat.) Griff. &Maubl. are remarkable different from the controlled longan. After inoculation with Lasiodiplodia theobromae (Pat.) Griff. &Maubl., productive rate of O₂^-· increased at first and then decreased, SOD and LOX activity enhanced sharply, CAT activity decreased gradually, APX activity and contents of endogenous antioxidant substances (AsA, GSH) increased at first and then decreased gradually during storage, however, these phenomena didn't happened at the controlled longan. From the results it can be seen that pathogen infection destroyed the system of reactive-oxygen-scavenging enzymes. AsA,GSH were consumed quickly, the content of hydrogen peroxide increased, productive rate of superoxide radical anion enhanced., membrane systems were damaged and membrane permeability increased. So the progress of aril breakdown was accelerated. It shows that pathogen infection is the dominant factor that lead to aril breakdown of postharvest longan fruit.3. The changes of cell wall metabolism and the activities of their hydrolases in aril of longan inoculated with Lasiodiplodia theobromae (Pat.) Griff. &Maubl. are remarkable different from the controlled longan. The content of cell wall components in longan after inoculation with Lasiodiplodia theobromae Pat. increased at first and then decreased gradually during storage, however, these phenomena didn't happened at the controlled longan. The activities of hydrolases in longan after inoculation with Lasiodiplodia theobromae Pat. increased continuously during the early storage, and its increased rate was significantly higher than the controlled longan. From the results it can be seen that pathogen infection stimulates the activity of hydrolases. So the structure of longan fruit was damaged and the cell wall components deteriorate fast. Ultimately it lead to the flesh juice outflows until corruption, and accelerate the progress of aril breakdown.