The Molecular Physiological Mechanism Of 1-MCP Regulation On Climacteric Fruit Postharvest Senescence And Flesh Tissue Browning

Climacteric fruits, "HujingmiltT peach [Prunus persica (L.) Batsch cv. 'Hujingmilu'] and "Bruno" kiwifruit (Actinidia delciosa cv. 'Bruno') were used to study the effects of 1-MCP on postharvest fruit softening, ethylene biosynthesis and chilling injury-induced browning, whose regulation mechanism was also investigated in the present experiment. And the obtained results were described as following:1. Lambda genomic DNA library was constructed from young leaves of kiwifruit, and successfully used as template to mine gene Ad-Exp3 coding for Expansins. In ripening peach fruit, Pp-Expl, Pp-Exp3, Pp-ACOl, Pp-PPO and Pp-ETRl was cloned by RT-PCR.2. Under 20℃ storage, LOX activity and 62' production rate increased rapidly at the initiation o f p each fruit s oftening, a nd r cached p eak v alue at72ha nd!20h, respectively. 1-MCP treatment inhibited LOX activity, slowed down O2-production rate, decreased ACS and ACO activities, suppressed ethylene biosynthesis, and thus delayed peach fruit senescence.3. In peach fruit, the mRNA levels of Pp-Expl and Pp-Exp3 accumulated during fruit softening, and could be allevated by 1-MCP treatment. The level of Pp-ACOl mRNA accumulation at 20℃ was relative low and could be enhanced by application of 1-MCP.4. 1 -MCP was applied at three stages of kiwifruit ripening including stage I (initial stage of softening), stage II (early stage of rapid softening) and stage III (middle stage of rapid softening). The results showed that the ability of 1-MCP in suppressing ethylene biosynthesis and delaying climacteric peak faded away with the fruit ripening.5. Peach fruit was transferred into 20℃ after 40 d storage at 0℃, which resulted in increase in relative electric conductivity significantly and led to flesh browning. The positive effects of 1-MCP treatment on fruit quality were not observed at 0℃ until fruit had been shifted to 20℃. 1-MCP treatment led to decrease in LOX activity, O2- accumulation, ethylene production, inhibited relative electric conductivity rise, suppressed PPO activity and declined total phenol content, andthus significantly alleviated flesh tissue browning. Northern blot of Pp-PPO showed that 1-MCP could inhibit Pp-PPO mRNA accumulation, which was consistent with that of the physiological changes. Furthermore, there existed significant positive relationship between flesh browning index and PPO activity (r= 0.9045**), and significant negative relationship between browning index and total phenol content (r= -0.8324**)...