Ethylene Regulation Of Fruit Ripening And Its Related Enzymes Activities And Genes Express In Muskmelon

Muskmelon (Cucumis melo L.var.reticulatus Nand) is a type of thick skin melon and is welcomed by the majority of consumers due to good appearance and unique aroma. However,after fruit harvested, flesh firmness decreased sharply at room temperature, that resulted in losses of nutrition composition and marketable goods rapidly,becames the key of effecting shipping, storage and shelf life for muskmelon fruit.The melon variety ’Xiangmier’ was used in this experiment, fruits were harvested 43 days after pollination (DAP). Experimental treatments are as the followings:1. fruits sprayed with 200 mg. L-1 AVG (ethylene synthesis inhibitor) and 100mg.L-1 at 35 DAP, respectively; 2. fruits fumigated with 1 mg.L-1 1-MCP (ethylene action inhibitor) for 24 hours at room temperature; 3. fruits soaked with 2000 mg/L ethephon for 10 min; 4. untreated fruit as the control (CK); The above treated fruits were storied at 22℃ to 24℃ and 80～85% RH; 5. untreated fruit was storied at 10 ± 2℃. The characteristics of fruits were determined, including flesh firmness, respiration rate, ethylene production, ethylene synthesis and cell wall metabolism related enzyme activities and its gene expression. The regulation mechanism of ethylene factors (1-MCP、AVG) and low temperature on fruit softening was discussed during muskmelon ripening, in order to guide of the postharvest handling for melon. The main findings are as follows:1. The flesh firmness of melon decreased gradually at room temperature during ripening. Changes of firmness can be divided into two stages:sharp softening at early 9 days storage, subsequently slow softening. AVG and 1-MCP treatments can significantly retard the decreasing in flesh firmness,it was no significant difference between the two treatment of AVG The firmness of fruit treated were in the order of AVG>1-MCP>CK>ethephon. Low temperature could significantly inhibit the decreasing of flesh firmness.2. The content of total soluble solid (TSS) and ripening index in fruit ripening gradually declined at room temperature, the titratable acid (TA) contents had little change, TA decreasing of fruits stored at low temperature was retarded,ethylene treatment increased TSS content and declined ripening index of fruits in the early storage; H* values of epicarp of fruits treated had no significant difference,however,after 14 days storage, H* values of epicarp by AVG,1-MCP and low temperature, respectively, were higher than that of epicarp by ethylene and control, the green in pericarp could be kept better.3. Comparied with control, AVG treatment can significantly inhibite respiration rate and ethylene production during early 9 days storage, the inhibitor effect of fruits with AVG of 100 mg.L-1 was superior to 200 mg.L-1.1-MCP can significantly inhibit increasing of respiration intensity,ethylene production in early storage. The fruits treated by ethephon had no significant difference with control fruit. The low tempetature can significantly inhibite the respiration and ethylene production in fruits ripening.4. During fruits ripening at room temperature, the ACC content and ACO enzyme activity increased gradually, while the enzyme activity of ACS declined slowly, the genes express of Cm-ACO1and Cm-ACS1 were up-regulated strongly,so was Cm-ACS2 only from 7 days to 9 days storage. AVG and low temperature treatment significantly inhibited the accumulation of ACC and the ethylene production, suppressed increasing of ACS and ACO activity, gene expression of Cm-ACS1 and Cm-ACO1,while gene express of Cm-ACS2 was up-reguled.1-MCP treatment reduced the gene expression of Cm-ACS1 and Cm-ACOl in the early storage of fruits,but the enzyme activities of ACS and ACO in fruits treated by 1-MCP was higher than that of the control fruit. It was not significant difference between ethephon treatment with control fruits in gene expression of Cm-ACS1 and enzyme activity of ACS.5. In earlier storage (from 4 to 9 days) at room temperature, the receptor genes of Cm-ETR1 and Cm-ERS1 were up-regulated expression strongly in control fruits, while there were down-regulated expression of fruits among other treatments, after 11 days’storage, Cm-ETR1 and Cm-ERS1 gene expression of fruits with AVG and 1-MCP treatments were recovered. There were the same tendency between fruits treated by ethephon and control in receptor expression of Cm-ETRl and Cm-ERS1. Low temperature promoted down-regulated expression of Cm-ETR1 and Cm-ERS1 in fruits.6. In the early 9 days’storage at room temperature, AVG treatment strongly inhibited genes express of Cm-PGl,decreased enzyme activities of PG and Cx, while enzyme activities of PG in fruits treated by 1-MCP was more than that in control fruits, The enzyme activities of PG in fruits treated by ethephon was highter than that in control fruits, subsequntly up-regulated express of Cm-PG1 was restored. Ethephon treatment significantly enhanced the increasing of Cx activity in the early 9 days storage, while low temperature inhibited increasing of Cx enzyme activities.