Cell Wall Metabolism And Its Regulation In Harvested Melon Fruit During Ripening

Melon(Cucumis melo L.)is an important horticultural crops.Oriental melon has short growing season and thinner peel.It was harvested in the hot season.Owing to its sharp physiological metabolism and flesh softening quickly,which leaded to decrease the quality of nutrition and goods rapidly after postharvest at room temperature,and limited the transportation and storage and shelf life.The melon variety‘Cuili’was used in this experiment.After 40 days after pollination(DAP),fruits were harvested.Experimental treatments are as the followings: 1.fruits sprayed with 130 μl/ L AVG(ethylene synthesis inhibitor)21 DAP;2.fruits fumigated with 1 μl/ L 1-MCP(ethylene action inhibitor)for 24 hours on the day of harvest;3.fruits treated with 10 μl / L ethylene for 24 h;4.untreated fruit as a control.The fruits were storied at room temperature(24 ℃~29 ℃)and 5 ± 2 ℃ respectively.The characteristics of fruit were determined,including flesh firmness,ethylene production,cell wall polysaccharide and their metabolism-related enzymes during melon storage.We studied ethylene factors(1-MCP、AVG)and low temperature,which can affect melon fruit softening and cell wall polysaccharide metabolism and its regulation mechanism,and in order to provide a theoretical basis for the guidance of postharvest handling of melon fruit.The main findings are as follows:1.Melon flesh firmness decreased gradually in the ripening process.Changes of firmness at room temperature can be divided into two stages,rapid softened in eight days after treatment,and then slowed down.AVG and 1-MCP treatments can significantly retard the decline in flesh firmness,effect of 1-MCP was better than that of AVG in early storage(8d).Ethylene and untreated fruit firmness were not significantly different.Low temperature could significantly inhibit the decreasing of flesh firmness.2.Ethylene production of melon fruit slowly increased in early storage at room temperature,and than rapidly declined.AVG and 1-MCP treatments can significantly inhibit ethylene production,and delay ripening process.Exogenous ethylene accelerated ethylene production of melon fruits.3.Melon CWM decreased gradually during storage at room temperature,and its contents significantly inhibited decreasing by AVG and 1-MCP treatments,and increased by ethylene at room temperature.The degradation of fruit CWM was delayed by low temperature storage.Fruit CWM contents of 1-MCP in normal temperature were higher than that of the control in low temperature.1-MCP treatment replaced some role of low-temperature.Melon fruit CWM contents were more conducive to keeping by low-temperature storage.Fruit cellulose contents had similar trends with CWM during storage.4.The water-soluble pectin(WSP)contents of melon increased during storage.The addition of fruit WSP contents was significantly delayed during early storage(14 d)by AVG,1-MCP,and low temperature.Ethylene treatment accelerated the contents of fruit WSP increasing during later storage.It had little difference between each treatment during later storage.5.Covalent pectin of melon fruit rose in the initial storage(14 d),and than declined.Fruit CSP was beneficial to keeping by AVG and 1-MCP treatments during early storage,and it was little effect during later storage.It had little difference between ethylene and control treatments.The addition of fruit CSP contents was delayed during low temperature storage.1-MCP treatment could replace low temperature during short-term storage.The closely integrated hemi-cellulose contents of melon fruit had similar trends with CSP during storage.6.Melon ionic pectin showed a trend that was up early,mid-fall,and later rising between different treatments.AVG and 1-MCP treatments could significantly inhibit the addition of melon ISP during normal temperature storage.It had no significant difference between ethylene treatment and control.It was gently growth in melon ISP contents during low temperature storage,and the rise of fruit ISP was inhibited by 1-MCP treatment.7.The contents of loose hemi-cellulose changed gently between each treatment at room temperature.The degradation of fruit loose hemi-cellulose was inhibited by AVG and 1-MCP treatments during early storage(8 d).It was little difference between ethylene treatment and control.The contents of loose hemicelluloses in melon had similar changes during storage at low and normal temperature.It was significantly inhibited the reduction of loose hemi-cellulose by low temperature storage.8.PG activity was decreased and PME activity was enhanced during early storage,reached the peak(14 days after treatment)and then decreased.β-gal activity and PME enzymes had similar trends during storage at room temperature.It was significantly retarded increasing of β-gal,PME and PG activity,and delayed fruit softening after ripening by AVG,1-MCP and low temperature.Ethylene treatment and control were no significant difference.The quality of fruits treated with 1-MCP in cold storage was optimum.9.Analysis of correlation showed that firmness had closely related to ethylene production,water soluble pectin and cellulose content.Temperature is the key factor in the degradation of fruit cell wall components.AVG treatment significantly suppressed fruit ethylene production,and inhibited the degradation of cell wall components.Ethylene-related regulating factors(AVG,1-MCP,and low temperature)inhibited fruit ethylene production,prevented the degradation of cellulose,and delayed the hydrolysis of cell wall components and fruit softening.PG enzyme activity in melon had an important relationship to ethylene production,cell wall components and fruit softening caused by structural changes,while PME and β-Gal enzymes activity may play a role in different stages of fruit softening.