| In this paper,‘Black Pearl’ wax apple fruit(Syzygium samarangense Merr.et Perry)were investigated in term of their changes of quality and physiology,cell wall metabolism and lignin metabolism and analysed the relationship of cell wall metabolism and lignin metabolism to the cottony softening of wax apple fruit after nitric oxide(NO)treatments,of which the effects on cottony softening of postharvest wax apple fruit and the possible mechanisms were discussed.The results were as follows:1.In this research,wax apple fruit were fumigated with 0(control group)、5、10、20μl/L NO gas.Cottony softening index,weight loss rate,fruits firmness,cellulose content and lignin content were analysed.The results showed that the cottony softening index increased and the cottony softening process intensified during storage.The weight loss rate increased,while the cellulose content gradually decreased and the lignin content increased.Compared with control group,NO fumigation could inhibit the fruit cottony softening development,delayed the increase of weight loss rate and the decrease of fruit firmness,and reduced effectively the decrease of cellulose content and the rise of content of lignin.We proposed that NO treatments can maintain the quality of postharvest wax apple,and could effectively postpone fruit ripeness and senescence process of postharvest wax apple.Further,10μl/L NO treatment presented the best effect of all the treatments which could significantly maintaining fruit quality during storage.2.Wax apple fruit were fumigated with 10μl/L NO gas to determine the influences of cell wall metabolism.Results showed that the cellulose content decreased,protopectin gradually decreased,while soluble pectin increased during storage.Polygalacturonase(PG)activity and pectin methylesterase(PME)activity were on the rise overall,we proposed that with the interaction of PG and PME,pectin degradated and resulted in the decline of fruit firmness.The β-galactosidase(β-Gal)activity peak appeared in the later period of storage,and we proposed that β-Gal may play an important role in the later softening stage of wax apple.Compared with control group,ntiric oxide treatment significantly inhibited the activities of PG,PME and β-Gal,delayed the degradation of pectin,and maintained the quality of wax apple fruits.Correlation analysis indicated that PG,PME and β-Gal were correlated with protopectin and soluble pectin.It means that PG,PME and β-Galwere directly involved in the disintegration of cell wall.Content of cellulose and content of lignin were significantly correlated with cottony softening index,and the content of protopectin were significantly negatively correlated with cottony softening index,while the content of soluble pectin were significantly positively correlated with cottony softening index.3.Wax apple fruit were fumigated with 10μl/L NO gas to determine the influences of lignin metabolism.Results showed that the lignin content increased overall,phenylalanin ammonialyase(PAL)activity,peroxidase(POD)activity and 4-coumarate: coenzyme A ligase(4-CL)activity were on the rise overall.Compared with control group,NO fumigation reduced effectively the rise of content of lignin,and inhibited the activities of PAL,POD and 4-CL.Correlation analysis indicated that the content of lignin were significantly positively correlated with cottony softening index,and the activities of PAL and 4-CL were significantly positively correlated with lignin content,while POD activity had certain relevance with lignin content.We proposed that lignin metabolism have certain relevance with cottony softening process of wax apple fruit.Nitric oxide treatments delayed lignin metabolism,therefore reduced the process of cottony softening of wax apple fruit.4.Expression of key enzyme genes in lignin metabolism of postharvest wax apple.Results from qRT-PCR showed that the relative gene expression level of PAL,POD and 4-CL increased during storage,and increased rapidly during the later stage of storage.The peak of expression appeared in the end of storage.Compared with control group,NO fumigation decreased the related gene expression of PAL,POD and 4-CL.Correlation analysis indicated that the related gene expression of PAL,POD and 4-CL were significantly correlated with the activities of responded enzymes,and were positively correlated with the lignin content.The expression of 3 genes showed significant correlation with each other which meant they had a closely relationship with lignin metabolism.It is believed that PAL,POD and 4-CL enzyme genes are key genes in lignin biosynthesis,and lignin biosynthesis is affected by the interaction of these genes,rather than the effect of individual genes. |
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