Effects Of Intermittent Warming And Exogenous Ethylene On The Postharvest Quality And Expression Of Ethylene Related Genes In Citrus Fruit

Loose skin mandarin is one of the most widely-cultivated citrus types in China. However, mandarins are very susceptible to storage conditions, which cause serious economic losses during postharvest storage. Citrus is non-climacteric fruit, to date, the regulation role of ethylene during fruit ripening is poorly understood. In the present study, the effect of intermittent warming treatment on fruit quality, and the expression of ethylene related genes in the mature fruit of’Guoqing No.1’(Citrus unshiu Marc) and’Egan No.1’(C. reticulata Blanco) were investigated. Meanwhile, the role of exogenous ethylene in citrus fruit degreening was analyzed at breaking stage of ’Guoqing No.1’(C. unshiu Marc),’Egan No.1’(C. reticulata Blanco) and ’Newhall’ navel orange (C. sinensis L. Osbeck) fruit. Changes of peel color, pigment and expression of ethylene related genes in the peel of fruit were examined. The results could help us get more knowledge on the postharvest application of intermittent warming and ethylene degreening treatment in citrus fruit. The main results were as follows:1. The results of soluble sugars and acids analyses by gas chromatography (GC) showed that, under intermittent warming treatment, contents of citric acid decreased in the pulp of’Guoqing No.1’, while no such changes were observed in’Egan No.1’. The contents of fructose, glucose and sucrose in the pulp of’Guoqing No.1’ and sucrose in’Egan No.l’were slightly increased. These results suggested that intermittent warming treatment slowed down citric acid metabolism in the pulp of ’Egan No.1’but accelerated soluble sugars accumulation in the pulp of’Guoqing No.1’.2. GC analysis revealed that ethylene production in’Guoqing No.1’ fruit under cold and intermittent warming storage was lower than that stored at 20℃. For’Egan No.1’, change in ethylene production was slower during intermittent warming storage than that stored at 6℃and 20℃. Therefore, intermittent warming inhibited ethylene production in’Guoqing No.1’.3. Real time RT-PCR analysis of ethylene related genes revealed that ACS gene showed high mRNA level in’Guoqing No.1’and’Egan No.1’fruit stored at 4℃, which suggested that ACS gene could be induced by low temperature.4. Fruit skin color was determined using a reflectance chroma meter. Exogenous ethylene treatment remarkably enhanced peel color adding rate and intensity in fruit of’Egan No.1’,’Guoqing No.1’and’Newhall’navel orange. Moreover, exogenous ethylene was more effective on the degreening in’Egan No.1’than that in’Guoqing No.l’and’Newhall’.5. The ultraviolet spectrophotometer analysis indicated that ethylene treatment accelerated carotenoid accumulation and the degradation of chlorophyll in peel of ’Egan No.1’,’Guoqing No.1’and’Newhall’, suggested that exogenous ethylene on the peel degreening was related to carotenoid synthesis and chlorophyll degradation. The changes in pigment suggested that mandarins were more sensitive to exogenous ethylene treatment than that in oranges, which might be caused by the thick and compact peel of oranges, preventing the osmosis of exogenous ethylene.6. GC analysis revealed that exogenous ethylene stimulated the production of endogenous ethylene in’Egan No.1’,’Guoqing No.1’and’Newhall’navel orange fruit, indicating that exogenous ethylene accelerated endogenous ethylene production at the breaking stage of citrus fruit.7. Real time RT-PCR analysis results showed that the gene expression of ACS, ACO and EIN3 f-box were higher in the peel of ethylene-treated fruit than that in control, suggesting that ethylene treatment induced ethylene-related genes expression, directly increasing ethylene production at the breaking stage of citrus fruit.