Role Of PDC And ADH In Accumulation Of Aldehyde And Ethanol In Postharvest Citrus Fruits

Citrus is one of the most important daily fruits in China,and storage is often used to prolong the shelf life of citrus.However,flavor deterioration occurs citrus during storage.Accumulate of acetaldehyde and ethanol seriously reduces the nutritional value of Citrus,which lead to negative impact on consumer experience.Therefore,the differences of acetaldehyde and ethanol accumulation in various citrus species and the effects of temperature and wax were studied.The main results are described as follows:1.Due to the low accuracy of ultraviolet and nitroblue tetrazolium method,we developed a MBTH(3-methyl-2-benzothiazole hydrazine)based colorimetric assay for measuring alcohol dehydrogenase(ADH)activity.By terminating the enzyme reaction with HC1,MBTH method could be used for batch determination and is superior to UV and NBT methods in sensitivity and accuracy.2.Fourteen ADH and two PDC(pyruvate decarboxylase)members were identified from published citrus genome data.Then based on two orange pulp transcriptome data,6 ADH and 2 PDC members with strong expression in pulp were identified.3.The study involved in differences of acetaldehyde and ethanol accumulation in various citrus species were carried out with 16 cultivars,including 7 mandarin cultivars,5 sweet orange cultivars,1 hybrids cultivar and 3 pomelo cultivars.It found that the content of acetaldehyde and ethanol in different citrus species were different,which could be 20.8 times and 61.1 times at harvest.For most citrus,the content of acetaldehyde and ethanol increased during storage,such as(Ponkan',the content of acetaldehyde and ethanol was 8.8 and 48.7 times higher than that in 0 d after 60 d storage,but 'Bingtangcheng' and 'Yuhuanyou' did not change a lot(the increase range was not more than 1 fold or even decreased).The difference of ADH activity among varieties was as high as 201.5 times(at harvest),and most of them tended to increase during storage(except 6Guangcheng').The expression of ADH1 increased during storage in most citrus,while the expression of ADH2 and ADH3 increased only after 60 d storage in individual citrus.PDC activity was also different among varieties,the different of which could be as high as 6.7 times during harvest,but did not change much during storage.The expression of PDC1 and PDC2 in different citrus species and during storage also chaneed slightly,mostly less than 1 fold.The correlation analysis of acetaldehyde and ethanol content.ADH and PDC enzyme activity.expression of ADH and PDC genes showed that the enzyme activity and expression of PDC were closely related to acetaldehyde and ethanol accumulation,while ADH enzyme activity is weakly related to that,suggesting that PDC might be a limiting factor in regulating acetaldehyde and ethanol accumulation in citrus fruit after harvest.4.For the further study the role of ADH and PDC in the accumulation of acetaldehyde and ethanol,we compared the effects of different temperatures and wax coating.The results showed that the content of acetaldehyde and ethanol at 5?increased slowly at the beginning of storage,and was always lower than that of Ponkan citrus stored at 15?.However,ethanol increased to close to that at 15? after 90 d.while the acetaldehyde was higher.Besides,the expression of ADH and PDC was higher than that at 15?.,but the activity of ADH and PDC enzyme was slightly lower.As for Ponkan,the correlation between ADH activity and acetaldehyde content was more than 0.9.Acetaldehyde and ethanol accumulated in Ponkon fruits after waxing treatment,which was higher than the control at the later stage,accompanied by higher ADH and PDC activity and gene expression than the control.The activities of ADH and PDC enzyme were highly correlated with the content of acetaldehyde and ethanol,respectively.