Volatile Profile Changes In Mangshanyegan Fruits At Different Development Stages And Juice Sacs Of Citrus Fruits Treated With ABA

Mangshanyegan(Citrus nobilis Lauriro)is a characteristic citrus germplasm resource native to China with its fruit covered with abundant fruit frost and emitting a unique aromatic odor.Its special aroma can be transmitted to the juice sacs of commercial varieties through pollination,thus,make it an ideal material in improving the aromatic quality of citrus fruits.In the study,changes of volatile profile in the peel of Mangshanyegan fruits at five different developmental stages were determined;furthermore,the effects of treatment with 100 ?mol/L ABA on volatile profiles in juice sacs of six citurs varieties,such as Huanong red pummelo(C.maxima cv.Huanong red pummelo)and Guoqing No.1 satsuma mandarin(Citrus unshiu cv.Guoqing No.1),were examined.The main results are as follows:1.The total content of volatile in the Mangshanyegan fruits gradually increased along with the fruit expansion,and decreased at color turning period,but increase again at maturity.The three monoterpenes with the highest content accounted for 90% of the total volatile content.Among them,the content of monoterpenoid showed an increasing tendency druing fruit expansion while decreasing along with fruit maturation.However,the contents of sesquiterpenoids were gradually decreased during early fruit expansion while increas along with the fruit maturation.2.In Huanong Red pummelo juice sacs and seeds in 2017,it was found that no difference between ACC and ABA in pollinated and open pollinated seeds and juice sacs.The content of IAA in open pollinated Huanonghong Red pummelo seeds was significantly higher than that of pollinated ones,while IAA-Ala was below the detection limit and was not significantly different from pollinated seeds.It may be inferred that the Xenia effect of Mangshanyegan endowed the special aroma to Huanong red pummelo partially as the result of the changing of endogenous hormones content.Corespondingly,transcriptomic analysis revealed that two key genes PYL and AGH(PP2C)in the ABA signaling pathway were significantly up-regulated in the juice sacs of mature fruits of Huanong red pummelo pollinated with Mangshanyegan.It implied the xenia effect of Mangshanyegan partially acts through the function of ABA signalling.3.The volatile profiles in the juice sacs of six citrus genotypes were measured after being treated with 100 ?mol/L ABA and cultured for 10 d at room temperature.The results showed that the ABA treatment had a significant effect on the metabolism of monoterpene and sesquiterpene in the juice sacs of Huanonghong red pummelo,Guoqing No.1 Satsuma mandarin,seedless Guanximiyou pummelo(Citrus maxima cv.Seedless guanximiyou)and Newhall navel orange(C.sinensis cv.Newhall navel orange).In the juice sacs of Huanonghong red pummelo,the treatment mainly affected the metabolism of sesquiterpene.Specifically,the contents of ?-eIemene,?-cubebene,?-ylangene and ?-elemene were significantly higher than the control while the contents of elemene isomer and carophyllene were significantly decreased;furthermore,in the ABA-treated juice sacs of Newhall navel orange,the contents of sesquiterpenes ?-copaene and sesquiterpenol epicubebol decreased to a non-detectable level,indicating the dual effect of ABA treatment on the sesquiterpenenoids biosynthesis in citrus.Compared with the control,in the ABA-treated juice sacs of Guoqing No.1 Satsuma mandarin,more substances were detected,such as ?-myrcene,?-terpinene,gemene D and(2Z,5Z)-2,5-pentadecadiene-1-ol;Moreover,the content of dlimonene(1386.8 ng/g)and ?-elemene(15.7 ng/g)increased by 10 folds.In seedless Guanximiyou pummelo,ABA treatment decreased the contents of ?-myrcene and 2,5-furandione,dihydro-3-methylene-significantly.Collectively,it indicates that ABA treatment did affect the volatile profile in citrus,esp.monoterpenes and sesquiterpenoids.However,exogenous ABA treatment could not significantly change the content of linalool oxides in citrus juice sacs.Thus,ABA signalling is not the direct reason of xenia effect of Mangshanyegan;ABA treatment can change the volatile profiles in citrus juice sacs,which is meaningful for the regulation of fruit aromatic quality.