Changes In Enzyme Activities And Gene Expressions Of Enzymes Involved In Aroma Formation During Fruit Ripening Of Jackfruit

Jackfruit is a famous tropical fruit tree, and aroma is an important quality factor of the fruit. In this study, 8 jackfruit germplasms(12As, 12 Bs, 12 Cs, 12 D, 12 E, 13 D,13K and 14A) were used as materials, and changes in the activities of 4 major enzymes involed in aroma formation and expression patterns of 11 genes during fruit ripening were investigated. The results would provide basis for further researches on breeding and cultivation of jackfruit. The main results were as follows:1. Changes in activities of lipoxygenase during fruit ripening of jackfruit were measured. The results showed that, lipoxygenase activities decreased during fruit ripening of all jackfruit genotypes, except for 12 E and 14 A. Analysises of expression patterns of 5 lipoxygenase enzyme genes(AhLOX1, AhLOX2, AhLOX3, AhLOX4 and AhLOX5) indicated that, lipoxygenase genes expressed mainly in the fruits at immature stage, and expression levels of 5 genes were different. In the germplasm of12 Cs, 12 D and 13 D, changes in expression levels of 5 genes were closely consistent with activities of LOX; also in 12 As and 13 K, expression levels of all LOX genes decreased along with LOX activities during fruit ripening, except for gene AhLOX1,changes in which were inconsistent with changes in LOX activities. In 12 Bs, 12 E and14A, changes of gene expression and enzyme activity are not fully consistent.2. Analysis of changes in activities of hydroperoxide lyase during fruit ripening of jackfruit showed that, in 12 As, 12 Cs, 12 D, 13 D and 14 A germplasms, enzyme activities peaked at fruit ripening stage I, while in 12 Bs and 12 E, enzyme activities peaked at fruit ripening stage III, and in 13 K, enzyme activitity peaked at fruit ripening stage IV. Analysis of expressions of hydroperoxide lyase gene(AhHPL1)indicated that, in all 8 germplasms, gene expression peaked at fruit ripening stage III,except for 12 D, in which peak of gene expression appeared at fruit ripening stage I. In12 As, 12 Cs, 13 D and 14 A, HPL activities decreased with the decline of gene expression, while in 12 Bs, 12 D, 12 E and 13 K, changes in gene expression and enzyme activity were not closely correlated.3、Determination of activities of alcohol dehydrogenase during fruit ripening of jackfruit showed that, in 12 As, 12 Cs and 12 D, activities of ADH decreased significantly from fruit ripening stage I to ripening stage II, and then maintained at a low level; in 12 Bs and 12 E, activities of ADH remained constant at a low level; in13 D, 13 K and 14 A, activities remained constant at a high level. Analysises of expression patterns of 4 alcohol dehydrogenase genes(AhADH1, AhADH2, AhADH4 and AhADH5) during fruit ripening of jackfruit indicated that, expression patterns of these genes differed among 8 germplasms. It was possible that different gene members of alcohol dehydrogenase gene family involved in aroma formation in different jackfruit germplasms.4、Determination of activities of alcohol acyltransferase during fruit ripening of jackfruit showed that, changes in AAT activities differed among germplasms and fruit ripening stages. In 12 Cs, 13 D, 13 K and 14 A, enzyme activities peaked at fruit ripening stage I, while in 12 Bs, enzyme activities peaked at fruit ripening stage II, and in 12 As and 12 E, enzyme activities peaked at fruit ripening stage III, and in 12 D,enzyme activitity peaked at fruit ripening stage IV. Analysises of expression patterns of alcohol acyltransferase gene(AhAAT1) during fruit ripening of jackfruit indicated that, levels of AhAAT1 gene expression were low in all germplasms, except for 12 Bs,in which, AhAAT1 gene abundantly expressed at the fruit ripening stage III and IV.Althogh changes in enyzme activities of AAT and expression levels of AhAAT1 were inconsistent, AhAAT1 gene would be a key gene in aroma formation of jackfruit based on other facts.