| In this study, main cultivars of four pear lines P. bretschneideri Rehd.(Huangguan, Yali), P. pyrifolia Nakai (Yuanhuang, Fengshui), P. ussuriensis Maxim(Jingbai, Nanguo), and P. communis L.(Bartlett) were chosen. The regulation ofsugar metabolism and quality changes of the four pear lines during storage time wasrevealed. Respiration intensity, firmness, total soluble solids, titratable acid, sugarscontent and the dynamic changes of the related enzymes were analized, thereafterthese indicators were verified by sensory evaluation. In order to study the mode ofsugar metabolism and the controling on gene levels in ‘Huangguan’ and ‘Yali’ pearduring the fruit growth and development, fruit weight, vertical and horizontaldiameter, titratable acid, sugar content, related enzyme activities and the geneexpressions of these enzymes were measured. The results were listed as follow:1. As an early-maturing variety,‘Huangguan’ pear entered a rapid growth period at33DAFD. The sorbitol content declined continuously in the whole period. Starchreached the peak at63DAFD and then degraded rapidly. At the same timefructose and glucose began to accumulate quickly and sucrose content roseslightly. The main sugar in fruit was hexose. Sugars content in mature pear fruitlisted orderly from high to low was fructose, glucose, sorbitol and sucrose. Totalsugars in mature ‘Huangguan’ pear fruit was97.2mg g-1FW. The mode of sugarmetabolism in developing ‘Huangguan’ pear fruit belonged to the typical middlemodel: sorbitol-starch-soluble sugars.2. As a late variety Yali pear fruit entered a rapid growth period at48DAFD.Sorbitol and sucrose content reached the maximum at48DAFD and thendegraded quickly. Starch reached accumulation peak at78DAFB and began todecompose. Hexose continued to accumulate until the harvest, thus Yali pearbelonged to hexose-accumulated type. Sugars content in mature pear fruit waslisted from high to low as follow fructose, glucose, sorbitol and sucrose. Totalsugars in mature ‘Yali’ pear fruit was93.2mg g-1FW. The mode of sugarmetabolism in developing ‘Yali’ pear fruit belonged to the middle model: sorbitolsucrose-starch-soluble sugars. 3. The activity of SS and SPS was high during the early period of growth anddevelopment of ‘Huangguan’ pear. In the later period the activity of AIV washigher than the other three significantly. The activity of SS and SPS and thecontent of fructose and glucose were obviously negatively related (p<0.01).Inversely, The activity of AIV and NI and the content of fructose and glucosewere significantly positively related (p<0.01). the gene expression of AIV and NIand the activity of AIV (p<0.05) and NI (p<0.01) was significantly related, whichindicated that the high expression level of invertase gene could enhance theenzyme activity and led to the rapid production and accumulation of hexose in thelate period of growth and development of Huangguan pear. AIV and NI was thekey enzyme related to sugar metabolism in developing ‘Huangguan’ pear fruit.4. The changes of enzyme activities in ‘Yali’ pear during fruit growth period weresimilar to ‘Huangguan’ pear. The activities of SS and SPS were high in the earlyperiod. In the later period the activity of AIV was higher than the other threeenzymes significantly. The activity of AIV was significantly positively correlatedwith the content of fructose and glucose (p<0.01). The activity of SPS wassignificantly positively correlated with the content of sucrose (p<0.01). The geneexpression of AIV was significantly related to the activity of AIV (p<0.05). AIVwas the key enzyme related to sugar metabolism in developing ‘Yali’ pear fruit.The high expression of AIV gene enhanced the enzyme activity which led to therapid production and accumulation of hexoses.5. The sugar metabolism and the quality changes in different cultivars from four pearlines were different. The hexoses content in P. bretschneideri Rehd. and P.pyrifolia Nakai was about60%of the total sugar, which was almost70%in P.ussuriensis Maxim, and P. communis L.. The content of sucrose, fructose andglucose and TSS increased firstly and then declined, and the accumulation peakappeared at90d. Because of after-ripening, the sugar content of P. ussuriensisMaxim and P. communis L. increased significantly which was higher than that ofP. bretschneideri Rehd. and P. pyrifolia Nakai in the end of storage. Therespiratory peak of most of the varieties appeared at30d and60d. Respirationmetabolism was associated with sugar metabolism significantly. After therespiration peak, the sugar content reached the maximum. AIV was the keyenzyme related to sugar metabolism in P. bretschneideri Rehd., P. pyrifolia Nakaiand P. communis L. in storage. All the four kinds of enzyme were involved in the sugar metabolism in P. ussuriensis Maxim, while AIV and NI played a leadingrole. According to the sensory evaluation at harvest and storage ending time, alsoand the physiological indexes, the harvested ‘Huangguan’ pear fruit had the bestquality within these cultivars, and ‘Nanguo’ pear was the best when the storagetime ending. |
PDF Full Text Request