Ripening characteristics and chilling sensitivity in Chinese pear fruit.

1. 成熟特性：从乙烯产量的角度研究了10个品种中国梨果实成熟行为的品种差异。众所周知，中国梨果是更年期水果之一，在成熟过程中会产生大量的乙烯。然而，在本研究中，我们发现两个品种的果实在成熟阶段不产生乙烯，但通过伤害产生了大量乙烯。ACC合成酶和ACC氧化酶是乙烯生物合成的两个关键酶，果实成熟过程中不产生乙烯的乙烯生物合成受到ACC合成酶活性低的限制。低温敏感性：采用中国梨13个品种果实的全果或愈伤组织，测定了不同品种对低温敏感性的差异。4个品种的果实或愈伤组织在5℃下经过2周或3周后呈现褐色果肉。从电解质泄漏的测定来看，这种病害似乎是低温病害。本研究结果表明，不同品种的梨果实对低温的敏感性存在明显差异。乙烯生物合成的分子生物学分析：为了研究不同品种中国梨果实中乙烯生物合成的差异，对ACC合成酶和ACC氧化酶的cdna进行了部分克隆。本研究成功地分析了克隆的ACC氧化酶DNA片段的DNA和氨基酸序列。目前正在对克隆的ACC合酶DNA片段进行同源性分析。此外，ACC合成酶和ACC氧化酶的基因表达调控研究将在近期展开。

1. Ripening characteristics : Varietal difference of ripening behavior in Chinese pear fruit was studied in term of ethylene production using ten cultivars. Chinese pear fruit is long known to be one of the climacteric fruits which produce large amount of ethylene during ripening. In this study, however, we found that the fruit of two cultivars did not produce ethylene at ripening stage, though produced large amount of ethylene by wounding. From the determination of ACC synthase and ACC oxidase, the two key enzymes in thylene biosynthesis, ethylene biosynthesis of the fruit which not be producd ethylene during ripening was shown to be limited by low level of ACC synthase activity.2. Chilling sensitivity : Varietal difference of chilling sensitivity was determined by using the whole fruit or callus tissue derived from fruit of thirteen cultivars in Chinese pear. Browned flesh was observed on the fruit or callus tissue of four cultivars after two or three weeks at 5 c. From the determination of electrolyte leakage, this disorder seemed to be low temperature disorder.It was shown in this study that the chilling sensitivity of chinese pear fruit differed clearly in accordance with cultivar.3. Molecular biological analysis of ethylene biosynthesis : In order to study on the differences of ethylene biosynthesis observed among different cultivars in Chinese pear fruit, partial cloning of cDNAs for ACC synthase and ACC oxidase was carried out. In this study, DNA and amino acid sequences of cloned DNA fragments for ACC oxidase was analyzed successfully. Now, homology analysis of cloned DNA fragment for ACC synthase are carring out. Furthermore, study on control of gene expression for ACC synthase and ACC oxidase is followed in near future.