PG与番茄果实成熟的关系

系统比较了转多聚半乳糖醛酸酶（PG）反义基因和对照番茄果实成熟过程中绿熟、转色、粉顶、粉红、全红5个时期的PG活性和与其相关的生理、生化组分的动态变化。实验表明,转基因果与对照果相比,PG活性始终处于较低水平,PG活性强烈被抑制是在全红期;果实的硬度、贮藏寿命指数都高于对照果;番茄红素合成积累进程被延缓;可溶性果胶含量、电解质外渗百分率均低于对照果。外源乙烯刺激引起对照果PG活性剧增,而转基因果表现钝化。讨论了PG活性与果实成熟、耐贮性及软化的关系,及对外源乙烯刺激的敏感性。首次明确提出PG活性在对照果中极大地表达,在转基因果中强烈被抑制是在全红期 ,而不是在整个成熟期;PG活性在果实软化中起直接和重要作用;PG活性的高低与番茄红素的合成与积累有关。     

番茄多聚半乳糖醛酸酶cDNA的克隆及其对番茄中PG表达的反义抑制

通过PCR扩增获得了包含多聚半乳糖醛酸酶(PG)全部阅读框架的1.5kb cDNA,经限制酶酶谱和部分序列分析鉴定无误后,将其以反方向插入含两个增强子的35s启动子和Nos3＇端之间,构建成表达PG反义RNA的双元载体,经农杆菌途径转化番茄品种“丽春”,获得了60株抗卡那霉素再生植株,经PCR检测,证明有2／3的再生植株有外源PG基因导入,成熟果实的PG粗提液的SDS—PAGE分析表明：若干株系中PG蛋白量较对照有不同程度的下降。PG活性亦同步下降,其中一个株系3^＃,PG酶活下降了93%。这些结果表明外源PG基因的反方向导入有效地抑制了内源PG基因的表达。     

番茄果实中乙烯与多聚半乳糖醛酸酶的关系

乙烯与多聚半乳糖醛酸酶(PG)都是果实成熟过程中关键的调节因子.一方面,在有乙烯合成缺陷的转反义ACS番茄和乙烯感受缺陷的Nr突变体番茄果实中PG基因表达量都明显下降,PG酶活性明显降低;用外源乙烯(100 μL/L)处理绿熟期番茄果实使PG基因的表达明显增强,而1-甲基环丙烯(1-MCP,1 μL/L)处理转色期番茄果实明显抑制PG基因表达.另一方面,转反义PG基因番茄果实乙烯释放量在授粉后低于其野生型,番茄乙烯受体基因LeETR4和乙烯反应因子LeERF2基因表达量比野生种低.PG降解果胶的产物D-GA(100 mg/L)促进未熟期番茄果实中的乙烯生成和LeETR4、LeERF2基因的表达.     

加工番茄多聚半乳糖醛酸酶（PG）基因的cDNA克隆的全序列测定

以加工番茄“87－5”为材料,采用反转录PCR（RT－PCR）技术将加工番茄G基因的cDNA序列克隆到pGEM-T载体上,并进行了全序列测定分析,结果表明,加工番茄的PG基因的cDNA与国内外报道的番茄PG基因的cDNA,在碱基序列及氨基酸序列上均有差异,说明番茄的PG基因具有多态性。     

PG在番茄果实成熟中的作用及二价金属离子与乙烯对PG活性的影响

对采后番茄果实的电镜观察表明:当果实成熟衰老时,叶绿体数量减少,多数基粒结构丧失;成熟果实胞壁中胶层水解成中空的电子透明区,初生壁的纤丝也发生一定程度的水解,相邻细胞分离;外源 PG(多聚半乳糖醛酸酶)提取物处理绿熟期果实组织,也可引起胞壁结构和叶绿体发生与正常衰老相同的变化。Ca~(2+)、Mg~(2+)、Co~(2+)二价金属离子处理果实,可明显降低番茄红素含量和 PG 活性,延缓果实软化。外源乙烯处理果实,可促进番茄红素的形成,提高 PG活性,并能解除钙对 PG 活性的抑制。本文也对 PG 在乙烯和 Ca~(2+)调节果实成熟中的作用进行了讨论。     

转反义PG基因番茄果实细胞结构变化的研究

经细胞学观察发现 ,转反义PG基因番茄果实在不同成熟期及存放前后 ,其果皮外面几层细胞的厚度都比未转基因的厚 1～ 5 μm ,细胞结构、细胞质和细胞核等的状态都有明显区别。尤以贮存后更为明显 ,未转基因果实的果皮细胞结构解体、细胞质凝聚、细胞核变的模糊程度都比转基因的严重。经外源乙烯处理后 ,转基因和未转基因果实的细胞结构也有相似的变化。结果表明 :反义PG基因的转入降低了PG活性 ,并且减弱了外源乙烯的作用 ,延缓了果实的衰老 ,提高了耐贮性能 ,从而起到果实保鲜作用     

转反义PG基因番茄果实细胞结构变化的研究

经细胞学观察发现,转反义PG基因番茄果实在不同成熟期及存放前后,其果皮外面几层细胞的厚度都比未转基因的厚1～5 μm,细胞结构、细胞质和细胞核等的状态都有明显区别。尤以贮存后更为明显,未转基因果实的果皮细胞结构解体、细胞质凝聚、细胞核变的模糊程度都比转基因的严重。经外源乙烯处理后,转基因和未转基因果实的细胞结构也有相似的变化。结果表明：反义PG基因的转入降低了PG活性,并且减弱了外源乙烯的作用,延缓了果实的衰老,提高了耐贮性能,从而起到果实保鲜作用。     

果实多聚半乳糖醛酸酶分子生物学研究进展

多聚半乳糖醛酸酶（PG酶）是一种在植物细胞壁降解中起重要的作用的酶。作者介绍了PG酶在果实成熟软化中的作用。概述了PG酶基因及其表达调控,评述了乙烯对PG酶合成的影响。     

表达多聚半乳糖醛酸酶反义RNA的转基因番茄分析

果实成熟是一系列基因在时空上有序表达的结果［１］,成熟阶段出现的多聚半乳糖醛酸酶（ＰＧ,Ｅ,Ｃ,３,２,１,１５）在果实软化过程中起作用［２,３］。番茄果实的软化与ＰＧｍＲＮＡ及ＰＧ活性增加呈平行关系［４］。ＰＧ的表达有发育阶段性［１,５］与组织特异性［６,７］,其调控主要是在转录水平［８,９］。本工作将ＰＧ反义基因转入番茄,对Ｔ０～Ｔ２代转基因果实的ＰＧ活性、生理后熟行为及品质进行了研究。１　材料和方法１．１　ＰＧ反义基因植物表达载体构建及Ｎｏｒｔｈｅｒｎ检测方法见前文［１０］。１．２　转化与…     

甜瓜成熟期间多聚半乳糖醛酸酶与乙烯的变化和果实软化的关系…

内源乙烯在河套蜜瓜成熟之前就已产生,其含量上升先于呼吸跃变。多聚半乳糖醛酸酶活力显著增加与果实软化平行相关,并与内源乙烯变化趋势一致。乙烯利处理后,该酶活力与乙烯生成量呈正相关。     

Effect of the Calcium on Polygalacturonase (PG) Activity and Synthesis at Different Ripening Stages of Tomato Fruits

It has been reported that PG is a key enzyme related to the tomato fruit ripening and that the application of calcium can dramatically decrease the PG activity and delay the ripening of fruits. In this paper the effects of calcium treament at various ripening stages on the transformation of absorbed calcium, PG activity and PG synthesis in tomato fruits were studicd. According to the analysis of calcium by atomic absorption spectroscopy, it was shown that the soluble and total calcium contents in pericarp of fruits treated with calcium at mature-green stage were increased significantly, and that more soluble calcium was transformed into bound calcium. Both the absorption and transformation of calcium decreased in fruits treated with calcium at later stage of ripening. The inhibition of calcium on PG activity was most effective by treatment at mature-green stage, but less effective at later stage of ripening. One reason for the decrease of calcium inhibition was probably due to the decline of calcium absorption as fruit ripening. The polyacrylamide gel electrophoresis of PG showed that PG with a molecular weight of 46.7 kD was absent in mature-green fruits, and PG synthesis occurred only at the later stage of ripening. It seems that the earlier the treatment was done the more effective of the calcium inhibition of PG synthesis. Based on the above results, it was concluded that the PG plays a major role in ripening and senescence of tomato fruits, and both PG synthesis and its activity were inhibited by calcium. In order to delay the ripening and senescence of tomato fruits, the treatment with calcium should be done at mature-green stage.     

The Role of Polygalacturonase (PG) in Tomato Fruit Ripening and Effects of Divalent Metal Ions and Ethylene on PG Activity

It has been reported that PG is a key enzyme related to the tomato fruit ripening. In this study tomato fruits were harvested at the mature-green stage and stored at room temperature. The cell ultrastructure of pericarp tissue was observed at different ripening stages, and the effects of treatments with ethylene and calcium on PG activity and fruit ripening were examined. The object of this study is to elucidate the role of PG in regulation of tomato fruit ripening by ethylene and calcium. PG activity, was undetectable at mature-green stage, but it rose rapidly as fruif ripening. The rise in PG activity was coincided with the dechnmg of fruit firmness during ripening of tomato fruits. The observation of cell ultrastructure showed that the most of grana in chloroplast were lost and the mitochondrial cristae decreased as fruit ripening. Striking changes of cell wall structure was most noted, beginning with dissolution of the middle lamella and eventual disruption of primary cell wall. A similar pattern of changes of cell wall and chloroplast have been observed in pericarp tissue treated with PG extract. In fruits treated with calcium and other divalent metal ions atmature-green stage, the lycopene content and PG activity decreased dramatically. Ethylene application enhanced the formation of lycopene and PG activity. The inhibition of Ca2+ on PG ac ivity was removed by ethylene. Based on the above results, it was demonstrated that PG played a major role in ripening of tomato fruits, and suggested that the regulation of fruit ripening by ethylene and Ca2+ was all mediated by PG. PG induced the hydrolysis of cell wall and released the other hydrolytic enzymes, then effected the ripening processes follow up.     

番茄果实成熟突变体的研究进展

番茄是一类比较重要的经济作物,具有很高的营养价值,长期以来番茄一直是研究肉质果实生长和成熟的模式生物。近年来,许多番茄果实成熟突变体的发现为研究果实成熟机制提供了重要的生物材料,综述了番茄果实成熟的影响因素、番茄果实成熟相关的突变体及基于突变体对果实成熟的相关研究,为今后突变体及果实成熟机制的研究提供参考。     

通过表达ACC脱氨酶基因控制番茄果实的成熟

乙烯在跃变型果实的成熟过程中起着触发呼吸跃变和促进果实成熟的作用。细菌来源的1-氨基环丙烷-1-羧酸(ACC)脱氨酶能降解乙烯的直接前体ACC,从而抑制植物体内乙烯的合成。我们用PCR方法从假单孢杆菌中克隆到ACC脱氨酶基因并通过农杆菌介导的方法将其转入番茄(Lycopersicun esculentum)中。再生植株经Southern blot检测证明,ACC脱氨酶基因已整合到番茄基因组中并稳定表达。转基因番茄果实成熟期的推迟时间与体内乙烯的抑制程度有相关性。转基因番茄植株乙烯的合成降低80%左右,果实在离体条件下可保鲜75d左右。研究ACC脱氢酶基因在植物体内的作用可阐明高等植物体内乙烯的作用机理并为培育耐贮藏果蔬品种打下基础。     

钙对不同成熟期番茄果实的PG活性及其合成的影响

本文研究了钙处理不同成熟期番茄果实对果壁组织中钙含量与转化、多聚半乳糖醛酸酶(PG)活性与 PG 合成的影响。结果表明,钙处理绿熟期的番茄果实可使总钙和可溶性钙含量明显增加,并较多转化为结合钙;后期处理,进入和转化的钙都减少。同样,钙处理愈早,对果实 PG 活性的抑制愈强,绿熟期处理可完全抑制 PG 活性。凝胶电泳结合钌红染色,证明绿熟期果实无 PG,PG 是在果实成熟过程中新合成的。钙处理愈早,对 PG 合成的抑制愈强,绿熟期钙处理可完全抑制 PG 合成。     

Glucose Inhibits ACC Oxidase Activity and Ethylene Biosynthesis in Ripening Tomato Fruit

Experiments were carried out to evaluate the effect of glucose on ripening and ethylene biosynthesis in tomato fruit (Lycopersicon esculentum Mill.). Fruit at the light-red stage were vacuum infiltrated with glucose solutions post-harvest and changes in 1-aminocyclopropane-1-carboxylic acid (ACC) synthase, ACC, ACC oxidase, and ethylene production monitored over time. ACC oxidase activity was also measured in pericarp discs from the same fruits that were treated either with glucose, fructose, mannose, or galactose. While control fruit displayed a typical peak of ethylene production, fruit treated with glucose did not. Glucose appeared to exert its effect on ethylene biosynthesis by suppressing ACC oxidase activity. Fructose, mannose, and galactose did not inhibit ACC oxidase activity in tomato pericarp discs. Glucose treatment inhibited ripening-associated colour development in whole fruit. The extent of inhibition of colour development was dependent upon the concentration of glucose. These results indicate that glucose may play an important role in ethylene-associated regulation of fruit ripening.