植物乙烯生物合成过程中活性氧的作用

大量的研究结果表明,活性氧参与植物乙烯生物合成过程具有明显的普遍性,超氧阴离子自由基是参与乙烯生物合成过程的主要活性氧。近年来研究的焦点主要从乙烯生物合成的关键调控酶ACC合酶及ACC氧化酶的酶活性、酶动力学特性、酶蛋白空间结构、酶基因表达水平等方面来阐明活性氧调控植物乙烯生物合成的机制。最新的研究表明：植物在各种正常或应激的生长条件下首先诱导了活性氧产生水平的变化,活性氧在基因或蛋白质水平上影响ACC合酶和ACC氧化酶的活性水平,从而调节乙烯的生物合成。本文首次综述了活性氧影响植物乙烯生物合成过程的最新研究进展,并对活性氧在植物乙烯生物合成中具有诱导与抑制并存的“双重性”作用进行了探讨。     

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.     

乙烯生物合成基因工程在果蔬保鲜中的应用

水果和蔬菜的成熟、衰老与乙烯密切相关。乙烯生物合成过程受到多种因素的综合调控。通过基因工程调节乙烯生物合成相关酶的含量或活性以阻断或减少果蔬中乙烯的产生,从而延缓果蔬成熟或衰老,是果蔬保鲜最重要的策略之一。多种果蔬ACC合成酶、ACC氧化酶与微生物ACC脱氨酶、SAM水解酶的基因已被克隆;采用基因工程调控这些酶基因在果蔬中的表达,可能延长果蔬的贮藏保鲜时间。乙烯生物合成基因工程在果蔬保鲜中具有良好的应用前景,少数耐贮藏转基因果蔬已经实现商品化生产。     

乙烯调控植物耐盐性的研究进展

乙烯具有复杂的生物学功能,它调节着植物生长发育和许多的生理生化过程。乙烯也被认为是一种胁迫应答激素,直到近几年关于乙烯生物合成及信号转导途径与植物盐胁迫的关系才逐渐被挖掘出来。乙烯在不同水平、层次参与盐胁迫反应,包括乙烯合成关键酶(ACS)和乙烯受体,细胞质中CTR1和EIN2以及细胞核中EIN3传导、响应盐信号。但是乙烯合成和信号转导途径在植物盐胁迫响应过程中仍然存在许多未解决的问题。主要介绍乙烯合成及信号转导途径的各组分与盐胁迫关系的最新研究进展,并讨论其存在的主要问题。     

Pollination-Induced Expression of Ethylene Biosynthetic Genes at Transcription Level in Orchid Flowers

The authors investigated pollination-induced ethylene production and expression patterns of genes encoding 1-aminocyclopropane-l-carboxylate (ACC) synthase and ACC oxidase in orchid flowers (Doritaenopsis hybrida Hort. ). Following pollination both ACC synthase and ACC oxidase mRNAs were detected in the different organs of flowers, and the patterns of both ACC synthase and ACC oxidase mRNA accumulation were similar, mRNA accumulation of ACC synthase mRNA was more organ-specific than that of ACC oxidase mRNA. However, ACC oxidase mRNAs were much more abundant than ACC synthase mRNAs in the flower organs.     

生长素与乙烯对兰花授粉后花发育的调节作用(英文)

以朵丽蝶兰为材料,对乙烯和生长素调节的授粉后花的发育进行了研究。实验结果显示,切花和植株上的花授粉后,乙烯的产生和花的发育无明显差异;花瓣的衰老、子房发育、花粉萌发和花粉管的伸长受乙烯调节;与切花相比,植株上花的子房内无ＡＣＣ合酶和ＡＣＣ 氧化酶ｍＲＮＡ 的积累。用生长素运输抑制剂２ ［（１ｎａｐｈｔｈａｌｅｎｙｌａｍｉｎｏ）ｃａｒｂｏｎｙｌ］ ｂｅｎｚｏｉｃａｃｉｄ（ＮＰＡ） 处理柱头,授粉诱导的子房发育在很大程度上受到抑制, 表明授粉后子房的发育需要转运来的生长素。     

春小麦水分胁迫响应中的ACC、MACC合成及乙烯的释放

水分胁迫使两个抗旱性不同的春小麦 (TriticumaestivumL .)品种“8139”(抗旱性较弱 )和“5 0 4”(抗旱性较强 )叶片ACC和MACC含量于胁迫初期下降后期升高 ,ACC合酶活性持续升高 ,乙烯释放量在 8139中下降而在5 0 4中先大幅升高而后下降。两种作用效果相反的抑制剂MGBG (抑制SAMDC活性 )和AOA (抑制ACC合酶活性 )均明显影响了两品种春小麦叶片以上各指标的变化。结果表明 ,水分胁迫下作物乙烯的释放量并不与其合成直接前体ACC的量成正相关 ;胁迫乙烯在抗性品种中于胁迫初期的升高可能是植物胁迫信号传导的响应之一 ,是一种干旱适应现象 ,可能与作物的干旱忍耐形成有关 ,而MACC具有调节胁迫乙烯释放的特殊生理作用。     

春小麦水分胁迫响应中的ACC、MACC合成及乙烯的释放

水分胁迫使两个抗旱性不同的春小麦 (Triticum aestivum L.) 品种"8139"(抗旱性较弱)和"504"(抗旱性较强)叶片 ACC 和 MACC 含量于胁迫初期下降后期升高,ACC 合酶活性持续升高,乙烯释放量在 8139 中下降而在 504 中先大幅升高而后下降.两种作用效果相反的抑制剂 MGBG (抑制SAMDC 活性)和 AOA (抑制 ACC 合酶活性) 均明显影响了两品种春小麦叶片以上各指标的变化.结果表明,水分胁迫下作物乙烯的释放量并不与其合成直接前体 ACC 的量成正相关;胁迫乙烯在抗性品种中于胁迫初期的升高可能是植物胁迫信号传导的响应之一,是一种干旱适应现象,可能与作物的干旱忍耐形成有关,而 MACC 具有调节胁迫乙烯释放的特殊生理作用.     

Structure of ACC synthase inactivated by the mechanism-based inhibitor L-vinylglycine

L-Vinylglycine (L-VG) is both a substrate for and a mechanism-based inhibitor of 1-aminocyclopropane-1-carboxylate (ACC) synthase. The ratio of the rate constants for catalytic conversion to alpha-ketobutyrate and ammonia to inactivation is 500/1. The crystal structure of the covalent adduct of the inactivated enzyme was determined at 2.25 Angstroms resolution. The active site contains an external aldimine of the adduct of L-VG with the pyridoxal 5'-phosphate cofactor. The side chain gamma-carbon of L-VG is covalently bound to the epsilon-amino group of Lys273. This species corresponds to one of the two alternatives proposed by Feng and Kirsch [Feng, L. and Kirsch, J.F. (2000) L-Vinylglycine is an alternative substrate as well as a mechanism-based inhibitor of 1-aminocyclopropane-1-carboxylate synthase. Biochemistry 39, 2436-2444] and presumably results from Michael addition to a vinylglycine ketimine intermediate.     

Effect of MGBG on Growth of the Callus Tissue,Induction of Somatic Embryogenesis of Alfalfa and Their Ethylene Biosynthesis

MGBG [methylglyoxal bis(guanylhydrazone)], when added to the initial of callus subculture, promoted ethylene production in callus grawn in Bsh medium, and enhanced the ACC (1-aminocyclopropane-l-carboxylic acid) level and the ACC synthase activity both in the callus grown in Bsh medimn, and in the suspension cultures in Bsg liquid medium for induction of somatic embryogenesis. However, MGBG reduced the malonyl-ACC (MACC) level of the suspension tissues. The treatments of MGBG caused growth of the cultured tissues and induction efficiency of somatic embryogenesis to reduce. Moreover, the effects of MGBG was enhanced when it was added at induction medium of somatic embryogenesis. It could be concluded that this inhibitory effect of MGBG could be due to its promotion of ethylene, ACC levels and ACC synthase activity which has shown to inhibit somatic embryogenesis. The reduction of MACC level could be also involved in the MGBG effect on induction of the embryogenesis.     

Ethylene biosynthesis in tissues of young and mature avocado fruits

Sitrit, Y., Blumenfeld, A. and Riov, J. 1987. Ethylene biosynthesis in tissues of young and mature avocado fruits.
Avocado (Persea americana Mill.) fruit tissues differ greatly in their capability to pro duce wound ethylene. In fruitlets, the endosperm lacks the ability to produce ethylene because no 1-aminocyclopropane-1-carboxylic acid (ACC) is synthesized and no activity of the ethylene-forming enzyme (EFE) is present. The cotyledons (embryo) do not produce significant amounts of ethylene at any of the developmental stages of the fruits, although in both young and mature fruits they contain a relatively high level of ACC synthase (EC 4.4.1.-) activity. Because of the very low EFE activity present in the cotyledons, most of the ACC formed in this tissue is conjugated. Of the various fruitlet tissues, the seed coat has the highest potential to produce ethylene. This is due to a high ACC synthase activity and particularly a high EFE activity. Also, the seed coat is very sensitive to the autocatalytic effect of ethylene. Fruitletpericarp possesses a lower potential to produce ethylene than the seed coat. Towardruit maturiy, the endosperm disappears and the seed coat shrivels and dies so that the pericarp and the cotyledons remain as the only active tissues in the mature fruit. At this stage, the pericarp is the only tissue producing ethylene. Mature precli macteric pericarp has a lower potential to produce ethylene than fruitlet pericarpThe role of ethylene in regulating various physiological processes at different stages of fruit maturation is discussed.     

The ethylene biosynthetic and perception machinery is differentially expressed during endosperm and embryo development in maize

The maize endosperm undergoes programmed cell death late in its development so that, with the exception of the aleurone layer, the tissue is dead by the time the kernel matures. Although ethylene is known to regulate the onset of endosperm cell death, the temporal and spatial control of the ethylene biosynthetic and perception machinery during maize endosperm development has not been examined. In this study, we report the isolation of the maize gene families for ACC synthase, ACC oxidase, the ethylene receptor, and EIN2 and EIL, which act downstream of the receptor. We show that ACC oxidase is expressed primarily in the endosperm, and only at low levels in the developing embryo late in its development. ACC synthase is expressed throughout endosperm development but, in contrast to ACC oxidase, it is transiently expressed to a significantly higher level in the developing embryo at a time that corresponds with the onset of endosperm cell death. Only two ethylene receptor gene families were identified in maize, in contrast to the five types previously identified in Arabidopsis. Members of both ethylene receptor families were expressed to substantially higher levels in the developing embryo than in the endosperm, as were members of the EIN2 and EIL gene families. These results suggest that the endosperm and embryo both contribute to the synthesis of ethylene, and they provide a basis for understanding why the developing endosperm is especially sensitive to ethylene-induced cell death while the embryo is protected.Electronic Supplementary Material Supplementary material is available in the online version of this article at Communicated by G. Jürgens     

Ethylene regulation of fruit ripening: Molecular aspects

Progress in ethylene regulating fruit ripening concerning itsperception and signal transduction and expression of ACC synthaseand ACC oxidase genes is reviewed. ACC synthase and ACC oxidasehave been characterized and their genes cloned from various fruittissues. Both ACC synthase and ACC oxidase are encoded bymultigene families, and their activities are associated withfruit ripening. In climacteric fruit, the transition toautocatalytic ethylene production appears to be due to a seriesof events in which ACC sythase and ACC oxidase genes have beenexpressed developmentally. Differential expression of ACCsynthase and ACC oxidase gene family members is probably involvedin such a transition that ultimately controls the onset of fruitripening.In comparison to ACC synthase and ACC oxidase, less is knownabout ethylene perception and signal transduction because of thedifficulties in isolating and purifying ethylene receptors orethylene-binding proteins using biochemical methods. However, theidentification of the Nr tomato ripening mutant as anethylene receptor, the applications of new potent anti-ethylenecompounds and the generation of transgenic fruits with reducedethylene production have provided evidence that ethylenereceptors regulate a defined set of genes which are expressedduring fruit ripening. The properties and functions of ethylenereceptors, such as ETR1, are being elucidated.Application of molecular genetics, in combination withbiochemical approaches, will enable us to better understand theindividual steps leading from ethylene perception and signaltransduction and expression of ACC synthase and ACC oxidase genefamily member to the physiological responses.     

乙烯生物合成途径及其相关基因工程的研究进展(综述)

在对植物激素乙烯生理功能作简要回顾的基础上着重对乙烯的生物合成途径中的关键酶,包括腺苷蛋氨酸合成酶、ACC合成酶及ACC氧化酶的性质和基因的研究进展作了综述,同时展现出了与调控内源乙烯生物合成有关的基因工程的整体轮廓。     

钙在植物乙烯生成及信号传递中的生理作用

Ｃａ＾２＋对植物乙烯生成的调节与作用位点有关,胞外Ｃａ＾２＋在维持质膜功能的同时,抑制乙烯生成,延缓衰老;过量Ｃａ＾２＋进入胞质,胞内Ｃａ＾２＋促进乙烯生成和衰老。内源ＣａＭ与乙烯生成关系密切,介入了乙烯代谢和外源激素对乙烯的调控。此外,Ｃａ＾２＋是乙烯信号传递所必需的。     

植物花色素苷生物合成的转录调控

转录调节是植物花色素苷生物合成途径中调节其结构基因表达的重要环节之一。近十多年来,通过调节转录因子的表达激活或抑制有效地调控植物中花色素苷的合成成了众多植物学家研究的重点。现简要介绍了花色素苷的合成运输过程与液泡的沉积扣押、转录因子与调控及转录调节在遗传改良中的应用等方面的研究进展。