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。     

乙烯生物合成及其控制研究进展

 综述近年来对乙烯生物合成重要中间产物S-腺苷甲硫氨酸(SAM)及1-氨基环丙烷-1-羧酸(ACC)各种分流途径的研究进展,重点介绍参与这些途径的关键酶及其基因的特性,并对控制乙烯生物合成的基因工程作一总结。     

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。     

园艺作物成熟和衰老的分子生物学

对园艺作物乙烯和果实成熟、乙烯生物合成途径中二个关键酶ACC合成酶和ACC氧化酶的分子特性,基因克隆和表达及转基因研究等方面问题进行了评述。     

乙烯和1-氨基环丙烷-1-羧酸合酶基因参与玫瑰花发育过程中细胞程序化死亡的调控

作为植物有性繁殖器官--花的花瓣通常生命周期短,其中有一个敏感的、严格控制的细胞程序化死亡过程.为了揭示细胞程序化死亡过程中发生的反应或者其组成成分,解释玫瑰花发育过程中的细胞程序化死亡过程的机理,测定了在整个花发育过程中玫瑰花瓣的乙烯释放速率、ACC合酶基因的转录产物(mRNA)、ACC合酶活性以及ACC含量.结果显示在花发育过程前期(阶段1、2)检测不到乙烯产生,在花瓣完全绽开时花瓣中乙烯开始产生.在花发育后期(阶段4、5)花的衰老与乙烯释放速率的升高同时发生.在花发育前期没有ACC合酶基因的转录产物积累,该基因在花瓣完全绽开时开始表达,在花发育后期逐渐增强.ACC合酶活性与ACC含量的变化趋势与乙烯的一致.在玫瑰花发育后期乙烯诱导和调控花瓣的细胞程序化死亡.ACC合酶基因、ACC合酶以及ACC都是玫瑰花瓣程序化死亡过程中的重要调控因子.     

高CO_2低O_2处理对苹果乙烯生成的抑制作用

乙烯是植物体内含有的五大激素之一。它除了对植物的生长发育等多种生理代谢活动有重要影响外,还对果实具有催熟作用,素有成熟激素之称。为此,在果蔬贮藏保鲜中,有关乙烯的生物合成及其调节作用的研究占有十分重要的地位。近年来,Adams等确认,1-氨基环内烷-1-羰酸(ACC)是植物体内形成乙烯的直接前体,ACC向乙烯的转化是一个需氧过程。低氧抑制乙烯生成的     

植物激素乙烯生物合成与乙烯感受的分子机理

乙烯是分子结构最简单的植物激素,其生物合成途径的最后两个酶是ACC合成酶和ACC氧化酶。这两个酶基因已从许多植物中克隆,两个酶均由多基因家族编码。通过对乙烯不敏感突变体和结构性三重反应突变体的遗传分析表明,乙烯感受以及信号传递途径是由ETR1、CTR1和EIN3等成分组成,最终导致乙烯调节基因的表达。     

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。     

ACC脱氨酶的作用机理和转基因的应用

ACC脱氨酶是一种抑制乙烯生物合成的胞内酶,目前在植物体内尚未发现该酶.其作用机理涉及植物体内乙烯生成的蛋氨酸循环途径,在植物的保鲜、寿命延长、以及对Cu、Fe、Zn、Co、Ni、Pb、Cd等重金属的吸附等方面起着重要的作用.就ACC脱氨酶的基因特征、在蛋氨酸循环途径中作用机理、以及转基因应用等方面进行了系统的阐述,并对今后进一步研究提出了适宜的建议.     

乙烯生物合成及其控制研究进展

综述近年来对乙烯生物合成重要中间产物Ｓ－腺苷甲硫氨酸（ＳＡＭ）及１－氨基环丙烷－１－羧酸（ＡＣＣ）各种分流途径的研究进展,重点介绍参与这些途径的关键酶及其基因的特性,并对控制乙烯生物合成的基因工程作一总结。     

Oxygen control of ethylene biosynthesis during seed development in Arabidopsis thaliana (L.) Heynh

An unforeseen side-effect on plant growth in reduced oxygen is the loss of seed production at concentrations around 25% atmospheric (50 mmol mol-1 O2). In this study, the model plant Arabidopsis thaliana (L.) Heynh. cv. 'Columbia' was used to investigate the effect of low oxygen on ethylene biosynthesis during seed development. Plants were grown in a range of oxygen concentrations (210 [equal to ambient], 160, 100, 50 and 25 mmol mol-1) with 0.35 mmol mol-1 CO2 in N2. Ethylene in full-sized siliques was sampled using gas chromatography, and viable seed production was determined at maturity. Molecular analysis of ethylene biosynthesis was accomplished using cDNAs encoding 1-aminocyclopropane-1-carboxylic acid (ACC) synthase and ACC oxidase in ribonuclease protection assays and in situ hybridizations. No ethylene was detected in siliques from plants grown at 50 and 25 mmol mol-1 O2. At the same time, silique ACC oxidase mRNA increased three-fold comparing plants grown under the lowest oxygen with ambient controls, whereas ACC synthase mRNA was unaffected. As O2 decreased, tissue-specific patterning of ACC oxidase and ACC synthase gene expression shifted from the embryo to the silique wall. These data demonstrate how low O2 modulates the activity and expression of the ethylene biosynthetic pathway during seed development in Arabidopsis.     

Synthesis and Degradation of 1-Aminocyclopropane-1-carboxylic Acid by Penicillium citrinum

1-Aminocyclopropane-1-carboxylic acid (ACC), which is a precursor of ethylene in plants, has never been known to occur in microorganisms. We describe the synthesis of ACC by Penicillium citrinum, purification of ACC synthase [EC 4.4.1.14] and ACC deaminase [EC 4.1.99.4], and their properties. Analyses of P. citrinum culture showed occurrence of ACC in the culture broth and in the cell extract. ACC synthase was purified from cells grown in a medium containing 0.05% L-methionine and ACC deaminase was done from cells incubated in a medium containing 1% 2-aminoisobutyrate. The purified ACC synthase, with a specific activity of 327 milliunit/mg protein, showed a single band of M _r 48,000 in SDS-polyacrylamide gel electrophoresis. The molecular mass of the native enzyme by gel filtration was 96,000 Da. The ACC synthase had the K _m for S-adenosyl-L-methionine of 1.74 mM and k _cat of 0.56 s^-1 per monomer. The purified ACC deaminase, with a specific activity of 4.7 unit/mg protein, showed one band in SDS-polyacrylamide gel electrophoresis of M _r 41,000. The molecular mass of the native ACC deaminase was 68,000 Da by gel filtration. The enzyme had a K _m for ACC of 4.8 mM and k _cat of 3.52 s^-1. The presence of 7 mM Cu²⁺ in alkaline buffer solution was effective for increasing the stability of the ACC deaminase in the process of purification.     

Blue light-induced acidification of the medium of a nitrate-starved Chlorella mutant

Sunflower ( Helianthus annuus L.) seedlings were grown in aeroponic chambers which allowed for easy access to and easy harvesting of undamaged roots. In different portions of these roots we followed the rate of ethylene production, levels of 1-aminocyclopropane-1-carboxylic acid (ACC), N-malonyl-ACC and ACC oxidase mRNA and activity of ACC oxidase. ACC oxidase was measured with an in vitro assay, ACC and N-malonyl-ACC by selected ion monitoring gas chromatography-mass spectrometry. Ethylene production was highest in the tip of the root and tower in the middle and basal (part nearest the hypocotyl) portions of the root. The levels of ACC and ACC oxidase mRNA mirrored the levels of ethylene production. The lowest quantities of N-malonyl-ACC were found in the root tips. Upon gentle transfer of seedlings from an aeroponic system to treatment tubes, ACC content transiently increased; the greatest increase occurred in the tips. This brief rise in ACC content was not correlated with an increase in ethylene production. ACC oxidase activity was lowest in the tip and higher in the middle and base; the opposite of the pattern of ethylene production. Treating the seedlings with ACC produced a rapid rise in ACC content and ethylene production and inhibited root elongation. ACC oxidase activity was not induced by ACC treatment.     

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.     

Expression of the ACC synthase and ACC oxidase coding genes after self-pollination and incongruous pollination of tobacco pistils

In tobacco, as in other species, ethylene is produced in response to pollination. Although tobacco is a self-compatible species, it displays unilateral incongruity with other Nicotianaplants. Incongruous pollination also results in ethylene production, but this production differs depending on the pollen used and is related to the extent to which pollen tubes grow in the tobacco style. In the investigation reported here we followed the expression of the ACC synthase- and ACC oxidase-coding genes upon pollination of tobacco pistils and compared self-pollination with incongruous pollination. The pattern of expression of these genes also correlated with pollen-tube growth, although wounding alone cannot explain the results obtained. We also examined the expression of these genes upon pollination of immature tobacco pistils, in which different pollen tubes grew indistinctly inside the tobacco style and reached the ovary at the same rate. In this situation no significant differences in gene expression could be observed between the different pollinations. Ethephon, a substance that produces ethylene, could, in some cases, minimize the arrest of incongruous pollen tubes inside the style.     

Effect of short-chain fatty acids on the ethylene pathway in embryonic axes of Cicer arietinum during germination

The effect of short-chain saturated fatty acids (C₅–C₁₀) on the biosynthesis of ethylene in embryonic axes of chick-pea ( Cicer arietinum L.) seeds was investigated. The emergence of radicle and fresh weight of embryonic axes diminished with increasing number of carbons. The inhibition of germination caused by lower concentrations (1 m M ) of fatty acids (C₅–C₁₀) was partially reversed by exogenous 1-aminocyclopropane-1-carboxylic acid (ACC), whereas exogenous ethylene was able to overcome the inhibitory effect provoked by all concentrations (1–5 m M ) of applied fatty acids (C₅–C₁₀). Ethylene production rates, and enzyme activities of ACC synthase and ACC oxidase decreased concomitantly with the molecular mass and increasing concentration of fatty acids. The inhibitory effect of these acids on ethylene production seems to result not only from a decreased ACC synthesis, but also from an enhancement of 1-malonylamino)cyclopropane-1-carboxylic acid (MACC) synthesis.     

嫁接对网纹甜瓜果实乙烯生物合成及CmACO1基因表达的影响

以“新汉城翠蜜”网纹甜瓜为接穗,以“圣砧一号”南瓜为砧木进行嫁接,研究嫁接对目光温室网纹甜瓜果实乙烯生物合成及CmACO1基因转录水平表达的影响。结果表明：嫁接明显降低了网纹甜瓜果实ACC含量及乙烯释放量,在乙烯释放高峰时,嫁接的网纹甜瓜果实乙烯释放量比自根的降低了12．6％;嫁接降低了果实中ACC合成酶和ACC氧化酶活性,其最大值分别比自根网纹甜瓜降低了9．0％和6．8％;嫁接抑制了CmACO1的表达,其相对表达量最大值比自根网纹甜瓜降低了39．0％;嫁接网纹甜瓜果实中乙烯释放高峰、ACC合成酶和ACC氧化酶活性峰值及CmACO1相对表达量峰值出现的时间均比自根的延迟了3d。