1-Aminocyclopropane-1-Carboxylic Acid Levels in Ripening Apple Fruits

1-Aminocyclopropane-1-carboxylic acid (ACC) in amino acid fractionsof apple fruits was assayed by chemical conversion to ethylene.The specificity of the assay was checked with other amino acids;homocysteine was the only naturally occurring compound foundto yield significant amounts of ethylene in the assay. Analysisof the thiol content of apples showed that homocysteine couldnot be a significant source of interference. Interference froman uncharacterized component of amino acid fractions was lessthan 20% of the ACC level in unripe fruit and insignificantin ripe fruit. Liquid chromatographic assay gave results inclose agreement with the standard assay. Higher apparent ACClevels were measured in unfractionated apple juice than in thestandard assay. Both of these methods and the liquid chromatographicassay were used on a number of apple samples during ripening.All three methods showed that ACC increased 30–40 foldwhereas ethylene production increased by a factor of 10⁴. Inindividual apples the ACC level increased about one day laterthan ethylene production. Key words: Apple fruit, 1-Aminocyclopropane-1-carboxylic acid, Analytical methods, Ethylene     

The Conversion of 1-(Malonylamino)cyclopropane-1-Carboxylic Acid to 1-Aminocyclopropane-1-Carboxylic Acid in Plant Tissues

Since 1-(malonylamino)cyclopropane-1-carboxylic acid (MACC), the major conjugate of 1-aminocyclopropane-1-carboxylic acid (ACC) in plant tissues, is a poor ethylene producer, it is generally thought that MACC is a biologically inactive end product of ACC. In the present study we have shown that the capability of watercress (Nasturtium officinale R. Br) stem sections and tobacco (Nicotiana tabacum L.) leaf discs to convert exogenously applied MACC to ACC increased with increasing MACC concentrations (0.2-5 millimolar) and duration (4-48 hours) of the treatment. The MACC-induced ethylene production was inhibited by CoCl₂ but not by aminoethoxyvinylglycin, suggesting that the ACC formed is derived from the MACC applied, and not from the methionine pathway. This was further confirmed by the observation that radioactive MACC released radioactive ACC and ethylene. A cell-free extract, which catalyzes the conversion of MACC to ACC, was prepared from watercress stems which were preincubated with 1 millimolar MACC for 24 hours. Neither fresh tissues nor aged tissues incubated without external MACC exhibited enzymic activity, confirming the view that the enzyme is induced by MACC. The enzyme had a K_m of 0.45 millimolar for MACC and showed maximal activity at pH 8.0 in the presence of 1 millimolar MnSO₄. The present study indicates that high MACC levels in the plant tissue can induce to some extent the capability to convert MACC to ACC.     

拟南芥乙烯合成酶ACS基因家族研究进展

1-氨基环丙烷-1-羧酸(1-aminocyclopropane-1-carboxylic acid,ACC)合酶(ACC synthase,ACS)是乙烯生物合成的限速酶。ACS酶活性是ACC和乙烯调控植物生长发育的基础,其酶活性调节主要涉及转录启动、翻译后修饰、酶高级结构形成、生化特性等方面。简要总结拟南芥ACS酶活性研究进展。     

Effect of 1-Aminocyclopropane-1-Carboxylic Acid on the Production of Ethylene in Senescing Flowers of Ipomoea tricolor Cav

Application of 1-aminocyclopropane-1-carboxylic acid (ACC) to rib segments excised from flowers of Ipomoea tricolor Cav. resulted in the formation of C₂H₄ in greater quantities than produced under natural conditions. The ability of ACC to enhance C₂H₄ production was independent of the physiological age of the tissue and its capacity to synthesize C₂H₄ without applied ACC. When ACC was fed to rib segments that had been treated with [¹⁴C]methionine, incorporation of radioactivity into C₂H₄ was reduced by 80%. Aminoethoxyvinylglycine and aminooxyacetic acid inhibited C₂H₄ production in rib segments of I. tricolor but had no effect on ACC-enhanced C₂H₄ production. Protoplasts obtained from flower tissue of I. tricolor did not form C₂H₄, even when incubated with methionine or selenomethionine. They produced C₂H₄ upon incubation with ACC, however. ACC-dependent C₂H₄ production in protoplasts was inhibited by n-propyl gallate, AgCl, CoCl₂, KCN, Na₂S, and NaN₃. ACC-dependent C₂H₄ synthesis in rib segments and protoplasts was dependent on O₂, the K_m for O₂ being 1.0 to 1.4% (v/v). These results confirm the following pathway for C₂H₄ biosynthesis in I. tricolor. methionine [selenomethionine] → S-adenosylmethionine [selenoadenosylmethionine] → ACC → C₂H₄.     

Transport and Compartmentation of 1-Aminocyclopropane-1-Carboxylic Acid and Its Structural Analog, alpha-Aminoisobutyric Acid, in Tomato Pericarp Slices

The uptakes of 1-aminocyclopropane-1-carboxylic acid (ACC), the immediate precursor to ethylene, and its structural analog, α-aminoisobutyric acid (αAIB) by tomato pericarp slices were investigated. Both uptakes show a biphasic (saturable-linear) dependence on external concentration of the transported amino acid. At low concentrations, ACC uptake is competitively inhibited by αAIB and vice versa. Both uptakes also are inhibited by other neutral amino acids but not by acidic or basic amino acids. ACC and αAIB uptakes are metabolically dependent and are increased with time of tissue incubation. αAIB efflux patterns from pericarp slices indicated three distinct αAIB compartments having efflux kinetics consistent with those for cell wall, cytoplasm, and vacuole. The bulk of the αAIB taken up by pericarp tissue is sequestered into the vacuole. The ability of pericarp tissue to accumulate αAIB in the vacuole declines with fruit development.     

Purification and Characterization of 1-Aminocyclopropane-1-Carboxylic Acid N-Malonyltransferase from Tomato Fruit

1-Aminocyclopropane-1-carboxylic acid (ACC) can be oxidized to ethylene or diverted to the conjugate 1-(malonylamino)cyclopropane-1-carboxylic acid (MACC) by an ACC N-malonyltransferase. We developed a facile assay for the ACC N-malonyltransferase that resolved [14C]MACC from [14C]ACC by thin-layer chromatography and detected and quantified them using a radioisotope-imaging system. Using this assay, we showed that ACC N-malonyltransferase activity has developmental and tissue-specific patterns of expression in tomato (Lycopersicon esculentum) fruit. In the pericarp, activity was elevated for several days postanthesis, subsequently declined to a basal level, increased 3-fold at the onset of ripening, and again declined in overripe fruit. In the seed, activity increased throughout embryogenesis, maturation, and desiccation. Treatment of fruit with ethylene increased activity 50- to 100-fold in the pericarp. ACC N-malonyltransferase was purified 22,000-fold to a specific activity of 22,000 nmol min-1 mg-1 protein using ammonium sulfate precipitation, DyeMatrex Green A affinity, anion-exchange, Cibacron Blue 3GA affinity, hydrophobic interaction, and molecular filtration chromatography. Native and sodium dodecyl sulfate-denatured enzyme showed molecular masses of 38 kD, indicating that the enzyme exists as a monomer. The enzyme exhibited a Km for ACC of 500 [mu]M, was not inhibited by D- or L-amino acids, and did not conjugate [alpha]-aminoisobutyric acid or L-amino acids.     

Nomenclatural updates in Ipomoea (Convolvulaceae)

The lectotypification of Ipomoea fimbriosepala, I. horsfalliae, I. marcellia, I. subincana and I. tenera is proposed herein. In addition, we suggest to change one name, from I. tubata to I. sidifolia since I. sidifolia predate I. tubata and must replace it.     

丹参ACC氧化酶基因(SmACO1)的克隆与序列分析

依据丹参转录组数据库序列信息,采用RT-PCR和染色体步移技术从丹参中首次克隆得到ACC氧化酶基因,命名为SmACO1(GenBank注册号为JQ026111)。该基因gDNA序列长1 347 bp,由3个外显子和2个内含子组成;cDNA全长1 117 bp,包含945 bp的开放阅读框,编码314个氨基酸残基。生物信息学分析显示SmACO1为无信号肽与跨膜结构域,且定位于细胞质的稳定亲水蛋白,含有Fe²⁺依赖的加氧酶结构域。实时荧光定量PCR结果表明,SmACO1基因在丹参不同组织器官中差异表达,花中表达量最高;其表达受到病原菌和茉莉酸甲酯的诱导,表明SmACO1基因可能在植物防御反应中发挥作用。     

A putative tropical American plant,Ipomoea nil (Convolvulaceae), in pre-Columbian Japanese art

The Heike Nôkyô, Japanese scrolls of Buddhist sutras created in 1164 AD, includes illustrations of anIpomoea that has long been identified by Japanese scholars asI. nil. What makes this occurrence ofI. nil in pre-Columbian Japan remarkable is that all of its closest relatives are American plants. We give a synopsis of the history of this economically important species. Then, using cladistic analysis, we show the relationships ofI. nil toI.eriocalyx,I. hederacea,I. indica,I. laeta,I. lindheimeri,I. meyeri, andI. pubescens. Six of these eight species inIpomoea seriesHeterophyllae are endemic to the New World.Ipomoea indica is pantropical, and may be carried by ocean currents. We offer four hypotheses as to how this putatively tropical American species may have arrived in Asia: 1)Ipomoea nil was introduced through long-distance dispersal by animals; 2)Ipomoea nil was introduced by humans in a pre-Columbian context; 3) TheIpomoea in theHeike Nôkyô scrolls does not representI. nil, but a different native Asian species; and 4)Ipomoea nil was introduced during post-Columbian times by Europeans. There are problems with accepting any of these possible alternatives.     

Changes of 1-Aminocyclopropane-1-Carboxylic Acid Oxidase Activity in Stressed Pinus Sylvestris Needles

Stimulation of ethylene biosynthesis in pine needles by hydrogen peroxide and sodium bisulfite coincided with the activation of ACC oxidase at the level of protein synthesis. Decrease in ethylene production at high concentrations of sodium bisulfite (above 7 mM) was apparently due to inhibition of ACC oxidase activity. Treatment of pine needles with aminotriazole caused an inhibition of both ethylene production and ACC oxidase activity. Both methylviologen and methyl jasmonate stimulated ACC oxidase activity in a concentration-dependent manner with no parallel changes in ethylene production. The presented results suggest that ACC oxidase plays an important role in regulation of ethylene formation in pine needles in response to different stimuli.     

1-Aminocyclopropane-1-Carboxylic Acid Enhanced Direct Somatic Embryogenesis from Oncidium Leaf Cultures

Influence of the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) and two ethylene inhibitors, silver nitrate (AgNO₃) and cobalt chloride (CoCl₂), on direct somatic embryogenesis were tested in vitro using leaf cultures of Oncidium cv. Gower Ramsey. Leaf cells of tips, adaxial sides and cut ends could directly form somatic embryos on a hormone-free 1/2-strength MS medium. The frequency of embryo-producing explants was 55, 52.5 and 30 %, respectively. The embryo numbers per embryo-producing explant was 20.3. ACC at lower concentrations (5 and 10 μM) significantly retarded direct embryo formation from cut ends. However, higher concentrations of ACC (20 and 50 μM) significantly promoted embryogenic response of leaf tips and adaxial sides. All concentrations of AgNO₃ and CoCl₂ significantly retarded direct embryo formation. The best response was found on 20 μM of ACC, and the frequency of embryo-producing explants were 90, 85 and 35 % on leaf tips, adaxial sides and cut ends, respectively. The embryo numbers per embryo-producing explant was 32.2. This revised version was published online in July 2006 with corrections to the Cover Date.     

Increased 1-Aminocyclopropane-1-Carboxylic Acid Oxidase Activity in Shoots of Flooded Tomato Plants Raises Ethylene Production to Physiologically Active Levels

Soil flooding increased 1-aminocyclopropane-1-carboxylic (ACC) acid oxidase activity in petioles of wild-type tomato (Lycopersicon esculentum L.) plants within 6 to 12 h in association with faster rates of ethylene production. Petioles of flooded plants transformed with an antisense construct to one isoform of an ACC oxidase gene (ACO1) produced less ethylene and had lower ACC oxidase activity than those of the wild type. Flooding promoted epinastic curvature but did so less strongly in plants transformed with the antisense construct than in the wild type. Exogenous ethylene, supplied to well-drained plants, also promoted epinastic curvature, but transformed and wild-type plants responded similarly. Flooding increased the specific delivery (flux) of ACC to the shoots (picomoles per second per square meter of leaf) in xylem sap flowing from the roots. The amounts were similar in both transformed and wild-type plants. These observations demonstrate that changes in ACC oxidase activity in shoot tissue resulting from either soil flooding or introducing ACC oxidase antisense constructs can influence rates of ethylene production to a physiologically significant extent. They also implicate systemic root to shoot signals in regulating the activity of ACC oxidase in the shoot.     

Metabolism of 1-Aminocyclopropane-1-Carboxylic Acid in Etiolated Maize Seedlings Grown under Mechanical Impedance

We investigated the metabolism of 1-aminocyclopropane-1-carboxylic acid (ACC) in etiolated maize (Zea mays L.) seedlings subjected to mechanical impedance by applying pressure to the growing medium. Total concentrations of ACC varied little in unimpeded seedlings, but impeded organs accumulated ACC. Roots had consistently higher concentrations of ACC than shoots or seeds, regardless of treatment. The concentration of ACC in the roots increased more than 100% during the first hour of treatment irrespective of the pressure applied; in shoots, total ACC concentration increased 46% at either low or high pressure during the first hour of treatment. The bulk of ACC synthesized under impeded and unimpeded conditions was present in a conjugated form, presumably, 1-(malonylamino)-cyclopropane-1-carboxylic acid. However, 1-(malonylamino)-cyclopropane-1-carboxylic acid increased 73% over controls after 10 hours at 25 kilopascals of pressure. Unimpeded tissue had about 77% ACC as the conjugate and 17% as free ACC, and less than 6% was used in ethylene production. Increased amounts of ACC were converted into ethylene under stress. In vivo ACC synthase activity in roots became six and seven times higher only 1 hour after initiation of treatment at 25 and 100 kilopascals of pressure, respectively, and remained high for at least 6 hours. However, the immediate and massive conjugation of mechanically induced ACC suggests that ACC N-malonyltransferase may play an important role in the regulation of mechanically induced ethylene production. After 8 hours, in vivo activity of the ethylene-forming enzyme complex increased 100 and 50% above normal level at 100 and 25 kilopascals, respectively. Furthermore, ethylene-forming enzyme complex activity was significantly greater at 100 kilopascals than in controls as early as 1 hour after treatment initiation. These data suggest that regulation of ethylene production under mechanical impedance involves the concerted action of ACC synthase, the ethylene-forming enzyme complex, and ACC N-malonyltransferase.     

Ethylene Production and 1-Aminocyclopropane-1-Carboxylic Acid Conjugation in Thermoinhibited Cicer arietinum L. Seeds

The effect of supraoptimal temperatures (30°C, 35°C) on germination and ethylene production of Cicer arietinum (chick-pea) seeds was measured. Compared with a 25°C control, these temperatures inhibited both germination and ethylene production. The effect of supraoptimal temperatures could be alleviated by treating the seeds with ethylene. It was concluded that one effect of high temperature on germination was due to its negative effect on ethylene production. This inhibitory effect of high temperature was due to increased conjugation of 1-aminocyclopropane-1-carboxylic acid to 1-(malonylamino)cyclopropane-1-carboxylic acid and to an inhibition of ethylene-forming enzyme activity.     

Potamogeton pectinatus Is Constitutively Incapable of Synthesizing Ethylene and Lacks 1-Aminocyclopropane-1-Carboxylic Acid Oxidase

A highly sensitive laser-driven photoacoustic detector responsive to [less than or equal to]2.1 nmol m-3 ethylene (50 parts per trillion [v/v]) was used for ethylene analysis. Dark-grown plants of Potamogeton pectinatus L. growing from small tubers made no ethylene. Exposure of shoots to white light, wounding, submergence in water followed by desubmergence, partial oxygen shortage, indole acetic acid, or carbon dioxide failed to induce ethylene production, although clear effects were observed in Pisum sativum L. Some ethylene was released after applying high concentrations of the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC; 10 mol m-3) to P. pectinatus, but the amount was trivial compared with that released by P. sativum. More endogenous ACC was found in P. pectinatus than in P. sativum. Considerable ACC oxidase activity was present in tissue extracts of P. sativum. However, no ACC oxidase activity was found in P. pectinatus, indicating that this is where ethylene production is arrested.     

Regulation of Auxin-induced Ethylene Production in Mung Bean Hypocotyls: Role of 1-Aminocyclopropane-1-Carboxylic Acid

Ethylene production in mung bean hypocotyls was greatly increased by treatment with 1-aminocyclopropane-1-carboxylic acid (ACC), which was utilized as the ethylene precursor. Unlike auxin-stimulated ethylene production, ACC-dependent ethylene production was not inhibited by aminoethoxyvinylglycine, which is known to inhibit the conversion of S-adenosylmethionine to ACC. While the conversion of methionine to ethylene requires induction by auxin, the conversion of methionine to S-adenosylmethionine and the conversion of ACC to ethylene do not. It is proposed that the conversion of S-adenosylmethionine to ACC is the rate-limiting step in the biosynthesis of ethylene, and that auxin stimulates ethylene production by inducing the synthesis of the enzyme involved in this reaction.     

Kinetin Enhanced 1-Aminocyclopropane-1-Carboxylic Acid Utilization during Alleviation of High Temperatures Stress in Lettuce Seeds

The thermoinhibition at 35 and 32°C of pregermination ethylene production and germination in lettuce (Lactuca sativa L. cv Mesa 659) seeds was synergistically or additively alleviated by 0.05 millimolar kinetin (KIN) and 10 millimolar 1-aminocyclopropane-1-carboxylic acid (ACC). The synergistic effect of KIN + ACC on ethylene production and germination at 35°C was inhibited by Co²⁺ (44-46%) but not by aminoethoxyvinyl glycine (AVG). The uptake of ACC by the seed was not influenced by KIN. Upon slitting of the seed coats (composed of pericarp, testa and endosperm), following the uptake of chemicals, ACC was readily converted into ethylene at all temperatures, and the synergistic effects of KIN + ACC at 35°C were lost. At 35°C, KIN acted synergistically with ACC or ethephon (ETH) in alleviating the osmotic restraint. At 25°C, ETH was more active than KIN or KIN + ACC in overcoming the osmotic restraint. Thus, the integrity of the seed coats, the KIN-enhanced ACC utilization, and an interaction of KIN with the ethylene produced may be the basis for the synergistic or additive effects of KIN + ACC at high temperature.     

全雌系苦瓜ACC合成酶基因cDNA克隆及序列分析

以全雌系苦瓜‘X-Hei-d-d’花蕾为材料,根据已报道ACC合成酶(1-aminocyclopropane-1-carboxylic acid synthase,ACS)保守氨基酸序列设计简并引物,采用RT-PCR技术及序列拼接,获得了全雌系苦瓜ACS基因cDNA序列,命名为Mc-ACS4(GenBank登录号:FJ459814)。该序列包含一个1 455 bp的完整开放阅读框,编码484个氨基酸,具有7个保守区;系统进化上与普通苦瓜ACS基因首先聚类,同源性达99%,二者仅有2个氨基酸差异,推测可能与全雌系苦瓜性别分化有关。     

五爪金龙茎的解剖结构

运用常规石蜡切片、显微观察及显微照相的方法, 对五爪金龙( Ipomoea cairica) 茎的结构进行了观察研究, 结果表明: 五爪金龙茎的解剖结构以初生结构为主, 维管形成层已经形成, 但次生结构尚不发达。通常具3～6 个空腔, 初步推断其为裂生式分泌道; 表皮外弦向壁增厚, 具角质层, 具气孔及气室;紧贴表皮内方的1～3 层和皮层最内1～3 层的细胞可能为分泌细胞; 具双韧维管束, 木质部极为发达, 导管细胞紧密排列, 围绕内韧皮部和中央的髓而成一圆周; 形成层位于外韧皮部与木质部之间; 茎中央是大型薄壁细胞构成的髓, 具簇晶。