Age-Dependent Discrimination between Stereoisomers of 1-Amino-2-Ethylcyclopropane-1-Carboxylic Acid in Carnation Petals

The ability of carnation petals (Dianthus caryophyllus L. cv White Sim) of different ages to convert the cis and trans isomers of 1-amino-2-ethylcyclopropane-1-carboxylic acid (AEC) to 1-butene was studied. Young petals, which produce ethylene at a low rate, convert both cis- and trans-AEC to 1-butene with low efficiency and at equal rates. In senescing petals, the rate of conversion of cis-AEC remains low, but there is a marked increase in the rate of trans-AEC conversion. Thus there is a clear evidence of stereodiscrimination between the isomers. Stimulating the rate of senescence by treatment with either 1-aminocyclopropane-1-carboxylic acid or ethylene further increases the rate of trans-AEC conversion. Delaying of petal senescence by silver thiosulphate or aminooxyacetic acid inhibits the rise in trans-AEC conversion.     

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。     

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     

Synthesis of Polyoxamic Acid (2-Amino-2-deoxy-l-xylonic Acid

The rate of precipitation of the retrograded amylose product from a dil. amylose solution was determined by the centrifugal method. The results showed that the relation of the quantity of precipitate vs. time did not fit the typical second order reaction for the coalescence of colloidal particles but fitted the crystallization formula, in appearance.

The rate of precipitation was in proportion to (c-c_a)^1.5, where c is the amylose concentration and c_a the concentration of the dil. solution phase in the phase-separated solution. When the temperature dependence of the rate was treated according to the crystallization of polymers, it was found that the rate was in proportion to T_m²/T(ΔT)², where T_m is the melting point of the polymer in solution and ΔT is (T_m?T). The T_m thus obtained was 120°C for an amylose solution. These results suggested a certain correlation between the amylose retrogradation and the crystallization.     

The Effects of l-Azetidine-2-Carboxylic Acid (Analogue of Proline) on Dental Cytodifferentiations in vitro

The action of t-azetidine-2-carboxylic acid (an analogue of proline) on the cytodifferentiation of odontoblasts and ameloblasts of mouse tooth buds cultivated In vitro has been studied. The results of our morphological, cytological and functional investigations suggest that the expression of differentiation of ameloblasts is partially conditioned by collagen and/or associated mucopolysaccharides contained in predentin.     

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.     

Evidence for 1-(Malonylamino)cyclopropane-1-Carboxylic Acid Being the Major Conjugate of Aminocyclopropane-1-Carboxylic Acid in Tomato Fruit

Tomato (Lycopersicon esculentum Miller) fruit discs fed with [2,3-¹⁴C]1-aminocyclopropane-1-carboxylic acid (ACC) formed 1-malonyl-ACC (MACC) as the major conjugate of ACC in fruit throughout all ripening stages, from immature-green through the red-ripe stage. Another conjugate of ACC, γ-glutamyl-ACC (GACC), was formed only in mature-green fruit in an amount about 10% of that of MACC; conjugation of ACC into GACC was not detected in fruits at other ripening stages. No GACC formation was observed from etiolated mung bean (Vigna radiata [L.] Wilczek) hypocotyls, etiolated common vetch (Vicia sativum L.) epicotyls, or pea (Pisum sativum L.) root tips, etiolated epicotyls, and green stem tissue, where active conversion of ACC into MACC was observed. GACC was, however, formed in vitro in extracts from fruit of all ripening stages. GACC formation in an extract from red fruit at pH 7.15 was only about 3% of that at pH 8.0, the pH at which most assays were run. Our present in vivo data support the previous contention that MACC is the major conjugate of ACC in plant tissues, whereas GACC is a minor, if any, conjugate of ACC. Thus, our data do not support the proposal that GACC formation could be more important than MACC formation in tomato fruit.     

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.     

植物的成花逆转

成花逆转是生长发发育过程中的特殊现象,与环境因素、成花决定的程度及遗传因素有关。逆转为我们从另一角度研究开花现象提供了一个枘地。文章主要介绍成花志的类型,研究成花的逆转的体系。引起成花逆转的因素以及逆转九一与成花决定之间的关系。     

Synthesis of dl-4-Amino-2-hydroxybutyric Acid

Male Wistar rats were given purified diets containing safflower (SAF), perilla (PER), or palm (PAL) oils with or without 1% tea polyphenols (TP) for 3 weeks, and chemical mediator releasing activity from rat peritoneal exudate cells (PEC) was measured. Histamine releasing activity was not influenced by TP, while histamine release and intracellular histamine content were significantly increased in the PAL-fed group. On the contrary, leukotriene B₄ (LTB₄) release was significantly lower in rats fed PER than in those fed SAF and PAL, and TP significantly decreased the release in all fat groups. TP also significantly inhibited the release of LTB₅, which was generated only in rats fed PER. TP significantly decreased the proportion of arachidonic acid (AA) in PEC in the SAF-fed group and that of eicosapentaenoic acid (EPA), the precursor of LTB₅ in the PER-fed group, but did not influence that of AA in the PAL- and PER-fed group. These results suggest that ingestion of TP improves type I allergic symptom through the inhibition of LT release though the inhibition by TP could not be totally explained by the reduction of substrate fatty acid.     

A Seven-Gene Locus for Synthesis of Phenazine-1-Carboxylic Acid by Pseudomonas fluorescens 2-79

Pseudomonas fluorescens 2-79 produces the broad-spectrum antibiotic phenazine-1-carboxylic acid (PCA), which is active against a variety of fungal root pathogens. In this study, seven genes designated phzABCDEFG that are sufficient for synthesis of PCA were localized within a 6.8-kb BglII-XbaI fragment from the phenazine biosynthesis locus of strain 2-79. Polypeptides corresponding to all phz genes were identified by analysis of recombinant plasmids in a T7 promoter/polymerase expression system. Products of the phzC, phzD, and phzE genes have similarities to enzymes of shikimic acid and chorismic acid metabolism and, together with PhzF, are absolutely necessary for PCA production. PhzG is similar to pyridoxamine-5′-phosphate oxidases and probably is a source of cofactor for the PCA-synthesizing enzyme(s). Products of the phzA and phzB genes are highly homologous to each other and may be involved in stabilization of a putative PCA-synthesizing multienzyme complex. Two new genes, phzX and phzY, that are homologous to phzA and phzB, respectively, were cloned and sequenced from P. aureofaciens 30-84, which produces PCA, 2-hydroxyphenazine-1-carboxylic acid, and 2-hydroxyphenazine. Based on functional analysis of the phz genes from strains 2-79 and 30-84, we postulate that different species of fluorescent pseudomonads have similar genetic systems that confer the ability to synthesize PCA.     

Export of Abscisic Acid, 1-Aminocyclopropane-1-Carboxylic Acid,Phosphate, and Nitrate from Roots to Shoots of Flooded Tomato Plants (Accounting for Effects of Xylem Sap Flow Rate on Concentration and Delivery)

We determined whether root stress alters the output of physiologically active messages passing from roots to shoots in the transpiration stream. Concentrations were not good measures of output. This was because changes in volume flow of xylem sap caused either by sampling procedures or by effects of root stress on rates of whole-plant transpiration modified concentrations simply by dilution. Thus, delivery rate (concentration x sap flow rate) was preferred to concentration as a measure of solute output from roots. To demonstrate these points, 1-aminocyclopropane-1-carboxylic acid (ACC), abscisic acid, phosphate, nitrate, and pH were measured in xylem sap of flooded and well-drained tomato (Lycopersicon esculentum Mill., cv Ailsa Craig) plants expressed at various rates from pressurized detopped roots. Concentrations decreased as sap flow rates were increased. However, dilution of solutes was often less than proportional to flow, especially in flooded plants. Thus, sap flowing through detopped roots at whole-plant transpiration rates was used to estimate solute delivery rates in intact plants. On this basis, delivery of ACC from roots to shoots was 3.1-fold greater in plants flooded for 24 h than in well-drained plants, and delivery of phosphate was 2.3-fold greater. Delivery rates of abscisic acid and nitrate in flooded plants were only 11 and 7%, respectively, of those in well-drained plants.     

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.     

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.