Differential Responsiveness in Zonal Growth of Cocklebur Seed Axes to CO2, C2H4, O2 and Respiration Inhibitors

The axial growth of de-coated cocklebur (Xanthium pennsylvanicumWallr.) seeds, whose axes were divided into 4 zones, was examinedin relation to the temperature-dependent shift of the effectof C₂H₄ on germination. At 23?C, where both C₂H₄ and CO₂ stimulatedgermination, CO₂ promoted the axial growth at the radicle tipzone, whereas C₂H₄ promoted growth in the proximal portion ofthe axis. At 33?C, C₂H₄ inhibited germination, and stronglysuppressed the growth at the radicle tip, whereas the effectof CO₂ did not change. The inhibition of growth at the radicletip zone was alleviated by O₂ enrichment, which also reversedthe inhibition of germination. It is thus apparent that thetemperature-dependent shift of the action of C₂H₄ is associatedwith a temperature-dependent responsiveness of the radicle tipzone to C₂H₄. Growth of the radicle tip zone was sensitive toNaN₃, whereas the proximal portion was sensitive to benzohydroxamicacid, an inhibitor of alternative respiration, suggesting thatthere may be an increase in the operation of the alternativerespiration path along a gradient of axial tissue from the tiptowards the cotyledonary side. The effects of CO₂ and C₂H₄ arediscussed in relation to the different respiratory activitiesin each axial zone of cocklebur seeds. (Received May 9, 1986; Accepted November 6, 1986)     

Geosmin production and polyphasic characterization of Oscillatoria limosa Agardh ex Gomont isolated from the open canal of a large drinking water system in Tianjin City,China

Taste and odor (T & O) episodes always cause strong effects on drinking water supply system. Luanhe River diversion into Tianjin City in China is an important drinking water resource. Massive growth of a benthic filamentous cyanobacterium with geosmin production in the open canal caused a strong earthy odor episode in Tianjin. On the basis of the morphological and molecular identification of this cyanobacterium as Oscillatoria limosa Agardh ex Gomont, the genetic basis for geosmin biosynthesis and factors influencing growth and geosmin production of O. limosa CHAB 7000 were studied in this work. A 2268-bp open reading frame, encoding 755 amino acids, was amplified and characterized as the geosmin synthase gene (geo), followed by a cyclic nucleotide-binding protein gene (cnb). Phylogenetic analysis implied that the evolution of the geosmin genes in O. limosa CHAB 7000 might involve a horizontal gene transfer event. Examination on the growth and geosmin production of O. limosa CHAB 7000 at different light intensities showed that the maximum geosmin production was observed at 10 μmol photons m⁻² s⁻¹, while the optimum growth was at 60 μmol photons m⁻² s⁻¹. Under three temperature conditions (15 °C, 25 °C, and 35 °C), the maximum growth and geosmin production were observed at 25 °C. Most amounts of geosmin were retained in cells during the growth phase, but high temperature and low light intensity increased the release of geosmin into the medium, implying that O. limosa CHAB 7000 had a high potential harm for the release of geosmin from its cells at these adverse conditions.     

Identification of geosmin as a volatile metabolite of Penicillium expansum.

Cultures of Penicillium expansum produce a musty, earthy odor. Geosmin [1,10-trans-dimethyl-trans(9)-decalol] was identified by gas chromatography-mass spectrometry from headspace samples of P. expansum cultures. Olfactory comparison of P. expansum cultures with a geosmin standard indicated geosmin is the primary component of the odor associated with P. expansum.     

The electronic structure of the C2H4O···2HF tri-molecular heterocyclic hydrogen-bonded complex: a theoretical study

The geometries of three isomers of the C₂H₄O···2HF tri-molecular heterocyclic hydrogen-bonded complex were examined through B3LYP/aug-cc-pVDZ calculations. Analysis of structural parameters, determination of CHELPG (charge electrostatic potential grid) intermolecular charge transfer, interpretation of infrared stretching modes, and Bader’s atoms in molecules (AIM) theory calculations was carried out in order to characterize the hydrogen bonds in each isomer of the C₂H₄O···2HF complex. The most stable structure was determined through the identification of hydrogen bonds between C₂H₄O and HF, (O···H), as well as in the hydrofluoric acid dimer, (HF^D–R···HF^D). However, the existence of a tertiary interaction (F^λ···H^α) between the fluoride of the second hydrofluoric acid and the axial hydrogen atoms of C₂H₄O was decisive in the identification of the preferred configuration of the C₂H₄O···2HF system. Figure Geometries of three isomers of the C₂H₄O···2HF tri-molecular heterocyclic hydrogen-bonded complex     

Identification of geosmin as a volatile metabolite of Penicillium expansum.

Cultures of Penicillium expansum produce a musty, earthy odor. Geosmin [1,10-trans-dimethyl-trans(9)-decalol] was identified by gas chromatography-mass spectrometry from headspace samples of P. expansum cultures. Olfactory comparison of P. expansum cultures with a geosmin standard indicated geosmin is the primary component of the odor associated with P. expansum.     

Odor Qualities and Thresholds of Physiological Metabolites of 1,8‐Cineole as an Example for Structure?Activity Relationships Considering Chirality Aspects

The present study aimed at analyzing the odor properties of a group of physiological human metabolites of the odorant 1,8‐cineole: 2,3‐dehydro‐, α2,3‐epoxy‐, α/β2‐hydroxy‐, α3‐hydroxy‐, 4‐hydroxy‐, 7‐hydroxy‐, 9‐hydroxy‐, 2‐oxo‐, and 3‐oxo‐1,8‐cineole. These metabolites constitute a group of structurally closely related molecules, which differ mainly in nature and position of O‐containing functional groups. They thus offer the possibility to correlate odor properties with molecular structure, i.e., to establish structure? odor relationships of compounds that are biologically generated from a potent odorant as parent substance. Generally, the metabolites preserved the eucalyptus‐like odor quality of 1,8‐cineole but showed additional odor notes such as sweet, citrus‐like, plastic‐like, earthy, musty, and faecal, which made them distinguishable. The individual enantiomers of chiral molecules also exhibited different odors. With the exception of 2,3‐dehydro‐1,8‐cineole, all metabolites showed a highly decreased odor threshold in comparison to 1,8‐cineole. The determination of odor qualities and odor thresholds was accomplished by gas chromatography/olfactometry (GC/O) on achiral and chiral GC capillaries. The results were correlated with common theories on structure? odor relationships.     

The role of hydroxyl radical as a messenger in Cr(VI)-induced p53 activation

The present study investigates whether reactive oxygen species (ROS)are involved in p53 activation, and if they are, which species isresponsible for the activation. Our hypothesis is that hydroxyl radical(·OH) functions as a messenger for the activation of this tumorsuppressor protein. Human lung epithelial cells (A549) were used totest this hypothesis. Cr(VI) was employed as the source of ROS due toits ability to generate a whole spectrum of ROS inside the cell. Cr(VI)is able to activate p53 by increasing the protein levels and enhancingboth the DNA binding activity and transactivation ability of theprotein. Increased cellular levels of superoxide radicals(O₂·), hydrogen peroxide(H₂O₂), and ·OH radicals were detected on theaddition of Cr(VI) to the cells. Superoxide dismutase, by enhancing theproduction of H₂O₂ from O₂·radicals, increased p53 activity. Catalase, anH₂O₂ scavenger, eliminated ·OH radicalgeneration and inhibited p53 activation. Sodium formate and aspirin,·OH radical scavengers, also suppressed p53 activation. Deferoxamine,a metal chelator, inhibited p53 activation by chelating Cr(V) to makeit incapable of generating radicals from H₂O₂.NADPH, which accelerated the one-electron reduction of Cr(VI) to Cr(V)and increased ·OH radical generation, dramatically enhanced p53activation. Thus ·OH radical generated from Cr(VI) reduction in A549cells is responsible for Cr(VI)-induced p53 activation.

     

Further Study on the Involvement of Cyanide-Resistant Respiration in the Germination of Cocklebur Seeds

The effect of propyl-gallate (PG) and benzohydroxamic acid (BHAM),inhibitors of cyanide-resistant, alternative respiration path(AP), on germination were examined using after-ripened upperand lower cocklebur (Xanthium pennsylvanicum Wallr.) seeds pre-soakedat 23?C for various periods. Germination was strongly suppressedby PG or BHAM at concentration above 2 mM. However, germinationwas enhanced by low concentrations of PG or BHAM (0.25 or 0.5mM) which reduced some portions of AP operation. Similarly,the high temperature-induced germination of pre-soaked upperseeds was promoted by the same low concentration range of PGor BHAM, in which PG and BHAM were effective only when appliedat the start of high temperature incubation. The inhibitionof germination by C₂H₄ at high temperature occurred only whenseeds were exposed to C₂H₄ during the earlier period of hightemperature incubation, and delayed application tended to promotetheir germination, although most of germinated seeds did notexhibit the normal germination behaviour of predominant radicleprotrusion. If the upper seeds had been subjected to a short-timepre-soaking, the inhibition of high temperature-induced germinationby C₂H₄ was prevented by the low concentrations of PG or BHAM,although the germination restored was mostly an abnormal, predominantlycotyldonary growth, suggesting that the germination inhibitionby C₂H₄ may be involved in some step of axial growth or in thegrowth of some specific axial zone. The lower concentrationsof PG or BHAM were promotive to the axial growth even at 33?C.Based on these results, the involvement of AP in cocklebur seedgerminaton is discussed in relation to the differential growthof axial and cotyledonary tissues. (Received May 2, 1986; Accepted October 27, 1986)     

Application of ion-pair high-performance liquid chromatography to detection of the atypical coproporphyrin isomers II and IV in human faeces

A highly selective and sensitive method has been developed for the detection of small amounts of the atypical isomers II and IV of coproporphyrin in human faeces. This method combines liquid—liquid extraction and solid-phase sampling techniques using talc and C₁₈-modified silica gel as the sorbents. Simultaneous separation of the four coproporphyrin isomers I–IV was achieved by isocratic ion-pair high-performance liquid chromatography. Stool samples of healthy subjects (n = 12) contained 1.1 ± 0.4% (mean ± S.D.) isomer II and 2.2 ± 0.9% isomer IV of total coproporphyrins. A somewhat higher content of isomer II (2.7%) and isomer IV (5.4%) was found in faeces of a patient suffering from porphyria variegata.     

New catalyst design for polymerization of norbornene esters by reducing intramolecular interaction

We have used density functional theory to study palladium-based catalysts commonly used for the polymerization of norbornene derivatives with an ester group. Exo–exo, exo–endo, and endo–endo isomers of catalyst complexes were investigated; the endo–endo isomer was the most stable and inactive due to an intramolecular interaction between Pd and O of the carbonyl group. Phosphine groups are effective in minimizing the Pd–O interaction in the endo–endo isomer and P(C₆H₁₁)₃ was found to be the most efficient reagent. The intramolecular Pd–O interactions were estimated using model complexes, and it was demonstrated that they play a crucial role in stabilizing the endo–endo isomer.Figure Methyl ester norbornene complex for endo–endo isomers with P(C₆H₁₁)₃     

Ethylene Production in Pea and Cocklebur Seeds of Differing Vigour

Relationships between seed vigour and ethylene (C₂H₄) productionwere studied using C₂H₄-responsive fatty cocklebur seeds (Xanthiumpennsyhanicum Wallr.) and C₂H₄-insensitive starchy pea seeds(Pisum sativum L. cv. Alaska), which had been harvested in differentyears and subjected to different storage conditions. In bothspecies, the seeds with the highest vigour evolved the largestamounts of C₂H₄ during a period of water imbibition. The reductionof C₂H₄ production in cocklebur seeds occurred concomitantlywith the reduction in the growth potentials of both axial andcotyledonary tissues. Similarly, the activity of ACC-C₂H₄ conversionincreased with soaking, and was greater in seeds of high vigourcompared with those of low vigour. However, the change in ACCcontent in pea seeds differed from that in cocklebur seeds.That is, pea seeds with high vigour accumulated less ACC duringan imbibition period than those with low vigour. From theseresults it was suggested that the inferior C₂H₄ production bylow vigour pea seeds is mainly attributable to low ACC-C₂H₄conversion, whereas that by low vigour cocklebur seeds is dueto the shortage of ACC supply in addition to the reduced ACC-C₂H₄conversion. However, germination of deteriorated cocklebur seedswas not restored by exposure to ACC or C₂H₄, suggesting thatthe loss of seed vigour reduces the responsiveness of seedsto C₂H₄ as well as C₂H₄ production. Key words: Pea, cocklebur, seed vigour, ethylene production, 1-aminocyclopropane-1-carboxylic acid     

Interrelation between Ethylene and Carbon Dioxide in Relation to Respiration and Adenylate Content in the Pre-Germination Period of Cocklebur Seeds

Effects of C₂H₄ and CO₂ on respiration of pre-soaked upper cocklebur(Xanthium pennsylvanicum Wallr.) seeds during a pre-germinationperiod were examined in relation to effects of the two gaseson germination. At 33?C, cocklebur seed germination was greatlystimulated. This high temperature-stimulated germination wasseverely inhibited by C₂H₄, but not by CO₂, although both gasesstimulated germination at 23?C. C₂H₄ promoted seed respirationat 23?C, but its promotive effect decreases with increasingtemperature and disappeared at about 35?C, while CO₂ stimulatedrespiration regardless of temperature. CO₂ augmented the operationof the CN-sensitive, cytochrome path (CP) regardless of temperature,resulting in an increase in the ratio of the CP flux to a CN-resistant,alternative path (AP) flux. On the other hand, C₂H₄ augmentedthe operation of both paths, particularly of the AP, at 23?C,where it promoted germination. However, at 33?C where germinationis suppressed by C₂H₄, C₂H₄ preferentially stimulated respirationvia the AP, thus leading to an extremely high ratio of AP toCP. The inhibitory effect of C₂H₄ on germination at 33?C disappearedcompletely in enriched O₂, under which conditions CP is knownto be augmented. At 23?C, CO₂ and C₂H₄ acted independently incontrolling seed respiration, but they were antagonistic at33?C. The independent action appeared when the AP flux was verylow relative to the CP flux, while the antagonism appeared whenthe AP flux had risen. This differential action of the two gasesat different temperatures was also observed in the ATP level,adenylate pool size and energy charge of the axial tissues.These results suggest that the germination-controlling actionsof both CO₂ and C₂H₄ are fundamentally manifested through themodification of respiratory systems. However, the germination-inhibitingeffect of C₂H₄ at 33 ?C was not removed by inhibitors of AP,and there was little difference in the adenylate compounds betweenthe C₂H₄-treated and non-treated seeds at 33?C. Therefore, thephysiological action of C₂H₄ can not be explained only in termsof regulation of the respiratory system. (Received January 24, 1986; Accepted November 17, 1986)     

Solvatothermal chemistry of organically-templated vanadium fluorides and oxyfluorides

The solvatothermal reactions of V₂O₅, the appropriate organoamine and HF in the temperature range 100-180 °C yielded a series of vanadium fluorides and oxyfluorides. The compounds [NH₄][H₃N(CH₂)₂NH₃][VF₆] (1) and [H₃N(CH₂)₂NH₃][VF₅(H₂O)] (2) contain mononuclear V(III) anions, while [H₃N(CH₂)₂NH₂(CH₂)₂NH₃]₂ [VF₅(H₂O)]₂[VOF₄(H₂O)] (3) exhibits both V(IV) and V(III) mononuclear anions. Both compound 4, [H₃NCH₂(C₆H₄)CH₂NH₃][VOF₄]·H₂O (4·H₂O) and compound 5, [HN(C₂H₄)₃NH][V₂O₂F₆ (H₂O)₂] (5) contain binuclear anions constructed from edge-sharing V(IV) octahedra. In contrast, [H₃N(CH₂)₂NH₂(CH₂)₂NH₃]₂[V₄O₄F₁₄(H₂O)₂], (6) exhibits a tetranuclear unit of edge- and corner-sharing V(IV) octahedra. Compound 7, [H₃N(CH₂)₂NH₂][VF₅], contains chains of corner-sharing {V^IVF₆} octahedra, while [H₂N(C₂H₄)₂NH₂]₃[V₄F₁₇O]·1.5H₂O (8·1.5H₂O) is two-dimensional with a layer of V(III) and V(IV) octahedra in an edge- and corner-sharing arrangement. In the case of [H₃N(CH₂)₂NH₃][V₂O₆] (9), there was no fluoride incorporation, and the anion is a one-dimensional chain of corner-sharing V(V) tetrahedra.     

Characterization of <Emphasis Type="Italic">Penicillium</Emphasis> Species Isolated from Grape Berries by Their Internal Transcribed Spacer (ITS1) Sequences and by Gas Chromatography–Mass Spectrometry Analysis of Geosmin Production

Geosmin (trans-1,10-dimethyl-trans-9-decalol), an earthy-musty compound, has been identified in wines and in grape juice, in which its presence is highly detrimental to the aromatic quality. Geosmin has a biological origin, and the analysis of rotten grape microflora has been done on two grape varieties (Semillon, Cabernet Sauvignon) from six parcels of the Bordeaux region over 3 years (1999, 2000, 2001). Forty-three Penicillium-related species have been analyzed by gas chromatography–mass spectrometry (GC–MS) for their geosmin production. GC–MS analysis has demonstrated that the earthy odor was always correlated with the presence of geosmin. Phenotypic characterization of Penicillium spp. being ambiguous, a molecular characterization by rDNA internal transcribed spacer (ITS1) sequencing was performed for all strains. The results evidenced that all strains producing geosmin belonged to only one species, P. expansum, and that the other strains, not producing geosmin, belonged to three species: P. purpurogenum, P. thomii, and Talaromyces wortmanii.     

Low Resolution Mass Spectra of Some Unsaturated δ-Lactones

Mass spectra of the δ-lactones of the following 5-hydroxy-2-enoic acids were determined: 5-hydroxyhex-2-enoic acid (I), 5-hydroxyoct-2-enoic acid (II), 5-hydroxydec-2-enoic acid (III), 5-hydroxydodec-2-enoic acid (IV), 5-hydroxy-8-methylnon-2-enoic acid (V), 5-hydroxy-6-ethyloct-2-enoic acid (VI), 5-hydroxy-5, 6, 6-trimethylhept-2-enoic acid (VII), and 5-hydroxy-5-methylnon-2-enoic acid (VIII). The following modes of fragmentation are consistent with observed m/e values, metastable peaks, and established modes of breakdown in compounds containing similar atomic groupings:—1. Loss of side chain, resulting in ions at m/e 97 for I-VI and at m/e 111 and 153 for VII and VIII (diagnostic peaks); 2. 1,4-Rupture of the ring giving an ion at m/e 68 (diagnostic peak) which loses CO to give m/e 40; 3. Loss of CO from m/e 97 fragment to give m/e 69 which breaks down further to m/e 41→m/e 39; 4. 1, 4-Rupture of m/e 111 and m/e 153 fragments to give m/e 43 and 85, further breakdown of m/e 85→57→41→39; 5. Loss of H₂O from the molecular ion providing there is a hydrogen atom on C₅ and the side chain is at least 3 carbon atoms in length, further loss of H₂O when the side chain is equal to C5 or C7; 6. Loss of CO₂ from the molecular ion of I, IV-VIII; 7. Loss of CO from all molecular ions; 8. Loss of 2×28 from the molecular ions of III, IV, V, VI; 9. Loss of (18 + 28) from the molecular ion of III, IV, V, VI; 10. Loss of 60 from the molecular ion of II, III, IV, V, VI; 11. Formation of M + 1 ion (169) of VII and VIII; 12. Formation of M + 1 ion (143) of saturated δ-octalactone and loss of H₂O from this M + 1 ion.     

Control of the germination of secondary dormant cocklebur seeds by various germination stimulants

The responsiveness of non-dormant, upper cocklebur (Xanthiumpennsylvanicum Wallr.) seeds to various germination stimulants,such as CO₂ C₂H₄ CS(NH₂)₂, BA and enriched O₂, decreased withincreasing periods of water imbibition and was completely lostin the state of secondary dormancy. Unlike CO₂ BA and CS(NH₂)₂however, C₂H₂ and enriched O₂ effectively prevented the developmentof secondary dormancy, and their combination was the most effectivefor stimulating the germination of seeds which had undergoneimbibition for a long time. CS(NH₂)₂ and BA were effective,not by themselves but either under anaerobiosis or elevatedO₂ tension. Growth of the axial and cotyledonary segments excisedfrom aged seeds remained responsive to these germination stimulantsand could be further stimulated by exogenous C₂H₂. With imbibitionat a lower temperature, the seeds maintained high germinationin response to various stimulants and a high rate of C₂H₂ andCO₂ production during a long period of water imbibition. Theseresults are discussed in terms of the two possible causes forthe loss of responsiveness or induction of the secondary dormancy. (Received June 27, 1978; )     

Microextraction and Gas Chromatography/Mass Spectrometry for improved analysis of geosmin and other fungal “off” volatiles in grape juice

Geosmin is a volatile fungal metabolite with an earthy aroma produced in grape products from rotten grapes. The accumulation of geosmin in grapes is caused by the interaction of Botrytis cinerea and Penicillium expansum. Solid Phase Microextraction (SPME) has great utility for collecting volatile compounds in wine. However, contamination with earthy odours may have occurred previously in the must and novel methods are required for this commodity. In the present report, several parameters of the SPME were evaluated to optimize geosmin extraction. The method permitted quantification of geosmin and other fungal volatiles by Gas Chromatography-Mass Spectrometer (GC-MS) at very low concentrations. Limits of detection and quantification (L_D and L_Q) for geosmin were 4.7 ng L⁻¹ and 15.6 ng L⁻¹ respectively. The RSD was 4.1% and the recovery rates ranged from 115% to 134%. Uniquely, haloanisoles were analyzed by using only one internal standard (2,3,6-trichloroanisole) thus avoiding the synthesis of deuterated anisole analogues that are used as internal standard in other methods. The method was used for the analysis of grape juice samples inoculated with B. cinerea and P. expansum. Geosmin and methylisoborneol were the compounds that appeared to contribute most to earthy odours, although other fungal compounds which are claimed to cause earthy or mouldy off-odours were detected (e.g. 1-octen-3-ol and fenchol).     

Origin of (−)-Geosmin on Grapes: On the Complementary Action of Two Fungi, <Emphasis Type="Italic">Botrytis Cinerea</Emphasis> and <Emphasis Type="Italic">Penicillium Expansum</Emphasis>

One of the consequences of rot on grapes is the development of volatile compounds giving fungal, mouldy or earthy odours. Among these compounds, (−)-geosmin (trans-1,10-dimethyl-trans-9-decalol), a powerful aromatic compound with an earthy smell is a persistent defect in grape juice and wines made with at least partially rotten grapes. A microbiota analysis of rotten grapes containing (−)-geosmin was carried out on sites from four French regions from 1999 to 2002, to clarify the involvement in geosmin appearance of Streptomyces spp. and Penicillium spp., two types of microorganisms present on grape, that are known for their ability to produce geosmin. In earthy grapes, Botrytis cinerea was largely present. Different species of Streptomyces were also isolated, but their pH sensitivity was an extremely limiting parameter for their development on grape juice, grapes or stem, and consequently for their potentiality to generate geosmin in the vineyard. Penicillium expansum, producing geosmin on a model medium, was omnipresent. Penicillium carneum, which is also a geosmin producer, was represented by a single colony during the 4 years of this study. P. expansum alone was able to produce geosmin on a model medium but not on grapes. However, after 7 days’ pre-culture of some B. cinerea strains on grape juice, this juice became favourable to geosmin production by P. expansum. We demonstrated the necessary and complementary action of B. cinerea and P. expansum in geosmin production in grape juice and in crushed grape berries.     

Ethylene Evolution from Bracts and Leaves of Poinsettia, Euphorbia pulcherrima Willd

Woodrow, L. and Grodzinski, B. 1987. Ethylene evolution trombracts and leaves ol Poinsettia, Euphorbia pulcherrima Willd.—J.exp. Bot. 38: 2024–2032. Ethylene release from fully expanded, red and white bracts andleaves of poinsettia, Euphorbia pulcherrima Willd., was compared.On a laminar (area) basis leaves contained about 50 times morechlorophyll and demonstrated 10 times the photosynthetic rateof the bracts. Both tissues contained starch, however, solublecarbohydrate in the bracts consisted primarily of reducing hexoseswhile the leaves contained mainly sucrose for translocation.The total free alpha-amino nitrogen content of the bract tissuewas twice that of the leaf tissue. The leaves contained moreACC (1-aminocyclopropane-1-carboxylic acid) and produced proportionallymore endogenous C²H⁴ than either the red or white bracts. ACC-stimulated₂H₄ release was also greatest from the green tissue indicatingthat the EFE (ethylene forming enzyme) was most active in theleaves. The specific activity of the ¹⁴C₂H₄/¹²C₂H₄ releasedfrom [2,3-¹⁴C]ACC confirmed ACC as the primary precursor ofC₂H₄ in this tissue. Ethylene release from the non-photosynthetic,bract tissue was not markedly affected by alterations in CO₂or light conditions. In green leaf tissue endogeneous ethylenerelease increased from 1·5 to 6·0 pmol C₂H₄ cm^–2h^–1 while ACC-stimulated ethylene release increased from10 to 35 pmol C₂H₄ cm^2– h^1– as the CO₂ partial pressureincreased from 100 to 1 200 µbar. Key words: Poinsettia, ethylene, bracts     

Properties of a Plant growth inhibitor extracted from immature tobacco leaves

Extracts of rapidly expanding tobacco leaves significantly inhibitedthe growth of wheat coleoptiles. Initial experiments showedthat the acitivity was not due to abscisic acid. Purificationof the extract gave a white crystalline compound(s), which hada melting point of 123?C, a molecular weight of 288, and a molecularformula of C₂₀H₃₂O. Principal absorptions in infrared were:3350 (broad), OH; 2910, 2880, 1430, CH₂, CH₃; 1380, 1370 gem-dimethyl;and 970 cm^-1, trans double bond. Ultraviolet data were ^EtOH_max208 nm ( 8,400). Complete reduction showed the presence of threedouble bonds. Chromic acid oxidation of the fully reduced productyielded three major compounds, which were separated by columnchromatography. The mass of each compounds was 292, and eachhad a molecular formula of C₂₀H₃₆O. Infrared analyses gave thefollowing values: 3500 (sharp); 2960, 2865, 1455, CH₂, CH₃;1680 (strong), C = O, 1380 and 1375 cm^–1 gem-dimethyl.However, the melting points varied and were 110, 105, and 80?C,respectively. The nuclear magnetic-resonance scans integratedfor approximately 36 protons and indicated chemical shifts forCH₃, CH₂ and CH ( 0.7–1.7). For these derivatives, theUV data were ^EtOH_max 208 nm (epsil; 410) 286 nm ( 70). Highresolution mass spectral analyses of the products substantiatedthe C₂₀H₃₂O molecular formula proposed for the parent molecule.These data strongly suggest a mixture of diterpene alcohols.The mixture significantly inhibits the growth of wheat coleoptiles. ¹Cooperative investigations of the University of Georgia, Collegeof Agriculture Experiment Station and the Southern Region, AgricultureResearch Service, United States Department of Agriculture. ²Plant Physiologist, USDA, Georgia Coastal Plain ExperimentStation, Tifton, Georgia. ³Microbiologist, National Peanut Research Lab, USDA, ARS, Georgia-SouthCarolina Area, Post Office Box 637, Forrester Drive, Dawson,Georgia. (Received May 17, 1973; )