Quantification of ethylene losses in different container-seal systems and comparison of biotic and abiotic contributions to ethylene accumulation in cultured tissues

Ethylene losses and release were compared in four container- seal systems for in vitro cultures: Erlenmeyer flasks sealed with silicone, caoutchouc or styrene butadiene stoppers and glass bottles with screw caps supplied with caoutchouc septa. The last systems Proved to be the most suitable (i. e. minimum ethylene loss and release) to determine ethylene accumulation during axillary budding of lavandin ( Lavandula officinalis Chaix × Lavandula latifolia Villars cv. Grosso). Gelling agents (agar and Gelrite) also discharges ethylene and agar was identified as the main abiotic source. Mathematical elaboration of experimental data was then performed to estimate biological ethylene production.     

The sealed storage of moist flax with and without the use of chemical preservatives

The suitability of ensilage as a means of preserving flax was investigated in a series of experiments in which 400 kg round bales of fresh flax were sealed in polyethylene film or plastic wrapped, with or without the addition of formic acid at 2.5 litre t^-1 or formalin at 5.6 litre t^-1 at the time of baling. Plastic wrapping provided a more effective seal than the bags which were easily punctured by the flax roots resulting in moulding and deterioration of the flax. Where the seal was not broken untreated flax underwent a clostridial fermentation and the pH fell to about 4.8. Cellulolytic activity degraded the flax fibre over a period of 3 to 6 months. The addition of formic acid reduced the cellulolytic activity provided the seal was not broken. In an experiment with 4 kg batches of flax of 65%, 40% or 25% MC sealed in polyethylene film, the addition of formic or propionic acids at 20 g kg^-1 DM did not prevent moulding and deterioration, but both NH₃ and SO₂ at 40 g kg^-1 DM preserved the physical structure of the flax. The NH₃ darkened the flax and made it pliable and unscutchable while the SO₂ bleached it and preserved the fibre without microbiological deterioration. The presence of acids on the moist stored flax appeared to inhibit the progress of normal water retting.     

Ethylene formation by cultures of Escherichia coli

Growth of Escherichia coli strain B SPAO on a medium containing glucose, NH₄Cl and methionine resulted in production of ethylene into the culture headspace. When methionine was excluded from the medium there was little formation of ethylene. Ethylene formation in methionine-containing medium occurred for a brief period at the end of exponential growth. Ethylene formation was stimulated by increasing the medium concentration of Fe³⁺ when it was chelated to EDTA. Lowering the medium phosphate concentration also appeared to stimulate ethylene formation. Ethylene formation was inhibited in cultures where NH₄Cl remained in the stationary phase. Synthesis of the ethylene-forming enzyme system was determined by harvesting bacteria at various stages of growth and assaying the capacity of the bacteria to form ethylene from methionine. Ethylene forming capacity was greatest in cultures harvested immediately before and during the period of optimal ethylene formation. It is concluded that ethylene production by E. coli exhibits the typical properties of secondary metabolism.Abbreviations HMBA 2-Hydroxy-4-methylthiobutyric acid (methionine hydroxy analogue) - KMBA 2-keto-4-methylthiobutyric acid - MOPS 3-[N-morpholino] propanesulphonic acid     

Significance of Oxygen Supply in Jarosite Biosynthesis Promoted by Acidithiobacillus ferrooxidans

Jarosite [(Na⁺, K⁺, NH₄ ⁺, H₃O⁺)Fe₃(SO₄)₂(OH)₆] is an efficient scavenger for trace metals in Fe- and SO₄ ^2--rich acidic water. During the biosynthesis of jarosite promoted by Acidithiobacillus ferrooxidans, the continuous supply of high oxygen levels is a common practice that results in high costs. To evaluate the function of oxygen in jarosite production by A. ferrooxidans, three groups of batch experiments with different oxygen supply levels (i.e., loading volume percentages of FeSO₄ solution of 20%, 40%, and 70% v/v in the flasks), as well as three groups of sealed flask experiments with different limiting oxygen supply conditions (i.e., the solutions were not sealed at the initial stage of the ferrous oxidation reaction by paraffin but were rather sealed at the end of the ferrous oxidation reaction at 48 h), were tested. The formed Fe-precipitates were characterized via X-ray powder diffraction and scanning electron microscope-energy dispersive spectral analysis. The results showed that the biosynthesis of jarosite by A. ferrooxidans LX5 could be achieved at a wide range of solution loading volume percentages. The rate and efficiency of the jarosite biosynthesis were poorly correlated with the concentration of dissolved oxygen in the reaction solution. Similar jarosite precipitates, expressed as KFe₃ (SO₄) ₂(OH)₆ with Fe/S molar ratios between 1.61 and 1.68, were uniformly formed in unsealed and 48 h sealed flasks. These experimental results suggested that the supply of O₂ was only essential in the period of the oxidation of ferrous iron to ferric but was not required in the period of ferric precipitation.     

The effects of ammonium sulphate deposition and root sinks on soil solution chemistry in coniferous forest soils

The effects of enhanced (NH_{4 2}SO₄deposition on soil solution cation and anion concentrations and annualionic fluxes were followed using a standardised experimental protocolin six European coniferous forests with contrasting soil types, pollutioninputs and climate. Native soil cores containing a ceramic suction cupwere installed in the field, roofed and watered every two weeks withlocal throughfall or local throughfall with added(NH₄)₂SO₄ at 75 kgNH₄ ⁺-N ha^-1 a^-1. Livingroot systems were established in half of the lysimeters.Untreated throughfall NH₄ ⁺-N deposition at thesites ranged from 3.7 to 29 kg ha^-1 a^-1Soil leachates were collected at two weekly intervalsover 12 months and analysed for volume, andconcentrations of major anions and cations. Increasesin soil solution NO₃ ^- concentrations inresponse to N additions were observed after 4–9months at three sites, whilst one sandy soil with highC:N ratio failed to nitrify under any of thetreatments. Changes in NO₃ ^- concentrationsin soil solution controlled soil solution cationconcentrations in the five nitrifying soils, withAl³⁺ being the dominant cation in the more acidsoils with low base saturation. The acidification responses ofthe soils to the (NH_{4 2}SO₄additions were primarily related to the ability of thesoils to nitrify the added NH₄ ⁺. pH and soiltexture seemed important in controllingNH₄ ⁺ leaching in response to the treatments,with two less acidic, clay/clay loam sites showingalmost total retention of added NH₄ ⁺, whilstnearly 75% of the added N was leached asNH₄ ⁺ at the acid sandy soils. The presenceof living roots significantly reduced soil solutionNO₃ ^- and associated cation concentrations attwo of the six sites. The very different responses of the sixsoils to increased (NH₄)₂SO₄deposition emphasise that the establishment of N critical loadsfor forest soils need to allow for differences in N storagecapacity and nitrification potential.     

Ethylene and ethane production in response to salinity stress

Abstract Ethylene and ethane production in mung bean hypocotyl sections were evaluated as possible indicators of stress due to contact with four salts that are common in natural sites. Ethylene production decreased with increasing concentrations of applied NaCl and KCl. When CaCl₂ was applied, the ethylene evolution was greater. However, when MgCl₂ was applied, ethylene evolution remained high then decreased and at higher salt concentrations again showed an increase. NaCl (up to 0.1 kmol m^?1) and KCl (up to 0.5 kmol m^?3) caused a concentration-dependent increase in ethane production. The ethane production with CaCl₂ was the lowest among the salts tested and only a minute increase was noticed with the increase of concentration from 0.01 to 1 kmol m^?3. Ethane production showed a distinct maximum at 0.2 kmol m^?3 MgCl₂. The introduction of 0.01 kmol m^?3 CaCl₂, as well as anaerobic conditions obtained by purging vials with N₂, eliminated that high ethane production. Respiratory activity of the mung bean hypocotyl sections in MgCl₂ concentrations from 0 to 0.5 kmol m^?3 was correlated with ethane but not with ethylene production. The ethane/ethylene ratio showed three patterns for the four salts tested.     

Ethylene as an endogenous inhibitor of root regeneration in tomato leaf discs cultured in vitro

We examined ethylene effects on root regeneration in tomato leaf discs cultured in vitro. Applied ethylene or Ethephon did not stimulate rooting in the leaf discs. In the presence of indoleacetic acid. 5 × 10^-6M, these substances significantly inhibited root formation. Ethylene production (nl C₂H₄· (24 h)^-1. flask^-1) was positively correlated with increased IAA concentrations at various times during the culture period and, as a consequence, with the rooting response after 168 h. However, separate testing of equimolar concentrations of seven different auxins and auxin-like compounds showed no positive correlation between the rate of ethylene production and subsequent rooting response. Aeration of gas-tight flasks containing leaf discs and absorption of ethylene evolved from the discs by mercuric perchlorate in gas-tight flasks or pre-treatment of leaf discs with AgNO₃ significantly enhanced IAA induced root regeneration. Thus, these studies indicate that ethylene is not a rooting hormone per se. Furthermore, ethylene (whether applied externally or synthesized by the tissue) does not appear to account for the ability of auxin to stimulate rooting.     

Loss of vacuum in rubber stoppered vials stored in a liquid nitrogen vapor phase freezer

A total of 1885 rubber stoppered 3-ml vials (NS-33 and NS-51 glass (expansion sizes), sealed under vacuum, were subjected to the ultracold temperatures of a liquid nitrogen vapor phase (LNVP) freezer for 16.5 hr and tested for vacuum loss after equilibration back to 25 °C. The presence of a vacuum in each vial was checked before and after freezing. Results with two lots of vials per glass expansion size showed positive or no negative pressure rather than a vacuum in 46.25% (NS-33), 98.25% (NS-33), 64.72% (NS-51), and 99.38% (NS-51) of the vials. Apparently, the fit or slight misfit of the stopper into the vial opening and the hardness of the butyl rubber stopper at ultracold temperatures enhance the chances of leakage around the stopper area under extremely cold temperatures. Storage of rubber stoppered vials containing lyophilized products sealed under vacuum in LNVP freezers is not advisable.     

Ethylene and the growth of rice seedlings

Etiolated whole rice seedlings enclosed in sealed vials produced ethylene at a rate of 0.9 picomole per hour per seedling. When 2-centimeter-long shoots were subdivided into 5-millimeter-long sections, the sections containing the tip of the shoot evolved 37% of the total ethylene with the remaining 63% being produced along a gradient decreasing to the base of the shoot. The tip of the coleoptile also had the highest level of the ethylene precursor 1-aminocyclopropane-1-carboxylic acid and of the ethylene-forming enzyme activity. Ethylene is one of the factors controlling coleoptile elongation. Decapitation of the seedling reduced ethylene evolution to one-third its original level and inhibited coleoptile growth. In short-term experiments, the growth rate of decapitated seedlings was restored to almost that of intact seedlings by application of ethylene at a concentration of 10 microliters per liter. Apart from ethylene, O₂ also participates in the control of coleoptile growth. When rice seedlings were grown in a gas mixture of N₂ and O₂, the length of the coleoptiles reached a maximum at a concentration of 2.5% O₂. Lower and higher concentrations of O₂ reduced coleoptile growth. The effect of exogenous ethylene on coleoptile growth was also O₂ dependent.     

Accurate control of oxygen level in cells during culture on silicone rubber membranes with application to stem cell differentiation

Oxygen level in mammalian cell culture is often controlled by placing culture vessels in humidified incubators with a defined gas phase partial pressure of oxygen (pO_2gas). Because the cells are consuming oxygen supplied by diffusion, a difference between pO_2gas and that experienced by the cells (pO_2cell) arises, which is maximal when cells are cultured in vessels with little or no oxygen permeability. Here, we demonstrate theoretically that highly oxygen‐permeable silicone rubber membranes can be used to control pO_2cell during culture of cells in monolayers and aggregates much more accurately and can achieve more rapid transient response following a disturbance than on polystyrene and fluorinated ethylene‐propylene copolymer membranes. Cell attachment on silicone rubber was achieved by physical adsorption of fibronectin or Matrigel. We use these membranes for the differentiation of mouse embryonic stem cells to cardiomyocytes and compare the results with culture on polystyrene or on silicone rubber on top of polystyrene. The fraction of cells that are cardiomyocyte‐like increases with decreasing pO₂ only when using oxygen‐permeable silicone membrane‐based dishs, which contract on silicone rubber but not polystyrene. The high permeability of silicone rubber results in pO_2cell being equal to pO_2gas at the tissue‐membrane interface. This, together with geometric information from histological sections, facilitates development of a model from which the pO₂ distribution within the resulting aggregates is computed. Silicone rubber membranes have significant advantages over polystyrene in controlling pO_2cell, and these results suggest they are a valuable tool for investigating pO₂ effects in many applications, such as stem cell differentiation. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2010     

Partitioning of mercury in aqueous biphasic systems and on ABEC™ resins

Poly(ethylene glycol)-based aqueous biphasic systems (PEG-ABS) can be utilized to separate and recover metal ions in environmental and hydrometallurgical applications. A concurrent study was conducted comparing the partitioning of mercury between aqueous layers in an ABS [Me-PEG-5000/(NH₄)₂SO₄] and partitioning of mercury from aqueous solutions to aqueous biphasic extraction chromatographic (ABEC-5000) resins. In ammonium sulfate solutions, mercury partitions to the salt-rich phase in ABS, but by using halide ion extractants, mercury will partition to the PEG-rich phase after formation of a chloro, bromo or iodo complex. The efficacy of the extractant increases in the order Cl⁻<Br⁻<I⁻. This behavior is also observed using the ABEC resins where halo complexes of mercury will adsorb to the resin from (NH₄)₂SO₄ solutions with retention following the same order. The onset of mercury extraction or adsorption is different for the three extractants, occurring at the lowest extractant concentration for I⁻, followed by Br⁻, and then Cl⁻. Fluoride does not extract mercury. Extraction or adsorption of mercury is improved at the lowest halide concentrations in the presence of sulfuric acid. The addition of sulfuric acid to (NH₄)₂SO₄ solution results in ABEC retention of mercury even in the absence of halide extractant.     

Physiological effects of long term exposure to low concentrations of SO2 and NH3 on poplar leaves

Shoots of poplar (Populus euramericana L. cv. Flevo) were exposed to filtered air, SO₂, NH₃ or a mixture of SO₂ and NH₃ for 7 weeks in fumigation chambers. After this exposure gas exchange measurements were carried out using a leaf chamber. As compared to leaves exposed to filtered air, leaves pretreated with 112 μg m^?3 SO₂ showed a small reduction in maximum CO₂ assimilation rate (P_max) and stomatal conductance (g_s). They also showed a slightly higher quantum yield and dark respiration. In addition, the fluorescence measurements indicated that the Calvin cycle of the leaves pretreated with 112 μg m^?3 SO₂ was more rapidly activated after transition from dark to light. An exposure to 64 μg m^?3 NH₃ had a positive effect on P_max, stomatal conductance and NH₃ uptake of the leaves. This positive effect was counteracted by an SO₂ concentration of 45 μg m^?3. The exposure treatments appeared to have no effect on the relationship between net CO₂-assimilation and g_s. Also, no injury of the leaf cuticle or of epidermal cells was observed. Resistance analysis showed that NH₃ transfer into the leaf can be estimated from data on the boundary layer and stomatal resistance for H₂O transfer and NH₃ concentration at the leaf surface, irrespective of whether the leaves are exposed for a short or long time to NH₃ or to a mixture of NH₃ and SO₂. In contrast SO₂ uptake into the leaves was only partly correlated to the stomatal resistance. The results suggest a large additional uptake of this gas by the leaves. The possibility of a difference in path length between SO₂ and H₂O molecules is proposed.     

Enzymatic ethylene formation from 1-aminocyclopropane-1-carboxylic acid by manganese,a protein fraction and a cofactor of etiolated pea shoots

The cofactor of enzymatic, 1-aminocyclopropane-1-carboxylic acid dependent ethylene formation was concentrated on cation exchange columns. When chelators of cations were added to the homogenates, cofactor activity was lost. Cofactor fractions were partly resistant to oxidation at 600° C. Mn²⁺ substituted for the cofactor in ethylene formation from 1-aminocyclopropane-1-carboxylic acid by a protein fraction isolated from etiolated pea shoots. In addition, Mn²⁺ enhanced the stimulatory effect of the concentrated cofactor. The elution volume for the cofactor on a Sephadex G-25 column was lower than that of MnCl₂. In paper electrophoresis the cofactor migrated to the cathode at pH 10.8 and 2.2. The R_F of cofactor on cellulose plates developed in butanol: acetic acid: H₂O was 0.4. After cellulose chromatography, cofactor activity had to be reconstituted by the addition of MnCl₂. Chelators, anti-oxidants, and catalase were inhibitors of Mn²⁺-cofactor-dependent ethylene formation. The protein necessary for 1-aminocyclopropane-1-carboxylic acid dependent ethylene formation in vitro was seperated from 95–98% of the total protein in homogenates by DE-52 cellulose chromatography and (NH₄)₂SO₄-fractionation.Abbreviations ACC 1-aminocyclopropane-1-carboxylic acid - EDTA ethylenediaminetetraacetic acid - DDTC diethyldithiocarbamate     

Effect of ammonium sulfate on the phytotoxicity, foliar uptake, and translocation of imazamethabenz in wild oat

Experiments were conducted in greenhouse, growth chamber, and laboratory conditions to determine the effect of ammonium sulfate [(NH₄)₂SO₄] on the phytotoxicity, foliar uptake, and translocation of imazamethabenz on wild oat. Rates of (NH₄)₂SO₄ up to 5% (w/v) applied with a greenhouse sprayer did not affect the phytotoxicity of the herbicide when the mix was applied at the one- to two-leaf stage. However, inclusion of 1 and 2% (NH₄)₂SO₄ increased the phytotoxicity of the herbicide when the mix was sprayed at the two- to three-leaf, or the three- to four-leaf stage. At 10%, (NH₄)₂SO₄ decreased the phytotoxicity of the sublethal dosage of the herbicide. When the herbicide was applied as individual drops to the growth chamber-grown plants, inclusion of (NH₄)₂SO₄ at 1% did not affect phytotoxicity as measured by shoot growth. The presence of (NH₄)₂SO₄ did not affect the amount of imazamethabenz retained by wild oat foliage, but it decreased [¹⁴C]imazamethabenz absorption, slightly antagonized acropetal translocation, and increased the basipetal translocation of [¹⁴C]imazamethabenz. It was concluded that application methods greatly modify the effect of (NH₄)₂SO₄ on imazamethabenz phytotoxicity. Herbicide absorption and translocation as determined by one method do not necessarily represent the absorption and translocation patterns when different application methods are used. Absorption and translocation were not the factors that were responsible for the observed effect of (NH₄)₂SO₄ on the herbicide phytotoxicity.Abbreviations SC suspension concentrate     

Early diagnosis of SO2-stress by volatile emissions in some crop plants

Summary Fumigation experiments with SO₂ performed on the seedlings of three plant species viz, tomato (Lycopersicon esculentum), mung bean (Vigna radiata) and maize (Zea mays) resulted in the emission of volatiles. Acetaldehyde and ethanol were produced in the fumigated plants. In addition, there was also an increased production of ethylene and ethane. The production of these volatiles was positively correlated to the SO₂ concentrations of 4.2 and 8.3 mol m^–3 (0.1 and 0.2 ppm). Ethylene was emitted primarily from SO₂-stressed yet healthy leaves, whereas high ethane levels were detected in leaves with visible injury symptoms. However, with the appearance of visible injury symptoms, there was a decline in ethylene, acetaldehyde and ethanol emissions. Synthesis of ethylene and ethane seems to be a result of different metabolic pathways. Ethane evolution and its inhibition by antioxidants indicate SO₂-mediated lipid peroxidation by free radical species formed during sulphite oxidation. Perturbation in the cellular respiratory machinery results in the formation of acetaldehyde and ethanol. Since the rates of emissions of ethane, acetaldehyde and ethanol fromplant species were positively correlated to their relative resistance to SO₂, the production of these gases could be used as a reliable diagnostic tool for biomonitoring air pollution (SO₂) stress.Abbreviations ADH alcohol dehydrogenase - NaHSO₃ sodium metabisulphite - O ₂ ^– superoxide radical - OH hydroxyl radical - pO₂ oxygen partial pressure - SO₂ sulphur dioxide - SO ₃ ^– sulphite radical - SOD superoxide dismutase     

Phytoextraction of Cadmium and Zinc By Sedum plumbizincicola Using Different Nitrogen Fertilizers,a Nitrification Inhibitor and a Urease Inhibitor

Cadmium (Cd) and zinc (Zn) phytoavailability and their phytoextraction by Sedum plumbizincicola using different nitrogen fertilizers, nitrification inhibitor (dicyandiamide, DCD) and urease inhibitor (N-(n-Butyl) thiophosphoric triamide, NBPT) were investigated in pot experiments where the soil was contaminated with 0.99 mg kg^?1 of Cd and 241 mg kg^?1 Zn. The soil solution pH varied between 7.30 and 8.25 during plant growth which was little affected by the type of N fertilizer. The (NH₄)₂SO₄+DCD treatment produced higher NH₄⁺?N concentrations in soil solution than the (NH₄)₂SO₄ and NaNO₃ treatment which indicated that DCD addition inhibited the nitrification process. Shoot Cd and Zn concentrations across all treatments showed ranges of 52.9–88.3 and 2691–4276 mg kg^?1, respectively. The (NH₄)₂SO₄+DCD treatment produced slightly higher but not significant Cd and Zn concentrations in the xylem sap than the NaNO₃ treatment. Plant shoots grown with NaNO₃ had higher Cd concentrations than (NH₄)₂SO₄+DCD treatment at 24.0 and 15.4 mg kg^?1, respectively. N fertilizer application had no significant effect on shoot dry biomass. Total Cd uptake in the urea+DCD treatment was higher than in the control, urea+NBPT, urea+NBPT+DCD, or urea treatments, by about 17.5, 23.3, 10.7, and 25.1%, respectively.     

Culture And Staining of Pollen Grains of Ricinus communis

Germinating and growing pollen grains (male gametophytes) of Ricinus communis L. in liquid culture is achieved as follows: Pollen is collected over a 10-15 min period from mature anther clusters which have been removed from the male flowers and which have been kept at 25° C and 40-60% relative humidity. Samples weighing between 2.5 and 5.0 mg are brought as quickly as possible into a Desicote treated vial containing 17% sucrose and 30 ppm H₃BO₃ in boiled distilled water. The proportion (w/v) of pollen to culture solution should be 1:100. Shed pollen is kept in a humidity chamber whenever it is not being handled. The air in the culture vial is replaced by O₂ at the pressure of 1 atmosphere plus 5 lb and the sealed vials are shaken gently for 8-10 hr while partially immersed in a waterbath kept at 30° C. The pollen is fixed by the addition to the incubation suspension of an absolute alcohol-lactic acid (4:1) fixing fluid. The proportion used is 36 parts of fixing fluid to 1 part of culture solution. The fixed pollen can be stored in the fixative. Smears are prepared by applying single drops of the constantly agitated suspension of fixed pollen to a microscope slide. After each drop has spread out and dried, an additional drop is added until 10-20 have been applied. The preparations are stained by adding a drop of 1% acetic-orcein and are sealed with fingernail lacquer. The method is well adapted to the following types of studies: pollen germination, physiology of pollen tube growth, morphology of the male gametocyte, and physiology and cytology of the generative cell and nucleus.     

Ethylene oxidation by Nitrosomonas europaea

Incubation of whole cells of the nitrifying bacterium Nitrosomonas europaea with ethylene led to the formation of ethylene oxide. Ethylene oxide production was prevented by inhibitors of ammonium ion oxidation, and showed properties implying that ethylene is a substrate for the ammonia oxidising enzyme, ammonia monooxygenase. Endogenous substrates, hydroxylamine, hydrazine and ammonium ions were compared as sources of reducing power in terms of rates and stoichiometries of ethylene oxidation. The highest rates of ethylene oxide formation (15 mol h^-1 mg protein^-1) were obtained with hydrazine as donor. The data suggest that at high concentrations of ethylene the rate of oxidation is limited by the rate at which reducing power can be supplied to the monooxygenase, not by an intrinsic V _max. Ethylene had an inhibitory effect on the rate of ammonium ion utilisation; an approximate K _i of 80 M was derived, but the results deviated from simple competitive behaviour. Measurement of relative rates of ethylene oxide formation and ammonium ion utilization led to a k _cat/K _m value for ethylene of 1.1 relative to NH ₄ ⁺ , or 0.04 relative to the true natural substrate, NH₃. The effects of higher concentrations of ethylene oxide on oxygen uptake rates were also investigated. The results imply that ethylene oxide is also a substrate for the monooxygenase, but with a much lower affinity than ethylene.     

Role of ethylene in chlorophyll degradation in radish cotyledons

The effect of age of radish seedlings on changes in chlorophyll concentration caused by ethylene was examined. Ethylene was produced at 2–4 nl g^?1 h^?1 following excision of cotyledons from 5-to 20-day-old seedlings. The youngest cotyledons maintained this rate, whereas ethylene synthesis declined by as much as 80% during a 24-h period in older cotyledons. The youngest cotyledons continued to accumulate chlorophyll in the dark, but after 7 days cotyledons lost chlorophyll and the proportion of chlorophyll lost increased with age. Ethylene promoted, and norbornadiene inhibited, this loss of chlorophyll; in combined treatments the effects of ethylene and norbornadiene were competitive. The maximal rate of chlorophyll loss occurred in 1μl L^?1 ethylene; extrapolation of the response to concentration indicated that half-maximum loss would occur at 0.005–0.01 μl L^?1 ethylene. In cotyledons from 20-day-old seedlings, chlorophyll degradation occurred mainly after 24 h from excision and transfer to the dark. Chlorophyll degradation during 48 h in the dark was affected by norbornadiene or ethylene applied from 0–24 h or from 24–48 h.     

Ammonium-Stimulated Root Hair Branching is Enhanced by Methyl Jasmonate and Suppressed by Ethylene in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis>

Root hair development is orchestrated by nutritional factors and plant hormones. We investigated the action of ammonium (NH₄⁺) and its interactions with methyl jasmonate (MeJA) and ethylene in Arabidopsis root hair growth. The formation of root hair branches was dramatically stimulated in media containing 1.25 to 20 mM NH₄⁺ at pH values of 4.0 to 6.5. The NH₄⁺-treated root hairs showed a very short tip growth stage and swells on the sides that indicated the emergence of branches. MeJA (0.08 to 10 μM) worked in synergism with NH₄⁺ to enhance hair branching. In contrast, ethylene had an antagonistic effect; the stimulation of hair branching by NH₄⁺ was suppressed by the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) and was diminished in ethylene-overproducing mutant eto1-1 seedlings. Moreover, the application of Ag⁺, an ethylene inhibitor, reduced the ACC-induced inhibition of NH₄⁺-stimulated hair branching and restored NH₄⁺-stimulated hair branching in eto1-1 seedlings. Thus, the actions of jasmonate and ethylene appear to be dependent on nutritional conditions such as available nitrogen.