Decreased Ethylene Production Research Articles

Ethylene production and 1-aminocyclopropane-1-carboxylic acid turnover in Picea abies hypocotyls after wounding

Cuttings were taken from 6-week-old seedlings of Norway spruce ( Picea abies [L.] Karst.) and placed in a nutrient solution. The immediate response of the hypocotyls to cutting was a decrease in ethylene production. Later, more than 6 h after cutting, ethylene production increased and reached values 5 times the initial 96 h after cutting. The capacity of the tissue to convert applied ACC into ethylene decreased during the first 6 h but increased later, showing a close correlation to ethylene production during the whole experimental period. The contents of ACC and ACC-conjugate were determined with a method based on synthesis of a benzoyl-derivative of ACC, which was purified on HPLC and analysed by GC-MS. Most of the available ACC was rapidly conjugated and both the rate of synthesis and conjugation of ACC increased as a result of wounding. Wound and stress ethylene production is considered important in triggering defense responses, like induction of pathogen-related proteins, resin production and lignification. The lack of an early burst of ethylene after wounding in spruce indicates that ethylene is not involved in rapid defense responses in this species.

Synergistic effect of ethylene inhibitors and putrescine on shoot regeneration from hypocotyl explants of Chinese radish (Raphanus sativus L. var. longipinnatus Bailey) in vitro

The role of ethylene and putrescine on shoot regeneration from hypocotyl explants of Chinese radish (Raphanus sativus L. var. longipinnatus Bailey cv. Red Coat) was investigated. Explants were recalcitrant in culture, but exogenous application of ethylene inhibitor [20-30 μM aminoethoxyvinylglycine (AVG) or AgNO3] enhanced shoot regeneration of explants grown on medium supplemented with 2 mg/l N(6)-benzyladenine and 1 mg/l 1-naphthaleneacetic acid. The best regeneration occurred in the medium containing AgNO3 in combination with AVG. Culture medium solidified with agarose in the presence of AgNO3 but not AVG was also beneficial to shoot regeneration. Exogenous putrescine, 2-chloroethylphosphonic acid and 1-aminocyclopropane-1-carboxylate had no effect on shoot regeneration. However, regeneration was greatly promoted by 10-25 mM putrescine in combination with 30 μM AgNO3 or AVG. Explants with high regenerability grown in the presence of AgNO3 or in combination with putrescine emanated high levels of ethylene throughout the 21-d culture period. By contrast, AVG or putrescine alone resulted in a decrease in ethylene production. For rooting of shoot cuttings, IAA and IBA at 1-5 mg/l were more effective than NAA.

Putrescine accumulation in wounded green banana fruit

The concentrations of putrescine (Put) and ethylene, and the effects of biosynthesis inhibitors on the production of polyamines and ethylene were examined in wounded pulp tissue of green banana fruit. The Put concentration in the sliced banana fruit, and the arginine decarboxylase (ADC, EC 4.1.1.19) activity increased with the increase of ethylene evolution. Difluoromethylarginine (DFMA) suppressed Put accumulation by 72% while difluoromethylornithine (DFMO) had no effect on the Put content. Methylglyoxal bis(guanylhydrazone) (MGBG) decreased ethylene production and suppressed Put accumulation. Aminooxyacetic acid (AOA) and norbornadiene (NBD) also depressed Put accumulation. These findings suggest that ethylene produced in the wounded pulp tissue affects the induction of ADC and the accumulation of Put.

Interactive role of ethylene and polyamines on shoot regenerabillty of Chinese kale ( Brassica alboglabra Bailey) in vitro

Summary The regulatory role of ethylene and polyamines (PAs) on shoot regeneration of Chinese kale ( Brassica alboglabra Bailey) grown on medium solidified with different gelling agents was investigated. Among the 4 gelling agents tested, medium solidified with 0.4 % agarose was the most effective in shoot regeneration. Shoot regenerability was further enhanced by incorporation of inhibitors of ethylene biosynthesis and action (25 μmol · L −1 aminoethoxyvinylglycine (AVG) or 10 μmol · L −1 AgNO 3 ) in the medium. AVG decreased ethylene production during the first week of culture, whereas AgNO 3 markedly stimulated ethylene synthesis. The promotive effect of AVG on shoot regeneration was overcome in the presence of 100 μmol · L −1 exogenous 1-aminocyclopropane-1-carboxylate or 2-chloroethylphosphonic acid, while AgNO 3 -enhanced regeneration was only slightly affected by these chemicals. Application of difluorometh-ylarginine at ≥0.1 mmol · L −1 also suppressed ethylene inhibitor-enhanced regeneration, however, growth could be restored by application of 10 mmol · L −1 putrescine. Difluoromethylornithine had no effect on shoot regenerability of the expiant. Apart from ethylene inhibitors, regenerability was also enhanced by exogenous application of 5–20 mmol · L −1 putrescine, 0.75 mmol · L −1 spermidine or 0.075 mmol · L −1 spermine, but ethylene synthesis of the expiant was not affected by exogenous PAs. The level of α-naph-thaleneacetic acid (NAA) in the medium was important to shoot regeneration, which occurred at a high frequency at 1 mg · L −1 NAA in combination with 2 mg · L −1 benzyladenine, despite the absence or presence of ethylene inhibitor. NAA at concentrations lower than 1 mg · L −1 was inhibitory to regeneration, although it stimulated ethylene production.

Characterization of ethylene production in developing strawberry fruit

Ethylene production, ACC content, and ACC oxidase activity were determined in strawberry fruit harvested at different stages of development and in fruit harvested green and developed in vitro in solutions containing sucrose. In fruit harvested at progressive stages of development from green through full ripe, ethylene production and ACC oxidase activity decreased whereas ACC content increased between the white and pink stages. Fruit detached at the green stage and developed to full ripe by immersion of the cut pedicel in sucrose solutions exhibited an increase in ACC content, decreased ethylene production, and no change in ACC oxidase activity. Detached green fruit provided with sucrose containing 0.5 mM silver (STS) had elevated ethylene production and more ACC oxidase activity than did fruit incubated without the silver salt. Green fruit provided with sucrose containing 1 mM ACC showed markedly increased ACC content, ACC oxidase activity, and ethylene production. These increases were noted following 4 days incubation in ACC, and were more pronounced after 11 days, at which time fruit of all treatments had attained a full-ripe stage of development. Calyx tissue exhibited more ACC oxidase activity, less ACC content, and similar ethylene production compared with receptacle tissue. ACC synthase could not be detected in fruit harvested at different developmental stages or in fruit detached and developed in vitro.

Inhibition of root growth by spermidine is not due to enhanced production of ethylene

Pretreatment of 3-day-old maize seedlings with spermidine induces an enhancement of ethylene production from roots compared to control tissues with no effect on 1-aminocyclopropane-1-carboxylate oxidase activity and 1-aminocyclopropane-1-carboxylic acid level, accompanied by a strong inhibition of root growth. Inhibitors of ethylene synthesis, cobalt chloride and aminoethoxy-vinylglycine, markedly inhibited ethylene production in both control and spermidine-pretreated roots. The decrease in ethylene production did not result in reversing the inhibition of root growth induced by spermidine. Results suggest that the stimulation of ethylene by spermidine, probably due to more available S-adenosylmethionine, is not responsible for the inhibitory effect of spermidine on root growth. This statement is substantiated by the ineffectiveness of silver thiosulfate, a known inhibitor of ethylene action, to remove spermidine-mediated inhibition of root growth.

Symptom expression and ethylene production in leaf blight of cotton caused by Alternaria macrospora and Alternaria alternata alone and in combination

The interaction between the cotton leaf pathogens Alternaria macrospora and Alternaria alternata was studied using dual inoculation at dosages (≈ 103 spores/(mL ∙ pathogen)) that did not produce symptoms with either pathogen alone. This dual inoculation produced the typical disease symptoms (spots and shedding) and disease severity similar to inoculation with 104 spores/mL of A. macrospora alone. Neither pathogen produced ethylene in culture; however, they induced production of ethylene concentrations by diseased tissue that were correlated to both disease severity and leaf shedding. Plants infected by both pathogens produced the highest concentration of ethylene. Leaf discs either from leaves exhibiting symptoms or from symptomless infected leaves produced similarly high concentrations of ethylene. Inoculation of any site of the leaf with A. macrospora alone or with both pathogens resulted in shedding of the leaf. Pretreating inoculated plants with several ethylene inhibitors or an auxin decreased ethylene production, disease severity, and leaf shedding. Alternaria alternata apparently triggers symptom expression by A. macrospora in leaf blight disease of Pima cotton, and disease is manifested by the production of ethylene that leads to the typical leaf shedding symptom. Key words: Alternaria macrospora, Alternaria alternata, cotton leaf blight, defoliation, ethylene, fungus – fungus interaction, leaf spot of cotton, symptomless infections, virulence.

De novo shoot morphogenesis and plant growth of mustard (Brassica juncea) in vitro in relation to ethylene

Role of ethylene in de novo shoot morphogenesis from explants and plant growth of mustard (Brassica juncea cv. India Mustard) in vitro was investigated, by culturing explants or plants in the presence of the ethylene inhibitors aminoethoxyvinylglycine (AVG) and AgNO3. The presence of 20 μM AgNO3 or 5 μM AVG in culture medium containing 5 μM naphthaleneacetic acid and 10 μM benzyladenine were equally effective in promoting shoot regeneration from leaf disc and petiole explants. However, AgNO3 greatly enhanced ethylene production which reached a maximum after 14 days, whereas ethylene levels in the presence of AVG remained low during 3 weeks of culture. The promotive effect of AVG on shoot regeneration was overcome by exogenous application of 25 μM 2‐chloroethylphosphonic acid (CEPA), but AgNO3‐induced regeneration was less affected by CEPA. For whole plant culture, AVG did not affect plant growth, although it decreased ethylene production by 80% and both endogenous levels of 1‐aminocyclopropane‐1‐carboxylate (ACC) synthase and ACC by 70–80%. In contrast, AgNO3 stimulated all 3 parameters of ethylene synthesis. Both AgNO3 and CEPA were inhibitory to plant growth, with more severe inhibition occuring in AgNO3. Leaf discs derived from plants grown with AVG or AgNO3 were highly regenerative on shoot regeneration medium without ethylene inhibitor, but the presence of AgNO3 in the medium was inhibitory to regeneration of those derived from plants grown with AgNO3.

Expression of Ethylene Biosynthetic Pathway mRNAs is Spatially Regulated within Carnation Flower Petals

The spatial regulation of ethylene biosynthesis within carnation (Dianthus caryophyllus L. cv. White Sim) flower petals was investigated. When detached petals separated into upper and basal portions were exposed to ethylene, autocatalytic ethylene production specifically in the basal portions resulted. Ethylene-induced ethylene production in the basal petal tissue was associated with the accumulation of mRNAs for 1-aminocyclopropane-1-carboxylate (ACC) synthase and ACC oxidase. In contrast, the upper petal portions did not accumulate ACC synthase mRNA nor exhibit an induction of ACC synthase activity in response to ethylene. Upper petal tissue exhibited a transient accumulation of ACC oxidase mRNA and increased ACC oxidase activity in response to ethylene, although the levels of both were significantly lower than that exhibited by basal tissue. Both upper and basal petal tissue responded to ethylene with the accumulation of senescence-related mRNAs represented by the cDNA clones pSR5 and pSR12, indicating that the lack of expression of ACC synthase and the limited accumulation of ACC oxidase mRNA were not a result of overall differences in ethylene responsiveness between upper and basal petal tissue. Upper portions isolated from intact senescing petals produced elevated levels of ethylene at approximately 25 % the rate of basal tissue and contained lower, but detectable levels of ACC synthase and ACC oxidase mRNAs as compared to basal petal tissue. Following dissection, the upper petal tissue exhibited a decrease in ethylene production, while the basal tissue continued to produce ethylene at elevated rates. These results indicate ethylene production in the upper tissue is largely the result of transport of ACC and ethylene from the basal tissue.

Effects of growth regulators on reproductive abscission in faba bean (Vicia fabacv. Troy)

SummaryGrowth regulators were applied to faba bean (field bean) plants in order to study hormonal control of premature reproductive abscission. Combined data from pairs of racemes sited in a consistently yielding region of the main stem indicated effects of growth regulator treatments. Decapitation increased pod numbers, but the inhibitory influence of the upper shoot could not be replaced completely by indol-3yl-acetic acid (IAA) applied to the cut stem stump. Blockage of auxin transport through the stem with the auxin-transport inhibitors 2, 3, 5-triiodobenzoic acid (TIBA) or methyl-2-chloro-9-hydroxyfluorene-9-carboxylate (CF, chlorflurenol) reduced pod numbers above the application point. The latter effects might have been indirect and due to elevated ethylene levels, since pod retention in this shoot region was decreased when sprayed with the ethylene-releasing compound 1-aminocyclopropane carboxylic acid (ACC) and increased when sprayed with ethylene-biosynthesis inhibitors 2-aminoethoxyvinyl glycine (AVG) or l-amino-2-cyclopropylcyclopropane carboxylic acid (cyclopropyl-ACC). Pod numbers were increased when the reproductive structures themselves were sprayed with IAA, gibberellic acid (GA3) or 6-benzylaminopurine (BAP), although a corresponding increase in total seed weight occurred only with the latter growth regulator. Application of BAP or abscisic acid (ABA) as root drenches showed that levels of reproductive abscission were raised or lowered with BAP treatment, depending on its concentration, and lowered with ABA treatment. It is suggested that growth regulator treatments leading to decreased ethylene production in the shoot and/or increased cytokinin and abscisic levels in the xylem sap are those most likely to reduce abscission.

EFFECT OF THE INTERACTION BETWEEN NaCl LEVELS AND ROOT-ZONE TEMPERATURE ON GROWTH AND SEED PRODUCTION OF CUCUMBER.

Cucumber plants )Cucumis sativa cv. Beta-al-pha) were grown in a glasshouse in pots of sand with 3 NaCl levels in the nutrient solution (0.40 and 60 mM) and placed in four large water baths controlled at different temperatures (13, 18,23, and 28°C). The increase of NaCl levels decreased the vegetative growth, seed yield, and seed quality, while the increase of root zone temperature up to 23C° increased the vegetative growth, seed yield and quality. Whereas, 28°C showed lower effect than 23°C. Ethylene production and the content of proline and free amino acids were increased with increasing NaCl levels. The increase of root zone temperature till 23°C decreased ethylene production, proline, and free amino acids contents. Zero NaCl (as control) obtained with 23°C root zone temperature appeared to be the best for the over-all growth, seed yield and seed quality of cucumber plants.

Improvement of regeneration of Lycopersicon pennellii protoplasts by decreasing ethylene production

Lycopersicon pennellii shoots, cultured in vitro for more than a year (type I plants) produced few viable protoplasts in contrast to shoots cultured in vitro for less than five months (type II plants). Ethylene production of both plant types was compared. The low viability of plant type I protoplasts could be correlated with high ethylene production and an increased cell sap osmolality. The ethylene action inhibitor silver thiosulphate improved protoplast yield and viability, especially when using donor tissue, germinated and cultured on medium containing silver thiosulphate (type III plants). Moreover, the choice of cell wall degrading enzymes influenced protoplast viability, since ethylene release was significantly lower using Cellulase R 10 than Cellulysin. All improvements together resulted in an efficient protocol for the isolation and regeneration of Lycopersicon pennellii protoplasts.

Interorgan Translocation of 1-Aminocyclopropane-1-Carboxylic Acid and Ethylene Coordinates Senescence in Emasculated Cymbidium Flowers

In Cymbidium flowers, emasculation by removal of the pollinia and the anther cap leads within 24 hours to red coloration of the labellum (lip). Lip coloration, being the first sign of senescence in these flowers, has been ascribed to the action of ethylene in the lip. When a small incision in the base of the lip is made prior to emasculation, or when the lip is excised and placed in water within 10 to 15 hours after emasculation, coloration is considerably delayed. This indicates that a coloration-associated factor is moving in or out of the lip. Measurements of ethylene production of excised flower parts, isolated at different times after emasculation, showed an increase only in the central column; the other flower parts, including the lip, did not show a measurable change. In contrast, in situ measurements of the ethylene production of the central column and the remaining portion of the flower revealed a simultaneous increase in all the flower parts following emasculation. Similarly, application of radiolabeled 1-aminocyclopropane-1-carboxylic acid (ACC) to the top of the central column in situ leads to the production of radiolabeled ethylene by all the flower parts. In addition, the ethylene production of isolated lips, measured immediately after excision, was initially high but ceased within 10 to 15 minutes. Treatment of the central column in situ with ethylene or ethephon did not stimulate ACC production but did stimulate lip coloration and this was accompanied by an increased internal ethylene concentration in the lip. The data indicate that endogenously produced as well as applied ACC is rapidly translocated from the site of production or application to all the other flower parts where it is immediately converted into ethylene. By excision of a flower organ, the influx of ACC is prevented, causing a rapid decrease in ethylene production. In addition, it was found that ethylene may also be translocated in physiologically significant amounts within the flower. The roles of ACC and ethylene as mobile senescence or wilting factors in emasculation- and pollination-induced senescence is discussed.

Ethylene Production and Wound Healing in Sweet Potato Roots

Abstract Cured storage roots of sweet potato [Ipomoea batatas (L.) Lam. cv. Centennial] were wounded and recured for 12 days with or without 2,5-norbornadiene, AOA, or CoCl2 treatments. Ethylene production, wound lignification, and wound periderm formation were measured 0, 3, 6, 9, and 12 days after wounding. Ethylene production preceded wound lignification and wound periderm formation by 24 to 48 hr, respectively. Blocking ethylene action with 2,5-norbornadiene increased ethylene production, blocked wound periderm formation for up to 12 days, and strongly suppressed and delayed lignification. Blocking ethylene synthesis with AOA or CoCl2 decreased ethylene production to 10% of the control. Lignification and wound periderm formation were also suppressed and initiation delayed. These results suggest that ethylene is involved in lignification and periderm formation in wounded sweet potato roots. Chemical names used: bicyclo[2.2.l]hepta-2,5-diene (2,5-norbornadiene); (aminooxy) acetic acid (AOA).

Phytochrome-controlled ethylene biosynthesis of intact etiolated bean seedlings

Intact etiolated bean (Phaseolus vulgaris L. cv. Limburgse vroege) seedlings were illuminated with red light (10.5 W·m(-2)) for 10 min. After different time intervals ethylene production, and contents of 1-aminocyclopropane-1-carboxylic acid (ACC) and 1-(malonylamino)cyclopropane-1-carboxylic acid were measured. The red-light-induced decrease of ethylene production in 8-d-old intact etiolated bean seedlings was fast, strong and long-lasting ad was mediated through the phytochrome system. This effect appeared to be strictly age-dependent, as it could not be detected in plants younger than 6 d or older than 11 d.The capacity for the conversion of ACC to ethylene was not affected by red light. The inhibitory effect of the light treatment on ethylene production could be related to a reduced free-ACC content. This reduction was a consequence of a temporary non-reversible increase of ACC malonylation and a long-lasting, for a certain time reversible, inhibition of ACC synthesis. The effect of a brief irradiation with red light on the decrease of ethylene production and free-ACC content was completed after about 2 h. Reversibility by far-red, however, persisted for at least 3 h, and was lost between 3 and 6 h.

Regulation of the developmental modes in Dictyostelium mucoroides by cAMP and ethylene

Abstract The cellular slime mold Dictyostelium mucoroides-7 (Dm7) and a mutant (MF1) derived from it exhibit clear dimorphism in development depending upon environmental conditions: macrocyst formation occurs during the sexual cycle, and sorocarp formation during the asexual process. As previously reported, exposure of cells to ethylene gas is favorable to macrocyst formation, while exogenously added 3′, 5′-cyclic adenosine monophosphate (cAMP) induces sorocarp formation. The significance of ethylene and cAMP for the mechanism involved in selection of the developmental pathways was further confirmed by determining the amounts of these substances in macrocyst- or sorocarp-forming cells. Aminooxy-acetic acid (AOA), an inhibitor of ethylene synthesis, was found to switch development of Dm7 and MF1 cells from macrocyst to sorocarp formation by decreasing ethylene production. The cAMP content was shown to be always higher in cells destined for sorocarp formation than in those destined for macrocyst formation, particularly at the aggregation stage. All of the results obtained strongly suggested that the amounts of cAMP and ethylene present, and possibly the ratio between them, may be of great importance for determining which mode of development will be realized.

Possible involvement of surface substances on germinated spores of Ceratocystis fimbriata, black rot fungus, in determination of host-parasite specificity.

We studied the role of surface substances on germinated spores in host-parasite interaction using rabbit antiserum against the substances from germinated spores of sweet potato strain of Ceratocystis fimbriata, compatible with sweet potato. The antiserum agglutinated the germinated spores of this strain and also decreased ethylene production in sweet potato root tissues infected by this strain, which was used here as an index of pathogenicity. On the other hand, the antiserum showed little effect on ethylene production in the root tissues infected by coffee strain, incompatible with sweet potato. The surface substances from germinated spores of sweet potato strain were fractionated into four fractions with ammonium sulfate; precipitates by 0-20%, 20-40%, and 40-60% saturation of ammonium sulfate and the final supernatant. These fractions were assayed for spore agglutination inhibitory activity, ethylene production stimulative activity and antiserum adsorptive activity. All three activities were localized in the same fraction, that precipitated by 0-20% saturation, suggesting the involvement of the same entity or entities in these activities.

Ethylene Production in Seedlings of Chenopodium rubrum, as Influenced by Seedlings Age, Light, and CO2 Concentration1)

Summary Ethylene formation in intact seedlings of a short-day plant Chenopodium rubrum was followed in the course of the first 26 d of growth. The highest values of ethylene evolution were found in the youngest (2 1/2-d-old) plants. Ethylene evolution then decreased up to the 4th d as expressed both on dry weight and on one plant basis. Later, ethylene evolution expressed on dry weight basis decreased till the 26th d, while that expressed on one plant basis increased from the 5th d onward, the rate of increase gradually leveling off. The peaks of flowering coincided with periods of low ethylene production, as expressed on dry weight. Light inhibited ethylene production in C. rubrum seedlings. A higher CO, level did not cancel such inhibition. A lower CO 2 level decreased ethylene production in darkness. ACC markedly increased ethylene evolution and this ACC-induced ethylene production is inhibited by light more strongly than that in the absence of ACC. The relationship between the levels of auxin and ethylene and the capacity for flowering is discussed.

Effect of glyphosate on indole-3-acetic acid metabolism in tolerant and susceptible plants

A comparison study was conducted on the effect of glyphosate (N-[phosphonomethyl]glycine) on indole-3-[2-14C]acetic acid (IAA) metabolism, ethylene production, and growth of 7-day-old seedlings of different plants. The plants tested were American germander (Teucrium canadense L.), soybean (Glycine max L. Merr.), pea (Pisum sativum L. cv. Alaska and Little marvel), mungbean (Vigna radiata L.), and buckwheat (Fagopyrum esculentum Moench). A spray with 2 mM glyphosate affected IAA metabolism to a varied degree. The induced increase of IAA metabolism was greater in buckwheat, Alaska pea, and mungbean than soybean, Little marvel pea, and American germander. The increased IAA metabolism was correlated with the inhibition of growth and with the decrease of ethylene production.

The effect of brassinosteroid on auxin‐induced ethylene production by etiolated mung bean segments

Brassinosteroid, an analogue of brassinolide, (BR) (2α, 3α, 22β, 23β‐tetrahydroxy‐24β‐methyl‐B‐homo‐7‐oxa‐5α‐cholestan‐6‐one), was tested in conjunction with indole‐3‐acetic acid (IAA), naphthaleneacetic acid (NAA), 2,4‐dichlorophenoxyacetic acid (2,4‐D), indole‐3‐butyric acid (IBA), indole‐3‐propionic acid (IPA), indole‐3‐pyruvic acid (IPyA), indole‐3‐aldehyde (IAld), indole‐3‐carbinol (ICB) or tryptophan (TRP) for its effects on ethylene production by etiolated mung bean (Vigna radiata (L.) Rwilcz cv. Berken) hypocotyl segements. The enhancement of ethylene production due to BR was greatest in conjunction with 1 μM IBA, 2,4‐D, IAA, or NAA (these increases were 2580, 2070, 890, and 300%, respectively). When increasing concentrations of IBA, 2,4‐D, IAA, or NAA were used, there was a decrease in the percentage stimulation by BR. Both IPyA and IPA had different optimal concentrations than the other auxins tested. Their BR‐enhanced maximum percentage stimulations (1430 and 1580%) were greatest with 5 μM IPya and 10 μM IPA, respectively. There was a marked reduction in the percentage stimulation by BR with either 100 μM IPyA or IPA. The inactive indoles (IAld, ICB, or TRP) did not synergize with BR at any of the concentrations tested. Four hours following treatment those segments in contact with 1 μM BR with or without the addition of 10 μM IAA began to show a stimulation in ethylene production above the control and this stimulation became greater over the following 20 h. It was necessary for BR to be in continual contact with the tissue to have a stimulatory effect on auxin‐induced ethylene production. When segments excised from greater distances below the hypocotyl hook, were treated with either IAA alone or in combination with BR, there was a decrease in ethylene production with increasing distance. There was no effect of hypocotyl length on BR stimulation of auxin‐induced ethylene production; however, there was a definite decrease in ethylene production when IAA was applied alone.