Abscission-inducing properties of methyl jasmonate,ABA, and ABA-methyl ester and their interactions with ethephon,AgNO3, and malformin

The biological activities of methyl jasmonate, ABA, methyl abscisate, and malformin were compared in a variety ofVigna radiata abscission tests. Although each compound diminished or completely negated the antiethylene properties of Ag⁺, differences in potency were observed. ABA and ABA-Me stimulated leaf abscission in the dark, potentiated abscission with low concentrations of ethephon, and interacted synergistically with malformin, whereas methyl jasmonate was inactive in each of these tests. Methyl jasmonate was most active in potentiating leaf abscission induced by high ethephon concentrations and stimulated petiole abscission, whether applied proximally or distally, from debladed explants. In two tests, negation of Ag⁺ activity and interaction with malformin, ABA concentrations as low as 0.1 μM were biologically active and indicated that ABA can be a highly active abscission-inducing compound. Based on differences in biological activity, it was concluded that the modes of action of methyl jasmonate, ABA, and malformin were different.     

Malformin negates the Inhibition of Ethrel-induced Leaf Abscission by AgNO3

In light, malformin completely abolished the ability of Ag⁺to inhibit Ethrel-induced leaf abscission from cuttings of Vignaradiata, even though Ag⁺ was applied 24 hr before malformin.Malformin itself did not induce abscission in the light. However,Ag⁺ was active on cuttings which had been pre-treated with malforminfor 2 days in the light. No evidence was obtained to suggestreaction between malformin and Ag⁺. In the dark, Ag⁺ had noeffect on stimulation of leaf abscission by malformin. (Received March 7, 1981; Accepted May 12, 1981)     

An explanation for the light requirement of AgNO3 to inhibit ethylene-induced abscission

The loss of the antiethylene activity of Ag⁺ on leaf abscission by incubation in the dark was investigated. When primary leaves were removed from cuttings of Vigna radiata previously sprayed with AgNO₃, dark-induced abscission of the petioles was inhibited, compared to untreated leafless controls, in the presence or absence of ethephon, an ethylene-releasing compound. Malformin did not negate inhibition of petiole abscission induced by Ag⁺. Although leaf removal restored the antiethylene activity of Ag⁺ in the dark, macerates of leaves from dark-aged cuttings did not negate the ability of Ag⁺ to inhibit petiole abscission in the dark. Abscisic acid completely abolished the ability of Ag⁺ to counteract ethephon-induced leaf abscission in the light, and almost completely abolished the Ag⁺-induced inhibition of petiole abscission from explants in the dark. It is proposed that the phytochrome requirement for the antiethylene activity of Ag⁺ on ethephon-induced leaf abscission involves prevention of the formation, accumulation, or transport of a substance in leaves in the dark which negates Ag⁺ activity. This substance may be abscisic acid or another substance with similar biological activity.     

Antiethylene properties of AgNO3 and 2,5-norbornadiene in light and dark inVigna radiata

The ability of the silver ion to prevent ethylene-induced leaf abscission was lost in the dark in both whole seedlings and rootless, bladed explants ofVigna radiata when either ethylene or ethephon (an ethylene-releasing compound) were used as defoliating agents. Loss of silver activity in the dark was also observed in bladed explants ofPhaseolus vulgaris andGlycine max. The silver ion was active in the dark in preventing ethylene-induced root curvatures and inhibition of root growth. The antiethylene properties of 2,5-norbornadiene were identical in both the light and dark, undiminished in the presence of ABA, but completely negated by malformin. Because malformin is known to react with sulfhydryl groups, the norbornadiene- and/or ethylene-binding site may contain a sulfhydryl group.Journal Paper No. 10,866 of the Purdue Agricultural Experiment Station.     

Factors Influencing Induction of Resistance to Dark Abscission by Malformin

Factors influencing induction of resistance to dark abscissionby malformin on cuttings of Vigna radiata during treatment inlight were examined. When light duration (13.5 W m^–2)increased from 0 to 48 h, the effect of malformin on subsequentdark abscission changed from stimulation only (0 to 4 h), stimulationfollowed by inhibition (8 to 12 h), to inhibition only (24 to48 h). Maximum abscission resistance occurred after 48 h whenirradiance was 6.6 W m^–2. Kinetin treatment in light reducedsubsequent dark abscission by controls but did not reduce abscissionon malformintreated cuttings. Hadacidin had no effect on inductionof abscission resistance by malformin. IAA, hydroxyproline,CaCl₂, sucrose, and NH₄NO₃ were inactive. ABA and ethephon completelyblocked induction of abscission resistance by malformin. Inhibitionof abscission induced by kinetin was also blocked by ABA. Becauseboth puromycin and malformin inhibited dark abscission followingtreatment in light, malformin may induce abscission resistanceby inhibiting protein synthesis or promoting formation of othersubstances which inhibit protein synthesis. Leaf blade removalfrom the distal end of the petioles abolished malformin-inducedabscission resistance. It is suggested that in light malformininduces formation of abscission-inhibiting compounds in leaveswhich are responsible for development of abscission resistance. (Received May 17, 1983; Accepted November 8, 1983)     

Enhanced paclitaxel production induced by the combination of elicitors in cell suspension cultures of Taxus chinensis

Taxus chinensis suspension cells were cultured in the modified Gamborg's B5 medium. Addition of 50 mg chitosan l^–1, 60 M methyl jasmonate and 30 M Ag⁺ resulted in the greatest paclitaxel production, at 25 mg l^–1 in the cultures, being almost 40 times higher than that of the control culture, 10 times higher than that of the culture exposed to Ag⁺, 6 times higher than that of the culture elicited by chitosan and almost double that of the culture elicited by methyl jasmonate.     

Modulation of carrier-mediated uptake of abscisic acid by methyl jasmonate in Phaseolus coccineus L

The effects of methyl jasmonate and jasmonic acid on uptake of abscisic acid (ABA) by suspension-cultured runner-bean cells and subapical runner-bean root segments have been investigated. Increasing concentrations of methyl jasmonate inhibit ABA uptake by the cultured cells with a K _i of 22±3 M. This is not due to cytoplasmic acidification or to effects on metabolism of ABA, and is not additive with inhibition of radioactive ABA uptake by nonradioactive ABA. Uptake of indol-3-yl acetic acid (IAA) is unaffected by methyl jasmonate. The maximum effect of nonradioactive ABA in inhibiting uptake of radioactive ABA, previously shown to reflect saturation of an ABA carrier, is generally greater than the effect of maximally inhibitory concentrations of methyl jasmonate. Similar results were obtained with root segments, but longer incubation times were necessary to observe inhibitory effects of methyl jasmonate. Demethylation of methyl jasmonate to jasmonic acid does not appear to be required since similar concentrations of jasmonic acid had no observable direct effect on ABA uptake other than that attributable to cytoplasmic acidification. Histidine reagents, a proton ionophore and acidic external pH all affect in parallel the inhibition by methyl jasmonate and nonradioactive ABA of uptake of radioactive ABA by the cultured cells. There is no effect of ABA or nonradioactive methyl jasmonate on uptake of radioactive methyl jasmonate by the cultured cells. It is proposed that methyl jasmonate interacts with the ABA carrier. Various models for this interaction are discussed.Abbreviations ABA abscisic acid - DMO 5,5-dimethyloxazolidine-2,4-dione - IAA indol-3-yl acetic acid     

Effect of shading individual soybean reproductive structures on their abscisic Acid content, metabolism, and partitioning

Pod set in soybean is related to carbon partitioning and may be, at least partially, regulated by abscisic acid (ABA) concentrations. The studies reported here examine the relationship between carbon and ABA partitioning, reproductive abscission and ABA metabolism. The partitioning of radiolabeled ABA and photoassimilates from leaves to flowers and endogenous ABA concentrations were determined in shaded and unshaded reproductive structures. Aluminum foil was gently placed over individual soybean reproductive structures for 48 hours at 0, 4, 12, 17, and 22 days after anthesis (DAA). Shading of flowers at 12, 17, and 22 DAA resulted in significantly reduced concentration of ABA. However, shading had no effect on the catabolism of exogenously supplied [³H] ABA. The shading treatment on the first four of the five dates reduced partitioning of photoassimilates and ABA from the subtending leaf to the flower. Shading of reproductive structures also caused a significant reduction in the amount of assimilate exported from the subtending leaf, at 17 DAA. We conclude that shade-induced premature reproductive abscission in soybean is not stimulated by high levels of ABA within reproductive structures, but that ABA may inhibit abscission of reproductive structures by playing a role in preferential assimilate partitioning.     

Abscisic acid- and ethylene-induced defoliation of Radermachera sinica L.

Radermachera sinica L. is an ornamental plant with demonstrated sensitivity to ethylene-induced leaf abscission. In this study, we examine the relationship between abscisic acid (ABA) and ethylene in initiating the abscission response. Treatment with 1 l L^\s-1 of ethylene, 1 mM 1-aminocyclopropane-1-carboxylic acid (ACC) or 1 mM ABA resulted in complete defoliation of leaf explants. Application of 0.125 mM silver thiosulfate (STS) inhibited ethylene- and ACC-induced abscission but had no effect on explants treated with ABA. The ABA-induced abscission was unaffected by treatment with aminoethoxyvinylglycine (AVG) or aminooxyacetic acid (AOA). Treatment of explants with 1 mM cobalt chloride (CoCl₂) or 2000 l L^\s-1 of norbornadiene (NBD) completely inhibited abscission in explants treated with 1 l L^\s-1 ethylene or 1 mM ACC but they were only marginally effective in blocking ABA-induced abscission despite the lower level of endogenous ethylene. ABA appeared to increase the sensitivity of explants to ethylene. However, the evidence suggests that ABA may also function independent of ethylene to induce leaf abscission in R. sinica.Abbreviations ABA abscisic acid - ACC 1-aminocyclopropane-1-carboxylic acid - AOA aminooxyacetic acid - AVG aminoethoxyvinylglycine - CoCl₂ cobalt chloride - NBD norbornadiene - STS silver thiosulfate     

Phytochrome involvement in the induction of resistance to dark abscission by malformin

The active portion of the visible spectrum which is required for malformin to produce leaves which are resistant to dark abscission from cuttings of Phaseolus aureus is red light. Abscission resistance was partially to almost completely lost by far irradiation prior to dark incubation. Although Ethrel, an ethylene releasing compound, stimulated dark abscission of resistant and control leaves, resistance was not lost because control leaves always abscised at a greater rate. The participation of phytochrome in the induction of abscission resistance by malformin is indicated.Abbreviations Pfr far-red absorbing form of the phytochrome system - R red radiation - FR far-red radiation - D dark     

Light Requirement for AgNO(3) Inhibition of Ethrel-Induced Leaf Abscission from Cuttings of Vigna radiata

To obtain information regarding the antiethylene properties and binding site of Ag⁺, studies were initiated to define conditions under which Ag⁺ does or does not inhibit ethylene action. AgNO₃, applied as a leaf spray, inhibited 2-chloroethylphosphonic acid (Ethrel)-induced leaf abscission from green cuttings of Vigna radiata in white light but lost considerable activity in the dark. In the absence of Ethrel, AgNO₃ stimulated abscission in the dark. When cuttings were dark-aged for 24 hours prior to treatment with AgNO₃ and aged for an additional 24 hours in the dark after treatment, good inhibition of subsequent Ethrel-induced abscission was restored by returning the cuttings to light. However, when dark aging was preceded by far-red irradiation, considerably less inhibition of Ethrel-induced abscission was restored in the light. AgNO₃ was completely inactive on cuttings aged in the dark and treated with Ethrel in the dark. Light is required for the antiethylene activity of AgNO₃ with regard to leaf abscission of Vigna.     

The effect of LAB 173711 and ethephon on time of flowering and cold hardiness of peach flower buds

Peach flowers are often killed during bloom by spring frosts. LAB 173711, a compound with abscisic (ABA)-like activity, and ethephon delayed flowering in peach trees. In greenhouse experiments, LAB 173711, at concentrations of 10^?3–10^?2 M, was most effective in delaying bloom when applied after a 5°C cold storage period, rather than before the dormancy breaking treatment. In contrast, ethephon delayed bloom most effectively when applied before 5°C cold storage; ethephon caused flower bud abscission when treatments were made after the chilling requirement had been satisfied. In field experiments, ethephon delayed flowering by 6–7 days, which reduced bud injury after a spring frost during bloom. No flower bud injury was found on ethephon-treated trees after temperatures of ?4.3°C; whereas without ethephon 25% of the flower buds were frost damaged. LAB 173711 delayed the time to 50% bloom by 2–3 days. However, this was not long enough to avoid low-temperature injury to the flower buds.     

Use of Persistent Analogs of Abscisic Acid as Palliatives against Salt-stress Induced Damage in Citrus Plants

The effectiveness of several abscisic acid (ABA) analogs as palliatives against salt stress in intact citrus plants has been tested in this work. The effect of ABA, 8′-methylene ABA, 8′-acetylene ABA, ABA methyl ester, 8′-methylene ABA methyl ester, and 8′-acetylene ABA methyl ester on citrus responses to salt stress was studied on 2-year-old grafted plants. Leaf abscission, chloride accumulation, ethylene production, and net photosynthetic rate were the parameters used to characterize the performance of plants under stress. Data indicate that 8′-methylene ABA was the most effective compound in delaying the deleterious effects of high salinity on citrus plants. Its regular application reduced leaf chloride concentration, ethylene production, and leaf abscission. Furthermore, it delayed the depletion of CO₂ assimilation under these adverse conditions. Abscisic acid and 8′-acetylene ABA also reduced salt-stress induced injuries in citrus, although to a lower extent. Neither ABA methyl ester nor its 8′-C modified analogs showed biological activity in these assays.     

The effect of LAB 173711 and ethephon on time of flowering and cold hardiness of peach flower buds

Peach flowers are often killed during bloom by spring frosts. LAB 173711, a compound with abscisic (ABA)-like activity, and ethephon delayed flowering in peach trees. In greenhouse experiments, LAB 173711, at concentrations of 10^–3–10^–2 M, was most effective in delaying bloom when applied after a 5°C cold storage period, rather than before the dormancy breaking treatment. In contrast, ethephon delayed bloom most effectively when applied before 5°C cold storage; ethephon caused flower bud abscission when treatments were made after the chilling requirement had been satisfied. In field experiments, ethephon delayed flowering by 6–7 days, which reduced bud injury after a spring frost during bloom. No flower bud injury was found on ethephon-treated trees after temperatures of –4.3°C; whereas without ethephon 25% of the flower buds were frost damaged. LAB 173711 delayed the time to 50% bloom by 2–3 days. However, this was not long enough to avoid low-temperature injury to the flower buds.     

Induction of resistance to dark abscission by malformin in white light

When cuttings or seedlings of Phaseolus aureus were treated proximally with malformin for 2 days in continuous white light, resistance to subsequent leaf abscission in the dark resulted. The amount of resistance diminished as the concentration of malformin decreased from 10 to 0.1 micromolar. Resistance to dark abscission persisted for 7 days in continuous light. Little resistance was obtained when cuttings were taken from seedlings grown under low irradiance and short photoperiods, but resistance gradually increased as the photoperiod increased. Resistance to dark abscission induced by malformin in light differs from inhibition of abscission by indoleacetic acid because when malformin is applied in the dark it stimulates abscission after distal or proximal application. Malformin induces resistance only in conjunction with light treatment.     

Effect of divalent cations on malformin-induced efflux and biological activity

The effect of malformin on permeability was determined by efflux.Malformin increased membrane permeability to various organicand inorganic compounds or ions and was inhibited by severaldivalent cations. From the time required to increase permeabilityand the amount of material effluxed malformin primarily increasedtonoplast permeability. Calcium inhibited malformin-inducedstem collapse, abscission, and to a slight extent, inhibitionof primary leaf expansion. Although calcium inhibited malformin-inducedroot curvatures, malformin did not enhance permeability of rootslices at concentrations optimal for the curvature response. (Received May 6, 1975; )     

Mediation of a plant response to malformin by ethylene

Malformin and ethylene stimulate abscission of the primary leaves of Phaseolus aureus Roxb. in the dark, and abscission stimulation by both compounds is inhibited by indeleacetic acid and CO₂. Ethylene production by malformin-treated buds is stimulated within 4 hours. and up to 8 days, after treatment. Malformin-induced growth disturbances in P. vulgaris L. and abscission in P. aureus are considered mediated by ethylene. Although root curvatures of Zea mays L. are induced by both malformin and ethylene, and malformin is inhibited by CO₂, ethylene production is not stimulated by malformin. A role of ethylene in root curvatures induced by malformin is neither proposed nor disproved.     

Methyl jasmonate and bean leaf abscission

The effect of rac-methyl jasmonate, both in solution and as a vapour, on the separation of pulvinar and petiolar tissues in explants containing the distal abscission zone of primary leaves of Phaseolus vulgaris var. Contender was investigated. The effects of rac-methyl jasmonate were compared to those of (±)-abscisic acid, -naphthalene acetic acid, ethylene and 2-chloroethylphosphonic acid. Abscission times were determined in explants prepared from 14-day-old control plants and in explants prepared from plants that had been pretreated for 24h with the ethylene-action inhibitor, silver thiosulphate. While silver-pretreatment, or treatment with -naphthalene acetic acid delayed abscission, treatment with ethylene or 2-chloroethylphosphonic acid accelerated tissue separation. However, (±)-abscisic acid delayed abscission under these conditions. In all instances, treatment with rac-methyl jasmonate had no apparent effect on abscission. The loss of chlorophyll from bean leaf discs incubated in the dark was enhanced by treatment with 2-chloroethylphosphonic acid or (±)-abscisic acid and was retarded in discs incubated in benzyl adenine. While incubation in -naphthalene acetic acid was without effect, incubation in solution of rac-methyl jasmonate also retarded chlorophyll loss when compared to water controls.     

Toxicity of biosynthetic silver nanoparticles on the growth,cell ultrastructure and physiological activities of barley plant

Silver nanoparticles (AgNPs) were biosynthesized using the cell-free filtrate of bacterium Proteus mirabilis, reacted with 1 mM of AgNO₃ solutions at 37 °C. The synthesis of AgNPs was monitored by UV–Vis spectroscopy and transmission electron microscopy (TEM) equipped with selected area electron diffraction (SAED). The results point to formation of spherical to cubical particles of AgNPs ranging in size from 5 to 35 nm with an average of 25 nm in diameter. The toxicity of Ag on barley (Hordeum vulgare L. cv. Gustoe) that was subjected to Ag⁺ as AgNO₃ and AgNPs was explored. The grain germination and seedling growth of barley decreased in the presence of 0.1 mM Ag⁺ and was inhibited at 1 mM Ag⁺. In contrast, our results indicated that the AgNPs at low concentration (0.1 mM) could be useful for barley grain germination and seedling growth. However, the higher concentrations of AgNPs (0.5 and 1 mM) reduced grain germination and exhibited a stronger reduction in the root length. A decline in the photosynthetic pigments and disorganization of chloroplast grana thylakoids in Ag⁺ and AgNPs-treated plants confirmed the leaf chlorosis. An increase of plastoglobuli within chloroplasts was observed in Ag⁺ and AgNPs-treated leaves. Ag⁺ caused dense aggregation of nuclear chromatin materials and degeneration of mitochondria. Ag⁺ and AgNPs increased contents of malondialdehyde, soluble proteins, total phenolic compounds and activity of guaiacol peroxidase in barley leaves; these results point to activation of plant defence mechanisms against oxidative stress in barley.     

Methyl jasmonate signaling and signal crosstalk between methyl jasmonate and abscisic acid in guard cells

Plants tightly control stomatal aperture in response to various environmental changes. A drought-inducible phytohormone, abscisic acid (ABA), triggers stomatal closure and ABA signaling pathway in guard cells has been well studied. Similar to ABA, methyl jasmonate (MeJA) induces stomatal closure in various plant species but MeJA signaling pathway is still far from clear. Recently we found that Arabidopsis calcium dependent protein kinase CPK6 functions as a positive regulator in guard cell MeJA signaling and provided new insights into cytosolic Ca²⁺-dependent MeJA signaling. Here we discuss the MeJA signaling and also signal crosstalk between MeJA and ABA pathways in guard cells.Key words: methyl jasmonate, abscisic acid, guard cell, reactive oxygen species, nitric oxide, calciumStomata, which are formed by pairs of specialized cells called guard cells, control gas exchanges and transpirational water loss. Guard cells can shrink and swell in response to various physiological stimuli, resulting in stomatal closing and opening.^1,2 To optimize growth under various environmental conditions, plants have developed fine-tuned signal pathway in guard cells. Abscisic acid (ABA) is synthesized under drought stress and induces stomatal closure to reduce transpirational water loss.² ABA signal transduction in guard cells has been widely studied. ABA induces increases of various second messengers such as cytosolic Ca²⁺, reactive oxygen species (ROS) and nitric oxide (NO) in guard cells. These early signal components finally evoke ion efflux through plasma membrane ion channels, resulting in reduction of guard cell turgor pressure.Jasmonates are plant hormones synthesized via the octadecanoid pathway and regulate various physiological processes in plants such as pollen maturation, tendril coiling, senescence and responses to wounding and pathogen attacks.³ Similar to ABA, jasmonates also trigger stomatal closure and the response is conserved among various plant species including Arabidopsis thaliana,⁴ Hordeum vulgare,⁵ Commelina benghalensis,⁶ Vicia faba,⁷ Nicotiana glauca,⁸ Paphiopedilum Supersuk⁹ and Paphiopedilum tonsum.⁹ A volatile methyl ester of jasmonic acid (JA), methy jasmonate (MeJA), has been widely used for studying jasmonate signaling pathway. To date, pharmacological and reverse genetic approaches have revealed many important signal components involved in MeJA-induced stomatal closure and suggest a signal crosstalk between MeJA and ABA in guard cells. In this review, we mainly focus on the three important second messengers, ROS, NO and cytosolic Ca²⁺ and discuss recent advance about MeJA signaling and signal interaction between MeJA and ABA in guard cells.