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)     

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.     

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.     

Detection and Characterization of Abscission-Inhibiting Substances in Leaves of Malformin-Treated Cuttings

Malformin, which induces resistance to dark leaf abscissionfollowing treatment in the light, did not alter the course ofdark aging (loss of chlorophyll, wet and dry weight) in Vigna.Peroxydisulfate, which destroys IAA, did not influence malformininducedabscission resistance. Leaf blades from cuttings treated withmalformin in the light contained higher levels of abscissioninhibitors, which could be divided into ethanolsoluble and water-solublefractions. The inhibitors appeared to be heat stable anionsthat are insoluble in ether. Although malformin also increasedthe amount of abscission inhibitors in leaves when applied inthe dark, where malformin stimulates abscission, a parallelincrease in abscission stimulators may explain the failure ofthese inhibitors to function in the dark. (Received June 25, 1984; Accepted August 20, 1984)     

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 malformin on phytochrome reactions in Vigna and Avena

The rate of destruction of the far red absorbing form of phytochrome(Pfr) in green or etiolated cuttings of Vigna radiata was slowerin the presence of malformin than in its absence. Malforminhad no effect on the accumulation of total phytochrome in thedark, or on the reaccumulation of phytochrome after destructionin red light. The amount of photoconversion of the red absorbingform of phytochrome (Pr) to Pfr or Pfr to Pr by given dosesof red or far red radiation was slightly but consistently lessin malformin-treated cuttings of V. radiata than in controls.Malformin had no effect on the rate of destruction or photoconversionof phytochrome in etiolated shoots of Avena sativa. The decreasein destruction rate of Pfr by malformin in V. radiata may contributeto the inhibition of dark abscission by malformin after lighttreatment. (Received October 3, 1979; )     

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.     

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 M 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.Journal Paper No. 9811 of the Purdue Agricultural Experiment Station.     

Studies on the stimulation of abscission by malformin on cuttings of Phaseolus aureus Roxb

White light irradiance required for complete and slight inhibitionof malformin-induced abscission by cuttings of Phaseolus aureuswas 13.5?10³ and 0.1?10³ ergs/cm^2. sec, respectively. Longerphotoperiods and higher irradiances were required to inhibitabscission by malformin-treated cuttings than by controls. Malforminstimulated dark abscission more rapidly, and at lower concentrations,than Ethrel or abscisic acid. The ability of light to inhibitmalformin-induced abscission diminished rapidly after 36 hrin the dark. Malformin accelerated chlorophyll and fresh anddry weight loss of leaves in the dark. The loss in fresh anddry weight, and perhaps chlorophyll, were inhibited by light.Hydroxyproline had little effect, but sucrose, hadacidin, kinetinand indoleacetic acid delayed malformin-induced abscission.Although puromycin, an inhibitor of protein synthesis, stimulatedabscission on controls, it inhibited malformin-induced abscission. (Received July 18, 1977; )     

Isolation and characterization of the cell wall receptor of 14C-malformin in Phaseolus vulgaris L.

¹⁴C-malformin attaches to at least two cell wall receptors inPhaseolus vulgaris. One receptor was extracted with Tris buffer(pH 8.5) and the other with 0.1 N NaOH. In both cases, priortreatment of the walls with wall degrading enzymes (macerase,cellulysin) was required. The two receptors differed with regardto ultrafiltration and gel filtration chromatography. The Tris-extractedreceptor is a protein, probably a glycoprotein, which containshydroxyproline and sulfhydryl groups. Although cuttings nottreated with malformin had Tris-extractable receptor, formationof the receptor appeared to be enhanced by malformin. ¹ Present address: American Cyanamid, P. O. Box 400, Princeton,New Jersey 08540, U. S. A. (Received August 2, 1976; )     

Effect of malformin on adventitious root formation and metabolism of indoleacetic acid-2-14C by Phaseolus vulgaris

Malformin inhibited rooting on cuttings of Phaseolus vulgaris.IAA antagonized malformin-induced inhibition of rooting, butmalformin inhibited IAA-induced swelling on the base of thecuttings. It was suggested that IAA-induced swelling was mediatedby ethylene. Malformin did not inhibit transport of root-promotingsubstances from upper portions of the cuttings or polar transportof IAA-2-¹⁴C, nor did it alter the melting point of DNA or thebinding of DNA to histone. Although malformin appeared to alterthe metabolism of IAA-2-¹⁴C, the effect may have been the resultof a marked and selective stimulation of efflux of IAA-2-¹⁴Cmetabolites by malformin. Efflux of IAA or its metabolites maycontribute toward inhibition of rooting by malformin. ¹ Journal Paper No. 4688 of the Purdue Agricultural ExperimentStation. Supported in part by grant GB-7158 from the NationalScience Foundation. ² Present address: Botanisches Institut der Technischen UniversitätBraunschweig, 3300 Braunschweig, Humboldtstraße 1. (Received March 9, 1972; )     

Abscission: Response to Red and Far-Red Light

Craker, L. E., Zhao, S. Y. and Decoteau, D. R. 1987. Abscission:response to red and far-red light.—J. exp. Bot. 38: 883–888. The dose-response and time relationship of red and far-red lightin the inhibition and promotion, respectively, of dark-inducedleaf abscission was quantified using cuttings of coleus (ColeusBlumei Benth.). A continuous photon flux of approximately 15nM m^–2 s^–1 of red light was sufficient to preventleaf abscission. Abscission was promoted by exposure to a photonflux of approximately 10 nM m^–2 s^–1 of far-red lightThe inhibition of abscission by red light could be reversedby treatment with far-red and the promotion of abscission byfar-red light could be reversed by treatment with red lightThe data were consistent with a phytochrome receptor systemlocated in the leaves that controlled the presence of an abscission-inhibitingsubstance in the abscission zones. Key words: Abscission, Coleus Blumei, far-red light red light     

Effect of Peroxydisulfate on Vigna radiata Abscission

K₂S₂O₈, applied to the basal end of cuttings of Vigna radiatastimulated leaf abscission in the light or dark. Because inhibitionof leaf sbscission in the dark by IAA was completely abolishedby K₂S₂O₈, and IAA decreased stimulation of abscission by K₂S₂O₈,destruction of IAA in the cuttings by K₂S₂O₈ is indicated. K₂S₂O₈had no effect on leaf abscission when applied as a foliar sprayor when roots of undisturbed seedlings were treated. When appliedproximally or distally to leafless explants, K₂S₂O₈ inhibitedpetiole abscission, and neither IAA nor ethylene had an effecton the inhibition. Although K₂S₂O₈ destroyed IAA in vitro, ithad no effect on abscission inhibitors in macerates of Vignaleaves and corn roots, nor did it destroy the biological activityof IAA added to such macerates. Substances liberated by macerationmay interfere with the ability of K₂S₂O₈ to destroy IAA. (Received May 2, 1981; Accepted August 24, 1981)     

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     

Effect of malformin on phytochrome- and Ethrel-mediated responses

On etiolated cuttings of Phaseolus vulgaris malformin inhibitedseveral phytochromemediated responses. This included hypocotylhook-opening, leaf expansion, and inhibition of stem elongation.Malformin also inhibited anthocyanin synthesis by sorghum, buthad no effect upon lettuce seed germination in the light ordark. Malformin alleviated Ethrel-induced hook-retention, inhibitionof stem elongation, and root curvatures, but not Ethrel-inducedstimulation of lettuce seed germination in the dark. (Received February 19, 1975; )     

Participation of phytochrome in the light inhibition of malformin-induced abscission

The ability of white light to inhibit malformin-induced abscissionon cuttings of Phaseolus aureus involved a red-far red reversiblephenomenon. Treatment with far red radiation prior to dark incubationenhanced abscission on both control and malformin-treated cuttings.The dark aging process, which enhances abscission on both controland malformin-treated cuttings, was inhibited by red radiationand was also far red reversible. The photoreceptor for lightinhibition of malformin-induced abscission was located in theprimary leaves. A role of phytochrome in the inhibition of abscissionon control and malformin-treated cuttings is indicated. (Received September 20, 1977; )     

Potentiation and inhibition of the effects of 2-chloroethylphosphonic Acid by malformin

Malformin completely inhibited Ethrel-induced swelling and fresh weight increase on the basal stem portion of Phaseolus vulgaris L. cuttings, but markedly potentiated Ethrel- or ethylene-induced abscission. With regard to abscission, malformin reacted synergistically with ethylene and dark aging, and in a manner which appeared to differ from that of ethylene and dark aging. The numerous effects of malformin on plant growth and development cannot be explained in simple terms of enhanced ethylene production.     

Stimulation and inhibition of respiration by malformin: Relationship to enhanced ethane production

When apical bud sections of Phaseolus vulgaris were vacuum-infiltratedwith malformin, their rate of respiration increased significantlywithout a lag and without altering the respiratory quotient.When tissues were soaked in solutions, the effect of malforminwas concentration dependent. At high malformin concentration(200 µM), a marked inhibition of respiration for 8 to10 hr was followed by a rapid increase of oxygen uptake whichreached a level nearly 3-fold greater than that of controls.At lower concentration (20 µM) malformin had no effecton respiration for 8 to 10 hr, but then stimulated respirationmarkedly. Ca²⁺ completely blocked the early inhibition of respirationby malformin (200 µM), but had little or no effect onthe subsequent stimulation of respiration. Oxygen deficiencymay be a contributing factor to the enhancement of ethane productionby malformin. ¹Present address: Mobil Chemical Company, P.O. Box 240, Edison,New Jersey 08817, U.S.A. (Received August 28, 1979; )     

Stimulation of ethylene or ethane production by malformin

Malformin stimulated ethylene production of Phaseolus vulgarisL. seedlings and explants. However, when malformin was vacuum-infiltratedinto apical bud sections, the production of ethylene was inhibited,ethane production was stimulated and the sections became softand pliable; in pure oxygen, ethylene production was- stimulatedand the sections remained firm. Prolonged stimulation of ethaneproduction by malformin-treated sections required oxygen. Indoleaceticacid (IAA) had no effect on the stimulation of ethane productionby malformin-infiltrated tissues; malformin and IAA stimulatedethylene production synergistically at the same time that malformininducedethane production had increased markedly. ¹This work was supported by grant GB-7158 from the NationalScience Foundation. ²Journal Paper No. 3560 of the Purdue Agricultural ExperimentStation. (Received July 23, 1969; )     

Partitioning of [14C]sucrose and Acid Invertase Activity in Reproductive Organs of Pepper Plants in Relation to Their Abscission Under Heat Stress

The effect of heat stress on processes related to carbohydratepartitioning was investigated in young bell pepper (Capsicumannum L. cv. Maor) plants in relation to abscission of theirreproductive organs at different stages of development. None of the reproductive organs abscised after 5 d in a normalday/night temperature regime (25/18°C). With a temperatureregime of 35°C day, 25°C night, abscission occurredin only a small portion of the flower buds and none of the flowersand fruitlets. However, when temperatures in the day and nightwere reversed (25/35°C, day/night) all the buds and someof the flowers abscised during that time period. The young fruitat the first node did not abscise under any temperature regime.The abscission rate of the flower buds was reduced under heatstress if the developing fruit at the first node had been removed. High temperature during either the light or dark periods reducedthe export of [¹⁴C]sucrose from the source leaf (fed for 48h with [¹⁴C]sucrose). Both heat stress and fruit presence reduced the relative amountof [¹⁴C]sucrose which was exported to the flower buds, flowersand roots. Likewise, these treatments reduced the concentrationof reducing sugars in the reproductive organs. Concomitantly,the heat stress and fruit presence on the first node reducedthe activity of soluble acid invertase in the flower buds andthe roots, but not in young leaves. Overall, the results show that heat stress causes alternationin sucrose distribution in the plant, but may also have specificeffects on metabolic activities related to sucrose import andutilization in flower buds and flowers which in turn may enhancetheir abscission. Bell pepper, (Capsicum annuum L. cv. Maor), abscission, acidinvertase, heat stress, reproductive organs, sink leaves. Bell pepper, (Capsicum annuum L. cv. Maor), abscission, acid invertase, heat stress, reproductive organs, sink leaves.