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; )     

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)     

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)     

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)     

White light requirements for stimulation of plant growth by malformin

Over a 3-day period, the minimum white fluorescent light intensity required for malformin-induced growth stimulation of etiolated and green cuttings of Phaseolus aureus was approximately 2.6 × 10³ and 0.4 × 10³ ergs/cm² · sec, respectively. High light intensities were unable to inhibit the ability of malformin to stimulate growth. Over 3 days, the minimum photoperiod for malformin-induced growth stimulation using etiolated and green cuttings and a light intensity of 13.5 × 10³ ergs/cm² · sec was 4 hours and 1 hour, respectively. Malformin must be present in the area of growth stimulation during the time of light treatment. Those changes induced by light and required for malformin-induced growth stimulation were estimated to undergo almost complete decay within 1 hour in the dark. By manipulating the experimental technique, it was possible to stimulate the growth of green cuttings with malformin with a 10-min light treatment (13.5 × 10³ ergs/cm² · sec). Although low light intensities and short photoperiods did not allow growth stimulation by malformin using etiolated cuttings, they prevented or alleviated growth inhibition induced by malformin in the dark.     

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     

Effects of Light on Degradation of Chlorophyll and Proteins during Senescence of Detached Rice Leaves

Regulatory effects of light on senescence of rice leaves wereinvestigated by measuring degradation of chlorophyll and proteinsin leaf segments which had been kept in the dark or under illuminationwith light of different intensities and colors. When leaveshad been left in total darkness for three days at 30°C,there was an initial long lag that lasted for one whole dayand then chlorophyll was rapidly degraded in the second andthird days. Breakdown of chlorophyll was strongly retarded bycontinuous illumination with white light of intensity as lowas 0.5 µmol photons m^–2 s^–1 but the effectof light decreased at intensities above 10 µmol photonsm^–2 s^–2. The initial lag and subsequent degradationof chlorophyll in the dark were little affected by illuminationwith red or far red light at the beginning of dark treatment.However, a brief illumination with red light at the end of thefirst and/or second day significantly suppressed degradationof chlorophyll during subsequent dark periods and the effectof red light was nullified by a short irradiation with far redlight. Thus, degradation of chlorophyll is regulated by phytochrome.Thylakoid membrane proteins and soluble proteins were also largelydegraded during three days in the dark. Degradation of membraneproteins such as the apoproteins of light-harvesting chlorophylla/b proteins of photosystem II and chlorophyll a-binding proteinsof reaction center complexes showed a long lag and was stronglysuppressed by illumination with weak white light. Thus, theloss of chlorophyll can be correlated with degradation of chlorophyll-carryingmembrane proteins. By contrast, light had only a weak protectingeffect on soluble proteins and ribulose-1,5-bisphosphate carboxylase/oxygenaserapidly disappeared under illumination with weak white light.Thus, breakdown of thylakoid membrane and soluble proteins aredifferently regulated by light. Artifacts which would be introducedby detachment of leaves were also discussed. ¹ Present address: Department of Applied Biology, Faculty ofScience and Technology, Science University of Tokyo, Yamazaki,Noda-shi, Chiba, 278 Japan. ² Present address: Department of Life Science, Faculty of Science,Himeji Institute of Technology, Harima Science Park City, Hyogo,678-12 Japan.     

Morphological and physiological characterization of IAA-less-sensitive and IAA-sensitive phases in rooting of Azukia cuttings

In disbudded epicotyl cuttings taken from light grown 5-dayold Azukia angularis Phaseolus angularis) seedlings, all adventitiousrootlets appeared on the second day of incubation. No root primordiawere observed within the first 24 hr and no increase in thenumber of roots occurred after 48 hr. Puromycin (5.5?10^–5M), p-fluorophenylalanine (1?10^–3M),2-thiouracil (2.3?10^–4M) and 2,6-diaminopurine (2?10^–5M)inhibited rooting when applied to cuttings on the second day,but showed no inhibition when applied on the first day. Unlike these inhibitors, pyrithiamine (7.2?10^–5M) inhibitedrooting when it was applied to cuttings on the first day. A rooting promoting effect was observed with actinomycin D (2.4?10^–6M),2,4-dinitrophenol (3?10^–5M) and p-fluorophenylalanine(1?10^–4M) applied to the cuttings on the first day, whereasindoleacetic acid (1.7?10^–4M) showed its promoting effectmost effectively on the second day. ¹Contribution No. 17 from the Botanical Gardens, Faculty ofScience, University of Tokyo, Tokyo, Japan. (Received June 4, 1969; )     

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.     

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.     

Effects of kinetin and gamma radiation on the growth and chlorophyll synthesis of isolated radish cotyledons

Seeds of Raphanus sativus L. were irradiated with 120 and 240Kr of gamma rays from a ¹³⁷Cs source. Chlorophyll synthesisand fresh weight increases (an estimate of cell expansion) ofisolated cotyledons proved to be radioresistant processes. Alag phase in chlorophyll synthesis, removable by kinetin (10mg/liter), was observed. Gamma radiation decreased the reactivityto kinetin in the removal of the lag phase, but did not affectthe kinetin-stimulated fresh weight increase both in light anddark. Addition of 8-azaguanine to the incubation media reducedthe kinetin-stimulated fresh weight increase. This inhibitionwas significantly enhanced by gamma radiation when the cotyledonswere incubated in light. (Received February 22, 1978; )     

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.     

Analysis of abscission responses to photodecomposition products of 1-naphthaleneacetic acid

This paper presents an analysis of abscission reponses of cottonexplants to (a) 1-naphthaneneacetic acid; (b) photodecompositionproducts of 1-naphthaleneacetic acid: 1-methylnaphthalene, 1-naphthaldehyde,1-naphthoic acid, naphthalene, and phthalic acid; and (c) arelated compound: naphthaleneacetyl aspartate. Abscission wasaccelerated by low amounts and retarded by high amounts of 1-naphthaleneaceticacid and 1-naphthoic acid. No significant effect on abscissionwas observed from 1- methylnaphthalene, 1-naphthaldehyde, orphthalic acid applied in amounts from 10^–8 to 10.0 µgper petiole; or with naphthalene from 10^–3 to 10.0µgper petiole. Naphthaleneacetyl aspartate had no effect at 5?10⁴to 5?10^–3 µg per petiole, but completely inhibitedabscission at 5 ? 10^–1 and 5.0 µg per petiole. Thedata are analyzed on part by a previously described mechanicalmethod for the determination of abscission indexes, and in partby a new method described herein, using a digital computer forthe analysis of the abscission time-course data. The resultshave significance to the understanding of the variability encounteredin fruit thinning by 1-naphthaleneacetic acid and related substances,and are discussed in relation to the known intermediate effectsof 1-naphthaleneacetic acid in fruit thinning. ¹Present address: Department of Biology, Univesity of California,Riverside, California 92502, U.S.A. (Received August 26, 1972; )     

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; )     

Low Temperature Treatments Induce an Increase in the Relative Content of Both Linolenic and {lambda}3-Hexadecenoic Acids in Thylakoid Membrane Phosphatidylglycerol of Squash Cotyledons

The effect of low temperatures on the fatty acid compositionof phosphatidylglycerol (PG) in thylakoid membranes, in particularon the ratios of nmol% 16:1(3t) (mg fresh weight)^–1 ofcotyledons and nmol 16:1(3t) (mg chlo rophyll)^–1 weremeasured during squash seedling growth. Plants were germinatedand grown for one day at 30°C then were either kept at 30°C(control plants) or trans ferred to low temperatures (18, 14or 10°C). When plant were transferred from 30°C to lowtemperatures, the increase in fresh weight was gradually limited.The lowe the temperature, the smaller was the fresh weight.In contrast, the relative content of 16:1(3t) and 18:3, as wella the ratios of nmol 16:1(3t) (mg chlorophyll)^–1 and mol%16:1(3t) (mg cotyledon fresh weight)^–1 increased indicatingthat the increase of fresh weight and chlorophyll was mor sensitiveto low temperature than PG desaturation in thyla-koid membranes.Furthermore, low temperatures inducei an increase in 16:1(3t)and 18:3 (the final products of PC synthesis) at the expenseof 16:0 and 18:1 (the initial products of PG synthesis). However,within a range of temperature from 10 to 18°C, the extentof these changes (nmol% of 18:3 or 16:1(3t) per day) was graduallylimited by lower temperatures. We therefore propose that lowtemperature inhibit both fatty acid synthesis and desaturationactivities. However, at low temperatures the fatty acid synthesisis likely to be more strongly inhibited than the desaturationactivities, thus explaining the observed increase in the relativecontent of PG-18:3 and PG-16:l(3t). Results an discussed interms of the mechanism which could be in volved in the metabolismof PG in squash cotyledons. (Received July 5, 1996; Accepted March 10, 1997)     

Effects of Monochromatic Radiations on Growth of Pelargonium Callus Tissue

Pith callus tissues were grown under continuous blue (450 mµ),green (545 mµ), red (650 mµ), and ‘white’(full-spectrum) light, and in the dark for 22 days at 27±2°C at energy levels of 15,000 ergs cm^–2 sec^–1. Mean increases in fresh weight of tissues grown under ‘white’and blue light were significantly greater than those of tissuesgrown in green and red light and in the dark. Tissues grownin the dark yielded mean fresh weight increases significantlylower than tissues grown under blue, red, and ‘white’light. No significant differences were shown between blue and‘white’, red and green, and green and dark treatmentsrespectively. Cell differentiation occurred in all treatmentsonly to the extent of vessel element formation. There were nodifferences in degree of differentiation between treatments. It was proposed that the high-energy reaction of photomorphogenesiswas in operation in the Pelargonium callus tissue. The resultsindicated the presence in the tissue of high-energy photoreceptor(s).The use of high-intensity, incandescent illumination for experimentalprocedures approximating natural conditions of irradiation wasindicated as desirable for pith callus tissues of Pelargoniumzonale var. Enchantress Fiat.     

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; )     

Perithecial formation in Gelasinospora reticulispora III. Inhibitory effects of near-UV and blue light during the inductive dark period

Growing hyphae of Gelasinospora reticulispora required a continuousdark period prior to photoinduction of perithecia. The inductivedark period was interrupted by brief exposure of the hyphaeto white light so that the formation of perithecia no longertook place. Photosensitivity of the hyphae in terms of the light-breakeffect gradually changed during the inductive dark period. Sensitivityreached its maximum at the 18th hr of the dark period when anirradiation of 1?10⁵ ergs cm^–2 of near-UV light or 4?10⁴ergs cm^–2 of blue-light was sufficient for the light-break.Red and far-red light had no effect at all. The light-breakeffect was limited to the irradiated portion of the hyphae anddid not affect any unirradiated portions. Inhibitory effecton perithecial formation of continuous white light could betotally replaced for several days with intermittent irradiationof near-UV or blue light if given for 5 min every 4 hr. (Received December 18, 1973; )     

Abscission: ethylene and light control

The role of ethylene in light control of leaf abscission im mung bean, Vigna radiata (L.) Wilczek cv Jumbo, cuttings was examined. While red light inhibits and far-red light promotes loss of break strength in abscission zones as compared with dark controls, changes in the rate of abscission could not be associated with changes in the rate of ethylene production. Reducing ethylene synthesis in tissue with aminoethoxyvinylglycine did not alter the effects of red or far-red light on abscission. Far-red light appeared to increase and red light appeared to decrease tissue sensitivity to ethylene.     

Acclimation of Tomato Leaves to Changes in Light Intensity; Effects on the Function of the Thylakoid Membrane

When young tomato plants grown in high light (400 µmolquanta m^–2s^–1 PAR) were transferred to low light(100 µmol quanta m^–2s^–1 PAR), non-cyclic electrontransport capacity was decreased and the rate of dark re-oxidationof Q^–, the first quinone electron acceptor of photosystemII, was decreased within 1–2 d. In contrast, the amountof coupling factor CF₁, assayed by its ATPase activity, decreasedmore gradually over several days. The total chlorophyll contentper unit leaf area remained relatively constant, although thechlorophyll a/chlorophyll b ratio declined. When young tomato plants grown in low light were transferredto high light, the ATPase activity of isolated thylakoids increasedmarkedly within 1 d of transfer. This increase occurred morerapidly than changes in chlorophyll content per leaf area. Inaddition, in vivo chlorophyll fluorescence induction curvesindicate that forward electron transfer from Q^– occurredmore readily. The functional implications of these changes arediscussed. Key words: Tomato, leaves, light intensity, thylakoid membrane