Role of ethylene in chlorophyll degradation in radish cotyledons

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

Role of ethylene in chlorophyll degradation in radish cotyledons

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

Chilling-Induced Ethylene Production in Relation to Chill-Sensitivity in Phaseolus spp.

Guye, M. G, Vigh, L. and Wilson, J. M. 1987. Chilling-inducedethylene production in relation to chill-sensitivity in Phaseolusspp.—J. exp. Bot. 38: 680–690. Ethylene production from the primary leaves of six bean (Phaseolusspp.) cultivars known to differ in chill-sensitivity, was monitoredat 23 ?C following chilling of whole plants at 5 ?C for 24 h.The more chill-tolerant cultivars produced greater amounts ofchilling-induced ethylene than the chill-sensitive cultivars.The onset of maximum ethylene production rates and the followingdecline in rates was more rapid in chill-tolerant cultivars.This pattern of ethylene production was also similar when chill-tolerancewas chemically enhanced by choline treatment. The low levelsof ethylene production in chill-sensitive genotypes was alsoreflected by their poor ability to convert the exogenously appliedethylene precursor, 1-aminocyclopropane-l-carboxylic acid (ACC),to ethylene. Moderate levels of leaf water deficit induced by chilling chill-tolerantcultivars and choline treated plants appeared to stimulate chilling-inducedethylene production. High levels of leaf wilt, shown by morechill-sensitive cultivars, reduced this stimulatory effect.Ethylene production was slightly greater when warming was carriedout in the light rather than in the dark. Key words: Ethylene, ACC, choline, chill-sensitivity, Phaseolus     

Elimination of the Far-Red-Induced Lag Phase of Chlorophyll a Accumulation by a Brief Light in Pharbitis nil Cotyledons

In dark-grown Pharbitis nil seedlings, far-red light (FR) irradiationof 48 h or less promotes Chl a accumulation in the first 2-hof a subsequent white light (WL) period, without a lag phaseof Chl a accumulation. However, continuous FR irradiation of72 h or more, causes the so-called FR-induced lag phase. A 5-minWL given 4 h before the onset of the continuous WL promotesChl a accumulation irrespective of the length of the precedingFR irradiation period, if a 4-h dark period is inserted betweenthe 5-min WL and continuous WL. This suggests that the effectof the brief WL is independent of and additive to the effectof the preceding FR irradiation, although the effect of theFR irradiation changes from promotive to inhibitory with anincrease in the irradiation period. Red light (R) is more active than blue light (B) in this brieflight effect. The R effect is reversed by subsequent exposureto FR when the period of the preceding FR irradiation is 24h, but not when it is 72 h. The relative effectiveness of Bto R increases after prolonged FR irradiation. (Received August 6, 1986; Accepted March 12, 1987)     

Effects of Light Illumination on the Population of Translatable mRNA in Radish Cotyledons during Dark-Induced Senescence

The population of translatable mRNA in radish cotyledons hasbeen shown to change strikingly during dark-induced senescenceby analyzing cell-free translation products from polyadenylatedRNA using two-dimensional electrophoresis (Kawakami and Watanabe1988, Plant Cell Physiol. 29: 33–42). In the present study,the translatable mRNAs in the cotyledons were studied afterre-illumination of seedlings which had been induced to senesceby dark treatment. All of the mRNA species which showed relativeincrease or decrease during a 24-h dark treatment returned totheir initial levels after a subsequent 24-h illumination withwhite light. When seedlings were kept in the dark for 48 h,21 mRNA species increased, but the increase in some of themwas no longer reversible; 9 out of the 21 mRNA species remainedat the same level even after 48 h of re-illumination. All ofthe 18 mRNA species which decreased during 48 h in the darkreturned to their initial levels upon re-illumination. The mRNAspecies that showed irreversible increase were also found toaccumulate in cotyledons senesced after a lengthy growth periodunder light. There were also some mRNA species whose contentwas not affected by dark treatment, but increased transientlyafter re-illumination of the seedlings. These observations arediscussed in relation to the progress of senescence in the cotyledons. (Received September 24, 1987; Accepted December 19, 1987)     

The Role of Cellulase and Polygalacturonase in Abscission of Young and Mature Shamouti Orange Fruits

During the first eight weeks after setting young citrus fruits gradually lose their ability to abscise at the abscission zone between the stem and the pedicel; in fruits older than eight weeks abscission occurs at the calyx area. The activity of cellulase and polygalacturonase in the two abscission zones was markedly increased before and during abscission, and was localized mainly in the abscission zone. Ethylene accelerated the increase in enzymic activity after an 8- to 10-h lag period; 2,4-D delayed abscission and enzymic activity when applied during the first 24 h after excision. During this period 2,4-D also partly suppressed the enhancing effect of ethylene. Early application of cyclo-heximide inhibited the formation of the enzymes and thus abscission was delayed to a certain extent. Although there are some indications that the relationship between enzymic activity and abscission is a complex one, the data presented indicate that cellulase and polygalacturonase play a significant role in abscission of citrus fruits at various developmental stages. Both enzymes act almost simultaneously and are equally controlled by ethylene and 2,4-D.     

Inhibition of photoperiodic floral induction in Pharbitis nil by ethylene

Application of ethylene at 100 ppm or higher completely inhibitedflowering in Pharbitis nil when made during an inductive darkperiod. Exposing plants to ethylene before or after the inductivedark period produced only slight or almost no inhibition. Ethylenewas effective when it was applied only to a cotyledon, but wasineffective when applied only to a receptor bud. Ethylene hadno effect on translocation of the floral stimulus. Ethylene-treatedcotyledon did not transfer any flower inhibiting entity. Thus,ethylene is considered to inhibit the induction process(es)in cotyledons. Except for an initial temporary cotyledon epinasty, ethylenetreatment had no effect on the subsequent growth and vigor ofplants. This temporary cotyledon epinasty disappeared withinthe next 24 hr. (Received May 4, 1972; )     

Spectral Dependence of Night-break Effect on Photoperiodic Floral Induction in Lemna paucicostata 441

A single dark period of longer than 8 hr induced flowering inLemna paucicostata 441 cultured in E medium. Monochromatic lightsof 450, 550, 650 and 750 nm with a half-power bandwidth of 9nm given for 10 min at the 8th hour of a 14-hr dark period inhibitedflowering. The fluence rates required for 50% inhibition were10, 0.5, 0.1 and 3 µmol m^–2. sec^–1, respectively.When applied between the 4th and the 10th hour of the dark period,lights of 450, 550 and 650 nm were inhibitory showing a maximumeffect at the 8th hour. But 750-nm light completely inhibitedflowering when applied at any time during the first 8 hr ofthe dark period. The inhibitory effect of 750-nm light givenat the beginning of the dark period was totally reversed bya subsequent exposure to 650-nm light, and the fluence-responsecurves for the effect of 750-nm light given at the 0, 4th and8th hour were essentially the same. This suggests that the presenceof P_FR is crucial for the floral initiation throughout the first8 hr of the inductive dark period. The role of phytochrome inthe photoperiodic flower induction of L. paucicostata is discussed. (Received January 4, 1982; Accepted March 19, 1982)     

Effects of Diazocyclopentadiene (DACP) and Silver Thiosulphate (STS) on Ethylene Regulated Abscission of Sweet Pea Flowers (Lathyrus odoratus L.)

The ethylene production rate of cut sweet pea flower buds increased37-fold during the first 48 h of their vase life. This increasein ethylene production was accompanied by petal wilting at 72h and abscission of the buds 24 h later. Exposure of the cutspikes to the ethylene action inhibitor diazocyclopentadiene(DACP, 170 µI 1^-1) for 18 h under fluorescent lights delayedsubsequent wilting and abscission and promoted bud opening.Silver thiosulphate (0·2 mM) was more effective thanDACP, delaying wilting for longer and preventing abscissionentirely.Copyright 1995, 1999 Academic Press Ethylene, abscission, silver thiosulphate, diazocyclopentadiene, flower senescence, wilting, sweet pea, Lathyrus odoratus L     

Photoperiodic Regulation of Cell Division and Chloroplast Replication in Heterosigma akashiwo

Cell division and chloroplast replication in Heterosigma akashiwo(Hada) Hada occurred as separate synchronous events during thecell cycle when cells were subjected to light-dark regimes.Under three different photoperiodic cycles of 10L/14D (10 hlight/14 h dark), 12L/12D or 16L/8D, cell division began athour 19–20 and finished at hour 23–26 after theonset of the light period, while chloroplast replication beganat hour 20–22 after the onset of the dark period. Almostall the cells divided only once in the 12L/12D cycle. The rateof increase in chloroplast number during one light-anddark cyclewas always equal to that in cell number in every photoperiodexamined. Light was essential for both cell division and chloroplast replication,but the minimum light period necessary for each event differed.When the light period was shorter than 6 h, no cell divisionoccurred; when it was shorter than 3 h, no chloroplast replicationoccurred. (Received February 26, 1987; Accepted June 17, 1987)     

Abscisic Acid, Auxin, and Ethylene in Explant Abscission

Experiments with explants of Phaseolus vulgaris L., cv. CanadianWonder, show that abscission and the associated rise in oarboxymethyl-cellulaseactivity in the separation zone are initiated by a peak in ethyleneproduction during senescence of pulvinar tissue distal to thezone. Distal applications of abscisic acid (ABA) induce an earlierpeak in ethylene production, increase cellulase activity, andpromote abscission. ABA is more effective in these ways if treatmentis delayed from 0 to 24 h after excision. With increasing concentrations of ABA the maximum rate of ethylene production is achievedsooner. Indol-3yl-acetic acid (IAA) and ABA are antagonisticin this system and have opposing effects. IAA retards the timeof peak ethylene-production and delays abscission. Explantsmay be retained for long periods without abscinding if incubatedin an ethylene-free atmosphere: the addition of ethylene forany one 24-h period (except the first 24 h after excision) willinduce abscission. The initial period of insensitivity to ethyleneis extended by distal applications of IAA. Ethylene-inducedabscission can be inhibited by IAA applied up to 72 h afterexcision provided the ethylene is not applied first. It is proposedthat abscission in the explant is controlled at two levels:(1) an auxin-dependent stage determining the duration of insensitivityto ethylene; (2) the timing of a rise in ethylene productionin senescing tissue distal to the separation zone. An auxin-ethylenebalance-mechanism at the separation zone is discussed.     

Ethylene, Nitrate and Nitrite Interactions in the Promotion of Dark Germination of Common Purslane Seeds

Ethylene (10 µ1^–1) caused about one-third of highlydark-dormant seeds of common purslane (Portulaca oleracea L.)to germinate in the dark. Attempts were made to increase germinationin the dark with nitrate and ethylene combinations. When applieddirectly to the seeds, KNO₃ did not stimulate germination andKNO₃ plus ethylene did not increase germination above that ofethylene alone. Pre-incubation of seeds in KNO₃ for 4 to 7 dbefore the ethylene applications significantly increased germination.The effects of the KNO₃ pre-incubation were additive at eachof four ethylene concentrations (0.1–100 µ11^–1).Potassium nitrate was effective only when ethylene followedthe KNO₃ pre-incubation period. Potassium nitrite stimulatedabout 25 per cent of the seeds to germinate without a pre-incubationperiod and without ethylene. Also, ethylene plus KNO₂ enhancedgermination above that achieved by either stimulus alone. Silvernitrate did not block the ethylene promotion of germination,but reversed the typical ethylene inhibition of seedling growthfollowing germination. The results support the views that nitrateexerted its effect via conversion to nitrite within the seedand that the rate of nitrate conversion may be a limiting factorin the dark germination of common purslane seeds. Ethylene mayfacilitate nitrite activity by increasing seed sensitivity tothe stimulus. Common purslane, Portulaca oleracea L., ethylene, nitrate, nitrite, germination, dormancy     

Involvement of Abscisic Acid and Indole-3-acetic Acid in the Flowering of Pharbitis nil

The involvement of abscisic acid (ABA) and indole-3-acetic acid (IAA) in the regulation of flowering of Pharbitis nil was investigated through exogenous applications and analyses of endogenous levels. Both hormones inhibited the flowering of P. nil when they were applied before or after a single 15-h dark treatment. The inhibitory effect of ABA and IAA was significant when they were applied before the dark treatment, and the application to plumules was more effective than that to cotyledons. In all applications, the inhibitory effect of IAA was stronger than that of ABA. Endogenous levels of ABA and IAA in the plumules were compared between flower-inductive (15-h dark treatment) and noninductive (continuous light) light conditions. There was no significant difference in the ABA level between light and dark conditions, whereas the level of IAA was decreased by the dark treatment. These results suggest that biosynthesis and/or catabolism of IAA is affected by the light treatment and therefore may be involved in the regulation of early flowering processes in the apex. The inhibitory effects of ABA and IAA were reversed by an application of gibberellin A₃, indicating that gibberellin A₃ counteracts the flowering processes affected by ABA and IAA. Application of aminoethoxyvinylglycine restored the flowering response inhibited by IAA, which suggests the possibility that the inhibitory effect of IAA is the result of enhanced ethylene biosynthesis. Received November 22, 1996; accepted February 17, 1997     

ATP Synthesis in Cotyledons of Cucumber and Mung Bean Seeds during the First Hours of Imbibition

ATP concentration increased rapidly during the first 6h of imbibitionin cotyledons of cucumber and mung bean seeds. The increasewas strongly inhibited by 1-h treatment of tissues with cyanidein both species. Carbonylcyanide m-chlorophenylhydrazone, anuncoupler of oxidative phosphorylation, showed little effectduring the first hour of the treatment, but its inhibitory effecton ATP synthesis became significant after 3 h. Mitochondrialfractions prepared from 6-h-old cucumber cotyledons were capableof phosphorylating ADP to ATP. These results suggest that mitochondrialoxidative phosphorylation may be involved in ATP synthesis duringthe early hours of imbibition in both cucumber and mung beanseeds. (Received December 7, 1987; Accepted April 9, 1988)     

Influence of ethylene on nucleic acid synthesis in etiolated Pisum sativum

Ethylene applied to intact etiolated seedlings of Pisum sativumcv. Alaska inhibits incorporation of ³H-thymidine into DNA insubsequently excised plumular and subapical tissue segmentsbut has no influence on incorporation of ³H-uridine into RNA.The effect on DNA synthesis begins about 2 hr after ethyleneis applied, and intensifies progressively. A similar inhibitionof DNA synthesis occurs when ethylene is applied directly toplumular sections cut from control plants, but not with subapicalsegments under these conditions. Inhibition of DNA synthesisby ethylene is reversed by benzyl adenine in plumular sections.Brief exposure of dark grown seedlings to red light causes asubsequent increase in DNA synthesis in plumular tissue. Thechanges in DNA synthesis in tissues exposed to ethylene, benzyladenine and red light are correlated with the effects of thesetreatments on the mitotic index. (Received March 12, 1973; )     

Dormancy and Impotency of Cocklebur Seeds. IX. Changes in ACC-Ethylene Conversion Activity and ACC Content of Dormant and Nondormant Seeds during Soaking

Differences in ethylene production between dormant (D) and nondormant(ND) lower seeds of cocklebur (Xanthium pennsylvanicum Wallr.)were studied with respect to changes in the activity of conversionof 1-aminocyclopropane-l-carboxylic acid (ACC) to ethylene andin the contents of ACC and malonyl-ACC in their axial-tissuesduring soaking. Superior ethylene production in ND seeds ascompared to D seeds became evident during a soaking period rangingfrom 12–24 h, when the radicle protrusion in ND seedshad not yet occurred. Ethylene production in ND seeds increasedabruptly after the radicle protrusion. The inhibitors of ethyleneproduction, aminoethoxyvinyglycine, cobaltous ion and -aminoisobutyricacid, inhibited the germination of ND seeds, whereas ACC enabledD seeds to germinate. Activity of ACC-ethylene conversion was absent in dry axialtissues and developed with soaking. After 24 h, this activityin ND axes was superior to that in D axes. Under hypoxia, however,the difference in the ACC-conversion activity appeared before24 h. On the other hand, the contents of ACC in both D and NDaxes remained almost unchanged until 24 h of soaking. It isthus suggested that the inferior ethylene production in D seedsis associated mainly with their low activity of ACC-ethyleneconversion, though partly with their low activity of ACC supply. Activity of ACC-ethylene conversion in the axes of ND seedsincreased sharply after radicle protrusion which occurred after24 h of soaking. Correspondingly, the contents of both ACC andmalonyl-ACC increased in the axes of germinated ND seeds. Theseimply that the high ethylene production in the ND seeds in thepost-germination period comes from the increasing activitiesof ACC supply as well as ACC-ethylene conversion in their axes. Key words: Cocklebur seeds, Dormancy, Ethylene production, 1-aminocyclopropane-1-carboxylic acid, Germination, Xanthium     

Role of the Photoperiod Preceding a Flower-Inductive Dark Period in Dark-Grown Seedlings of Pharbitis nil Choisy

Flowering responses to a single photoperiod, of various durationsand irradiances, followed by an inductive dark period were investigatedwith dark-grown seedlings of Pharbitis nil Choisy. The numberof flower buds induced in each plant (NFB) increased with theincrease of both duration and irradiance of the photoperiod.Reciprocity did not hold for this photoresponse within the rangeof 0-16 h and 2.5-10 W-m^-2, NFB depending on the duration ratherthan the irradiance. With lengthening of the dark period followinga photoperiod of 8 h or less, two different phases alternatelyappeared so that NFB sharply increased at 20-24 h and 40-43h after the onset of the photoperiod, then gradually decreased.When the photoperiod was longer than 8 h, NFB sharply increasedat 12–16 h after the end of the photoperiod and remainedaround the saturated value with longer dark periods. Far-redlight given immediately after the photoperiod inhibited flowering,the inhibitory effect being stronger the shorter the photoperiod.This far-red effect is mediated by phytochrome and P_FR seemsto be required during the inductive dark period following ashort photoperiod for floral induction. (Received December 23, 1983; Accepted April 12, 1984)     

Studies on the Photoreceptors for the Promotion and Inhibition of Flowering in Dark-Grown Seedlings of Pharbitis nil Choisy

Three-day-old etiolated seedlings of Pharbitis nil were exposedto red light for 10 min and sprayed with N⁶-benzyladenine beforetransfer to a 48-h inductive dark period, after which they weregrown under continuous white light. A second red irradiationpromoted flowering when given at the 5 and 24th hour of theinductive dark period but inhibited flowering at the 10 and15th hour. Far-red light inhibited flowering when given at anytime during the first 24 h of the dark period. Red/far-red reversibilitywas clearly observed at the 0, 5, 10 and 24th hour, but notat the 15th hour when both red and far-red lights completelyinhibited flowering. The action spectrum for the inhibition of flowering at the 15thhour of the inductive dark period had a sharply defined peakat 660 nm and closely resembled the absorption spectrum of theP_R form of phytochrome. The photoreceptors involved in thesephotoreactions are discussed. (Received June 10, 1983; Accepted July 6, 1983)     

Initiation of Rapid Ethylene Synthesis by Apple and Pear Fruits in Relation to Storage Temperature

The influence of storage temperature on the onset of rapid ethyleneproduction was investigated for fruits of Conference pear (Pyruscommunis L.) and five cultivars of apple (Malus domestica Borkh.).The time taken from harvest to rapid ethylene production wasshorter and more uniform at 3 ?C than at 18–20 ?C forConference pears and Golden Delicious apples. Increases in internalethylene concentration, 1-amino cyclopropane-1-carboxylic acidconcentration and ethylene production were simultaneous in GoldenDelicious apples at 3 ?C. When Golden Delicious apples wereheld at 3 ?C for 48 h and then kept at 20 ?C the mean time ofonset of ethylene production was similar to that for applesheld continuously at 20 ?C. However, two periods of 48 h at3 ?C caused earlier ethylene production. Conversely, ethyleneproduction at 3 ?C was delayed by transfer to 20 ?C for twoperiods of 48 h. Cox's Orange Pippin and other apple cultivarstended to show more synchronous ethylene production at 3 ?Cthan at higher temperatures but the mean time of onset was eitherunaffected by temperature or slighdy delayed at lower temperature.Acceleration of the onset of ethylene production by low temperaturewas never observed in Cox's Orange Pippin apples harvested atweekly intervals from 10 August to 17 September. Key words: Ethylene, Storage temperature, Pyrus communis, Malus domestica     

Evidence that Ethylene is not Involved in Red-light-induced Stimulation of Chlorophyll Formation in Etiolated Cucumber Cotyledons

The involvement of ethylene in red-light-induced stimulationof chlorophyll (Chl) formation was studied because one of thered-light effects on Chl formation (the lateappearing effect)interacts with the ethylene effect in 3-day-old excised etiolatedcotyledons of cucumber (Cucumis sativus L. cv. Aonagajibai).Ethylene production by etiolated cotyledons of intact seedlingsin the dark is enhanced by a red-light pulse, but the effectdoes not occur in excised cotyledons. Application of ethylenein the dark to 3-day-old intact seedlings has little effecton Chl formation in the cotyledon during subsequent continuousillumination, although ethylene pretreatment of 5-day-old seedlingssignificantly stimulates Chl formation. Removal of endogenousethylene by mercuric perchlorate [Hg(ClO₄)₂] does not specificallysuppress the red-light action on Chl formation in both attachedand excised cotyledons. Inhibition of ethylene synthesis byaminoethoxyvinylglycine does not affect the red-light effecton Chl formation in excised cotyledons. These facts indicatethat ethylene does not operate as a mediator of red light instimulating Chi formation in either attached or excised cotyledons. (Received December 13, 1981; Accepted March 30, 1981)