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)     

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     

Leaf Abscission and Stem Lesions (Intumescences) on Poplar Clones after SO2 and O3 Fumigation: A Link with Ethylene Release?

Differences in premature leaf abscission and in visible steminjury in genetic lines of poplar followed continuous fumigationswith air pollutant levels of SO₂ (90–100 nl l^–1)and O₃ (70–80 nl l^–1) either separately or together.The clones used were: Populus deltoides var. missiouriensisMarsh., P. nigra cv. ‘italicd’ L., and the hybridsP. nigra cv. ‘italica’ xP. deltoides (He-X/3) andP. nigra cv.‘italica’ x P. nigra cv. ‘Serres’(He-K/7). While most leaf abscission occurred within 20 d fromthe start of fumigation, stem lesions (intumescences), appearedonly after 72 d. Their anatomical characteristics include theformation of lysigenous aerenchyma in the lower parts of theintumescence, the sloughing of superficial cells from the injuredarea, and the development of crystalline formations on the surfaceof the lesions. P. deltoides exhibited the least morphologicalresponse to the gases. Ethylene released from fumigated leaves was determined at thesame gas concentration of SO₂ (100 nl l^–1), O₃ (75 nll^–1) and their mixture. Leaves of P. deltoides consistentlyshowed the lowest ethylene production after the gas treatments.P. ‘italica’ production was higher but was littlealtered by the treatments. The two hybrids He-X/3 and He-K/7showed the greatest increases in ethylene evolution with time.With He-K/7 exposed to the gas mixture the production of ethylenedecreased after the initial sharp rise during days 1–2,and reflected the considerable leaf damage observed after day3. The results suggest that sensitivity to air pollution, (as shownby leaf abscission and the formation of stem intumescences)can be correlated with the level of pollutant-induced ethyleneevolution from leaves. Initially high levels could induce abscission,whilst prolonged production could be responsible for intumescenceinitiation. The discussion proposes a series of events fromSO₂ and/or O₃ entry into the leaf and the physiological reasonsfor the clonal differences. Key words: Sulphur dioxide, ozone, ethylene, poplar, leaf abscission, stem lesions     

Effect of Ethylene on Peroxidase Activity

Ethylene increased the peroxidase activity of nine out of ten varieties of sweet potato (Ipomoea batatas (L.) Lam.) root disks tested. The increase which was observed four hours after ethylene treatment was partially overcome by carbon dioxide. The increase was inhibited by actinomycin D and cycloheximide, indicating de novo protein synthesis. Electrophoretic separation on polyacrylamide gels indicated the appearance of two new peroxidase bands. Peroxidase activity in bean petiole explants was localized around the separation layer. Ethylene caused a small increase in peroxidase activity in the petiolar portion of the explant. Phenolic substances had no effect on abscission consistent with their proposed roles as cofactors for auxinoxidase, indicating that auxin-oxidase does not play a role in abscission of Coleus blumei Benth. abscission zone explants.     

Characterization of a Non-abscission Mutant in Lupinus angustifolius L.: Physiological Aspects

A single-gene recessive mutant (Abs^-) of Lupinus angustifoliusL. ‘Danja’ that does not abscise any organs wascompared with its parent during continuous exposure of explantsfrom 14 d old seedlings to 10 µl l^-1ethylene. Both endo-(1,4)-ß- D -glucanase (cellulase) and polygalacturonase(PGA) activities increased significantly and progressively inpetiole-stem abscission zones of the parent before the onsetof abscission, and were reflected in a rapid decline in breakstrengthfrom 300 to 70 g within 32 h. In the mutant there was negligibleincrease in hydrolytic enzyme activity, breakstrength declinedslowly (to 180–200 g by 72 h) and there was no abscission.Isoelectric focusing showed two cellulase isoforms (pI 5.0 andpI 8.5) expressed in abscission zones of the parent; these wereexpressed at much lower levels in the mutant. These data areinterpreted to indicate that expression of at least two formsof cellulase activity is enhanced by ethylene in normal petioleabscission zones of lupin. PGA activity also increased in theabscission zone tissue of the parent but to a lesser extentin that of the mutant. We attribute the Abs^-phenotype to mutationof a gene regulating ethylene-responsive expression of abscission-specifichydrolytic enzymes. Copyright 2001 Annals of Botany Company Lupinus angustifolius, abscission, breakstrength, cellulase, ethylene, legume, lupin, mutant, polygalacturonase     

CHANGE OF B-TYPE HAEM CONTENT IN RELATION TO PEROXIDASE BIOSYNTHESIS IN INJURED SWEET POTATO ROOTS

The methods of quantitative analysis of b-type haem in plantswere investigated. With an improved method developed was determinedthe haem content in the supernatant, mitochondrial, and microsomalfractions of sweet potato tissue. The activities of peroxidase,catalase, and cytochrome oxidase, as well as the contents ofb-type haem and acid-insoluble nitrogen in the cellular fractionswere determined at different incubation times after cuttingof sweet potato tissue. Peroxidase and catalase increased withtime in each celluler fraction, following a short lag phase.In the mitochondrial fraction, b-type haem, cytochrome oxidase,and acid insoluble nitrogen increased linearly with time. Inthe microsomal and supernatant fraction, b-type haem increasedwith time following a short lag phase. The increase in haemcontent of the supernatant fraction appeared to be associatedwith peroxidase formation. Time course analysis showed that ⁵⁹Fe-incorporation into b-typehaem of the supernatant fraction increased with time and thatincorporation was markedly inhibited by blasticidin S. The incorporationof ⁵⁹Fe into mitochondrial haem did not increase with time andwas not inhibited by blasticidin S. Blasticidin S inhibited⁵⁹Fe-incorporation into microsomal haem. Time course analysisof b-type haem content, ⁵⁹Fe-incorporation into b-type haem,and peroxidase activity suggest that in the injured tissue haemis synthesized from low molecular weight compounds and is incorporatedinto peroxidase as the haem moiety. ¹ This paper constitutes Part 57 of the Phytopathological Chemistryof Sweet Potato with Black Rot. ² Present address: Institute for Plant Virus Research, Chiba.     

Nucellar Senescence and Ethylene Production as they Relate to Avocado Fruitlet Abscission

Events preliminary to avocado (Persea americana Mill) fruitletabscission include senescence of the nucellus and seed coat.The dynamics of nucellar deterioration and ethylene productionleading to seed abortion and abscission in avocado was examined.Excised branches bearing clusters of fruit from 1.0–2.5cm diameter were placed in humid chambers to reduce transpirationalwater loss. Fruitlets synchronously began nucellar and seedcoat deterioration 27–33 h after excision and rapidlyprogressed through stages of increasing degradation culminatingin abscission approximately 2 days later. The nucellus-seedcoat produced a temporary burst of ethylene at the first visiblesign of nucellar senescence followed by less ethylene productionin the mesocarp approximately 12 h later. All fruit underwentnucellar degradation prior to abscission. Exogenously appliedethylene accelerated fruitlet abscission with concentrationsas low as 1.0µ 1^–1 and with maximum response at100µl^–1 or greater. Maximal response took 2 days.Aminoethoxyvinyl-glycine (AVG) at 30 µ M inhibited ethyleneproduction and fruitlet abscission. The senescence process,however, was not af fected in any way by ethylene or AVG treatments.Observations of attached fruit suggest that nucellar-seed coatsenescence, concomitant ethylene production, and resulting abscissiontake place in a manner and within a time period similar to thatobserved on detached branches. It is concluded that nucellarand seed coat senescence is prerequisite to avocado fruitletabscission, and the time required from the first indicationof nucellar breakdown to abscission of that fruitlet appearsto be approximately 2 days. The senescence process is responsiblefor a large, transient rate increase in ethylene productionby the nucellus and perhaps seed coat. Ethylene is consideredto be the result rather than the cause of nucellar-seed coatsenescence. The ethylene thus produced induces fruit abscission.     

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     

Ethylene and 1 -Aminocyclopropane-1-Carboxylic Acid Production in flacca, a Wilty Mutant of Tomato, Subjected to Water Deficiency and Pre-treatment with Abscisic Acid

Neill, S. J., McGaw, B. A. and Horgan, R. 1986. Ethylene and1-aminocyclopropane-l-carboxylic acid production in flacca,a wilty mutant of tomato, subjected to water deficiency andpretreatment with abscisic acid —J. exp. Bot. 37: 535–541. Plants of Lycoperstcon esculentum Mill. cv. Ailsa Craig wildtype and flacca (flc) were sprayed daily with H²O or 2?10^–2mol m^–3 abscisic acid (ABA). ABA treatment effected apartial phenotypic reversion of flc shoots; leaf areas wereincreased and transpiration rates decreased. Leaf expansionof wild type shoots was inhibited by ABA. Indoleacetic acid (IAA), ABA and l-aminocyclopropane-l-carboxylicacid (ACC) concentrations were determined by combined gas chromatography-massspectrometry using deuterium-labelled internal standards ABAtreatment for 30 d resulted in greatly elevated internal ABAlevels, increasing from 1?0 to 4?3 and from 0?45 to 4?9 nmolg^–1 fr. wt. in wild type and flc leaves respectively.Endogenous IAA and ACC concentrations were much lower than thoseof ABA. IAA content ranged from 0?05 to 0?1 nmol g^–1 andACC content from 0?07 to 0?24 nmol g^–1 Ethylene emanationrates were similar for wild type and flc shoots. Wilting of detached leaves induced a substantial increase inethylene and ACC accumulation in all plants, regardless of treatmentor type. Ethylene and ACC levels were no greater in flc leavescompared to the wild type. ABA pretreatment did not preventthe wilting-induced increase in ACC and ethylene synthesis. Key words: ABA, ACC, ethylene, wilting, wilty mutants     

Regulation of Stem Abscission and Callus Growth in Shoot Explants of Sweet Orange [Citrus sinensis (L.) Osbeck]

Two-node explants from Sweet Orange cv. St Ives Valencia orangeshoots produced prolific callus and formed secondary abscissionzones within internodes when cultured in vitro with abscisicacid (ABA, 5 µM) or -naphthaleneacetic acid (NAA, 5 µM).Benzyladenine (BA, 1 µm) induced callus but had littleeffect on abscission. Secondary abscission zone formation wasassociated with ABA-induced and auxin-induced ethylene formation.Treatment of explants with inhibitors of ethylene synthesis[aminoethoxyvinyl glycine (AVG), Co²⁺, PO₄^3–] preventedformation of secondary abscission zones but had variable effectson callus formation. Newly made explants contained high concentrationsof endogenous ABA (up to 6000 ng g^–1 f.wt), as measuredby GC/MS/SIM. Long-term subculture of explants (two years) inmedia containing BA (1 µm) led to a reduction in endogenousABA level (40 ng g^–1 f. wt) and to loss of capacity toform extensive callus and secondary abscission zones. Citrus sinensis (L.) Osbeck cv. St Ives Valencia, sweet orange, secondary abscission zones, in vitro, ethylene, endogenous ABA, endogenous IAA     

The Role of 1-Aminocyclopropane-1-carboxylic acid in the Control of Low Temperature Induced Ethylene Production in Leaf Tissue of Phaseolus vulgaris L .

Ethylene production from leaf discs of dwarf bean (Phaseolausvulgaris L.) was less than 02 nl g^–1 h^–1 at 5 Cbut rapidly increased tenfold on transfer to 25 C. The lowethylene production at 5 C and the potential for overshootproduction on transfer to 25C were not associated with accumulationof the ethylene synthesis intermediate 1-aminocyclopropane-1-carboxylicacid (ACC). Addition of exogenous ACC to leaf discs incubatedat 5C increased ethylene production, while similarly incubatedleaf discs did not synthesize increasing amounts of endogenousACC until they were transferred to 25 C. The basis for theovershoot in ethylene production when leafdiscs were transferredfrom 5 to 25 C appears to reside in changes to the pathwayleading to the synthesis of ACC or an earlier intermediate inthe pathway of ethylene biosynthesis. Ethylene, 1-aminocyclopropane-l-carboxylic acid, Phuseolru vulgaris L., dwarf bean, temperature     

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.     

Protein Dysfunction and Inhibition of Amino Acid Incorporation in Root Segments from Wheat and Mung Bean Seedlings caused by some Amino Acid Analogues

The effects of para-fluorophenylalanine (p-FPA) and azetidine-2-carboxylicacid (AZ) on acid phosphatase and peroxidase activity, and onL-leucine incorporation, in root segments of Triticum aestivumL. cv. Fenman and Vigna radial a (L.) Wilczek, were studied.Incubation with 50 mmol^–3 AZ significantly reduced phosphataseand peroxidase activities in wheat roots, but with 20 mol m^–3p-FPA, only the peroxidase activity was reduced. In mung beanroots, phosphatase activity was inhibited by both AZ and p-FPA.Effects of the ortho- and meta- isomers of FPA on wheat rootphosphatase and peroxidase, and on mung bean phosphatase, werealso examined. Leucine uptake and incorporation were not inhibitedby 5 h pre-incubation with either p-FPA or AZ, but were inhibitedafter 24 h of pre-incubation. The results support the view that,in the shorter term, the analogues inhibit enzyme activity bybecoming incorporated to produce non-functional protein and,in the longer term, metabolism is further affected by inhibitionof protein synthesis. Key words: Fluorophenylalanin, Azetidine-2-carboxylic acid, Triticum aestivum, Vigna radiata     

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)     

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; )     

Metabolism of 1-Aminocyclopropane-l-Carboxylic Acid during Apple Fruit Development

The metabolism of [U^–14C] 1-aminocyclopropane-1-carboxylicacid (ACC) supplied to whole fruits of apple (Malus domesticaBorkh., cv. Cox's Orange Pippin) was investigated. Radioactiveethylene was recovered in mercuric acetate traps and an acidicmetabolite was formed in proportions which varied little withthe absolute amount of substrate supplied. The amount of ACCusually supplied did not cause immediate, rapid ethylene productionby mature, pre-climacteric fruit but the onset of productionwas earlier than in untreated fruit. The radioactive acidic metabolite was purified by four chromatographicprocedures and activity was coincident with authentic 1-malonylamino)cyclopropane-1-carboxylic acid (MACC). The presence of thiscompound was confirmed by gas chromatography linked to massspectrometry. MACC was a major metabolite of [¹⁴C] ACC supplied to applesthroughout fruit development. The proportion converted to ethylenewas low but increased with endogenous ethylene production inthe final samples. MACC was shown to be a natural constituent of apple fruits andto accumulate to the amol kg^–1 level. Key words: 1-Aminocyclopropane-l-carboxylic acid, Ethylene, 1 (Malonylamino) cyclopropane-1-carboxylic acid, Malus domestica     

The Role of Basipetal Auxin Transport in the Positional Control of Abscission Sites Induced in Impatiens sultani Stem Explants

If segments of Impatiens sultani stem are explanted and incubated,separation layers often form across them and lead to abscission.To test the suggested role of auxin concentration in controllingthe position of abscission sites, explants were labelled byapplying [¹⁴C]IAA to the shoot tip 4 h prior to explanting;transport of auxin applied in this way seems to resemble thatof endogenous auxin. During subsequent incubation of explantsfor 20 h, basipetal transport resulted in ¹⁴C accumulating justabove the base of the explants (nearly 80 % in the bottom 4mm of 24 mm explants). In internodal explants that had beenwounded at explanting by incising one side so as to sever avascular bundle, and in nodal explants with the leaf removed,the ¹⁴C also accumulated just above the wound or node to abouttwice the concentration otherwise expected; this accumulationwas probably due to basipetal transport being impeded by vasculardiscontinuity at the wound or node. Accumulation just abovethe base, or above a wound or node, resulted in gradients of¹⁴C concentration (presumably reflecting endogenous auxin concentration)decreasing in the morphologically upward direction at each ofthese three positions where abscission sites tend to occur. Impatiens sultani, abscission, auxin, IAA, node, polarized transport, positional control, separation layer, wounding     

Malate: A Possible Source of Error in the NAD Glutamate Dehydrogenase Assay

The effects of externally induced metabolic perturbations areoften studied through changes of the enzyme activity patternsin crude plant extracts. From glutamate dehydrogenase (GDH)it is reported that environmental changes not only influencethe amount of the enzymatic activity, but also the ratio ofthe aminating to the deaminating activities (NADH/NAD⁺ ratio).Using crude cell extracts of suspension cultures of wheat (Triticumaestivum L. cv. Heines Koga II) we find evidence that the pretreatmentof the homogenate directly influences this ratio. Dialysis ofthese crude cell extracts resulted in a 70% loss of the NAD⁺activity, while the NADH activity remained unchanged. The deaminatingactivity in the dialysed extract could be completely restoredupon addition of a dialysable factor which was identified tobe malate. The interference of malate with the glutamate dehydrogenasereaction is caused through the action of malate dehydrogenaseand glutamate oxaloacetate transaminase which are both presentin high activities in the extracts. Only in exhaustively dialysedcell extracts can the proper deaminating GDH activity be determined.The results are discussed in the light of the controversialreports on the variable ratio of the NADH/NAD⁺ activity of GDH. Key words: Glutamate dehydrogenase, malate, NADH/NAD⁺, activity, Triticum aestivum     

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, acid invertase, heat stress, reproductive organs, sink leaves     

The Relationship between Sucrose Supply, Sucrose-cleaving Enzymes and Flower Abortion in Pepper

Abortion of pepper flowers depends on the light intensity perceivedby the plant and on the amounts of sucrose taken up by the flower(Aloni B, Karni L, Zaidman Z, Schaffer AA. 1996.Annals of Botany78: 163–168). We hypothesize that changes in the activityof sucrose-cleaving enzymes within the flower ovary might beresponsible for the changes in flower abortion under differentlight conditions. In the present study we report that the activityof sucrose synthase, but not of cytosolic acid invertase, increasesin flowers of pepper plants which were exposed, for 2 d, toincreasing photosynthetically active radiation (PAR) in therange of 85–400 µmol m^-2s^-1at midday. Sucrose synthaseactivity increased in parallel with the increasing concentrationsof starch in the flower ovary. Feeding flower explants, preparedfrom 3-d-predarkened plants, with 100 mM sucrose for 24 h, causeda 23% increase in reducing sugars and a 2.5-fold increase instarch concentration, compared with explants fed with buffer.Likewise, feeding explants of pepper flowers with sucrose, glucose,fructose and also mannitol increased the sucrose synthase activityin the ovaries. Concomitantly, sucrose, glucose and fructose,but not mannitol, reduced the abortion of flower explants. Itis suggested that sucrose entry into the flower increases theflower sink activity by inhibiting abscission and inducing metabolicchanges, thus enhancing flower set. Pepper; Capsicum annuum L.; abscission; light; pepper flowers; sucrose; glucose; fructose; starch; acid invertase; sucrose synthase