The Abscission of Rose Petals

Petal abscission was studied in twelve hybrid tea rose (Rosahybrida L.) cultivars. At about 20 °C the time to petalabscission in uncut stems in greenhouses was the same as incut stems placed in water in the greenhouse or in a climate-controlledroom. The time between petal unfolding and abscission dependedon the cultivar, and varied between 12 and 35 d. The time topetal abscission of the cultivars was inversely correlated withtheir flower diameter at full bloom (linear regression, r² =0·82). In the cultivars with a relatively large flowerdiameter (10-18 cm) the petals fell without visible desiccationsymptoms, whereas in the group with a small diameter the petalswere partially or fully desiccated when shed. Fertilization occurred in some flowers of a few cultivars studied.In cultivars with a relatively large flower diameter (Papa Meilland,Cocktail, Dr. Verhage, Tineke) it had no effect on the timeto abscission in Motrea, Europa, and Carolien roses, which bearsmall flowers, the petals fell after fertilization, whereasin unfertilized flowers of the latter group of cultivars anabscission zone just above the uppermost node became activeand all parts above this node (pedicel and flower) turned brownand desiccated, though remained attached for more than a month. It is concluded that in the cultivars investigated: (a) thetime to petal abscission was inversely related to their flowerdiameter, (b) abscised petals were more desiccated in cultivarsin which the time to abscission was longer, (c) fertilizationhad little effect on the time to abscission in most cultivars,whereas the absence of fertilization prevented petal abscissionin a number of the small-diameter cultivars where it was replacedby flower abscission, and (d) cutting and placement in waterat 20 °C did not affect the time to abscission.Copyright1995, 1999 Academic Press Abscission, fertilization, flowers, petals, Rosa hybrida L., rose, water stress, carbohydrate stress     

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     

Resistance to Water Loss from the Mesophyll Cell Surface in Plant Leaves

A method is described for the accurate measurement of the apparentresistance to water loss from the mesophyll cell walls of plantleaves (r_w), and for studying the mechanism underlying thisresistance. The method for distinguishing possible mechanismsinvolves a comparison of the calculated values of r_w at differentrates of evaporation. The value of r_w remained below 50 s m^–1at relative water contents greater than 11 ± 3% and 7± 2% for Pelargonium hortorum Bailey and Vicia faba L.respectively. Therefore r_w is relatively insignificant at normalphysiological water contents in these species. When r_w did increaseit was not sensitive to evaporation rate, suggesting that alowering of the vapour pressure at the evaporating sites wasnot involved. This contrasted with the results for cellulosefilter paper, where r_w was more sensitive to evaporative flux.     

Ethylene Co-ordinates Petal Abscission in Red Raspberry (Rubus idaeus L.) Flowers

The time-course of flower development of Rubus idaeus L. cv.Glen Clova was studied on detached buds opened in the laboratory.After sepal and petal opening petal abscission occurred withthe petals from an individual flower being shed over 3-4 h.Abscission was accompanied by a peak in ethylene production.Treatment of flowers with aminoethoxyvinylglycine eliminatedthe peak in ethylene production but did not prevent petal abscission.However, petal loss was much slower, taking place over a periodof days rather than hours. Abscission was more effectively retardedby silver thiosulphate. Exogenous ethylene accelerated the rateof petal abscission and senescence. The increase in ethyleneproduction coincident with petal abscission appears to accelerateand co-ordinate the shedding of the separate petals on an individualflower. If ethylene is important in the induction of abscissionit would appear that the low rate of production sustained inthe presence of aminoethoxyvinylglycine must be sufficient.Copyright1993, 1999 Academic Press Rubus idaeus L., raspberry, flower, petal, abscission, ethylene     

Categories of Petal Senescence and Abscission: A Re-evaluation

In a previous paper (Woltering and van Doorn, 1988, Journalof Experimental Botany39: 1605–1616) we identified threetypes of flower life cessation: by petal wilting or withering,which was either ethylene-sensitive or insensitive, and by abscissionof turgid petals, which was ethylene-sensitive. These categoriestended to be consistent within families. Here we re-examinethese relationships by testing a further 200 species, and anumber of other families. As previously, flowering shoots wereexposed to 3 ppm ethylene for 24 h at 20 °C, in darkness.Most monocotyledonous species tested showed ethylene-insensitivepetal wilting, although ethylene-sensitive wilting occurredin the Alismataceae and Commelinaceae. Petals of the dicotyledonousspecies tested were generally sensitive to ethylene, exceptfor a few groups showing wilting (Crassulaceae, Gentianaceaeand Fumariaceae, and one subfamily in both the Ericaceae andSaxifragaceae). Petal abscission was generally ethylene-sensitive,but ethylene insensitivity was found in some Tulipa cultivarsand three Saxifraga species. In most tulip cultivars tested,the petals wilted and then fell. It is concluded that (a) theresponse to ethylene is often consistent within either familiesor subfamilies; and (b) a fourth category, ethylene-insensitivepetal abscission, exists both in monocotyledons and dicotyledons.Copyright 2001 Annals of Botany Company Ethylene sensitivity, flower longevity, petal abscission, petal wilting, petal withering, petal senescence, taxonomic categories     

Petal Abscission in Rose Flowers: Effects of Water Potential, Light Intensity and Light Quality

Petal abscission was studied in roses (Rosa hybrida L.), cvs.Korflapei (trade name Frisco), Sweet Promise (Sonia) and CaraMia (trade name as officially registered cultivar name). Unlikeflowers on plants in greenhouses, cut flowers placed in waterin the greenhouse produced visible symptoms of water stress,depending on the weather during the experiment and on the cultivar.Cut Frisco roses showed no visible signs of water stress andthe time to petal abscission was as in uncut flowers. In Soniaroses the symptoms of water stress varied from mild to severe,and the number of flowers in which the petals abscised variedfrom 100% (mild stress) to 0% (severe stress). An antimicrobialcompound in the vase water of Sonia roses, or removal of theleaves, alleviated the symptoms of water stress and increasedthe number of stems in which the petals abscised. Cut Cara Miaroses showed severe symptoms of water stress in all experimentsand petal abscission was found in only a few flowers, even whenthe stems were placed at 20 °C and low photon flux (15 µmolm^-2s^-1). Abscission in Sonia and Cara Mia roses was low or absentwhen the water potential of the leaves reached values below-2.0 MPa within the first 5 d of the experiment; such low valueswere not reached in Frisco roses. Addition of sucrose to the vase solution, together with an effectiveantimicrobial compound, had no effect on the time to petal abscission,at any light intensity. Placing flowers in far-red light alsohad no effect on abscission, compared with flowers placed inred light or white light of the same photon fluence. It is concluded that petal abscission in the rose cultivarsstudied is not affected by their water status unless the plantsreach a low water potential (about -2 MPa) early on during vaselife. Petal abscission is not inhibited by low light intensitynor affected by the Pr/Pfr ratio. Abscission; light intensity; petals; phytochrome; Rosa hybrida L.; rose; sugars; water potential     

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.     

Density Studies on Lupins: I. Flower Development

In an August-sown experiment the pattern of flower developmentwas followed for cv. Ultra (Lupinus albus L.) and cv. Unicrop(L. angustifolius L.) grown at low (10 plants m^–2) andhigh (93 and 83 plants m^–2, Ultra and Unicrop respectively)densities. Dry weight increase of flowers on the main-stem inflorescenceand first lateral below the main-stem were compared at differentfloral stages. Maximum flower weight was reached just priorto the open flower stage and remained constant or declined untila pod formed or abscission occurred. The time period betweenmaximum flower weight and pod formation or abscission was upto 10 days. Emergence of the inflorescence was earlier and thefirst flower of Ultra opened 10 days before Unicrop. Developmentof each terminal raceme (inflorescence) was acropetal, withpods having formed on lower flower nodes when terminal flowerswere still quite immature. Laterals forming the next generationof inflorescences grew from axillary leaf buds below an inflorescencewhile it was in full flower. Sources of competition from connectedreproductive and vegetative metabolic sinks are discussed. Lupinus spp., lupins, flower development, planting density     

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     

Regulation of Free Calcium Concentration in the Pitchers of the Carnivorous Plant Sarracenia purpurea: A Model for Calcium in the Higher Plant Apoplast?

The pitcher of the carnivorous plant Sarracenia purpurea L.contains an entrapped body of liquid within which its prey isdigested. Free calcium in the pitcher is derived from eitherthe pitcher walls or from prey falling into the pitcher; inthe absence of exogenous (prey-derived) calcium it will dependon the active and passive calcium regulatory properties of thepitcher walls and may to some extent therefore mimic calciumin the apoplast of plant cells. Using a calcium-specific electrode,the free calcium concentration of the pitchers of Sarraceniaplants was investigated and the effect of adding a variety ofconcentrations of calcium in water determined. The mean pitcherfree calcium concentration in vivo was 2.3 x 10^–5 M±2.5x 10^–5 M; when pitchers were washed and filled with watercontaining lower calcium concentrations, the concentration inthe pitcher water rose to 1–5 x 10^–5 M. When highercalcium concentrations (up to 1 x 10^–4 M) were added,the pitcher calcium concentration declined to 1–7 x 10^–5M. Concentrations of calcium above 1 x 10^–4 M were alsoreduced, but to a lesser extent. Metabolic inhibition of activeion transport, while inhibiting pitcher acidification, did notinhibit regulation of pitcher free calcium, suggested that itoccurs as a result of calcium exchange sites in the pitcherwalls. The data are discussed in relation to the physiologyof Sarracenia pitchers and to the usefulness of the pitcheras a model for free calcium in the higher plant apoplast. Sarracenia purpurea L., carnivorous plant, pitcher, free calcium, plant apoplast     

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     

Anthocyanins in Modern Roses: Chemical and Colorimetric Features in Relation to the Colour Range

With respect to intravarietal variability, the petals of 15rose (Rosa x hybrida) varieties, representative of the colourrange expressed by modern roses primarily pigmented with anthocyanins,were investigated from chemical and. colorimetric viewpoints.Depending on the variety, the observed colour variations werebased on a more or less complex mixture of cyanidin 3,5-diglucoside,pelargonidin 3,5-diglucoside, quercetin and kaempferol glycosides.The total anthocyanin content ranged from 4 to 109 mg g^–1petal dry wt., while the total amount of flavonol glycosideswas never less than 8 mg g^–1 and could reach 136 mg g^–1petal dry wt. Between cultivars, the pH of the petal outer epidermisvaried from 3·6 to 5·4 units. Using a spectrocolorimeter,the petal colour of each variety was measured. In order to allowquantitative comparisons of colours, the reflectance curveswere further translated into indices calculated using the CIELabsystem. In the aggregate, there were good correlations betweenchemical parameters and colorimetric indices that are lightness(L^*), chroma (C^*) and hue angle (h). Both of these criteria(chemical and colorimetric) appeared sufficient to explain thevisual sense of the petal colour. Key words: Rose, colour, flavonoid, colorimetry, CIELab system     

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     

L-Leucine Transport in Isolated Protoplasts of Vinca Suspension Culture: Characterization of Uptake

The uptake of L-leucine into Vinca protoplasts was studied undervarious conditions. The uptake was highly pH-dependent, withthe optimal pH between 3.0 and 4.0. The uptake was also energydependent, since azide, 2,4-dinitrophenol (DNP), carbonyl cyanidem-chlorophenyl hydrazone (CCCP), and iodoacetate inhibited theuptake. Oligomycin, N,N'-dicycIohexyI carbodiimide (DCCD) andvanadate, but not ouabain, inhibited the uptake, suggestingthat ATPase for H⁺ electrogenic extrusion was necessary to theuptake of L-leucine. The uptake showed stereospecificity, butwas partially inhibited by other L-amino acids. A kinetic studyof the uptake showed that the uptake was multiphasic with threesaturable phases and one unsaturable phase which occurred atconcentrations of L-leucine over 1 mM. The K_m values of thethree affinity sites were 1.4 x 10^–3 M, 1.3 x 10^–4M, 4.3 x 10^–5 M; the maximum velocity values were 3.3x 10^–8, 4.5 x 10^–9, 1.8 x 10_–9 mol/10 min/4x 10⁶ cells. (Received April 18, 1981; Accepted August 25, 1981)     

Isolation of Protoplasts from Kappaphycus alvarezii var. tambalang (Rhodophyta) and Secretion of i-Carrageenan Fragments by Cultured Cells

A method for generating protoplasts from the carrageenan-producingred alga Kappaphycus alvarezii was developed. Digestions withcellulase and _k-carrageenase produced only a few cortical cellprotoplasts, while digestions with cellulase and i-carrageenaseonly produced epidermal cell protoplasts. When both carrageenaseswere used in the digestion media with cellulase, protoplastswere released from all cell types and yields ranged from 1·0to 1·2x10⁷ cells g^–1 with sizes from 5 to 200 µmdiameter. Protoplasts were subsequently cultured to study cellwall regeneration. Calcofluor-positive material (probably cellulose)was detected within 6 h after removal of protoplasts from thewall digestion media, whereas, i-carrageenan fragments weredetected in all regenerating protoplast cultures 24 h afterremoval from the digestion media. Protoplasts continued to produceCalcofluorpositive material and secrete carrageenan fragmentsinto culture media for several days. However, cells culturedin media augmented with K⁺ ions stopped secreting carrageenanfragments after 24 h. Cells cultured for 48 h in seawater labelledweakly with an i-carrageenan hybridization probe, but not atall with a corresponding _k-probe. Cells cultured for 48 h, blottedto nylon membranes and probed with anti-carrageenan monoclonalantibodies, showed the presence of gelling carrageenan subunitsin the cell walls. Key words: -Carrageenan, Kappaphycus, protoplasts, Rhodophyta     

Mating type specific induction of cell wall lytic factor by agglutination of gametes in Chlamydomonas reinhardtii

When mt⁺ and mt^– gametes of Chlamydomonas reinhardtiiwere mixed, shedding of cell walls took place in both matingtypes during massive agglutination and/or pairing. This wascaused by a cell wall lytic factor that had been induced byflagellar agglutination and excreted into the medium by cellsconcurrently with their cell wall release. When glutaraldehyde-fixed gametes and isolated flagella of onemating type caused isoagglutination of live gametes of the othermating type, the live mt⁺ gametes induced the lytic factor andshed their walls, whereas none of the live mt^– did this.The cell walls of mt^– gametes were lost only when thelytic factor, which had been excreted by mt⁺ gametes into themedium, acted from the outside. These data imply that mt⁺ gametesare responsible for the induction of the lytic factor by agglutination,which acts on cell walls of both mating types either endogenouslyor exogenously. (Received February 28, 1978; )     

Effects of indoleacetic, p-chlorophenoxyisobutyric and 2,4,6-trichlorophenoxyacetic acids on three phases of rooting in Azukia cuttings

In adventitious root formation of disbudded epicotyl cuttingstaken from light-grown, 5-day-old Azukia angularis seedlings,indoleacetic acid (IAA), 1 x 10^–4 M, applied during thefirst day showed no effect, but enhanced the effect of IAA,1 x 10^–4 M, applied during the second day. Treatment duringthe second day promoted rooting by about 70%, and a combinationof treatments for the first and second days promoted rootingsome 200%. p-Chlorophenoxyisobutyric acid (PCIB), 3 x 10^–4M, and2,4,6-trichlorophenoxyacetic acid (2,4,6-T), 2 x 10^–44M, applied the first day also enhanced the effect of IAA, 2x 10^–4 M, applied the second day. When applied the second day, PCIB, 2 x 10^–4M, increasedthe number of root primordia or clusters of small cells, butnot die number of protruded roots. Formation of the cell clusterwas inhibited by 2,4,6-T, 3 x 10^–4M, applied the secondday. Rooting processes in Azukia cuttings seem to include at leastthree phases: the first phase is induced not only by IAA butalso by PCIB or 2,4,6-T, the second phase is induced by IAAor PCIB and the diird phase depends specifically on IAA. (Received October 28, 1970; )     

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     

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     

Relationship between petal abscission and programmed cell death in <Emphasis Type="Italic">Prunus yedoensis</Emphasis> and <Emphasis Type="Italic">Delphinium belladonna</Emphasis>

Depending on the species, the end of flower life span is characterized by petal wilting or by abscission of petals that are still fully turgid. Wilting at the end of petal life is due to programmed cell death (PCD). It is not known whether the abscission of turgid petals is preceded by PCD. We studied some parameters that indicate PCD: chromatin condensation, a decrease in nuclear diameter, DNA fragmentation, and DNA content per nucleus, using Prunus yedoensis and Delphinium belladonna which both show abscission of turgid petals at the end of floral life. No DNA degradation, no chromatin condensation, and no change in nuclear volume was observed in P. yedoensis petals, prior to abscission. In abscising D. belladonna petals, in contrast, considerable DNA degradation was found, chromatin was condensed and the nuclear volume considerably reduced. Following abscission, the nuclear area in both species drastically increased, and the chromatin became unevenly distributed. Similar chromatin changes were observed after dehydration (24 h at 60°C) of petals severed at the time of flower opening, and in dehydrated petals of Ipomoea nil and Petunia hybrida, severed at the time of flower opening. In these flowers the petal life span is terminated by wilting rather than abscission. It is concluded that the abscission of turgid petals in D. belladonna was preceded by a number of PCD indicators, whereas no such evidence for PCD was found at the time of P. yedoensis petal abscission. Dehydration of the petal cells, after abscission, was associated with a remarkable nuclear morphology which was also found in younger petals subjected to dehydration. This nuclear morphology has apparently not been described previously, for any organism.