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     

Vascular occlusion in stems of cut rose flowers exposed to air: Role of xylem anatomy and rates of transpiration

Stems of cut rose flowers were exposed to air at 20°C and 60% relative humidity and then placed in water. The rate of water uptake in Frisco, Sonia, Madelon, and Cara Mia roses was maximally inhibited after 72, 36, 24, and 3 h of exposure to air. respectively. Anatomical observations showed no tyloses, gums, or deposition of hydrophobic material in the xylem conduits (tracheids and vessels) of any of the investigated cultivars. Frisco, Sonia, Madelon, and Cara Mia roses showed no difference in the number, the length, the wall thickness, or the diameter of the lumina of either the tracheids or the vessels. This indicates that differences in recovery are not related to capillary diameter or length.
During exposure to air the decrease in transpiration rate, fresh weight, and water potential was the same in Sonia, Madelon, and Cara Mia roses. Upon exposure to air Frisco roses lost less water than the other cultivars studied In Frisco roses stomatal conductance was similar to that of other cultivars, but the rate of cuticular transpiration was lower.
It is concluded that conservation of water through low cuticular transpiration is one of the reasons for the relatively slow development of the vascular occlusion in Frisco roses, but the differences between Sonia. Madelon and Cara Mia roses were not related to their rates of transpiration.     

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     

Possible Roles of Methyl Glucoside andMyo-inositol in the Opening of Cut Rose Flowers

Methyl glucoside andmyo-inositol are present in all organs ofrose (Rosa hybridaL.). To investigate the possible role of thesecarbohydrates in the opening of cut roses, flowers with a 10,20 or 40-cm-long stem and a single flower bud (about 1.5 cmin diameter) were placed in water and flower opening and changesin sugar content in flowers and stems examined for 7 d. Thelonger the stem of the cut flower, the larger was the flowerdiameter. In stems, the concentration of carbohydrates, includingmethyl glucoside andmyo-inositol markedly decreased before floweropening. In petals, contents of glucose, methyl glucoside andmyo-inositolalso decreased before flower opening, but those of fructose,sucrose and xylose did not. When glucose and methyl glucosidewere added to the vase water (4%) flower opening was clearlypromoted; this was accompanied by an increase in methyl glucosideand fructose concentrations in petals. On the contrary,myo-inositolinhibited flower opening, and this was accompanied by an increaseinmyo-inositol and xylose concentrations in petals. These resultssuggest that methyl glucoside and/or its metabolites are transportedinto the petal cells, thereby lowering the osmotic water potentialand promoting flower opening.Myo-inositol is not readily metabolized,and exogenousmyo-inositol given at a high concentration mayact as an extracellular osmolyte, which inhibits water uptakeand flower opening.Copyright 1999 Annals of Botany Company Cut flowers, methyl glucoside,myo-inositol,Rosa hybrida,soluble carbohydrate.     

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     

Anatomy of Ethylene-induced Petal Abscission in Pelargonium x hortorum

When viewed under the light microscope, the abscission zoneat the petal base of Pelargonium x hortorum consisted of smallcells which, when stained with Toluidine Blue, possessed denselystained cells walls. After treatment with 1 µl l^-1 ethyleneat 22°C, the force required to separate the petals fromthe receptacle declined after a lag phase of only 30 min, withseparation complete 60-90 min later depending upon the stageof development of the flower. Transmission electron micrographsof the petal abscission zones showed evidence of cell wall degradation,particularly in the middle lamella. These cells also containedextensive rough endoplasmic reticulum and numerous Golgi bodiesribosomes. When abscission was complete, cells at the fractureface showed evidence of breakdown of cellular compartmentalization,often with little sign of an intact tonoplast. Scanning electronmicrographs of recently-abscissed surfaces showed that the epidermalcells surrounding the abscisson zone were turgid and rounded,whereas those of the mesophyll cells were partially collapsed.The micrographic evidence is consistent with the hypothesisthat ethylene-induced separation is caused by rapid enzymaticof the cell walls.Copyright 1993, 1999 Academic Press Abscission, cell walls, ethylene, flower, Pelargonium x hortorum     

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.     

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     

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     

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     

Relationship between cavitation and water uptake in rose stems

Cavitation in rose stems ( Rosa hybrida L.) was assessed in both intact plants and excised flowers, by measurement of ultrasonic acoustic emissions at the stem surface and determination of the air-conductivity of 2.5-cm segments that were attached at one end to air at low pressure (0.01 MPa). On sunny days the stems of intact rose plants showed acoustic emissions and conductivity to air, starting early in the morning. In Cara Mia and Sonia rose plants the cavitations were repaired during the late afternoon; in Madelon plants this repair only occurred overnight. Water flow was seriously impaired in stems of Cara Mia roses cut around midday, on sunny days.
During dehydration of cut roses in air the onset of a high rate of acoustic emissions coincided with a low rate of water uptake when stems were subsequently placed in water. High emission frequency occurred after 2.4 ± 0.7 h, 6.8 ± 4.3 h and 19.8 ± 9.0 h of exposure to air in Cara Mia, Madelon and Sonia roses, respectively. A low rate of water uptake in excised stems placed in water was found after 3–4, 9–12 and 24–36 h of desiccation in air, respectively. The onset of the high emission frequency corresponded with a water potential of −1.7, −2.9 and −3.8 MPa in the three cultivars, respectively.
It is concluded that a high number of cavitations may occur in noncut stems of rose plants, leading to low water uptake immediately after excision, depending on the weather and the cultivar, and that the low rate of water uptake after a period of dry storage, among the three rose cultivars investigated, is correlated with the presence of a high number of cavitated xylem elements.     

Physiological response of cut rose flowers to cold storage

The effects of low temperature storage on the physiology of cut rose flowers ( Rosa hybridaL. cv. Mercedes) were studied. Extension of cold storage or increase in temperature (from 3 to 8°C) was accompanied by shortening of vase life and advancement of petal senescence, as reflected in an advance in the timing of the rise in ethylene production and an increase in membrane permeability (ion leakage). Although storage at a relative humidity (RH) of 65% reduced petal water content by 20% in comparison with flowers stored at 95% RH, it did not shorten vase life. The progression of petal senescence was measured during storage at 3°C and during aging at 22°C. Both ethylene production rates and membrane microviscosity measured by fluorescence depolarization increased with time at 3°C and at 22°C, but more slowly at 3°C. At 3°C membrane permeability measured by ion leakage did not increase. Following cold storage the rate of ethylene production in the petals was increased by up to eight times the rate in unstored flowers. Silver thiosulphate extended the vase life of both stored and fresh flowers equally by 2 days, but did not increase the life of stored flowers to that of treated fresh flowers. It is concluded that the primary effect of cold storage on roses is to slow down senescence and that the continued slow senescence leads to shorter vase life. The possible occurrence of sequential processes during senescence and the effects of temperature on these processes is discussed.     

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.     

Transient Water Stress in Carnation Flowers: Effect of Amino-oxyacetic Acid

A short and temporary water stress imposed on cut carnationflowers (Dianthus caryophyllus L., cv. White Sim) flowers advancedsenescence symptoms, including ethylene production and wilting.Pretreatment with amino-oxyacetic acid (AOA) resulted in anincrease of the resistance of the flowers to water stress: waterloss during stress was reduced, recovery was more rapid andwilting was delayed. Water stress accelerated the decrease inlevel of membrane phospholipids, but pretreatment with AOA counteractedthis effect. Since the content of membrane sterols was not affectedby the treatments, the mole ratio of sterol to phospholipidincreased in water-stressed flower petals but not in stressedflowers pretreated with AOA. Membrane permeability and fluiditywere also adversely affected by water stress and AOA: waterstress alone resulted in an increase in permeability and a decreasein fluidity, but in AOA-pretreated stressed flower petals theseparameters were similar to those of nonstressed control flowerpetals. On the basis of these results two main conclusions can be drawn:(a) Water stress induces alterations in the physical and compositionalproperties of carnation petal membranes, (b) Pretreatment ofthe flowers with AOA influences petal membrane traits, mostprobably via modifications in phospholipid turnover, in a waywhich counteracts the effects of water stress. Key words: Amino-oxyacetic acid, Water stress, Carnation flowers     

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     

Abscission of flowers and floral parts

The abscission of inflorescences, flowers, petals, sepals, styles,and stamens is discussed, with emphasis on the anatomy and ultrastructureof the abscission zones, and the role of cell wall degradingenzymes and hormonal control. Shedding of these parts is usuallydue to cell wall dissolution, but abscission of petals, stamens,and styles in some species occurs due to the forces generatedby the growing fruit. Flower abscission is clearly regulatedby ethylene, whilst auxins apparently decrease the sensitivityto ethylene. Petal, style and stamen abscission also seems tobe controlled by endogenous ethylene. Auxin is apparently involvedin abscission of styles and stamens, but in petals its roleis at yet unclear. The ultrastructural data indicate high proteinsynthesis and high secretory activity of material toward cellwalls of abscission zone cells. The physiological evidence indicatesa role of both polygalacturonase and cellulase in cell walldissolution, whilst the role of other cell wall degrading enzymesis still unknown. The physiological processes occurring in thewalls of the separating cells should be distinguished from thoserelating to defence against microbial intrusion, such as depositionof lignin and suberin and tylose formation. Experimentationusing mutants and transgenic plants may aid in separating theseprocesses. Sequencing of the isoenzymes specific for the abscissionzone and a search for abscission zone-specific promoters seemsa requirement for the successful evaluation of the enzymes involvedin cell wall degradation. Key words: Abscission, anatomy, abscission zone, hormonal control, cell wall degrading enzymes, inflorescences     

Role of Aminocyclopropane-1-carboxylic Acid (ACC) in Control of Ethylene Production in Fresh and Cold-stored Rose Flowers

The relationships between ethylene production, aminocyclopropane-1-carboxylicacid (ACC) content and ethylene-forming-enzyme (EFE) activityduring ageing and cold storage of rose flower petals (Rose hybridaL. cv. Gabriella) were investigated. During flower ageing at20 °C there was a climacteric rise in petal ethylene production,a parallel increase in ACC content, but a continuous decreasein EFE activity. Applied ACC increased petal ethylene productionc. 200-fold. During cold storage of flowers at 1 °C therewere parallel increases in petal ethylene production and ACCcontent, to levels greater than those reached in fresh flowersheld at 20 °C. EFE activity decreased during storage. Immediatelyafter cold-stored flowers were transferred to 20 °C ethyleneproduction and ACC levels were c. four times greater than infreshly cut flowers. These levels increased to maximum valuesof two to four times the maximum values reached during ageingof fresh, unstored, flowers. It was concluded that in rose petalsethylene synthesis is probably regulated by ACC levels and thatcold storage stimulates ethylene synthesis because it increasesthe levels of ACC in the petals. Key words: Rose flower, senescence, ethylene     

The Importance of the Stigma in Flower Senescence in Petunia (Petunia hybrida)

Senescence of flowers of Petunia hybrida Vilm. cv Gypsy is characterizedby colour changes, wilting and abscission. In emasculated detachedflowers the onset of these processes is hastened by any treatmentwhich reduces the vigour of the stigma. Thus pricking it, excisingsegments, or freezing with liquid nitrogen all reduce the timeto morphological changes associated with corolla senescence.Removal of the stigma has the most dramatic effect, reducinglifespan of the flower by about 50 per cent, to 3 d. This reductioncan be lessened if IAA or 2,4-D is applied to the cut surfaceof the style. In intact flowers, the style may usually be implicatedin the production of a stimulus leading to corolla abscission,but abscission will also occur in the absence of the style.Some senescence acceleration takes place not only in the completeabsence of the style, but also when the upper part of the ovaryhas been excised in addition. The speeding up of senescenceand of corolla abscission cannot be due solely to damage perse since when the corolla limb was excised, leaving only thecorolla tube, the tube abscised at about the same time as thecontrols, despite the quite extensive wounding. This also impliesthat the distal parts of the corolla do not play a major rolein the development of the abscission zone at the base of thecorolla tube. A healthy, undamaged stigma appears to be very important incorolla longevity and one of its roles may be to prevent theproduction of an abscission/wilting stimulus by some other componentof the flower. Possibly auxins in the stigma are important inthat either they are mobile and protect the abscission zoneor they create a sink for other substances which are implicatedin flower senescence. Petunia hybrida, abscission, auxins (IAA, 2,4-D), corolla, flower senescence, stigma, style, wilting     

Changes of Carbohydrates in Pepper (Capsicum annuum L.) Flowers in Relation to Their Abscission Under Different Shading Regimes

Abscission of pepper flowers is enhanced under conditions oflow light and high temperature. Our study shows that pepperflowers accumulate assimilates, particularly in the ovary, duringthe day time, and accumulate starch, which is then metabolizedin the subsequent dark period. With the exception of the petals,the ovary contains the highest total amounts of sugars and starch,compared with other flower parts and contains the highest totalactivity, as well as activity calculated on fresh mass basis,of sucrose synthase, in accordance with the role of this enzymein starch biosynthesis. Low light intensity or leaf removaldecreased sugar accumulation in the flower and subsequentlycaused flower abscission. The threshold of light intensity fordaily sugar accumulation in the sink leaves was much lower thanin flowers, resulting in higher daytime accumulation of sugarsin the sink leaves than in the adjacent flower buds under anylight intensity, suggesting a competition for assimilates betweenthese organs. Flowers of bell pepper cv. ‘Maor’and ‘899’ (sensitive to abscission) accumulatedless soluble sugars and starch under shade than the flowersof bell pepper cv. ‘Mazurka’ and of paprika cv.‘Lehava’ (less sensitive). The results suggest thatthe flower capacity to accumulate sugars and starch during theday is an important factor in determining flower retention andfruit set. Pepper; Capsicum annuum L.; abscission; shading; pepper flowers; ovary; leaves; sugars; starch; acid invertase; sucrose synthase     

Aroma production from cut sweet pea flowers (Lathyrus odoratus): the role of ethylene

The major components of the scent of cut sweet pea flowers ( Lathyrus odoratus L. cv Royal Wedding) are (E) and (Z)-ocimene, linalool, nerol, geraniol and phenylacetaldehyde. The aroma is almost exclusively produced by the standard and wing petals, with very little emanating from the keel petals and other floral structures. Only traces of these volatiles were detected in the liquid excreted by glandular trichomes on the surface of the scented petals. Once flowers are cut for display they produce increasing amounts of ethylene which induces wilting after 48 h and petal abscission 24 h later. The rate of linalool and ocimene emission declines over the first 48 h to approximately 10% of that directly after harvest. Ethylene production is not saturating during the first 24 h of vase life and exogenous ethylene further accelerates the senescence processes and loss of fragrance. Addition of the ethylene antagonists 1-methylcyclopropene (1-MCP) and silver thiosulphate (STS) delayed wilting and abscission for several days and similarly inhibits the decline in terpenoid emission.