A Senescence Factor and Foliar Abscission in Catharanthus roseus

Abscission-accelerating activity was found in naturally senescentpetioles, and senescent leaves of Catharanthus indicating thepresence of a senescence factor (SF) in these tissues. No SFactivity was observed in non-senescent petioles, or non-senescentleaves at various defined developmental stages. The resultsare discussed in relation to the auxin-auxin balance theoryfor the control of leaf abscission and the auxin-SF balancetheory.     

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     

Senescence and the Fluidity of Rose Petal Membranes : RELATIONSHIP TO PHOSPHOLIPID METABOLISM

In previous work, senescence of rose petal cells has been shown to be accompanied by a gradual decrease of membrane fluidity, as measured by a fluorescence polarization technique. Concomitantly, an increase in the free sterol-to-phospholipid ratio was found. Both observations were verified in this study. Further, experiments carried out on whole tissue and isolated protoplasts during senescence revealed that there was no quantitative change in the level of free sterols. The content of phospholipids decreased without any significant change in their composition. Results from experiments measuring the incorporation of [³²P]orthophosphate indicated a reduced capacity for phospholipid synthesis in senescent cells. Both young and old tissue showed phospholipase A and D activity, the former increasing with age.     

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     

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     

Ethylene Action and Loss of Membrane Integrity during Petal Senescence in Tradescantia

Senescence of isolated petals of Tradescantia is accompanied by a large increase in membrane permeability, and application of ethylene hastens the onset of this increase. There is a 1- to 2.5-hour lag between ethylene application and the onset of anthocyanin efflux (an indicator of increased membrane permeability). Simultaneous application of 0.1 millimolar cordycepin or cycloheximide with ethylene abolishes the response to ethylene. Analysis of phospholipid levels in these petals during senescence has shown that the increase in membrane permeability is accompanied by a massive loss of phospholipids. Factors which enhance or retard the rate of anthocyanin efflux exert a corresponding effect on the rate of phospholipid loss. The composition of the phospholipid fraction remains unchanged during senescence. The activity of phospholipase D declines during senescence whereas that of acyl hydrolase remains essentially constant.     

Changes in Endogenous Cytokinin Levels During Abscission and Senescence of Streptocarpus Leaves

The cytokinin levels of butanol and aqueous extracts of proximalportions of Streptocarpus leaves showed very little change duringthe summer and early autumn months, whereas those of the distalportions changed markedly. These changes appear to be closelyrelated to the formation of abscission layers and the subsequentsenescence of the distal part of the leaves. It is postulatedthat the increase in butanol-soluble cytokinins during Januarymay induce abscission, while the decrease in February appearsto be directly related to senescence of the distal portionsof the leaves.     

Programmed Cell Death in Relation to Petal Senescence in Ornamental Plants

Cell death is a common event in all types of plant organisms. Understanding the phenomenon of programmed cell death (PCD) is an important area of research for plant scientists because of its role in senescence and the post-harvest quality of ornamentals, fruits, and vegetables. In the present paper, PCD in relation to petal senescence in ornamental plants is reviewed. Morphological, anatomical, physiological,and biochemical changes that are related to PCD in petals, such as water content, sink-source relationships,hormones, genes, and signal transduction pathways, are discussed. Several approaches to improving the quality of post-harvest ornamentals are reviewed and some prospects for future research are given.     

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.     

Programmed Cell Death in Relation to Petal Senescence in Ornamental Plants

Cell death is a common event in all types of plant organisms. Understanding the phenomenon of programmed cell death (PCD) is an important area of research for plant scientists because of its role in senescence and the post-harvest quality of ornamentals, fruits, and vegetables. In the present paper, PCD in relation to petal senescence in ornamental plants is reviewed. Morphological, anatomical, physiological,and biochemical changes that are related to PCD in petals, such as water content, sink-source relationships,hormones, genes, and signal transduction pathways, are discussed, Several approaches to improving the quality of post-harvest ornamentals are reviewed and some prospects for future research are given.     

湖北咸宁地区桂花开花和衰老过程中花瓣的某些生理生化指标变化

3个品种桂花花瓣的呼吸速率和乙烯释放量均出现跃变型高峰;细胞质膜透性和丙二醛（MDA）含量不断升高;过氧化物酶（POD）和过氧化氢酶（CAT）活性先上升,后下降,呈现明显的峰值。3个品种的各项指标变化趋势基本一致,但花期较长的‘软叶丹桂’呼吸速率、乙烯释放量、CAT和POD峰值出现比‘柳叶桂’和‘四季桂’晚1～2d,细胞质膜透性和MDA上升趋势较缓慢,‘柳叶桂’和‘四季桂’之间差异不显著。     

A Comparison of Abscission of Rubber (Hevea brasiliensis) Leaves Infected with Microcyclus ulei with Leaf Abscission Induced by Ethylene Treatment, Deblading and Senescence

Studies on the histology and on effects of growth substancesand phenols as well as changes in activities of pectinmethylesterase indicated that the mechanism of abscission of Hevealeaflets infected with Microcyclus ulei differed from the mechanismof abscission of debladed, ethylene treated and senescent leaves.An abscission layer which was formed during abscission of debladed,ethylene-treated and senescent leaves was absent during abscissionof heavily diseased leaves. The ratio of pectinmethyl esteraseactivities in tissues distal to the abscission zone to activitiesin tissues proximal to the zone decreased in debladed and ethylenetreated leaves but such decreases were not detected during abscissionof Hevea leaves infected with M. ulei. Hevea brasiliensis Muell. Arg., rubber, leaf abscission, Microcyclus ulei, ethylene, indol-3-ylacetic acid, kinetin     

N4-Hexanoylspermidine,a New Polyamine-Related Compound That Accumulates during Ovary and Petal Senescence in Pea

A previously unknown polyamine conjugate that accumulates in senescing ovaries of pea (Pisum sativum L.) was shown by mass spectrometry, nuclear magnetic resonance, and chemical synthesis to be N4-hexanoylspermidine (hexanoyl-spd) This structure was indicated by analysis of the dansylated polyamine using fast atom bombardment mass spectrometry, following purification by high-performance liquid chromatography. Furthermore, acid hydrolysis of the compound yielded spermidine and hexanoic acid. 1H-nuclear magnetic resonance suggested that spermidine was substituted at N4 in the conjugate. Hexanoyl-spd was synthesized, and its didansyl derivative was shown to have an identical mass spectrum and high-performance liquid chromatography retention time as the derivatized natural compound. Further confirmation of its structure was obtained by comparison of the synthetic and natural polyamines as trifluoroacetyl derivatives using gas chromatography-mass spectrometry. This new polyamine conjugate is present in pea ovaries at low levels at anthesis and its concentration remains low in developing seeded fruit or in parthenocarpic fruit that have been induced by application of growth regulators to emasculated flowers or by topping the plant. Conjugate levels are also low in parthenocarpic fruit induced naturally in the slender (la crys) mutant. However, levels of hexanoyl-spd increase progressively in senescing petals and ovaries, beginning at anthesis or 2 d later, respectively.     

Abscission: role of cellulase

Cellulase (β-1,4-glucan-glucanohydrolase EC 3.2.1.4) activity increased during abscission and was localized in the cell separation layer of Phaseolus vulgaris L. cv. Red Kidney (bean), Gossypium hirsutum L. cv. Acala 4-42 (Cotton) and Coleus blumei Benth. Princeton strain (Coleus) abscission zone explants. Cellulase activity was optimum at pH 7, was reduced by one-half after heating to 55° for 10 min, and was associated with the soluble components of the cell. Explants treated with aging retardants (indoleacetic acid, ⁶N-benzyladenine, and coumarin), CO₂, actinomycin D or cycloheximide had less cellulase activity than untreated controls. Ethylene increased cellulase activity of aged explants after a 3-hr lag period but had no effect on cellulase activity of freshly excised explants. It was concluded that 1 of the roles of ethylene in abscission is to regulate the production of cellulase which in turn is required for cell separation.     

Abscission: ethylene and light control

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

Abscission: movement and conjugation of auxin

A 1-hour application of indole-3-acetic acid to bean (Phaseolus vulgaris L. cv. Red Kidney) explants inhibited abscission for an 8-hour aging period. Use of indole-3-acetic acid-¹⁴C showed that the applied indole-3-acetic acid was conjugated within explant tissue and that this conjugation mechanism accounts for loss of effectiveness of indole-3-acetic acid in inhibiting abscission after 8 hours. Reapplication of indole-3-acetic acid to an explant at a later time, before the induced aging requirement was completed reinhibited abscission. 2,4-Dichlorophenoxyacetic acid, which is not destroyed or conjugated by this system, did not lose its ability to inhibit abscission. It was concluded that indole-3-acetic acid destruction is one of the processes involved in the aging stage of abscission in explants.