Ethylene- and dark-induced flower abscission in potted Plectranthus: Sensitivity,prevention by 1-MCP,and expression of ethylene biosynthetic genes

Prevention of ethylene- and shipping-induced flower abscission is necessary to maintain the quality of both cut flowers and potted plants during handling, transport and retail display. The aims of the present work were to determine the sensitivity of Plectranthus cultivars to applied ethylene, to alleviate ethylene- and shipping-induced flower abscission in intact potted plants using 1-methylcyclopropene (1-MCP), and to investigate the possible causes of dark-induced flower abscission. All cultivars were sensitive to ethylene in a concentration-dependent manner, and complete abscission occurred within 24 h with 1 and 2 μl l^− 1 ethylene. Unopened buds were more sensitive to applied ethylene, and exhibited greater abscission than open flowers. Ethylene synthesis remained below detection limits at all time points under control and continuous dark conditions. Dark treatment significantly increased flower abscission in Plectranthus cultivars, and like ethylene-induced flower abscission, this could be prevented by continuous 1-MCP treatment. Gene expression of ethylene biosynthetic enzymes ACS and ACO was examined as possible causes for the accelerated flower abscission observed in plants kept in continuous darkness. Expression patterns of ACS and ACO varied between different cultivars of Plectranthus. In some cases, increased expression of ACS and ACO led to increased flower abscission. Gene expression was higher in open flowers when compared to unopened flowers suggesting a cause for the observed preferential shedding of open flowers in some cultivars. Although the cause of dark-induced abscission in Plectranthus remains elusive, it can be effectively controlled by treatment with 1-MCP.     

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     

Stimulation of ethylene evolution and abscission in cotton by 2-chloroethanephosphonic Acid

Ethrel, a mixture of 2-chloroethanephosphonic acid and its ethyl ester, hastens abscission of leaves, debladed petioles, and flower buds of cotton plants (Gossypium hirsutum, L.). Both young and old leaves abscissed while still green. Application of Ethrel stimulated evolution of ethylene, and this response preceded abscission. Air concentrations of ethylene around enclosed, treated-plants were adequate to produce abscission in plants. Non-treated plants defoliated when enclosed with plants sprayed with Ethrel. The stimulation of abscission of explant petioles by Ethrel was reversed by naphthalene acetic acid. The stimulation of abscission by Ethrel was concluded to be mediated by ethylene.     

Hormonal Regulation of Pedicel Abscission in Begonia Flower Buds

In order to analyse the hormonal regulation of flower bud shedding in Begonia, levels of indoleacetic acid (IAA), abscisic acid (ABA) and ethylene were determined in buds and pedicels. The translocation and metabolism of ¹⁴C-labeled IAA in pedicel segments were also studied. In a monoecious Begonia fuchsioides hybrid, abscising male flower buds contain about 1% of the IAA present in non-abscising female flowers. In a male Begonia davisii hybrid, the seasonal variation in bud drop coincides with changes in the IAA content of the buds, while also the release of IAA from the bud to the pedicel is hampered. Abscission zones of these pedicels always contain abscission promoting ethylene concentrations. The tissue is prevented from responding with abscission by IAA from the flower buds. The buds also contain ABA but without influencing abscission considerably. Pretreatment with ethylene or ABA does not affect IAA transport in pedicel segments. The rate of this transport is 4–6 mm × h^–1:; the capacity increases with the transverse area. In young segments, IAA is decarboxylated and also otherwise metabolized.     

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     

Growth retardation of woody species by three growth regulators

Flower-bud blasting in Iris occurs in the winter when low light intensities and short days prevail. After introduction of ¹⁴CO₂ to one leaf the transport of assimilates was studied under controlled culture conditions in a control light treatment and in a treatment of 7 days darkness followed by standard light conditions. Little assimilate transport was found in the direction of the bud in dark-treated plants. However, zeatin injection into the flower buds of the plants subjected to the dark treatment clearly promoted assimilate transport ot these buds. Abscisic acid levels, determined by gas chromatography, were found to increase in the buds of dark-treated plants. Zeatin injection into the flower bud resulted in a suppression of the abscisic acid level. The latter treatment also resulted in higher percentage of flowering. Removal of flower parts was found to inhibit peduncle elongation. The peduncle elongation of complete flowers started in a well defined period, and the fresh weight of buds was found to increase mainly in the last part of that period. Assimilate transport under low light intensities in relation to abscisic acid and supposed gibberellin is discussed.     

The role of free polyamines in the alternate-bearing of pistachio (<Emphasis Type="Italic">Pistacia vera</Emphasis> cv. Pontikis)

The present study was conducted in order to examine the physiological role of free polyamines in flower bud abscission. For this reason five 15-year old pistachio trees cv. "Pontikis" were selected and half of the main branches were manually defruited in early May. Polyamines were analyzed in three different organs (shoots, leaves and flower buds) from both fruiting and non-fruiting branches, during the period of kernel growing. Five samplings took place and the polyamines putrescine, spermidine and spermine were assayed. The flower bud abscission percentage was recorded every 5–10 days during kernel formation. Polyamine concentration declined during the period that coincides with that of kernel development, in both fruiting and non-fruiting branches, while significant bud abscission occurred from mid-July till late September in fruiting branches. Polyamine concentration in organs from fruiting branches was in most cases lower than that of non-fruiting ones. Most of the individual polyamines exhibited a high and significant negative correlation with bud abscission. By measuring the spermidine content of leaves and the spermine content of buds, it was possible to estimate the forthcoming bud abscission with significant accuracy (approximately 93%). On the other hand, the total polyamine content of the buds exhibited a significant strong negative relationship with bud abscission. Consequently, polyamines could have an important physiological function in the development of flower bud abscission of pistachio.     

Plant responses to insect herbivore damage are modulated by phosphorus nutrition

Interactions between plants and their herbivores are often multidimensional, complicating interpretation of herbivore‐impact studies. A previous study, directed toward understanding variation in incidences of flower bud abscission among cotton plants attacked by Lygus plant bugs, revealed an unanticipated correlation between levels of phosphorus nutrition and the propensity of plants to abscise developing flower buds. Here, we further investigate the relationship between phosphorus nutrition and cotton [Gossypium hirsutum Tod. (Malvaceae)] plant responses to herbivory by tarnished plant bugs, Lygus hesperus Knight (Hemiptera: Miridae). Complementary experimental approaches and survey data both suggest that levels of phosphorus nutrition falling within the normal range of variation can influence the manner by which plants respond to herbivory. In particular, higher levels of phosphorus nutrition resulted in elevated bud abscission rates when buds were damaged. Interestingly, increased levels of abscission under high‐phosphorus regimes did not translate into a decrease in overall cotton lint yield, suggesting that the ‘phosphorus effect’ may ultimately reflect how environmentally contingent differences in the allocation of vegetative vs. reproductive investments can provide parallel pathways to equal yields.     

Studies on the abscission of flowers and fruits of cotton (Gossypium barbadense L.)

Effects of exogenous application of auxin, GA3, abscisic acid, ethrel, methionine and α-alanine to the cut ends of the pedicels of flower buds, flowers and fruits on their abscission behaviour were studied. Fruit pedicels required more time for abscission compared with flower and flower bud pedicels. NAA inhibited abscission of all types of pedicels and the inhibition was maximum in matured fruit pedicels and minimum in flower bud pedicels. Flower pedicels were more sensitive towards the abscission promotive effects of GA3, abscisic acid and ±-alanine and the flower bud pedicels towards ethrel and methionine. The duration of Stage-I of abscission was maximum in cut pedicels of fruit and minimum in those of flower buds. Biochemical analyses revealed greater quantities of endogenous amino acids in the epicalyx of flowers with the exception of methionine and aspartic acid which were found to be present in higher quantities in the epicalyx of flower buds. Levels of IAA-like compounds were maximum in the epioalyx of flower buds and minimum in the epicalyx of flowers. Higher levels of abscisic acid were found in the epicalyx of matured fruits and the epicalyx of flower buds showed a minimum amount of abscisic acid-like compound.     

ANTHOCYANIN SYNTHESIS IN SALPIGLOSSIS SINUATA

Measurements were made of the growth and pigment content of developing flower buds of Salpiglossis sinuata. From the time the buds were approximately 10 mm long they grew in length exponentially until they reached their final length. The logarithm of bud length increased linearly with time and served as a convenient morphological index on which to relate the progress of anthocyanin synthesis. Buds shorter than about 42 mm had no anthocyanin, but when buds reached this length, anthocyanin production was initiated and proceeded rapidly. The maximum relative pigment concentration (pigment/mg fresh weight) was attained by the buds about 17 hr after the initiation of pigment synthesis. In the mahogany-colored variety used in these studies, two anthocyanidins were found and identified as cyanidin and delphinidin. Buds excised from the plants could be cultured in vitro. Buds started in culture at a length of 30–35 mm when they contained no anthocyanins developed pigment during their growth. The amount of pigment formed increased with increasing light intensity, while only small amounts of pigment could be formed in buds cultured in darkness. The anthocyanidins of these cultured buds were the same as those of the intact flowers, but the ratio of delphinidin to cyanidin decreased with decreasing light intensity. Brief daily irradiation of dark-grown buds with red, far-red or blue light did not increase pigment synthesis nor change the anthocyanidin ratio. If buds were placed in culture at 20–25 mm and grown in darkness, they developed a third anthocyanidin, identified as malvidin, which was not present in intact flowers, light-grown buds or 30–35-mm buds cultured in darkness.     

Abscission of cotton flower buds and petioles caused by protein from boll weevil larvae

Protein extracted from boll weevil larvae causes abscission of cotton flower buds and debladed petioles. Abscission of buds is preceded by a rapid and persistent flaring of bracts; cell proliferation is induced in the abscission zone of debladed petioles. A possible mode of transmission of the agent from larva to bud tissue is discussed.     

Ethylene, indoleacetic acid and apical dominance in peas: A reappraisal

Decapitation of peas ( Pisum sativum L. cv. Greenfeast) promoted sprouting of the lower buds with the most active growth in the first week occurring in the bud at the lowest fully expanded leaf node. Addition of 3-indolyl acetic acid (IAA; a 0.03 M solution, applied al 10 and 25 μg/plant) inhibited bud outgrowth whether added to the cut stump or injected above or below the lowest leaf node. Ethylene evolution by the nodal region decreased following decapitation, but increased greatly if IAA was added to the cut stump. Ethylene gas (3, 15 and 1 500 ul/l) or the precursor ACC (l-aminocyclopropane-I-carboxylic acid) reduced bud outgrowth while factors which scrub ethylene (mercuric perchlorate). inhibit ethylene synthesis (canaline), or prevent its action (silver nitrate), enhanced bud growth on decapitated plants, It was concluded that auxin-induced inhibition of bud growth through an increase in ethylene synthesis is a more logical hypothesis than the direct inhibition by auxin per se since a) acropetal movement of the inhibitory principle occurred whereas [¹⁴C] IAA movement in stems was basipetal, b) a decline in the levels of ethylene evolution was correlated with bud outgrowth in decapitated plants and c) exogenous application of chemical agents which increase or decrease ethylene level or response lead to correlative decreases or increases in bud outgrowth, respectively.     

The Role of Light in Leaf and Flower Bud Break of the Peach (Prunus persica)

The effect of light on peach leaf and flower bud break was examined. It was found that leafless dormant shoots were light-perceptive organs. Darkness, after light preconditioning during dormancy, reduced leaf bud opening; however, light was obligatory when the shoots were preconditioned in the dark. Relatively short exposures to light were sufficient to stimulate leaf bud break. Terminal buds were less inhibited by darkness than were laterals. Flower bud break was inhibited in light after dark preconditioning. The red region of the spectrum was found to be active; the phytochorome system seems to be involved in the light reactions, as the red light effect was reversible with subsequent far-red illumination. Supplementary light, producing long-day conditions, could partly compensate for insufficient chilling. A possible sequence of reactions in the plant is suggested.     

Effects of Varying Light Intensities and Temperature Treatments Applied to Whole Plants, or Locally to Leaves or Flower Buds, on Growth and Pigmentation of 'Baccara' Roses

Varying light intensity and temperature treatments were applied to whole plants, or to the leaves, or to the flower buds of ‘Baccara’ roses. The effect of these treatments on flower dimensions and pigmentation of the petals was examined. Cooling only the leaves had no effect; cooling only the buds enhanced both bud weight and pigmentation, but the effect was less marked than when the whole plant was cooled. Reducing plant temperature by misting with desalinated water enhanced both pigmentation and flower size. Darkening of only the leaves, or their removal, resulted in an inhibition of the pigmentation and also in a decrease in bud weight. Darkening of only the flower bud did not affect either pigmentation or bud weight, but caused bud elongation. It is suggested that light intensity and temperature affect flower growth and pigmentation via their effects on the availability of sugars in the flower bud.     

The Effect of Temperature on the Production and Abscission of Flowers and Pods in Snap Bean (Phaseolus vulgaris L.)

The effect of temperature on production and abscission of flowerbuds, flowers and pods was studied in a determinate snap-beancultivar (cv. Tenderette). Under moderate temperature (e.g.27/17 °C) the onset of pod development was associated withcessation of flower bud production and with enhanced abscissionof flower buds. Raising night temperature from 17 °C to27 °C strongly reduced pod production, mature pod size andseeds per pod, while an increase in day temperature from 22°C to 32 °C had smaller and less consistent effects.Pod production under high night temperature was not constrainedby flower production since 27 °C at night promoted branchingand flower bud appearance. Under 32/27 °C day/night temperaturethe large reduction in pod set was due to enhanced abscissionof flower buds, flowers and young pods (< 3 cm). Flowershad the highest relative abscission followed by young pods andflower buds. Therefore, the onset of anthesis and of pod developmentwere the plant stages most sensitive to night temperature. Podslarger than 3 cm did not abscise but usually aborted and shrivelledunder high night temperature. The effects of 32/27 °C werenot due to transient water stresses and were observed even undercontinuous irrigation and mist-spraying. High temperature, flower production, pod set, seed set, abscission, snap bean, Phaseolus vulgaris L., cv. Tenderette     

Endogenous ethylene and abscisic Acid relative to phytogerontology

Endogenous production of ethylene and endogenous levels of abscisic acid were measured from Hibiscus rosa-sinensis L. abscission zone explants at six stages of development: tight bud, open flower, closed flower, petal abscission, calyx abscission, and peduncle abscission.     

Inhibition by Ethylene of Auxin-Promotion of Flower Bud Formation in Tobacco Explants Is Absent in Plants Transformed by Agrobacterium rhizogenes

The in vitro regeneration of flower buds was studied in pedicel explants from tobacco (Nicotiana tabacum L., cv Petit Havana) transformed with Agrobacterium rhizogenes, pRi 1855 (agropine type). At a low concentration (0.1 micromolar) of 1-naphthalene-acetic acid, pedicel strips from phenotypically aberrant plants regenerated two to three times more flower buds than explants from untransformed tobacco. Intermediate bud numbers were observed in transformants with a less extreme phenotype. The results can be explained by an increased sensitivity of the transformed explants to auxin with respect to flower bud regeneration. The effect of transformation on the auxin response is fully accounted for by the absence of a negative interaction of endogenous ethylene with 1-naphthaleneacetic acid, a phenomenon normally encountered in untransformed tissues. Three observations led to this conclusion. Application of 1 micromolar AgNO₃ to untransformed explants increased the number of flower buds to the level observed in transformed tissues but had no effect on transformed pedicel strips; exposure to 10 microliters per liter ethylene strongly reduced the response to auxin at all concentrations in untransformed explants but was almost ineffective in the transformed tissues; and endogenous ethylene synthesis occurred at the same rate in both types of explants.     

The Effect of Temperature on the Production and Abscission of Flowers and Pods in Snap Bean (Phaseolus vulgaris L.)

The effect of temperature on production and abscission of flowerbuds, flowers and pods was studied in a determinate snap-beancultivar (cv. Tenderette). Under moderate temperature (e.g.27/17°C) the onset of pod development was associated withcessation of flower bud production and with enhanced abscissionof flower buds. Raising night temperature from 17°C to 27°Cstrongly reduced pod production, mature pod size and seeds perpod, while an increase in day temperature from 22°C to 32°Chad smaller and less consistent effects. Pod production underhigh night temperature was not constrained by flower productionsince 27°C at night promoted branching and flower bud appearance.Under 32/27°C day/night temperature the large reductionin pod set was due to enhanced abscission of flower buds, flowersand young pods ( 3 cm). Flowers had the highest relative abscissionfollowed by young pods and flower buds. Therefore, the onsetof anthesis and of pod development were the plant stages mostsensitive to night temperature. Pods larger than 3 cm did notabscise but usually aborted and shrivelled under high nighttemperature. The effects of 32/27°C were not due to transientwater stresses and were observed even under continuous irrigationand mist-spraying. High temperature, flower production, pod set, seed set, abscission, snap bean, Phaseolus vulgaris L, Tenderette     

Involvement of ethylene in the action of the cotton defoliant thidiazuron

The effect of the defoliant thidiazuron (N-phenyl-N′-1,2,3-thiadiazol-5-ylurea) on endogenous ethylene evolution and the role of endogenous ethylene in thidiazuron-mediated leaf abscission were examined in cotton (Gossypium hirsutum L. cv Stoneville 519) seedlings. Treatment of 20- to 30-day-old seedlings with thidiazuron at concentrations equal to or greater than 10 micromolar resulted in leaf abscission. At a treatment concentration of 100 micromolar, nearly total abscission of the youngest leaves was observed. Following treatment, abscission of the younger leaves commenced within 48 hours and was complete by 120 hours. A large increase in ethylene evolution from leaf blades and abscission zone explants was readily detectable within 24 hours of treatment and persisted until leaf fall. Ethylene evolution from treated leaf blades was greatest 1 day posttreatment and reached levels in excess of 600 nanoliters per gram fresh weight per hour (26.7 nanomoles per gram fresh weight per hour). The increase in ethylene evolution occurred in the absence of increased ethane evolution, altered leaf water potential, or decreased chlorophyll levels. Treatment of seedlings with inhibitors of ethylene action (silver thiosulfate, hypobaric pressure) or ethylene synthesis (aminoethoxyvinylglycine) resulted in an inhibition of thidiazuron-induced defoliation. Application of exogenous ethylene or 1-aminocyclopropane-1-carboxylic acid largely restored the thidiazuron response. The results indicate that thidiazuron-induced leaf abscission is mediated, at least in part, by an increase in endogenous ethylene evolution. However, alterations of other phytohormone systems thought to be involved in regulating leaf abscission are not excluded by these studies.