Pedicel abscission and rachis morphology of soybean as influenced by benzylaminopurine and the presence of pods

The cytokinin 6-benzylaminopurine (BAP) increases pod set of soybean Glycine max (L.) Merr. This study was performed to determine the effect of site and method of BAP application on pedicel abscission and the accompanying changes in rachis anatomy. Spraying racemes with BAP in solution, or applying in a lanolin suspension to proximal nodes on a rachis where proximal pedicels had been excised, delayed pedicel abscission at distal nodes. Applying BAP in lanolin to distal pedicels following flower excision failed to delay their abscission. BAP caused rachis swelling only when pods were present, but BAP could delay pedicel abscission either in the presence or absence of pods. These results suggest that rachis swelling following BAP treatment does not have a causal relationship to a delay or decrease of pedicel abscission.Alabama Agricultural Experiment Station Journal No. 6-912843P.     

Isolation of an Ethylene-induced Putative Nucleotide Laccase in Miniature Roses (<Emphasis Type="Italic">Rosa hybrida</Emphasis> L.)

Using differential display we isolated five ethylene-responsive cDNAs from Rosa hybrida L. and identified for the first time an ethylene-induced cDNA homologous to a laccase gene. Three cDNAs were isolated from petioles and two cDNAs from pedicels. Expression levels of all cDNAs in pedicels were higher than in petioles. The laccase homolog cDNA was termed the RhLAC (Rosa hybrida Laccase) gene. The RhLAC gene encodes for a putative protein of 573 amino acids containing three conserved domains characteristic of the multicopper oxidase family. Southern blot hybridization analyses indicated that there are multiple copies of the RhLAC gene in the Rosa species. Comparison of the relative expression of isolated RhLAC in various organs showed that it was highly induced in the leaf abscission zone of petioles and the bud abscission zone of floral bud pedicels, whereas it was low in both leaf blades and petioles. These results suggest that RhLAC may play an important role in senescence and abscission in roses.     

Gibberellins and <Emphasis Type="Italic">N</Emphasis>-(2-chloro-4-pyridyl)-<Emphasis Type="Italic">N′</Emphasis>-phenylurea improve retention force and reduce water core in pre-mature fruit of Japanese pear cv. Housui

A study of the effect of a gibberellin A₃ + A₄ mixture (GAs) on pre-harvest fruit drop of Japanese pear cv. Housui is reported. The GAs was applied alone or in combination with N-(2-Chloro-4-pyridyl)-N′-phenylurea (CPPU) in a lanolin paste to the abscission zone at the spur-end of the pedicel. The results showed that the GAs and CPPU combination treatment increased the pedicel–spur retention force relative to that of the untreated controls. Histological studies showed an accelerated rate of cambium division and the development of secondary xylem in the abscission zone near the spur-end of pedicels treated with the GAs plus CPPU paste, which delayed the formation of the abscission zone. Fruit quality (sugar, acid, firmness, color) was not adversely affected by the application of GAs plus CPPU, although the application of GAs alone promoted ripening. In contrast, the addition of CPPU to the two GAs delayed fruit ripening, which was measured as ethylene efflux. All treatments were without adverse effects on return bloom, measured as bud size. The CPPU plus GAs treatment also suppressed the incidence of water core, whereas the application of the GAs alone accelerated water core in this water core susceptible pear variety.     

The application of various anatomical techniques for studying the hydraulic network in tomato fruit pedicels

The abscission zone in fruit pedicels plays an important role in affecting not only water uptake in the developing fruit, but also in the transport of chemical signals from root to shoot. In order to characterize the hydraulic network of tomato fruit pedicels, we applied various techniques, including light, fluorescence microscopy, electron microscopy, maceration, tissue clearing, and X-ray computed tomography. Because of significant changes in xylem anatomy, the abscission zone in tomato fruit pedicels is illustrated to show a clear reduction in hydraulic conductance. Based on anatomical measurements, the theoretical axial xylem conductance was calculated via the Hagen–Poiseuille law, suggesting that the hydraulic resistance of the abscission zone increases at least two orders of magnitude compared to the pedicel zone near the stem. The advantages and shortcomings of the microscope techniques applied are discussed.     

Peroxidases in Tobacco Abscission Zone Tissue: II. Time Course Studies of Peroxidase Activity during Ethylene-induced Abscission

Ethylene-induced abscission in flower pedicels of Nicotiana tabacum L. cv. Little Turkish causes a progressive increase in peroxidase activity during the first 4 hours of a 5-hour time course ethylene treatment period, with decrease in peroxidase activity occurring between 4 hours and 5 hours, when the supernatant extracts of abscission zone segments are tested spectrophotometrically for peroxidase activity, using guaiacol and hydrogen peroxide. Nonethylene-treated tissue has a much lower level of peroxidase activity over the same time course period. In ethylene-treated tissue the decline in break-strength correlates with the beginning of increase in peroxidase activity (3 hours). When the abscission zone area of the pedicel is further divided into proximal, abscission zone, and distal portions, respectively, the ethylene-treated tissue has the highest peroxidase activity in the abscission zone portion, with the maximum peak occurring at 4 hours and decreasing between 4 hours and 5 hours. Acrylamide gel electrophoresis of enzyme breis from ethylene-treated aand nonethylene-treated plants reveals that no new peroxidase isozymes are formed in response to ethylene, indicating an increase in the amount of one or in both of the two already existing isozyme banding patterns. The measurement of protein in the proximal, abscission zone, and distal segments, over a 5-hour ethylene treatment period, indicates that it is being translocated in a distal to proximal direction in the abscission zone pedicel. The possible participatory role for peroxidase in ethylene-induced tobacco flower pedicel abscission are discussed.     

Methyl jasmonate induces the formation of secondary abscission zone in stem of Bryophyllum calycinum Salisb

Methyl jasmonate (JA-Me) at a concentration of 0.5 % induced the formation of secondary abscission zone and senescence in several types of stem explants (only internode segment, internode segment with nodes and without leaves, internode segment with nodes and debladed petioles) of Bryophyllum calycinum when it was applied in various places of the stem or the debladed petiole as lanolin paste. In the presence of small leaves in stem explants methyl jasmonate also induced the formation of secondary abscission zone and senescence but the presence of larger leaves completely inhibited methyl jasmonate-induced processes. Auxin, (indole-3-acetic acid, IAA), at a concentration of 0.1 % extremely prevented the formation of secondary abscission zones and senescence in the stem tissues induced by methyl jasmonate. Similar relationship between auxin and methyl jasmonate to induce the formation of secondary abscission zone and senescence was found in decapitated shoot of the intact plant. Mechanisms of the formation of secondary abscission zone are also discussed in terms of the interaction of methyl jasmonate with auxin.     

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.     

Interactions between jointless and wild-type tomato tissues during development of the pedicel abscission zone and the inflorescence meristem.

The jointless mutation of tomato results in the formation of flower pedicels that lack an abscission zone and inflorescence meristems that revert to vegetative growth. We have analyzed periclinal chimeras and mericlinal sectors of jointless and wild-type tissue to determine how cells in different meristem layers (L1, L2, and L3) and their derivatives interact during these two developmental processes. Cells in the inner meristem layer, L3, alone determined whether the meristem maintained the inflorescence state or reverted to vegetative growth. Moreover, L3 derivatives determined whether a functional pedicel abscission zone formed. Limited and disorganized autonomous development of wild-type L2-derived cells occurred when they overlay mutant tissue. Adjacent mutant and wild-type L3-derived tissues in pedicels developed autonomously, indicating little or no lateral communication. Only the outermost L3-derived cells within the pedicel were capable of orchestrating normal pedicel development in overlying tissues, revealing the special status of those cells as coordinators of development for L1- and L2-derived cells, whereas the innermost L3-derived cells developed autonomously but did not influence the development of other cells.     

Changes in distribution of cell wall polysaccharides in floral and fruit abscission zones during fruit development in tomato (Solanum lycopersicum)

After fruit development has been triggered by pollination, the abscission zone (AZ) in the pedicel strengthens its adhesion to keep the fruit attached. Unpollinated flowers are shed at their respective AZs, whereas an enlargement of the same tissue is observed in pollinated flowers. After the fruit has developed and is fully ripened, shedding occurs easily at the AZ, indicating an acceleration of abscission. Cell wall degradation and synthesis may play important roles in these processes; however, little is understood. In this report, we have visualized changes in polysaccharide distribution in the AZs of pollinated versus unpollinated flowers and in the ripened fruits using immunohistochemistry. During floral abscission, a large increase was observed in LM15 labeling of xyloglucan specifically at the AZ in the abscising pedicel. LM5 and LM6 labeling of galactan and arabinan, respectively, also increased—LM5 throughout the pedicel and LM6 at the basal side of the AZ. The results suggest that xyloglucan, pectic galactan and arabinan play key roles in the abscission process. During fruit abscission, unlike in floral abscission, no AZ-specific cell wall polysaccharide deposition was observed; however, high autofluorescence was seen in the AZ of over-ripe fruit pedicels, suggesting secondary cell wall synthesis and lignification of the AZ prior to fruit abscission.     

Seasonal Changes in the Levels of Some Cellular Components in the Abscission Zone of Coleus Leaves of Different Ages

The present study with intact petioles of Coleus of varyingages suggests an involvement of the phenomenon of mobilizationwith the abscission process. There was a gradual increase inthe levels of chlorophyll and nucleic acids and also solublenitrogen compounds in the proximal tissues with the approachof abscission with a concomitant decrease of these substancesin the distal tissues. This increase of metabolites in the proximaltissues was clearer in petioles at the first node than at thefourth node suggesting a lesser degree of metabolic activityof the proximal tissues in older petioles. The change of levelsof chlorophyll and nucleic acids and also of soluble nitrogenwas more marked in winter than in summer months. The application of NAA to petioles of the third node; just afterdeblading (i.e. in the auxin-inhibited stage 1), not only stoppedthe decline of nucleic acid levels (particularly RNA) at thedistal tissues but also caused an increase of nucleic acidsover the initial levels. This effect was more pronounced insummer than in winter months. If the initially inhibitory concentration of NAA was appliedin the auxin-promoted stage 2 of abscission, instead of an increase,there followed a quicker rate of decrease in nucleic acids (particularlyRNA). This effect was also more prominent in summer.     

Factors concerned in the Rooting Responses of Isolated Leaves

The rooting responses of isolated leaves of the dwarf Frenchbean and the ivy were studied by applying solutions of growthsubstances to the petiole: ß-indolyl-butyric acid(I.B.A.) for the former and -naphthyl-acetic acid (N.A.A.) forthe latter. The following factors were investigated:

1. The variation in response of successive leaves from the apextowards the base of the plant.
2. The optimal concentrationsof the growth substances and therelation between duration ofapplication and concentration.
3. The relation of age of theleaf and optimal concentration(ivy).
4. The nutritive factorsconcerned in the response were studied,(a) by varying periodsof contact between lamina and petiole,(b) by varying durationof light, (c) by varying the amountof light, and (d) by feedingwith sucrose and asparagine.

The most responsive leaf in the bean was the 2nd from the apex,in the ivy the 9th leaf. Very young leaves were killed. Withpetioles immersed for 24 hours the optimal concentrations wereI.B.A. at 2·5 parts per million (p.p.m.) for the bean,and N.A.A. 100 p.p.m. for the ivy. It was shown that the activesubstance entered mainly through the cut end in the transpirationstream; entry through the cuticle was much slower. Starvation of the cuttings whether by low light intensity, darkness,or separation of the lamina from the petiole reduced root formation.Feeding with sucrose and asparagine increased the response. Analysis of the leaves was carried out at regular intervalsfor total sugar, total and soluble nitrogen. In the bean solublenitrogen increased slightly in the petiole during the first5 days after treatment, after which insoluble nitrogen continuedto accumulate until the 7 day, when the roots first emerged.After this the total nitrogen decreased. Sugar content of thepetiole at first increased but rapidly fell before the rootsemerged and then again increased. In the ivy petiole the increasein soluble and total nitrogen was very slow, the former beinggreatest on the 15th day and the latter on the 20th day aftertreatment. The total sugar increased to the 10th day, but thendecreased until the emergence of roots, after which it againincreased. Treated leaves of the bean and ivy of different agesand the leaves starved for varying periods were also analysedfor total sugars and total nitrogen. Treated bean leaves receivingvarying periods of daily illumination were also analysed toelucidate their rooting response. Histological examination showed that in the bean the roots arosein the rays between the vascular bundles and in the ivy externalto the vascular bundles opposite the phloem. The growth of the rooted leaves was followed for more than amonth in the bean and over one year in the ivy. Some growthwas found in the immature bean leaves which survived treatment,but the final size was much below that of the control leavesattached to the plant. In the ivy very little further growthoccurred although the leaves produced a large root system andafter 2 years are still alive: the original differences in sizeof the successive leaves at the time of removal from the plantstill remain.     

Dianthus caryophyllus stems and Zantedeschia aethiopica petioles/pedicels show anatomical features indicating efficient photosynthesis

The fine structure of the green stem of Dianthus caryophyllus, the leaf petiole and the flower pedicel of Zantedeschia aethiopica were studied using light and scanning electron microscopy. It was revealed that these non-foliar plant parts of both species possess epidermis with numerous stomata. Stomatal density of D. caryophyllus stem was found to be relatively high (79 vs 100 per mm² found on leaf surface). Z. aethiopica petioles and pedicels also possess numerous stomata (17 per mm²), yet stomatal density was found to be about half of that of leaves. Anatomical differences observed between petioles and pedicels were only minor. Stems of D. caryophyllus as well as petioles and pedicels of Z. aethiopica have a chlorenchyma-type tissue whose fine structure is quite similar to the leaf palisade chlorenchyma. Yet, the palisade of Z. aethiopica petioles and pedicels shows a peculiar arrangement: palisade cells are arranged with their long axis parallel to the longitudinal organ axis. Palisade tissue found in the aforementioned non-foliar plant organs in both species shows strong red chlorophyll auto-fluorescence under epi-fluorescence optics, consists of cells with abundant chloroplasts, possesses high percentage of intercellular spaces (13 and 20%, respectively) and its cells expose considerable part of their surface to the intercellular air. The fine structure of this stem palisade tissue along with the abundance of functional stomata found on the epidermis may support efficient photosynthesis.     

Abscission in Coleus: Light and Phytohormone Control

Light control of leaf abscission in Coleus (Coleus blumei Benthcv. Ball 2719 Red) appears to be regulated by the quantity ofendogenous auxin transported from the leaf blade to the abscissionzone. Gas chromatographic—mass spectrophotometric analysisindicated that diffusate collected from leaf tissue treatedwith red light contained significantly higher levels of auxinthan dark and far-red light-treated leaf tissue. In addition,diffusate from red light-treated tissue inhibited abscissionof leafless petioles while diffusate from far-red light-treatedtissue promoted abcission when compared with diffusate fromdark-treated tissue. The effect of red light on abscission couldbe mimicked by IAA, but not by other phytohormones. An auxintransport inhibitor, 2, 3, 5-triiodobenzoic acid (TIBA), appliedeither as a lanolin ring around the petiole or vacuum infiltratedinto tissue, could completely eliminate any red light effecton abscission. The data are consistent with a phytochrome-mediatedlight regulation of endogenous auxin level in the leaf whichthen controls abscission. Key words: Abscission, Coleus, IAA, plant hormones, red (far-red) light, TIBA     

The roles of abscisic acid and ethylene in the abscission and senescence of cocoa flowers

Cocoa flowers have a limited period of longevity; more than 90% of unpollinated flowers abscised within 32 h after anthesis. Abscisic acid (ABA) levels increased significantly prior to abscission. By 21 h after anthesis, ABA levels had increased almost 10-fold, and by 32 h flowers had 20-fold higher levels of ABA than at anthesis. Fluridone completely inhibited both the increase in ABA, the formation of an abscission zone, and the abscission and senescence of flowers. In contrast, ethylene production increased only slightly 21 h after anthesis and was only 2-fold higher after 32 h. Aminoethoxyvinylglycine (AVG) delayed but did not prevent abscission. In cocoa flowers, ABA is the primary regulator of abscission; ethylene accelerates abscission but only in the presence of ABA. Naphthalene acetic acid (NAA) treatment of flowers at anthesis prevented abscission zone formation and flower abscission, but did not induce fruit set. All parts of the NAA-treated flower except the pedicel senesced after 6 days. NAA+AVG treatment only delayed, whereas fluridone treatment completely prevented flower senescence.     

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.     

The regulation of sweet cherry fruit abscission by polar auxin transport

Inconsistency of cropping is an important problem for UK sweet cherry production. Premature fruit abscission in Prunus can reduce yields severely, however, the environmental cues and hormonal signals that trigger abscission have not been identified. Auxin (IAA) is known to delay abscission by reducing the sensitivity of cells in the abscission zone to ethylene, a promoter of abscission. Therefore, the capacity for polar auxin transport (PAT) through sweet cherry pedicels was examined in relation to fruit abscission. Cherry ‘spurs’ (short shoots) with similar leaf areas and different fruit numbers were phloem-girdled to restrict assimilate movement. Abscission from spurs with many fruit (eight or more) occurred within 14 days of girdling, whereas abscission from spurs with few (two) fruit was minimal. The pedicels’ capacity for PAT in spurs with different fruit numbers was determined 1, 3 and 9 days after girdling (DAG). Fruit were analysed for endogenous IAA concentration 3, 5, 7 and 9 DAG. PAT inhibitors 2,3,5-triiodobenzoic acid or 1-N-naphthylphtalamic acid were applied to pedicels of fruit not expected to abscise, i.e. on spurs with few fruit. The effect of these inhibitors on fruit abscission was determined 14 DAG. The proportion of the transported [³H]-IAA was lower from the outset in pedicels from spurs with many fruit. By 9 DAG, symptoms of fruit abscission were apparent and 40% less [³H] -IAA was transported through pedicels on spurs with many fruit. Fruit endogenous IAA concentrations were similar in the two groups of spurs. Application of PAT inhibitors shortly after girdling increased fruit abscission by 30%. The results suggest that although a decline in PAT is not the only cause of fruit abscission, the maintenance of PAT contributes to fruit retention.     

The Effect of Prolonged Chilling on Water Movement and Radial Growth in Trees

1. The woody shoots of young saplings of Fraxinus.excelsior andAcer Pseudo-platanus in pots were subjected to continuous coolingto about 2° C. during the growth season, with the resultthat radial growth was almost completely inhibited throughoutthe woody stem.
2. The chilling did not adversely affect extensiongrowth exceptthat it was later in commencement and proceededmore slowly.
3. If the temperature around the stem is loweredfrom 2° C.to 0° C., water conduction is cut down tosuch an extentas to cause wilting of the leafy shoots; turgidityis recoveredwhen the temperature is again raised to 2°C.
4. This wilting effect is discussed particularly in relationtothe part played by living cells in the upward movement ofwaterin the wood.

     

Ethylene-promoted tomato flower abscission and the possible involvement of an inhibitor

The abscission zone in tomato (Lycopersicon esculentum (L.) Mill. flower pedicels is morphologically distinguishable prior to separation and is delineated by an indentation of the epidermis. Exposure of excised pedicels with the flower attached to ethylene results in abscission within 12 h and this can be accelerated by flower removal. Abscission of excised pedicels with the flower removed takes place in the absence of exogenous ethylene but this is delayed by pretreatment with aminoethoxyvinyl glycine, an inhibitor of ethylene biosynthesis. The data presented support the hypothesis that flower tissue is the source of an abscission inhibitor.Abbreviations AVG aminoethoxyvinyl glycine - IAA indole-3-acetic acid