Lateral Bud Growth in Phaseolus vulgaris L. and the Levels of Ethylene in the Bud and Adjacent Tissue

Ethephon and the ethylene inhibitors Ag⁺ and aminoethoxyvinylglycine (AVG) inhibited outgrowth of the axillary bud of thefirst trifoliate leaf in decapitated plants of Phaseolus vulgaris.Endogenous ethylene levels decreased in the stem upon decapitationalthough it is not conclusive that a causal relationship existsbetween this decrease and the release of axillary buds frominhibition. The proposition that auxin-induced ethylene is responsiblefor the suppression of axillary bud growth in the decapitatedplant when the apical shoot is replaced by auxin is not borneout in this study. Application of IAA directly to the axillarybud of intact plants gave rise to a transient increase in budgrowth. This growth increment was annulled when AVG was suppliedwith IAA to the bud despite the fact that the dosage of AVGused did not affect the normal slow growth rate of the bud ofthe intact plant or bud outgrowth resulting from shoot decapitation.     

Interaction between Hormones, Light, and Nutrition on Extension of Lateral Buds in Phaseolus vulgaris L.

Gibberellic acid (GA₃), kinetin, and indol-3yl-acetic acid (IAA)contained in lanolin were applied in various combinations andconcentrations to decapitated stems and petioles and to budsof Phaseolus vulgaris L. GA₃ applied alone usually promotedgrowth of main stems and laterals but this was by no means consistentand occasionally it acted in the opposite way. IAA applied alonereduced lateral bud extension slightly, but not consistently;however, when applied with GA₃ or GA₃ plus kinetin, it oftenmarkedly inhibited the promotion caused by these compounds.On occasions, however, GA₃ and IAA acted synergistically topromote and sometimes to inhibit lateral shoot growth. Kinetinalone showed few significant effects on lateral shoot growthbut applied with GA₃ it often dramatically increased GA₃-inducedgrowth of main stems and laterals. The diversity of these results,which parallels that found in the literature, was shown to bepartly dependent on the point of hormone application and ageof the plant or bud, on concentration of hormone and on lightintensity or nutrition. However, no meaningful relationshipswere found and it is concluded that growth of laterals and mainstems is dependent on a hormone balance which can be criticallymodified by a wide range of internal and external factors thenature of which is still to be determined.     

Exogenous Auxin Effects on Lateral Bud Outgrowth in Decapitated Shoots

In 1933 Thimann and Skoog demonstrated exogenous auxin repressionof lateral bud outgrowth in decapitated shoots ofVicia faba. This evidence has given strong support for a role of auxinin apical dominance. Most, but not all, investigators have confirmedThimann and Skoog's results. In the present study, auxin treatmentswere carried out on ten different species or plant types, manyof which were treated with auxin in different forms, media andunder different light conditions. The Thimann–Skoog experimentdid work for most species (i.e. exogenous auxin did repressbud outgrowth) including thedgt tomato mutant which is knownto be insensitive to auxin in certain responses. Toxic auxinsymptoms were observed in some but not all species. The Thimann–Skoogexperiment did not work for greenhouse-grownColeus or forArabidopsis. Light was shown to reduce apical dominance inColeus andIpomoeanil . apical dominance; lateral bud outgrowth; axillary bud; auxin; IAA; decapitation; Vicia faba ; Ipomoea nil ; Pisum sativum ; Phaseolus vulgaris ; Lycopersion exculentum ; dgt ; Coleus blumei ; Arabidopsis thaliana ; Helianthus annuus ; Thimann–Skoog     

Correlative Inhibition of Lateral Bud Growth in Phaseolus vulgaris L.--Influence of the Environment

The influence of various environmental factors upon main stemand lateral bud growth has beeninvestigated using Phaseolusvulgaris, with the object of discovering why there is variabilityin the response of lateral buds on decapitated plants to apically-appliedIAA. Light intensity, light quality and temperature had differentand specific effects on main stem and lateral bud growth inintact plants and on the effectiveness of IAA in inhibitingprimary leaf axillary bud growth in decapitated plants. Photoperiod,on the other hand, was apparently ineffective. It is concluded that environmental factors, as well as contributingto the normal regulation of apical dominance, could also partlyor wholly account for the variation in effectiveness of appliedIAA found by different workers. IAA was least effective whenthe temperature was lower at night than during the day.     

Correlative Inhibition of Lateral Bud Growth in Pisum sativum L. and Phaseolus vulgaris L.: Studies of the Role of Abscisic Acid

The possibility has been investigated that abscisic acid (ABA)might act as a correlative inhibitor of lateral bud growth inPisum sativum and Phaseolus vulgaris. Application of ABA insmall quantities (2µg) to axillary buds on decapitatedplants of P. sativum caused appreciable inhibition of theirgrowth, and induced a compensatory growth of the bud on an adjacentnode. Application of this same quantity of ABA to axillary budson decapitated plants of Phaseolus vulgaris was without effect,but a high concentration in lanolin (1 mg g^–1) did substantiallyreduce bud outgrowth. Endogenous ABA-like substances in Phaseolusvulgaris, detected by bioassay and electron capture g.l.c.,were present in similar concentrations in shoot tips, lateralbuds on intact plants and lateral buds on plants decapitated24 h earlier. The effects of applied ABA suggested that it might be involvedin the mechanism of correlative inhibition in Pisum sativum,but it was not possible to test this hypothesis by determiningendogenous ABA levels in axillary buds because of their smallsize. The evidence presented here suggests that ABA is not acorrelative inhibitor in Phaseolus vulgaris even though at highconcentration it can inhibit the growth of axillary buds.     

Hormone Interaction in Apical Dominance in Phaseolus vulgaris L.

Gibberellic acid (GA₃), kinetin, and indole-3yl-acetic acid(IAA) were applied to roots of Phaseolus vulgaris under twodifferent light intensities and when either young or old leaveswere removed In all cases GA₃, promoted stem and lateral growth,especially when light intensity was reduced. Promotion by GA₃,of stem growth under reduced light was reduced if IAA and kinetinwere present; promotion of lateral growth under reduced lightwas reduced if IAA was added and eliminated if kinetin or kinetinplus IAA were added to GA₃. Removal of young and mature leavesreduced main stem growth; removal of young leaves promoted,and of mature leaves reduced, lateral shoot growth. We suggestthat shoot growth and apical dominance are governed by the balanceof hormones present in elongating internodes. There may be twoways of modifying this balance; firstly by altering light, temperature,or nutrients, or by applying hormones generally to the plant.Secondly, local modifications can be made by removing apicesor young leaves, or applying hormones in lanolin to specificareas. Knowledge of both the general and local conditions maybe necessary for a complete understanding of apical dominance.     

Effect of plant growth substances on the growth of axillary buds in cultured stem segments of Phaseolus vulgaris L.

The hormonal control of axillary bud growth was investigated in cultured stem segments of Phaseolus vulgaris L. When the stem explants were excised and implanted with their apical end in a solid nutrient medium, outgrowth of the axillary buds-located at the midline of the segment-was induced. However, if indoleacetic acid (IAA) or naphthaleneacetic acid (NAA) was included in the medium, bud growth was inhibited. The exposure of the apical end to IAA also caused bud abscission and prevented the appearance of new lateral buds.In contrast to apically inserted segments, those implanted in the control medium with their basal end showed much less bud growth. In these segments, the auxin added to the medium either had no effect or caused a slight stimulation of bud growth.The IAA transport inhibitor N-1-naphthylphthalamic acid (NPA) relieved bud growth inhibition by IAA. This suggests that the effect of IAA applied at the apical end requires the transport of IAA itself rather than a second factor. With the apical end of the segment inserted into the IAA-containing medium, simultaneous basal application of IAA relieved to some extent the inhibitory effect of the apical IAA treatment. These results, together with data presented in a related article [Lim R and Tamas I (1989) Plant Growth Regul 8: 151–164], show that the polarity of IAA transport is a critical factor in the control of axillary bud growth.Of the IAA conjugates tested for their effect on axillary bud growth, indoleacetyl alanine, indoleacetic acid ethyl ester, indoleacetyl-myo-inositol and indoleacetyl glucopyranose were strongly inhibitory when they were applied to the apical end of the stem explants. There was a modest reduction of growth by indoleacetyl glycine and indoleacetyl phenylalanine. Indoleacetyl aspartic acid and indoleglyoxylic acid had no effect.In addition to IAA and its conjugates, a number of other plant growth substances also affected axillary bud growth when applied to the apical end of stem segments. Myo-inositol caused some increase in the rate of growth, but it slightly enhanced the inhibitory effect of IAA when the two substances were added together. Gibberellic acid (GA₃) caused some stimulation of bud growth when the explants were from younger, rather than older plants. The presence of abscisic acid (ABA) in the medium had no effect on axillary bud growth. Both kinetin and zeatin caused some inhibition of axillary buds from younger plants but had the opposite effect on buds from older ones. Kinetin also enhanced the inhibitory effect of IAA when the two were applied together.In conclusion, axillary buds of cultured stem segments showed great sensitivity to auxins and certain other substances. Their growth responded to polarity effects and the interaction among different substances. Therefore, the use of cultured stem segments seems to offer a convenient, sensitive and versatile test system for the study of axillary bud growth regulation.     

Abscisic Acid and Apical Dominance in Phaseolus coccineus L. The Role of Tissue Age

Abscisic acid (ABA) applied to the decapitated second internodeof runner bean plants enhanced outgrowth of lateral buds onlywhen internode stumps were no longer elongating. Applied toelongating internodes of slightly younger plants, ABA causesinhibition of bud outgrowth. Together with 10^–4 M indol-3-ylacetic acid (IAA), ABA stimulated internode elongation and interactedadditively in the inhibition of bud outgrowth. A mixture of10^–5 M ABA and 10^–6 M gibberellic acid (GA₃ ) causedsimilar effects on internode growth as IAA + ABA, but was mutuallyantagonistic in effect on growth of the lateral buds. Abscisic acid, apical dominance, gibberellic acid, indol-3yl acetic acid, Phaseolus coccineus, bean     

Internodal Extension in the First Trifoliate Leaf Axillary Bud of Phaseolus vulgaris L. following Shoot Decapitation

Phaseolus vulgaris L. decapitated at the third internode showedaccelerated growth of the uppermost axillary bud remaining onthe stem (the first trifoliate axillary bud) after a lag periodof 3–5 h Much of the initial growth increment could beattributed to cell expansion Phaseolus vulgaris L, dwarf bean, correlative inhibition, cell expansion     

The Anther Smut of Sea Campion: A Study of the Role of Growth Regulators in the Dwarfing Symptom

The sympton of dwarfing in the sea campion, Silene vulgaris(Moench) Garcke sub sp. maritima(With.) A. & D. Löveinfected with the anther smut fungus Ustilago violacea (Pers.)Fuckel, a systemic, perennial parasite, has been investigated. Extracts of both healthy and diseased plants contain IAA andGA₃, but diseased plants contain less gibberellins than healthyplants. Neither IAA nor gibberellins were detected in significantquantities in the medium when U. violacea was grown in pureculture, but IAN was present. IAN was also found m extractsof diseased plants and it is tentatively suggested that it isformed by the fungus and may accumulate in the host owing tothe inability of the plant to convert IAN to IAA The exogenousapplication of IAN to healthy plants does not produce any diseasesymptoms. The dwarfing symptom of the diseased plant may be due to thelower levels of gibberellins which it contains compared withhealthy plants since the exogenous application of GA₃, restoresthe diseased plant to normal growth     

Seasonal Effects in the Hormonal Control of Growth in the Submerged Aquatic Macrophyte Ceratophyllum demersum

The season dependent changes in growth response to treatment with auxin or gibberellin were studied in the aquatic macrophyte Ceratophyllum demersum. Control plants show, under experimental conditions, a maximum growth in length in February. In the same period most of the lateral buds appear. Growth of the lateral buds occurs later. IAA causes a stimulation of growth in length from late November or December until February, in concentrations of 10^?9M and 10^?6M. There is almost no stimulation of lateral bud formation by IAA, only a slight increase from late November until December occurs by the lowest concentrations used. The highest concentration used, 10^?4M, is in most cases supraoptimal for lateral bud formation; only when plants become dormant (August), this high dose may stimulate the process. GA₃, in concentrations of 10^?9, 10^?6 or 10^?4M, exhibits a dose dependent increase of the response with respect to growth in length and lateral bud formation. The response occurs earlier than that for IAA: already early in November, or December, until February. Growth of the lateral buds may show only a slight stimulation by IAA as well as GA in winter. From February until April all GA concentrations used could cause a small increase of the growth of sprouts. In the case of IAA, however, only the lowest concentration could cause a small increase.     

Changes of endogenous hormones in lateral buds of chrysanthemum during their outgrowth

The character of branching for two chrysanthemum (Chrysanthemum × morifolium) cvs. Jinghai and Jingyun was observed, and the changes of endogenous hormones in apical and lateral buds were investigated to determine the relationship between the pattern of hormone distribution, apical dominance, and lateral bud outgrowth. The growth rate of Jinghai lateral buds was higher than that of Jingyun. In vegetative growth stage, IAA level in apical buds of Jingyun was significantly higher than in Jinghai. After flower induction, IAA level in apical buds of two cultivars decreased remarkably, but the IAA level decreased in Jingyun faster than in Jinghai. These results showed that the higher was the IAA level in apical buds the stronger was inhibition of lateral bud outgrowth. An increase in IAA and iP/iPA and a decrease in ABA concentrations were closely associated with lateral bud growth alterations in chrysanthemum.     

Apical Dominance in Vicia faba

Apical dominance phenomena have been studied in seedlings ofVicia faba particularly in relation to the movement about theplant of uracil-2-¹⁴C applied to the cotyledons. Decapitationjust below the second node releases the growth of the lowermostlateral bud and inhibition is completely reimposed by applicationof indole-3-acetic acid (IAA) to the cut surface. Uracil-2-¹⁴Capplied in solution to the cotyledons is distributed in thestems of all experimental seedlings with no consistent differencesdue to decapitation or IAA application. On the other hand, decapitationresults in a rapid increase in uracil-2-¹⁴C content in the lateralbuds which far exceeds their promoted growth. This uptake iscompletely suppressed by IAA application. A ring of tri-iodobenzoicacid (TIBA)-lanolin paste around the stem above the bud suppressesIAA action both in bud growth and on uracil-2-¹⁴C uptake, andalso on the movement of IAA-1-¹⁴C down the stem. TIBA-application to the base of the bud does not prevent IAAaction on bud growth, but also does not prevent the movementof IAA-1-¹⁴C (or a water soluble product of its metabolism)into the bud. Direct application of kinetin to the lateral bud of intact plantscauses a short-lived release of growth. Gibberellic acid producesa smaller and scarcely significant increase which is additiveto the kinetin effect. Neither has any effect on uracil-2-¹⁴Cmovement into the bud. The implications of these findings are discussed in relationto various existing theories of the mode of auxin action inapical dominance and it is concluded that their strongest supportis for a mechanism involving the suppression of phloem differentiationin the vascular supply to the bud.     

Apical Dominance in Phaseolus vulgaris L.

Although determinations of the ABA content of lateral buds ofPhaseolus vulgaris revealed no difference between decapitatedand intact control plants in the first 12 h following decapitation,a relative decrease in the ABA content of lateral buds of decapitatedplants was detectable 24 h following decapitation. Shoot decapitationwas also observed to result in a decrease in the ABA contentof stem tissue. The application of IAA to the stem of decapitatedplants prevented these changes and increased the ABA contentof stem tissue relative to that of intact plants. The levelsof IAA and ABA were also determined in the stem tissue fromthe nodes of intact bean plants. The possible interdependenceof these two plant hormones was further investigated by a studyof [2_–14ClABA metabolism. The results are discussed inrelation to the possible role of these hormones in apical dominance. Key words: Apical dominance, Abscisic acid, Indole-3-acetic acid     

Apical Dominance in the Tomato: Some Further Observations on Isogenic Lines Showing Varying Degrees of Side-shoot Development

A study has been made of the distribution of substances resemblingindol-3-ylacetic acid (IAA), abscisic acid (ABA) and cytokinin-likesubstances in the stem tissue of Craigella tomato plants ascompared with that found in two isogenic lines of this variety,Craigella Blind (blbl) and Craigella Lateral Suppressor (lsls),in both of which side shoot growth is suppressed to varyingdegrees. There was no evidence to suggest that the distributionof these hormones in the stem had any association with the differentpatterns of side shoot development of the three types, thoughsome of the lateral suppressor plants which exhibited only partialbud inhibition did show a relation between high auxin and abscisicacid levels and lack of side shoot development from the centralnodes of the shoot. Decapitation led to a stimulation of bud outgrowth from allnodes of the Craigella plants but the lateral suppressor plantsremained inhibited. The blind plants were found to initiatebud primordia at the cotyledonary nodes only when the severedapex was replaced by exogenous IAA. The results are discussed in relation to our knowledge of themechanisms controlling apical dominance in the tomato. Lycopersicon esculentumL, tomato, apical dominance, growth regulation, indol-3-ylacetic acid, abscisic acid, cytokinins     

Effect of Localized Anoxia on Phaseolus vulgaris L. Root Growth

Heterogeneity within the root environment results in differentialgrowth within root systems. The response of five Phaseolus vulgarisL. cultivars to non-uniform root aeration was evaluated. Threetreatments were applied to a split root system for a periodof 72 h. Treatments consisted of an aerated control, a non-aeratedcontrol (both halves non-aerated, using N₂). and localized anoxia(one-half the root system aerated and the remaining half subjectedto N₂). Shoot and root growth were reduced in the anoxic controlbut not in the aerated control or localized anoxia treatment. Root growth was greatest in the aerated portion of the localizedanoxia treatment for all genotypes. Contributions of the rootcomponents to the compensatory responses differed dependingon the plant cultivar examined. The growth of branched and lateralroots present before the treatment period increased by 65% inline 31908. A 50% increase in the growth of lateral roots whichemerged during the treatment period occurred in another line(Swan Valley). Other genotypes responded in an intermediatemanner. These observations indicate differences in cultivarresponses to localized soil stress. Key words: Phaseolus vulgaris L., Anoxia, Root growth     

Some aspects of daughter bulb growth and development and apical dominance in bulbous Iris

Apical dominance appears to have minimal direct involvementin daughter bulb formation in the bulbous Iris cultivar Ideal.Daughter bulb number and growth relate to the size and reproductivestate of the mother bulb and are not markedly influenced bymeristem destruction. In contrast, destruction or removal ofthe apical meristem promotes lateral bud sprouting in intactbulbs, and lateral bud elongation in Iris meristem explants.These results show that, in contrast to certain other bulbousplants, apical dominance does not direcdy limit daughter bulbnumber in bulbous Iris, but does prevent lateral bud sprouting. (Received September 6, 1978; )     

Effects of N-1-naphthylphthalamic acid on the growth and bud formation of tobacco callus grown in vitro

The effect of N-1 -naphthylphthalamic acid (NPA), indole-3-aceticacid (IAA) and kinetin on callus growth and bud formation wasstudied mainly by a tobacco callus culture method. Callus producedfrom Nicotiana tabacum var. Wisconsin 38 was used as the testplant material. Callus growth on nutrient agar containing 2mg/liter of IAA was promoted by NPA added at a concentrationof 0.5 mg/liter with 0.4 mg/liter of kinetin or by NPA addedat 5 mg/liter in the absence of kinetin. At a high concentrationof 50 mg/liter, however, NPA inhibited growth on the mediumcontaining 2 mg/liter IAA and no kinetin. Kinetin reduced thisNPA inhibition. In the presence of 0.4 mg/liter kinetin and2 mg/liter IAA, when the concentration of NPA was 50 mg/liter,buds were initiated after calluses were grown on the test mediumfor 7 weeks in dim light, but no buds formed when NPA was omittedfrom the above medium. The control of callus growth and bud initiation is based onthe active ratio of auxin (IAA) to cytokinin (kinetin) in themedium and NPA added to the medium can promote or inhibit callusgrowth and induce bud formation. Therefore, it is proposed thatNPA can itself reduce auxin activity or enhance cytokinin activityand hence change the active ratio of the two regulators. NPAmay enhance the activity of cytokinin (here supplied as kinetin)but cannot substitute for it. ¹Present address: Department of Biology, Wisconsin State University,Oshkosh, Wisconsin 54901, U. S. A. (Received March 10, 1969; )     

Stimulation of ethylene or ethane production by malformin

Malformin stimulated ethylene production of Phaseolus vulgarisL. seedlings and explants. However, when malformin was vacuum-infiltratedinto apical bud sections, the production of ethylene was inhibited,ethane production was stimulated and the sections became softand pliable; in pure oxygen, ethylene production was- stimulatedand the sections remained firm. Prolonged stimulation of ethaneproduction by malformin-treated sections required oxygen. Indoleaceticacid (IAA) had no effect on the stimulation of ethane productionby malformin-infiltrated tissues; malformin and IAA stimulatedethylene production synergistically at the same time that malformininducedethane production had increased markedly. ¹This work was supported by grant GB-7158 from the NationalScience Foundation. ²Journal Paper No. 3560 of the Purdue Agricultural ExperimentStation. (Received July 23, 1969; )     

Studies on the Dormancy of Calluna vulgaris (L.) Hull, During Winter: Classification of Dormancy

Experiments are described in which plants of Calluna vulgariswere transferred from a high altitudinal blanket bog to controlledenvironment rooms under a range of conditions, to determinethe type of dormancy mechanism which occurs in this speciesduring the winter months. It was found that in autumn, Callunaexhibits semi-dormancy, bud break not occurring under shortphotoperiods. From December onwards, bud break will occur under short photoperiodsif warm temperatures are applied; at this time the plants arein a state of post-dormancy. Calluna lacks a period of truedormancy since it can always be forced to resume growth by longphotoperiods. Although in autumn, plants will not break dormancy under shortdays, after experiencing the natural outdoor conditions of winter,they will break dormancy equally readily under long and shortdays when brought into warm controlled environment rooms inthe spring. Calluna vulgaris (L.) Hull., heather, dormancy, pre-dormancy, post-dormancy, semi-dormancy