Changes in abscisic acid and indole-3-acetic acid in axillary buds of Elytrigia repens released from apical dominance

Growth of axillary buds on the rhizomes of Elytrigia repens (L) Nevski is strongly dominated by the rhizome apex, by mechanisms which may involve endogenous hormones. We determined the distribution of indole-3-acetic acid (IAA) and abscisic acid (ABA) in rhizomes and measured (by gas-chromatography-mass spectrometry) their content in axillary buds after rhizomes were decapitated. The same measurements were also made in buds induced to sprout by removing their subtending scale leaves. The ABA content tended to be higher in the apical bud and in the axillary buds than in the adjacent internodes, and tended to decline basipetally in the internodes and scale leaves. IAA was similary distributed, except that there was less difference between the buds and other rhizome parts. After rhizomes were decapitated, the ABA content of the first axillary bud declined to 20% of that of control values within 24 h, while the IAA content showed no marked tendency to change. The ABA content also declined within 12 h in the first axillary bud after rhizomes were denuded, while the content of IAA tended to increase after 6 h. These changes occurred before the length of the first axillary bud increased 24–48 h after rhizomes were decapitated or denuded. We conclude that the release of axillary buds from apical dominance in E. repens does not require IAA content to be reduced, but is associated with reduced ABA content.     

Changes in Cytokinins and Gibberellin-Like Substances in Pinus radiata Buds during Lateral Shoot Initiation and the Characterization of Ribosyl Zeatin and a Novel Ribosyl Zeatin Glycoside

Based on detection and quantitation by bioassay, endogenous gibberellin-like substances (GAs) and cytokinins (CKs) in Pinus radiata D. Don buds during sequential shoot initiation shift from less polar to more polar forms (GAs) and from conjugated to free forms (CKs). As the terminal bud moves from the production of “short shoots” (needle fascicles) to “long shoots” (lateral branches or female conebuds), a more polar GA appears while a glucoside-conjugate of zeatin riboside is reduced, and zeatin riboside levels increase markedly.     

Spatial and temporal changes in multiple hormone groups during lateral bud release shortly following apex decapitation of chickpea (Cicer arietinum) seedlings

Although the co-ordination of promotive root-sourced cytokinin (CK) and inhibitory shoot apex-sourced auxin (IAA) is central to all current models on lateral bud dormancy release, control by those hormones alone has appeared inadequate in many studies. Thus it was hypothesized that the IAA : CK model is the central control but that it must be considered within the relevant timeframe leading to lateral bud release and against a backdrop of interactions with other hormone groups. Therefore, IAA and a wide survey of cytokinins (CKs), were examined along with abscisic acid (ABA) and polyamines (PAs) in released buds, tissue surrounding buds and xylem sap at 1 and 4 h after apex removal, when lateral buds of chickpea are known to break dormancy. Three potential lateral bud growth inhibitors, IAA, ABA and cis -zeatin 9-riboside (ZR), declined sharply in the released buds and xylem following decapitation. This is in contrast to potential dormancy breaking CKs like trans -ZR and trans -zeantin 9-riboside 5'phosphate (ZRMP), which represented the strongest correlative changes by increasing 3.5-fold in xylem sap and 22-fold in buds. PAs had not changed significantly in buds or other tissues after 4 h, so they were not directly involved in the breaking of bud dormancy. Results from the xylem and surrounding tissues indicated that bud CK increases resulted from a combination synthesis in the bud and selective loading of CK nucleotides into the xylem from the root.     

Changes after Decapitation in Concentrations of Indole-3-Acetic Acid and Abscisic Acid in the Larger Axillary Bud of Phaseolus vulgaris L. cv Tender Green

Early changes in the concentrations of indole-3-acetic acid (IAA) and abscisic acid (ABA) were investigated in the larger axillary bud of 2-week-old Phaseolus vulgaris L. cv Tender Green seedlings after removal of the dominant apical bud. Concentrations of these two hormones were measured at 4, 6, 8, 12 and 24 hours following decapitation of the apical bud and its subtending shoot. Quantitations were accomplished using either gas chromatography-mass spectrometry-selected ion monitoring (GS-MS-SIM) with [¹³C₆]-IAA or [²H₆]-ABA as quantitative internal standards, or by an indirect enzyme-linked immunosorbent assay, validated by GC-MS-SIM. Within 4 hours after decapitation the IAA concentration in the axillary bud had increased fivefold, remaining relatively constant thereafter. The concentration of ABA in axillary buds of decapitated plants was 30 to 70% lower than for buds of intact plants from 4 to 24 hours following decapitation. Fresh weight of buds on decapitated plants had increased by 8 hours after decapitation and this increase was even more prominent by 24 hours. Anatomical assessment of the larger axillary buds at 0, 8, and 24 hours following decapitation showed that most of the growth was due to cell expansion, especially in the intermodal region. Thus, IAA concentration in the axillary bud increases appreciably within a very few hours of decapitation. Coincidental with the rise in IAA concentration is a modest, but significant reduction in ABA concentration in these axillary buds after decapitation.     

Correlation of Endogenous Gibberellic Acid with Initiation of Mango Shoot Growth

Stems of mango (Mangifera indica L.) rest in a nongrowing, dormant state for much of the year. Ephemeral flushes of vegetative or reproductive shoot growth are periodically evoked in apical or lateral buds of these resting stems. The initiation of shoot growth is postulated to be primarily regulated by a critical ratio of root-produced cytokinins, which accumulate in buds and by leaf-produced auxin, which decreases in synthesis and transport over time. Exogenously applied gibberellic acid (GA3) delays initiation of bud break but does not determine whether the resulting flush of growth is vegetative or reproductive. We tested the hypothesis that endogenous GA3, which influences release of these resting buds, may decrease in stem tips or leaves with increasing age of mango stems. GA3 and several other GAs in stem tip buds and leaves were identified and quantified in stems of different ages. The major endogenous GAs found in apical buds and leaves of vegetative mango stems were early 13-hydroxylation pathway gibberellins: GA1, epi-GA1, GA3, GA19, GA20, and GA29, as identified by gas chromatography-mass spectrometry (GC-MS). A novel but unidentified GA-like compound was also present. The most abundant GAs in apical stem buds were GA3 and GA19. Contrary to the hypothesis, the concentration of GA3 increased within buds with increasing age of the stems. The concentrations of other GAs in buds were variable. The concentration of GA3 did not change significantly with age in leaves, whereas that of most of the other GAs declined. GA1 levels were greatest in leaves of elongating shoots. These results are consistent with the concept that rapid shoot growth is associated with synthesis of GAs leading to GA1. The role of GA3 in delaying bud break in mango is not known, but it is proposed that it may enhance or maintain the synthesis or activity of endogenous auxin. It, thereby, maintains a high auxin/cytokinin ratio similar to responses to GA3 that maintain apical dominance in other plant species.     

Correlation of Endogenous Gibberellic Acid with Initiation of Mango Shoot Growth

Stems of mango (Mangifera indica L.) rest in a nongrowing, dormant state for much of the year. Ephemeral flushes of vegetative or reproductive shoot growth are periodically evoked in apical or lateral buds of these resting stems. The initiation of shoot growth is postulated to be primarily regulated by a critical ratio of root-produced cytokinins, which accumulate in buds and by leaf-produced auxin, which decreases in synthesis and transport over time. Exogenously applied gibberellic acid (GA3) delays initiation of bud break but does not determine whether the resulting flush of growth is vegetative or reproductive. We tested the hypothesis that endogenous GA3, which influences release of these resting buds, may decrease in stem tips or leaves with increasing age of mango stems. GA3 and several other GAs in stem tip buds and leaves were identified and quantified in stems of different ages. The major endogenous GAs found in apical buds and leaves of vegetative mango stems were early 13-hydroxylation pathway gibberellins: GA1, epi-GA1, GA3, GA19, GA20, and GA29, as identified by gas chromatography-mass spectrometry (GC-MS). A novel but unidentified GA-like compound was also present. The most abundant GAs in apical stem buds were GA3 and GA19. Contrary to the hypothesis, the concentration of GA3 increased within buds with increasing age of the stems. The concentrations of other GAs in buds were variable. The concentration of GA3 did not change significantly with age in leaves, whereas that of most of the other GAs declined. GA1 levels were greatest in leaves of elongating shoots. These results are consistent with the concept that rapid shoot growth is associated with synthesis of GAs leading to GA1. The role of GA3 in delaying bud break in mango is not known, but it is proposed that it may enhance or maintain the synthesis or activity of endogenous auxin. It, thereby, maintains a high auxin/cytokinin ratio similar to responses to GA3 that maintain apical dominance in other plant species.     

罗汉果花芽分化过程中形态及其激素水平变化特征

采用石蜡切片和酶联免疫法(ELISA)对罗汉果雄性、雌性、两性花芽分化过程的形态和激素水平变化进行观测,为罗汉果开花调控和品种选育提供科学依据。结果表明:(1)罗汉果雄性、雌性、两性花的花芽分化过程均可分为花芽未分化期、花芽分化初期、花序分化期、萼片原基分化期、花瓣原基分化期、雄蕊原基分化期和雌蕊原基分化期7个阶段。雄蕊原基分化期前,3种花芽分化过程无明显差异,各时期形态特征均依次为:茎端呈圆锥状(花芽未分化期)→茎端经半球形变成扁平状(花芽分化初期)→距茎端5~7节位处分化出穗状花序(花序分化期)→小花原基周围形成5个萼片原基(萼片原基分化期)→萼片原基内侧形成5个花瓣原基(花瓣原基分化期)。雄蕊和雌蕊原基分化期,3种花芽分化过程存在明显差异,雄蕊原基内侧出现雌蕊原基后,雄花芽雄蕊原基继续发育成雄蕊,雌蕊原基停滞生长,退为一个小突起;雌花芽雌蕊原基继续发育成雌蕊,雄蕊原基生长缓慢,退化为小花丝;两性花芽雌蕊和雄蕊原基均继续发育,形成外观正常的雌蕊和雄蕊。(2)内源激素脱落酸(ABA)、赤霉素(GAs)和玉米素核苷(ZR)含量在3种花芽分化过程中变化规律相似,即ABA含量在花芽生理分化期降低,花芽形态分化期升高,而GAs和ZR含量则基本保持不变;吲哚乙酸(IAA)含量在3种花芽分化过程中变化存在明显差异,雌花芽IAA含量在花芽生理分化期升高,花芽形态分化期逐渐降低,而雄性和两性花芽的IAA含量则基本保持不变。ABA/GAs、ABA/IAA、ZR/IAA和ZR/GAs激素含量比值在3种花芽分化过程中变化规律相似,ABA/GAs在花芽生理分化期降低,花芽形态分化期升高,而BA/IAA、ZR/IAA和ZR/GAs则基本保持不变。研究认为,罗汉果花芽分化过程经历一个"两性期",高ABA含量和ABA/GAs比值有利于罗汉果花芽分化,IAA可能对罗汉果花性分化具有重要作用。     

The Initiation and Growth of Axillary Bud Primordia in Relation to Flowering in Trifolium repens L.

The initiation and growth of axillary bud primordia in relationto the growth of their subtending leaves was observed at theapices of three clones (A. B. and C) of white clover grown invarious combinations of photoperiod and temperature. ClonesA, B, and C flower in response to low temperatures, and clonesA and C, but not B, in response to a transfer from short tolong photoperiods at higher temperatures. The rate of growth of buds and leaves from node to node waslittle influenced by the various treatments imposed, but theinitiation of axillary bud primordia relative to the apicaldome was stimulated in conditions conducive to flowering. The number of budless leaf primordia at the apex ranged froma maximum average of 2.25 at 20° C. to approximately o.8oat 10° C. in all three clones. At the higher temperatures,runners possessed 2.06 budless nodes in short days but only1.12 in long days in clones A and C. In clone B, daylength didnot influence bud initiation at the higher temperature. The results provide evidence of the homology between vegetativeand repro-ductive axillary bud primordia. It is suggested thatflowering is brought about by the removal of an inhibition withinthe apex which leads to the precocious initiation of axillarybud primordia. Following the initiation of axillary bud primordia, the resultsshow their growth to be uninhibited for 6-7 plastochrons. Rapidinflorescence development occurs during this phase. Apical dominancehas no apparent influence on vegetative axillary buds untilthe onset of rapid petiole elongation in their subtending leaves.     

Seasonal Changes in the Levels of Free and Bound Abscisic Acid in Blackcurrant (Ribes nigrum) Buds and Beech (Fagus sylvatica) Buds

Free and bound abscisic acid (ABA) levels in blackcurrant andbeech buds have been determined by an extraction procedure involvingseveral thin-layer chromatography purification stages and finalbioassay in the wheat coleoptile straight-growth test. In bothspecies the highest level of free ABA occurs in the autumn atabout the time of onset of winter dormancy. The free ABA contentthen declines throughout the winter months reaching its lowestvalue just before bud burst. These results strengthen the viewthat free ABA plays an important role in the induction and maintenanceof winter dormancy. The bound ABA level increases in both species throughout theautumn and winter until halfway through the bud swelling phaseand then declines. It is proposed that the bound ABA accumulatesin the buds because it cannot be translocated or further metabolizedduring the winter months. The ratios of free to bound ABA were plotted and the resultingcurves show a distinctive annual cycle with the highest freeABA/ bound ABA ratio (F/B) occurring in the autumn and the highestbound ABA/ free ABA ratio (B/F) coinciding with bud burst. Agradual increase in the B/F ratio during bud swelling may indicatea feed-back reaction between free and bound ABA which maintainsthe free ABA at a sufficiently high level to put a gentle brakeon growth. At bud burst the B/F ratio falls very sharply anda period of very rapid growth ensues.     

DEVELOPMENTAL POTENTIAL OF AXILLARY BUDS OF WATER HYACINTH,EICHHORNIA CRASSIPES SOLMS. (PONTEDERIACEAE)

Buds axillary to foliage leaves of water hyacinth can elongate either as vegetative stolons or as renewal shoots produced in association with the terminal inflorescence. Stolons differ from renewal shoots in position within the shoot system, morphology, and function. Renewal shoot buds always expand, whereas stolon buds may or may not. A stolon bud develops in conjunction with the subtending leaf; as that leaf matures, the stolon bud reaches a critical period in development. At this point, the bud either continues to expand, producing a stolon, or it stops growth and matures. Maturation is not irreversible, but the probability of a bud expanding decreases as bud age increases. In the field, buds on plants at the water hyacinth mat edge frequently produce stolons, whereas buds on plants inside the mat rarely do so. Leaf morphology also varies between plants in these two regions of the mat. The particular association of leaf and branch type found in the field, however, can be reversed experimentally, indicating that although leaf and bud development are coordinated, the particular course of each is independent.     

Dynamics of non-structural carbohydrates in developing leaves, bracts and floral buds of cotton

Development of cotton (Gossypium hirsutum L.) squares (i.e. floral buds with bracts) is fundamental for yield formation. A 2-year field study was conducted to determine dry weight (DW) accumulations of cotton leaves, floral bracts and floral buds, and the changes in concentrations of non-structural carbohydrates (hexoses, sucrose and starch) in these tissues during square ontogeny as affected by fruiting positions within the plant canopy. During square development, DW accumulation of a subtending sympodial leaf and floral bracts followed a sigmoid growth curve with increasing square age, whereas the DW increase of a floral bud followed an exponential curve. Main-stem node (Node 8, 10 or 12) and branch position (proximal vs. distal) within a plant canopy significantly affected DW accumulations of the leaf, bracts and floral bud. Starch was the dominant non-structural carbohydrate in the three tissues, accounting for more than 65% of total non-structural carbohydrates (TNC). Subtending leaf TNC increased as square age increased. The bracts exhibited a smaller change in TNC than leaves. Non-structural carbohydrate concentration was the lowest in 10-day-old floral buds, and had little change during the first 15 days of square development. Within 5 days prior to anthesis, the floral-bud TNC increased dramatically, tripling at the time of floral anthesis compared with 15-day-old floral buds. Square age and fruiting position significantly affected non-structural carbohydrate concentrations of subtending leaves, bracts, and floral buds. The correlation did not exist between final boll retention and non-structural carbohydrate concentrations of floral buds at different fruiting positions under normal growth conditions. The pattern of floral-bud non-structural carbohydrates during square ontogeny suggests that major events in carbohydrate metabolism occur just prior to anthesis.     

Mammary ductal elongation: differentiation of myoepithelium and basal lamina during branching morphogenesis

Elongation of mammary ducts in the immature mouse takes place as a result of rapid growth in end buds. These structures proliferate at the apex of elongating ducts and are responsible for penetration of the surrounding adipose stroma; by turning and branching, end buds give rise to the characteristic open pattern of the mammary ductal tree. We have used a variety of techniques to determine the cellular and structural basis for certain of these end bud activities, and now report the following. (1) The end bud tip is covered with a monolayer of epithelium, the "cap cells," which are characterized by a relative lack of intercellular junctions and other specialized features. (2) The cap cell layer extends along the end bud flank and neck regions where it is continuous with the myoepithelium which surrounds the subtending mature duct. A linear sequence of differentiative changes occur in the cap cells in this region as they progressively alter in shape and accumulate the cytological features of mature myoepithelium. Cap cells may therefore be defined as a stem cell population providing new myoepithelial cells for ductal morphogenesis and elongation. (3) Differentiation of cap cells into myoepithelium is associated with conspicuous changes in the basal lamina. At the tip, cap cells form a 104-nm lamina similar to that described in expanding mammary alveoli and in embryonic tissues. Along the end bud flanks the basal lamina is raised from the cell surface and extensively folded, resulting in a greatly thickened lamina, measuring as much as 1.4 microns. At the surface of the subtending ducts the lamina becomes structurally simplified and resembles that at the tip, but has a significantly greater thickness, averaging 130 nm. (4) The codifferentiation of myoepithelium and its basement membrane is associated with changes in the surrounding stroma. Undifferentiated mesenchymal-like cells attach to the surface of the basal lamina in the midportion of the end buds and become increasingly numerous in the neck region, forming a monolayer over the myoepithelial basal lamina. These stromal cells progressively differentiated into fibrocytes which participate in collagen fibrillogenesis and give rise to the fibrous components of the stroma surrounding the mature duct.     

DEVELOPMENT AND PHYLLOTAXIS OF THE VEGETATIVE AXILLARY BUD OF MICHELIA FUSCATA

Tucker, Shirley C. (Northwestern U., Evanston, III.) Development and phyllotaxis of the vegetative axillary bud of Michelia fuscata . Amer. Jour. Bot. 50(7): 661–668. Illus. 1963.—The vegetative axillary buds of Michelia fuscala are dorsiventrally symmetrical with 2 ranks of alternately produced leaves. The direction of the ontogenetic spiral in each of these buds is related both to the symmetry of the supporting branch and to the position of the bud along the branch. On a radially symmetrical branch, all the axillary buds are alike—all clockwise, for example. But in a dorsiventrally organized branch the symmetry alternates from clockwise in 1 axillary bud to counterclockwise in the next bud along the axis. Leaf initiation and ontogeny of the axillary apical meristem conform with those of the terminal vegetative bud. The axillary bud arises as a shell zone in the second leaf axil from the terminal meristem. During this process the axillary apex develops a zonate appearance. The acropetally developing procambial supply of the axillary bud consists wholly of leaf traces. At the nodal level the bud traces diverge from the same gap as the median bundle trace of the subtending leaf. Only the basal 1–2 axillary buds which form immediately after the flowers elongate each year, while the majority remains dormant with 3 leaves or fewer.     

Changes of Respiration Rate, Ethylene Evolution, and Abscisic Acid Content in Developing Inflorescence and Young Fruit of Olive (Olea europaea L. cv. Konservolia)

Simultaneous measurements of respiration, ethylene production, and abscisic acid (ABA) concentrations, as well as the growth parameters length, fresh weight (FW), and dry weight (DW) of olive (Olea europaea L. cv. Konservolia) inflorescence were carried out at short intervals (3–7 days) during the period from bud burst until the 3rd week after full bloom (AFB), when young fruit reached 8 mm in length. The axis of inflorescence elongated remarkably during the 3rd week after bud burst (ABB), massive bract shedding occurred during the 4th week ABB, full bloom (FB) was observed 7 weeks ABB, and massive floral organ abscission 1 week AFB. The results showed a continuous increase in inflorescence FW and DW from bud burst until 4 days before FB. Respiration rate, ethylene production, and levels of ABA were relatively high during the first 3 weeks ABB. After this period, respiration and ethylene followed a similar pattern of changes, inversely to that of ABA concentration. An accumulation of inflorescence ABA 6 and 4 days before FB was associated with the minimum values of respiration and ethylene production on the same dates. The sharp decrease in the ABA concentration during FB and 3 days later was followed by a high rise in ethylene and an increase in respiration rate, which both rose further 1 week AFB. The results suggest a possible correlation of ABA with the early stage of floral abscission, whereas ethylene production seems to be correlated with the terminal separatory activity in olive inflorescence abscission processes. Received May 28, 1998; accepted November 17, 1998     

AXILLARY AND DICHOTOMOUS BRANCHING IN THE PALM CHAMAEDOREA

In both Chamaedorea seifrizii Burret and C. cataractarum Martius each adult foliage leaf subtends one axillary bud. The proximal buds in C. seifrizii are always vegetative, producing branches (= new shoots or suckers); and the distal buds on a shoot are always reproductive, producing inflorescences. The prophyll and first few scale leaves of a vegetative branch lack buds. Transitional leaves subtend vegetative buds and adult leaves subtend reproductive buds. Both types of buds are first initiated in the axil of the second or third leaf primordia from the apex, P2 or P3. Later development of both types of bud tends to be more on the adaxial surface of the subtending leaf base than on the shoot axis. Axillary buds of C. cataractarum are similarly initiated in the axil of P2 or P3 and also have an insertion that is more foliar than cauline. However, all buds develop as inflorescences. Vegetative branches arise irregularly by a division of the apex within an enclosing leaf (= P1). A typical inflorescence bud is initiated in the axil of the enclosing leaf when it is in the position of P2 and when each new branch has initiated its own P1. No scale leaves are produced by either branch and the morphological relationship among branches and the enclosing leaf varies. Often the branches are unequal and the enclosing leaf is fasciated. The vegetative branching in C. cataractarum is considered to be developmentally a true dichotomy and is compared with other examples of dichotomous (= terminal) branching in the Angiospermae.     

Endogenous gibberellin and abscisic Acid content as related to senescence of detached lettuce leaves

Levels of gibberillins (GAs) and of abscisic acid (ABA) in attached leaves of romaine lettuce (Lactuca sativa L.) declined as the leaf became older. The time course of changes in hormone levels, determined in detached lettuce leaves kept in darkness, revealed that a sharp decline in GAs accompanied by a moderate rise in ABA occurred before the onset of chlorophyll degradation. As senescence advanced, no GAs could be detected and a considerable rise of ABA was observed. A similar sequence of hormonal modifications, but more pronounced, was observed in the course of accelerated senescence induced by either Ethephon or water stress. When kinetin or GA₃ was applied to detached leaves, the loss of chlorophyll and the rise in ABA were reduced. Bound GAs were detected in senescent leaves. They were not found in the kinetin-treated leaves, which contained a relatively high level of free GAs. The results suggest that senescence in detached romaine lettuce leaves is connected with a depletion of free GAs and cytokinins, which is thereafter followed by a great surge in ABA.     

Abscissic acid localization by light microscopic immunohistochemistry in Chenopodium polyspermum L. Effect of water stress

An indirect immunohistochemical technique was developed using a rabbit anti-abscissic acid (ABA) serum and the soluble peroxidase-antiperoxidase (PAP) complex for the localization of endogenous ABA in the aerial parts of Chenopodium. Terminal bud, axillary bud bearing nodes, and adult leaves were prefixed by a soluble carbodiimide to obtain the coupling of ABA on cellular proteins and postfixed by a conventional mixture of aldehydes. They were then embedded in paraffin or in plastic. Numerous controls were carried out on sections and on a model system to test the validity of the technique. Based on the staining patterns observed along the plant, an apico-basal gradient of ABA was revealed. In the older buds, ABA was mainly concentrated in the quiescent meristematic cells of the apex. Phloem cells of the main axis and chloroplasts of the leaves were specifically labeled. No reaction product was visualized in the parenchyma cells or in the cambial zone. Water stress, which is known to increase ABA content, induced an increase of immunoreactivity within the same compartments. This physiological test validates the stain.     

Correlative inhibition of lateral bud growth in Phaseolus vulgaris L. timing of bud growth following decapitation

Summary On intact, 3-week-old plants of Phaseolus the larger bud in the axils of the primary leaves shows slow, continuous elongation growth. Release from correlative inhibition can be detected within 30 min following decapitation. When 0.1% indoleacetic acid in lanolin is applied to the decapitated stem stump, the lateral bud shows slow growth during the first 7 h, then stops completely for a further 15 h but after 2 days a further gradual increase in length is observed.The movement of ¹⁴C-labelled assimilates from the subtending primary leaf into the lateral bud increases following removal of the shoot apex. When indole acetic acid is applied to decapitated plants the ability of the buds to import ¹⁴C increases for 5–7 h and then declines to a negligible amount. Little or no radioactivity from tritiated indoleacetic acid is transported into the lateral buds of decapitated plants during the first 48 h following removal of the apex and it appears that rapid metabolism of the compound occurs in the stem tissues.     

The Effects of Exogenously Applied Abscisic Acid on Bud Burst in Salix spp

When cut stems of three species of Salix were transferred tolong day conditions conducive to growth, the number of budswhich grew within a 4 week period was dependent on various factors,including the species and the position of the buds on the stem.In addition, the removal of leaves from the stems at the startof the experiment resulted in a diminution of the number ofbuds which commenced growth while there was a substantial increaseas spring approached. Abscisic acid (ABA) at 10^–4 M was also capable of depressingbud burst in certain circumstances although this effect diminishedas spring approached. The effect of ABA was also significantlygreater in at least two of the three species if the leaves wereremoved from the stems at the time of transfer to long day conditions. Interactions were also observed between species and harvestdates, bud position and species and bud position and harvestdate. Salix spp, willow, bud burst, abscisic acid     

The influence of expanding leaves and the reproductive stem apex on apical dominance in Lolium multiflorum

In vegetative plants of Lolium multiflorum removal of the two youngest emerging leaves resulted in increased expansion of basal tiller buds. A similar release of inhibition of tiller buds took place if the floriferous apex was removed. The surgical procedures did not affect the response. Under conditions of N-deficiency total tiller number was reduced but on removal of the apex the deficient plants showed an increased initial rate of tiller bud expansion. Apical dominance during the vegetative stage of growth in this grass was apparently due to the expanding leaves in the vegetative apex, but in the flowering plant the control was exerted by the inflorescence or the elongating stem.