Regeneration from Rhizome Fragments of Agropyron repens (L.) Beauv. III. Effects of Nitrogen and Temperature on the Development of Dominance Amongst Shoots on Multi-node Fragments

Not all buds developed equally when 7-node rhizome fragmentsof Agropyron repens (L.) Beauv. were incubated in the dark at23 °C. Instead, after an initial flush of several shoots,buds were inhibited in a highly ordered sequence to leave onlyone dominant shoot growing. Applying an exogenous supply ofnitrogen KNO₃) early during this sequence increased the meanshoot lengths and delayed the onset of dominance. Additionally,the application of nitrogen after eight days incubation alteredthe sequence of shoot growth such that, in some instances, smallrapidly-growing basal shoots ‘dominated’ largerand more slowly-growing apical ones. Dominance (correlativeinhibition) was maintained in untreated fragments for up to383 days Numbers of active budsand shoot extensionrate weremaximal intherange 13°to 23 °C where dominance was establishedwithin 30 days. Incontrast only 6 per cent of rhizome fragmentskept at 33 °C had dominant shoots after 65 days. At 3 °Cshoot growth was so slow that dominance was not permanentlyestablished within 150 days. Numbers ofactive budsand shoot extensionrate weremaximal intherange 13° to 23°C where dominance was establishedwithin 30 days. Incontrast only 6 per cent of rhizome fragmentskept at 33 °C had dominant shoots after 65 days. At 3 °Cshoot growth was so slow that dominance was not permanentlyestablished within 150 days It is suggested that the effects of nitrogenand temperatureon dominance in multi-noderhizome fragments can be interpretedin terms of competition for nutrients between shoots, and theantagonistic effects of nitrogen on an auxin-mediated inhibitionby the dominant shoot.     

The Influence of Cotyledons in Axillary and Adventitious Shoot Production from Cotyledonary Nodes of Cucumis sativus L. (Cucumber)

Cucumber explants including at least part of the cotyledon,a short section of hypocotyl, and the apical bud, are capableof producing multiple axillary buds from the seedling apex andadventitious shoots from the hypocotyl base in a medium whichcontains 2·0 mg dm^–3 of kinetin. Removal of theapical bud triples the number of shoots produced from the apexof explants with two intact cotyledons but does not affect shootproduction from explants with some or all of their cotyledonsremoved. The area of intact cotyledon also influences morphogenesis,as explants with both cotyledons removed, failed to produceadventitious shoots from the hypocotyl base. Culture in continuousdarkness entirely prevents shoot development from the explantbase, but has little influence on shoot production from theapex. The influence of endogenous growth regulators and apicaldominance on the morphogenesis of shoots in cucumber seedlingsare discussed. Key words: Cucumber, cotyledons, apical dominance, morphogenesis, adventitious shoots, Cucumis sativus     

Correlative Inhibition of Lateral Bud Growth in Phaseolus vulgaris L. Ethylene and the Physical Restriction of Apical Growth

Restriction of apical growth in Phaseolus by enclosing the upperpart of the shoot in sealed or ventilated tubes induced developmentof axillary buds beneath the enclosure. Enclosed parts of shootsshowed a reduction of leaf growth and, in experiments wherethe tubes were sealed, of internode extension. Enclosure ofthe shoots in large vessels that did not restrict leaf expansion,but which contained 0?5 vols 10^–6 ethylene, similarlyinduced axillary bud growth. Analysis of the gaseous extractof physically restricted shoots showed a 2?5-fold increase inethylene concentration. The results suggest involvement of ethylenein the release of correlative inhibition brought about by physicalrestriction of apical growth.     

Effects of Indol-3yl acetic Acid on Floral Induction and Apical Differentiation in Chenopodium rubrum L.

Indol-3yl acetic acid (10^–4M) was applied to the plumulesof Chenopodium rubrum. Effects on the anatomical structure andthe growth pattern in the apical meristem, as well as DNA synthesisand nucleolus size were investigated. When auxin is applied before or during photoperiodic inductionit inhibits DNA synthesis and meristematic activity. The axillarymeristem (i.e. a group of cells in the axils of the leaf primordia)is most affected. A similar inhibition of the axillary meristemwas also observed in non-induced control plants grown in continuouslight. Auxin applied simultaneously with photoperiodic inductioncounteracts the reduction of apical dominance in the apex andthus inhibits the onset of floral differentiation. Auxin appliedfollowing induction inhibits the previously-formed buds andmakes possible a more complete development of the apical flower. The dual effect of IAA on flowering, inhibitory and stimulatory,manifests itself as a growth response at different stages ofthe changing shoot apex.     

Differential Inhibition of Shootvs.Root Growth at Low Temperature and its Relationship with Carbohydrate Accumulation in Different Wheat Cultivars

Shoot and root growth rate, carbohydrate accumulation (includingfructan), reducing sugar content and dry matter percentage weremeasured in six wheat cultivars, ranging from winter to springtypes, grown at either 5 or 25 °C. At 5 °C (comparedwith 25 °C), the relative growth rate (RGR) of shoots wassimilarly reduced in all cultivars, but the RGR of shoots wasmore affected in winter wheats. This difference resulted insmaller root:shoot ratios than in spring wheats, which alsodeveloped more first-order lateral roots. A direct relationshipbetween carbohydrate accumulation at low temperatures and reductionin root growth was established. These results suggest that differentialshootvs.root growth inhibition at low temperature may play akey role in carbohydrate accumulation at chilling temperatures.This differential response might lead to improvements in survivalat temperatures below 0 °C, regrowth during spring, andwater and nutrient absorption at low temperatures.Copyright1997 Annals of Botany Company Wheat; Triticum aestivum; low temperatures; root growth; root: shoot ratio; sugar accumulation     

Apical Dominance Control in Ipomoea nil: The Influence of the Shoot Apex, Leaves and Stem

The outgrowth of lateral buds is known to be controlled by theupper shoot tissues, which include the apex, the young leavesand the upper stem. An analysis of the influence of these plantparts on axillary bud elongation in Ipomoea nil was carriedout by various treatments on these specific tissues. A restriction of elongation in the main shoot due to eitherdecapitation or shoot inversion resulted in the release of apicaldominance A non-linear type of compensating growth relationshipwas observed between the 13 cm apical growing region of thestem and the lateral buds. It was determined by decapitation,defoliation and AgNO₃ treatments that both the 13 cm stem-growthregion and the young leaves (1–5 cm in length) had a muchgreater inhibitory influence on the outgrowth of specified lateralbuds than did the stem apex (consisting of the terminal 0.5cm of the shoot). The specified lateral buds which were analyzedfor outgrowth were located a number of nodes below the shootapex. The intervening nodes were debudded. Although the importanceof young leaves in the control of apical dominance has beenpreviously recognized, the most significant result from thepresent study with Ipomoea was the strong influence of the 13cm apical growth region of the stem on the out growth of thelateral buds. Apical dominance, Ipomoea nil L., Pharbitis nil, growth region, lateral bud outgrowth, decapitation, defoliation, shoot inversion     

Development and Growth Potential of Axillary Buds in Roses as Affected by Bud Age

The effect of axillary bud age on the development and potentialfor growth of the bud into a shoot was studied in roses. Ageof the buds occupying a similar position on the plant variedfrom 'subtending leaf just unfolded' up to 1 year later. Withincreasing age of the axillary bud its dry mass, dry-matterpercentage and number of leaves, including leaf primordia, increased.The apical meristem of the axillary bud remained vegetativeas long as subjected to apical dominance, even for 1 year. The potential for growth of buds was studied either by pruningthe parent shoot above the bud, by grafting the bud or by culturingthe bud in vitro. When the correlative inhibition (i.e. dominationof the apical region over the axillary buds) was released, additionalleaves and eventually a flower formed. The number of additionalleaves decreased with increasing bud age and became more orless constant for axillary buds of shoots beyond the harvestablestage, while the total number of leaves preceding the flowerincreased. An increase in bud age was reflected in a greaternumber of scales, including transitional leaves, and in a greaternumber of non-elongated internodes of the subsequent shoot.Time until bud break slightly decreased with increasing budage; it was long, relatively, for 1 year old buds, when theysprouted attached to the parent shoot. Shoot length, mass andleaf area were not clearly affected by the age of the bud thatdeveloped into the shoot. With increasing bud age the numberof pith cells in the subsequent shoot increased, indicatinga greater potential diameter of the shoot. However, final diameterwas dependent on the assimilate supply after bud break. Axillarybuds obviously need a certain developmental stage to be ableto break. When released from correlative inhibition at an earlierstage, increased leaf initiation occurs before bud break.Copyright1994, 1999 Academic Press Age, axillary bud, cell number, cell size, pith, shoot growth, Rosa hybrida, rose     

Topophysis affects the Potential of Axillary Bud Growth, Fresh Biomass Accumulation and Specific Fresh Weight in Single-stem Roses (Rosa hybrida L.)

Topophysis, the effect on growth and differentiation of positionof axillary buds along the shoot, was studied by propagatingfive-leaflet-leaf single-node cuttings which were excised fromseven stem positions and grown as single stemmed plants. InRosahybrida ‘Korokis’ Kiss®, ‘Tanettahn’Manhattan Blue®, and ‘Sweet Promise’ Sonia®,following release of the buds from apical dominance by excision,morphogenetic development was studied until anthesis. The timefrom excision/planting until onset of bud growth, visible flowerbud appearance, and anthesis was generally shorter in plantsoriginating from apical bud positions than from basipetal positions.Topophysis mainly affected the onset of axillary bud growth;the earliest growth and development was found in cuttings fromthe second uppermost node position. This node tended to havethe lowest plastochron value, which indicated the existenceof a transition between sylleptic and proleptic buds. Stem lengthat visible flower bud and at anthesis generally increased asthe cutting position changed basipetally until the second lowestposition, and the number of five-leaflet-leaves at anthesisand the total number of nodes generally increased basipetally.For internode length, growth rate, and fresh biomass efficiencythe cuttings taken from the uppermost and lowermost positionsgenerally had significantly lower values than cuttings fromall medial positions. At anthesis, plants originating from cuttingsexcised from lower medial positions generally had a higher freshweight, greater flower stem diameter, and a significantly higherspecific fresh weight than those plants originating from apicalor basal positions. Among the cultivars, Sonia was the mostefficient in increasing fresh biomass and had the highest growthrate, whereas Manhattan Blue possessed the highest specificfresh weight, indicating a higher plant quality. It is suggestedthat topophysis inRosa is an independent phenomenon intrinsicto the axillary bud. apical dominance; axillary bud growth; fresh biomass accumulation; cut rose; flowering; Rosaceae; Rosa hybrida L.; rose; shoot growth; single-stem roses; specific fresh weight; topophysis; quality     

Effect of Root and Shoot Meristem Temperature on Shoot to Root Dry Matter Partitioning and the Internal Concentrations of Nitrogen and Carbohydrates in Maize and Wheat

Maize (Zea mays L.) and spring wheat (Triticum aestivum L.)were grown in nutrient solution at uniformly high air temperature(20 °C), but different root zone temperatures (RZT 20, 16,12 °C). To manipulate the ratio of shoot activity to rootactivity, the plants were grown with their shoot base includingthe apical meristem either above (i.e. at 20 °C) or withinthe nutrient solution (i.e. at 20, 16 or 12 °C). In wheat, the ratio of shoot:root dry matter partitioning decreasedat low RZT, whereas the opposite was true for maize. In bothspecies, dry matter partitioning to the shoot was one-sidedlyincreased when the shoot base temperature, and thus shoot activity,were increased at low RZT. The concentrations of non-structuralcarbohydrates (NSC) in the shoots and roots were higher at lowin comparison to high RZT in both species, irrespective of theshoot base temperature. The concentrations of nitrogen (N) inthe shoot and root fresh matter also increased at low RZT withthe exception of maize grown at 12 °C RZT and 20 °Cshoot base temperature. The ratio of NSC:N was increased inboth species at low RZT. However this ratio was negatively correlatedwith the ratio of shoot:root dry matter partitioning in wheat,but positively correlated in maize. It is suggested that dry matter partitioning between shoot androots at low RZT is not causally related to the internal nitrogenor carbohydrate status of the plants. Furthermore, balancedactivity between shoot and roots is maintained by adaptationsin specific shoot and root activity, rather than by an alteredratio of biomass allocation between shoot and roots.Copyright1994, 1999 Academic Press Wheat, Triticum aestivum, maize, Zea mays, root temperature, shoot meristem temperature, biomass allocation, shoot:root ratio, carbohydrate status, nitrogen status, functional equilibrium     

Axillary Bud Inhibition Induced by Young Leaves or Bract in Euphorbia pulcherrima Willd

In plants held under long days in the vegetative stage, youngexpanding leaves of poinsettia (Euphorbia pulcherrima Willd.‘Brilliant Diamond’) are the main source of axillarybud inhibition, while the apical bud, which includes the meristem,primordial leaves and small unfolded leaves, is a secondaryinhibition source. Removal of these expanding leaves resultedin rapid release and growth of axillary buds. Decapitation ofthe apical bud resulted in delayed axillary bud release. Inreproductive plants kept in short days, the pigmented bractsare the primary source of axillary bud inhibition and the cyathiaare the secondary source. Applications of NAA —substitutedfor both young leaves and bract inhibition — maintainedapical dominance. The concentration of endogenous auxin washighest in the apical bud. However, when calculated on wholeorgan basis the auxin level was greater in young developingvegetative leaves and in reproductive bracts than in the apicalbud. Euphorbia pulcherrima Willd, apical bud, apical dominance, auxin, correlative inhibition, cyathia, poinsettia, IAA, NAA     

The Effect of Temperature on Growth and Development of Echinochloa Millets

Accumulation of dry weight and leaf plus stem area were measuredin Echinochloa utilis and E. frumentacea grown at temperatureregimes from 15/10°C to 33/28°C (day/night). Tilleringand height were recorded in addition to leaf number which wassubsequently used as a developmental index. In both species shoot dry weight increased with temperatureup to 33/28°C; the increase in relative growth rate (RGR)was negligible above 27/22°C. Below 27/22°C the RGRof E. frumentacea decreased sharply and at 15/10°C it madeno effective growth. At low temperatures the RGR of E. frumentaceawas lower than that of E. utilis due to slow leaf area expansion,and in particular smaller individual leaves. E. frumentaceatillered more than E. utilis. Plant development was retardedat low temperatures but was not as responsive to temperatureas dry weight and leaf area. The different responses to temperatureof the two species were described in equations suitable forinclusion in predictive growth models. Echinochloa spp., millet, growth, development, temperature, relative growth rate     

Effects of Orientation and Root Position on Apical Dominance in a Tropical Woody Plant

Stem cuttings of cassava (Manihot esculenta Crantz), rootedat one or both ends, were grown at a range of orientations fromthe vertical. Basally rooted cuttings showed strong apical dominanceonly in upright or near-upright positions. Basal shoots generallydominated when the stem was horizontal, while completely invertedstems exhibited weak apical dominance or no dominance at all.Cuttings rooted at the apical end were little affected by changedorientation, apical dominance being present throughout. Effectsof each root system could be detected in cuttings rooted atboth ends. The results are discussed in relation to currentthinking on the mechanism of apical dominance, gravimorphiceffects in woody plants, and the role of the ‘root-factor’in the control of shoot growth.     

Effect of Nitrogen Supply on the Grass and Clover Components of Simulated Mixed Swards Grown under Favourable Environmental Conditions I. Carbon Assimilation and Utilization

Simulated mixed swards of Perennial Ryegrass (Lolium perenneL.) cv. S23 and White clover (Trifolium repens L.) cv. S100were grown from seed under a constant 20 °C day/15 °Cnight temperature regime and their growth and carbon economyexamined. The swards received a nutrient solution daily, whichcontained either High (220 mg l^–1) or Low (10 mg l^–1)nitrate N. Rates of canopy photosynthesis and respiration, and final drymatter yields were similar in the two treatments although theproportions of grass and clover differed greatly. The Low-Nswards were made up largely of clover. The grass plants in theseswards had high root: shoot ratios and low relative photosyntheticrates – both signs of N deficiency – and were clearlyunable to compete with the vigorously growing Low-N clover plants.These had higher relative growth rates and dry matter yieldsthan their High-N counterparts. In the High-N swards clovercontributed around 50 per cent to the sward dry weight throughoutthe measurement period despite having a smaller proportion ofits dry weight in photosynthetic tissue (laminae) than grassover much of it. The latter was compensated for, initially bya higher specific leaf area than grass, and later by a higherphotosynthetic rate per unit leaf weight. The results are discussedin relation to observed declines in the clover content of swardsafter the addition of nitrogen fertilizer in the field. Trifolium repens, white clover, Lolium perenne, perennial ryegrass, nitrogen, photosynthesis, carbon balance     

Analysis of Dry Matter Partitioning in Dactylis glomerata during Vegetative Growth Using a Carbon Budget Model

The dry matter partitioning in vegetative plants of Dactylisglomerata was studied from experiments performed in controlledenvironments. Plants were grown hydroponically in growth chambers,at two constant temperatures (17 and 25 °C). In both experimentsthe root fraction decreased regularly with time, an effect thatwas more accentuated in the higher temperature regime. In orderto explain the change in dry matter partitioning, the experimentalshoot and root growth were analysed using a carbon budget modelwhich includes shoot and root maintenance requirements. Themodel predicts a relationship between the root specific growthrate and the product of shoot specific growth rate and shootto root dry weight ratio. In the range of experimental accuracy,this relationship was found to be linear at both temperatures,which should indicate that the partitioning coefficients andthe root maintenance coefficient remained constant during vegetativegrowth. The effect of temperature on the value of these coefficientscan be specified from a linear regression analysis. Between17 and 25 °C, the root maintenance coefficient increasedby about a factor of two, whereas the partitioning coefficientsdid not vary significantly. On the basis of these results, itwas shown that the decrease in root fraction during vegetativegrowth should be mainly attributed to the decrease in net specificactivity of shoots.Copyright 1994, 1999 Academic Press Dactylis glomerata L., vegetative growth, model, partitioning, root:shoot ratio, shoot specific activity, maintenance requirements     

Auxin–cytokinin interactions in the control of shoot branching

In many plant species, the intact main shoot apex grows predominantly and axillary bud outgrowth is inhibited. This phenomenon is called apical dominance, and has been analyzed for over 70 years. Decapitation of the shoot apex releases the axillary buds from their dormancy and they begin to grow out. Auxin derived from an intact shoot apex suppresses axillary bud outgrowth, whereas cytokinin induced by decapitation of the shoot apex stimulates axillary bud outgrowth. Here we describe the molecular mechanisms of the interactions between auxin and cytokinin in the control of shoot branching.     

Tillering in Tussock Grasses in Relation to Defoliation and Apical Bud Removal

Experiments with five caespitose grass species from temperateand tropical environments showed that the number of lateralshoots (tillers) which emerged following defoliation was notincreased by leaving a greater residual leaf area. Increasedavailability of photosynthate (and perhaps other resources)was effective, however, in increasing the rate of growth anddegree of flowering of new lateral shoots in one tropical species,Panicum maximum. In two temperate Agropyron tussock grasses, decapitation (apicalbud removal) did not stimulate lateral shoot growth. This indicatedthat apical dominance was not a factor preventing growth oflateral buds just prior to inflorescence emergence on the parenttillers. However, defoliation, where both terminal buds andfoliage were removed from the parent tillers stimulated lateralbud growth. Hormones other than those produced by the apicalbud or light quality or intensity may control lateral bud growthin these species. In contrast to the temperate species, lateralbud growth was stimulated by both decapitation and defoliationin the three tropical species. This response is consistent withthe model of correlative inhibition by apical dominance. Agropyron desertorum, Agropyron spicatum, Heteropogon contortus, Panicum maximum, Themeda triandra, crested wheatgrass, bluebunch wheatgrass, black speargrass, green panic grass kangaroo grass, apical dominance, tillering, regrowth, grazing, tussock grasses     

Bud Structure in Relation to Shoot Morphology and Position on the Vegetative Annual Shoots of Juglans regia L. (Juglandaceae)

The length and basal diameter of all lateral and terminal budsof vegetative annual shoots of 7-year-oldJuglans regia treeswere measured. All buds were dissected and numbers of cataphylls,embryonic leaves and leaf primordia were recorded. Each axillarybud was ranked according to the position of its associated leaffrom the apex to the base of its parent shoot. Bud size andcontent were analysed in relation to bud position and were comparedwith the size and number of leaves of shoots in equivalent positionswhich extended during the following growing season. Length andbasal diameter of axillary buds varied according to their positionon the parent shoot. Terminal buds contained more embryonicleaves than any axillary bud. The number of leaves was smallerfor apical and basal axillary buds than for buds in intermediatepositions on the parent shoot only. All new extended shootswere entirely preformed in the buds that gave rise to them.Lateral shoots were formed in the median part of the parentshoot. These lateral shoots derived from buds which were largerthan both apical and basal ones. Copyright 2001 Annals of BotanyCompany Juglans regia L., Persian walnut tree, branching pattern, preformation, bud content, shoot morphology     

Factors controlling Flowering in the Chrysanthemum: V. DE-VERNALIZATION IN RELATION TO HIGH TEMPERATURE AND LOW LIGHT INTENSITY TREATMENTS

Experiments are described which indicate that the annual vernalizationrequirement of the basal shoots of the Chrysanthemum is dueto annual devernalization of these shoots as the main axis growsup and flowers. Plants sprayed with varying concentrations ofmaleic hydrazide were arrested in their growth for considerableperiods, but this enforced ‘dormancy’ did not affecttheir vernalization status. This makes it appear unlikely thatmere suppression of growth through apical dominance of the mainshoot is the cause of this de vernalization of basal shoots.Fully or partly vernalized plants heated to 40° C. for upto 30 hours did not become dc-vernalized. Heat treatment at35° C. for as long as 30 days also failed to achieve completedc-vernalization, but here flowering was delayed by periodsequivalent to the time spent at high temperature. However, atthe end of the heat treatment progress towards flowering wasresumed at the normal rate. Complete dc-vernalization can bebrought about by prolonged exposure to low intensity illumination.This treatment appears to be effective right up to the stagewhen the first morphological changes leading to inflorescenceformation take place. These results are discussed in relationto similar experiments on the de-vernalization of rye and Hyoscyamusniger.     

Development of shoot inHydrangea macrophylla II. sequence and timing

The development of axillary buds, terminal buds, and the shoots extended from them was studied inHydrangea macrophylla. The upper and lower parts in a nonflower-bearing shoot are discernible; the preformed part of a shoot develops into the lower part and the neoformed part into the upper part (Zhou and Hare, 1988). These two part are formed by the different degrees of internode elongation at early and late phases during a growth season, respectively. Leaf pairs in the neoformed part of the shoot are initiated successively with a plastochron of 5–20 days after the bud burst in spring. The upper axillary buds are initiated at approximately the same intervals as those of leaf pairs, but 10–30 days later than their subtending leaves. Changes in numbers of leaf pairs and in lengths of successive axillary buds show a pattern similar to the changes in internode lengths of the shoot at the mature stage. The uppermost axillary buds of the flower-bearing shoot often begin extending into new lateral shoots when the flowering phase has ended. The secondary buds in terminal and lower axillary buds are initiated and developed in succession during the late phase of the growth season. Internode elongation seems to be important in determining the degrees of development of the axillary buds. Pattern of shoot elongation is suggested to be relatively primitive. Significances of apical dominance and environmental conditions to shoot development are discussed.     

Enhancement of Tuberization of Axillary Shoot Buds of Potato (Solarium tuberosum L.) Cultivars Cultured In Vitro

Factors controlling growth and tuberization of axillary budsin shoots of plantlets of potato (Solarium tuberosum L.) culturedin vitro were investigated. Correlative inhibition restrainedgrowth and tuberization of the axillary buds. Exposure of intactplantlets for various periods (4 to 48 h) to low (2 or 12C)or high (30 C) temperatures as comparedto 18C, did not alleviatecorrelative inhibition. Removal of the apical part of the shoot,the roots or both was generally ineffective Elevating sucroseconcentration from 30 to 80 g dm^–3 promoted tuberizationon axillary buds, and the cytokinin 6-(-dimethylallylamino)purine (2iP), alleviated correlative inhibition and enhancedtuberization in intact plantlets. In the whole plantlet mostof the tubers were formed on the basal nodes, however, oncecorrelative inhibition was eliminated by the dissection of theshoot to single node sections, tubers were formed on every axillarybud. The single most effective factor inducing tuberizationin single node sections was the growth retardant ancymidol,an inhibitor of giberellin biosynthesis. Key words: Potato, Solanum tuberosum L., in vitro tuberization, correlative inhibition