The Rest Period of RhododendronFlower Buds I. EFFECT OF THE BUD SCALES ON THE ONSET AND DURATION OF REST

Shortly after flower differentiation, Rhododendron flower developmentis interrupted by a rest period. The results reported here showthat the onset and duration of rest depended upon the presenceof the flower bud scales. When the scales were removed beforethe onset of rest, the flowers continued to elongate and attainedanthesis. Intact buds stopped growing and remained in rest forat least four months. Scale removal after the onset of restterminated the rest period, though there was a lag phase beforethe flowers began to elongate. The duration of the lag phasewas related to the time of scale removal. The scales preventedflower development in situ, on detached stems and in vitro.Theresults further show that the rest period of each flower budwas independent of the rest period of adjacent flower buds andthat the resting terminal flower buds correlatively inhibitedthe growth of the lateral vegetative apices. The correlativeinhibition was eliminated by removing the terminal flower budor by breaking the rest period of the flower bud.     

Modelling Temperature Effects in Breaking Rest in Red-osier Dogwood (Cornus sericea L.)

Temperature requirements for bud development after a rest period(breaking rest) from maximum rest to end of rest were determinedto develop an empirical model for predicting rest developmentin terminal vegetative buds of red-osier dogwood (Cornus sericeaL.). One-year-old plants at maximum rest were exposed to temperaturesfrom 5 to 20 °C a 12 h photoperiod (SD) in growth chambers.Depth of rest was measured by days to bud break in either 16h photoperiod (LD) or natural daylength at 20/15 °C/nighttemperature. Developmental stages during rest development wereexpressed by degree growth stage (°GS). Chilling was effective breaking rest after plants attained maximumrest (270 °GS). Development during rest (breaking rest)increased with decreasing temperature. No significant developmentoccurred at 20 °C. Rate of rest development (°GS h^–1)at all temperatures varied during the breaking rest period anddepended on developmental stage (°GS). A °GS model describedand quantified rest development (°GS). Using temperatureand developmental stage, the model predicted end of rest (315°GS)within 3 days and daily rest development (°GS) in both years. Cornus sericea L, Cornus stolonifera Michx, dogwood, bud development, dormancy, temperature effects, chilling, degree growth stage     

Regulation of Branching in Decussate Species with Unequal Lateral Buds

In the decussate plants Alternanthera philoxeroides and Hygrophilasp. the opposite axillary bud primordia are of unequal sizefrom the time of their inception; the larger or + buds lie alongone helix and the smaller or – buds along another (helicoidalsystem). In decapitated plants of Alternanthera both buds grewout, but unequally; if the node was vertically split growthof the two shoots was more equal, and if the + buds were excisedgrowth of the – shoots approximately equalled that ofcontrol + shoots. In decapitated shoots of Hygrophila grownin sterile culture only one bud, the + or larger one, grew outat each of the upper nodes. In excised cultured nodes, also,only the + bud grew out; but if the nodes were split longitudinallyboth buds grew out, initially rather unequally. These experimentssupport the view that the regulation of branching in these specieshas two components, apical dominance and the dominance of thelarger (+) bud over the smaller (–) bud at the same node.The restriction of growth potentiality imposed on the –bud is not permanent but can be modified. Further correlativeeffects on bud outgrowth include those of the subtending leavesand of buds at other nodes.     

Flower Formation from Citrus unshiu Buds Cultured In Vitro

Flowers were formed in vitro when buds of Satsuma mandarin (Citrusunshiu Mare) from the summer flush of growth harvested duringthe winter rest period before the onset of flower initiation,were grown on a solid Murashige and Skoog medium supplementedwith sucrose and a cytokinin. Flower development was dependentupon illumination, and was enhanced when a piece of stem wasattached to the bud. The percentage of flowering explants wasalways lower than the percentage of naturally flowering budsin spring, but treatments such as ringing which increase floweringin vitro, increased the number of explants flowering int vitroas well. Citrus unshiu Marc, ‘Satsuma’ mandarin, in vitro flowering, ringing     

Regeneration from Leaf Squares of Peperomia sandersii A .DC: a Relationship between Rooting and Budding

Evidence is presented to show that in leaf squares of Peperomiasandersii bud initiation does not occur independently of rooting.Buds were formed close to the point of origin of roots and,in treatments where rooting was delayed, budding was affectedsimilarly. Promotion of root formation by pretreatment of squareswith 3-indolylbutyric acid was accompanied by increases in thenumber of buds initiated. Kinetin and N⁶-benzyladenine whichinhibited the initiation of roots also inhibited the initiationof buds. This was in contrast to the effect of these two compoundson leaf squares of Begonia rex where rooting was similarly inhibitedbut bud initiation was markedly promoted. When leaf squaresof Peperomia were grown in contact with relatively high concentrationsof kinetin buds were occasionally formed in the absence of roots.Removal of roots from leaf squares of Peperomia by excisionprevented the formation of buds.     

Supercooling Ability, Water Content and Hardiness of Rhododendron Flower Buds during Cold Acclimation and Deacclimation

The relationship between supercooling ability and water contentand killing temperature of flower buds during cold acclimationand deacclimation were studied using R. kiusianum and R. x akebono.The occurrence of multiple floret exotherms and their shiftto a narrow range at lower subzero temperatures, as well asthe marked decrease of florets water content, were observedas the symptoms of cold acclimation occuring in flower budsfrom fall to winter, and vice versa in spring buds during deacclimation.In R. kiusianum, the fully acclimated period was from Novemberto March and two months longer than that of R. x akebono. Thesupercooling ability of the former was about –25°Cand about –20°C in the latter. Although the watermigration within bud tissues during the freezing process wasdetermined in the acclimated and deacclimated buds for R. xakebono, no significant water changes could be observed, evenin the acclimated buds. Thus, it is conceivable that deep supercoolingin florets may result not necessarily from water migration fromflorets and bud axes to scales in response to freezing, butfrom low water content in situ of cold-acclimated or artificiallydehydrated flower buds. (Received July 29, 1981; Accepted October 12, 1981)     

Adventitious Bud Formation from Mature Embryos of Picea chihuahuana Martinez, an Endangered Mexican Spruce Tree

Zygotic embryos of Picea chihuahuana Martínez were cultivatedin vitro to determine the time of organogenic competence andto maximize adventitious bud induction. The induction mediumconsisted of modified B5 substrate supplemented with N⁶-benzyladenine(with or without naphthalene acetic acid) or kinetin (with orwithout 2-4, dichlorophenoxyacetic acid) at different concentrationsand induction times. The minimum induction time required forbud formation was 14 d with kinetin and 17 d with N⁶-benzyladenine.After induction embryos were transferred to the proliferationmedium (modified B5 substrate with 50% of its components andwithout growth regulators) for 30 d. The subsequent buds weretransferred every 15 d to Schenk and Hildebrandt medium at halfits concentration without growth regulators. The most effectivetreatments were 3 and 5 mg l^-1kinetin or N⁶-benzyladenine whichproduced five to seven buds per embryo. The largest shoots weresubjected to rooting trials with pulses of different concentrationsof indole butyric acid resulting in only one bud developinga root. Histological analysis revealed clusters of three tofour cells that became more evident as induction time increased.Kinetin promoted the development of an organized structure priorto adventitious buds formation sooner than N⁶-benzyladenine.Copyright 2000 Annals of Botany Company Competence, plant tissue culture, micropropagation, Picea chihuahuana, endangered species, spruce     

In Vitro Plantlet Formation in Mangosteen (Garcinia mangostana L.)

Optimum conditions were determined for in vivo growth and multiplicationof Garcinia mangostana L. using explants from aseptically germinatedseedlings and field-grown plants. Proliferating shoots wereobtained from cotyledon segments cultured on modified Murashigeand Skoog's (1962) medium with 6-benzylaminopurine. Juvenileleaf segments produced adventitious buds on Woody Plant Medium(Lloyd and McCown, 1981). Root segments gave few buds. Shoottip, nodal, and internodal explants gave multiple axillary andadventitious buds. Shoots were multiplied by enhanced axillaryand adventitious bud formation. The shoots were rooted withindolebutyric acid treatment. Rooted shoots were readily establishedin vermiculite: sand (1:1) mixture. Garcinia mangostana L., Mangosteen, tissue culture, shoot regeneration, bud development     

The Influence of Ringing on Bud Development and Flowering in Satsuma Mandarin

Ringing of Satsuma mandarin (Citrus unshiu Marc.) trees showedincreased flowering in the following spring when performed duringSeptember and October, but not during November. Most of theeffect on flowering was due to an enhancement of both bud sproutingand the number of flowering shoots formed per node. In addition,a direct effect of ringing on flower initiation was demonstrated,since the number of vegetative shoots was reduced. The response of the buds to ringing was rapid as demonstratedby changes in bud weight, protein content, and electrophoreticpattern and behaviour when cultured in vitro. Buds from ringedtrees readily flowered in vitro when forced during the winterrest period and flower formation was enhanced by the additionof cytokinin. Buds from control trees formed a smaller numberof flowers in vitro, and flowering was much less enhanced bythe addition of cytokinin. It is concluded that ringing acceleratesflower initiation in the buds and this effect takes place beforethe winter rest period. Key words: Bud sprouting, Citrus unshiu Marc., flower initiation, flowering, in vitro flowering, Satsuma mandarin, ringing     

Basipetal Gradient of Axillary Bud Inhibition Along a Rose (Rosa hybridaL.) Stem: Growth Potential of Primary Buds and their Two Most Basal Secondary Buds as Affected by Position and Age

InRosa hybridaL. cv. Ruidriko ‘Vivaldi’®, theeffect of position on growth and development potentials of axillarybuds was investigated by single internode cuttings excised alongthe floral stem and its bearing shoot. The experiments werecarried out in both glasshouses and in a phytotron. The studyfirstly concerned the development of the primary shoot fromthe onset of bud growth until anthesis. The primary shoot wasthen bent horizontally to promote the growth of the two mostproximal secondary buds, the collateral buds, already differentiatedinside the primary bud. They gave rise to basal shoots. In thebasipetal direction, the axillary buds along the floral stemexhibited both an increase in the lag time before bud growthand a decrease in bud growth percentage, demonstrating the existenceof a physiological basipetal gradient of inhibition intrinsicto the buds or due to short range correlations. The same basipetalgradient of inhibition was observed along the floral stem andits bearing shoot, demonstrating that the age of the bud wasnot a major factor in determining the rate of bud growth. Afterbending the primary shoot, the percentage of collateral budgrowth was also affected by the cutting position. The more proximalthe cutting, the lower the sprouting ability of collateral buds.The growth potential of these buds appeared to be already determinedinside the main bud before cutting excision.Copyright 1998 Annalsof Botany Company Axillary bud; basal shoot; cutting; development; endodormancy; growth; paradormancy; position; primary shoot;Rosa hybridaL.; rose; secondary bud; topophysis.     

Influence of Several Growth Regulators and Amino Acids on in vitro Organogenesis of Torenia fournieri Lind.

The effects of several growth regulators and amino acids onin vitro organogenesis of Torenia fournieri Lind. were determinedusing internodal segments. Treatment with 2,4-D¹ resulted innodular callus formation, while NAA and IAA induced roots constantlybut much less frequently shoot buds. Individually BA, zeatin,and 4-PU induced bud formation, but these shoot buds did notdevelop further. Formation of buds by cytokinin was influencedby a simultaneous application of NAA or 2,4-D, but not of IAA,its degree being reduced when BA was simultaneously appliedwith NAA or 2,4-D. When zeatin or kinetin was added with NAA,numerous roots were induced. The effects of various L-amino acids on in vitro organogenesiswere also investigated using the defined medium in which KNO₃was a principal source of nitrogen. The formation of buds wasconsiderably stimulated by alanine and asparagine, and slightlyby glutamic acid in the medium containing both NAA and BA, inwhich bud formation was easily induced. On the other hand, allamino acids except for glutamic acid and aspartic acid inhibitedroom formation in this medium. Root formation was greatly stimulated by proline, alanine, glutamine,glutamic acid, and aspartic acid, and slightly by arginine andtryptophan in the medium containing NAA but no BA. Glutamicacid and aspartic acid also enhanced bud formation in this medium.     

Effects of IAA, Zeatin, Ammonium Nitrate and Sucrose on the Initiation and Development of Floral Buds in Torenia Stem Segments Cultured In Vitro

In Torenia stem segments cultured on a defined medium from whichammonium nitrate and growth regulators were omitted, adventitiousbuds were readily formed from epidermal tissue, with subsequentdifferentiation of floral buds. Using this plant material, thecorrelation between the time of application of various chemicalsand the time-course of floral bud differentiation was investigated.Histological examination showed that adventitious buds werevegetative during the first two weeks of the culture, and floralprimordia appeared after about three to four weeks of culture.We divided the flowering process in Torenia stem segments intothe following 3 phases: the first phase (first 2 weeks) duringwhich adventitious buds are formed, the second phase (3rd and4th weeks) during which floral buds are initiated and the thirdphase (5th to 12th weeks) during which floral buds develop.Then we added IAA, zeatin, ammonium nitrate or a high concentrationof sucrose to the medium during one, two or three of these phases.Ammonium nitrate added during the third phase suppressed floralbud development, but the high concentration of sucrose givenduring this phase stimulated it. These two chemicals influencedonly the development of floral buds previously initiated. Theapplication of IAA during the first phase promoted both theinitiation and development of floral buds. However, its applicationafter 2 weeks of culture failed to promote floral bud formation.Zeatin inhibited floral bud formation in a manner similar toammonium nitrate, but if it was added to the medium only duringthe first phase, it slightly promoted the initiation and developmentof floral buds. (Received July 7, 1981; Accepted October 12, 1981)     

Tissue 11In vitro Bud Formation on Explants from the Inflorescence of Nicotiana tabacum L.

Croes, A. F., Creemers-Molenaar, T., van den Ende, G., Kemp,A. and Barendse, G. W. M. 1985. Tissue age as an endogenousfactor controlling in vitro bud formation on explants from theinflorescence of Nicotiana tabacum L.—J. exp. Bot. 36:1771–1779. The in vitro formation of generative buds was studied on explantsfrom flower and fruit stalks and from internodes of the floralramifications of tobacco. A floral gradient was found to existalong the axis of the branch. The gradient concerns the numberof flower buds formed in vitro and is present in both typesof tissues. The number of flower buds is greater on tissuesfrom the apical than from the basal portion of the branch. Thecapacity to generate these buds is largely determined by tissueage at the moment of the excision. Consequently, the gradientmoves along the axis during the outgrowth of the inflorescence. The alternative possibility that some apex-derived stimuluspredetermines the morphogenetic capacity of the tissue priorto excision is excluded by the observation that the gradientremains virtually unaltered if the apex is removed one weekbefore the onset of culturing. Auxin affects the floral gradient Increasing the auxin concentrationin internode tissue culture causes a steeper gradient of flowerbud generation by almost completely abolishing bud formationon older tissues. Key words: Auxin, flower buds, gradient, tissue culture, tobacco     

Initiation, Orientation and Early Development of Primary Rhizomes in Sorghum halepense (L.) Pers.

Axillary buds on the most basal portion of the seedling shootof Sorghum halepense differentiate directly into rhizome buds.The initial orientation of these buds is upwards, but this orientationstarts to be reversed almost immediately. The reversal is causedby the combined effect of differential radial expansion of thebasal internodes immediately above and below the bud, and differencesin the extent of mitotic activity on the abaxial and adaxialsides of the bud. Reorientation is a geotropic and is progressivelyless with acropetal nodal position of the bud. Further growthof the rhizomes proceeds in the same orientation as that ofthe bud from which they had developed, until they change theirorientation again by exhibiting diageotropic, or negativelygeotropic responses. The second reorientation coincides moreor less with the onset of flowering and it exhibits a positionalgradient, such that the change is more extensive the higherthe nodal position of the rhizome. Sorghum halepense, rhizome, geotropism, morphogenesis, perennial weeds     

Effect of Sucrose on Starch Accumulation in and Adventitious Bud Formation on Embryos of Picea abies

Adventitious buds were initiated on embryos of Picea abies (L.)Karst. after a pulse treatment with cytokinin. The initial stagesof bud formation could take place on culture medium lackingsucrose, but sucrose was required for further development ofmeristematic centres into bud primordia and buds. Sucrose atone per cent was optimal for adventitious bud formation. Embryoscultured on media containing sucrose started to accumulate starchduring the first day. Starch accumulation occurred especiallyin the cortex cells where starch grains were frequently presentin the chloroplasts. The starch accumulation increased withhigher sucrose concentrations in the culture medium. Embryoscultured on medium lacking sucrose did not accumulate starchbefore the formation of meristematic centres. Starch accumulationwas never observed in meristematic cells from which adventitiousbud primordia developed. Picea abies (L.) Karst., Norway spruce, adventitious bud, starch accumulation, sucrose concentration     

Physiological and Hormonal Factors Influencing Organogenesis in Rudbeckia bicolor Explants Cultured In vitro

Factors influencing organogenetic responses and bolting of adventitiouslyformed buds were investigated in in vitro cultured cotyledon,stem and leaf explants of Rudbeckia bicolor. Application ofnaphthaleneacetic acid (NAA) induced adventitious root formationand that of benzyladenine (BA) induced adventitious bud differentiation.When NAA at a low concentration was added together with BA,bud initiation and development were promoted further, althoughoptimal concentrations of NAA and BA varied with the kind ofexplants used. Gibberellic acid caused stem elongation of adventitiousbuds, and occasionally differentiation of floral buds on theapices of developed shoots. The action of N-phenyl-N'-(4-pyridyl)urea(4PU) and its derivative (4PU-Cl) on adventitious bud formationwas also examined. (Received August 8, 1981; Accepted November 9, 1981)     

Endogenous Cytokinins in Flower Bud Forming Explants of Tobacco

The accumulation of endogenous cytokinins was studied in pedicelexplants of tobacco (Nicotiana tabacumL.) during regenerationof flower buds in vitro. Maximal bud formation was induced onmedia containing 1.0 mmol m^–3 of benzyladenine or dihydrozeatin.No buds were formed in the absence of cytokinin. The levelsof dihydrozeatin, zeatin, and the corresponding ribosides weredetermined in explants cultured in the presence or absence ofcytokinin by means of a competitive ELISA technique. In explantsincubated without a cytokinin, only the dihydrozeatin concentrationincreased significantly during the first day of incubation anddecreased during the second day. No increase was observed inexplants incubated in the presence of benzyladenine. The concentrationof dihydrozeatin in these bud-forming explants was only 10 to15% of the concentration built up in explants cultured on dihydrozeatininstead of benzyladenine. This suggests that the endogenouscytokinins only play a minor role in the regeneration of flowerbuds in vitro. Key words: cytokinin, flower bud development, tissue culture, tobacco     

UNUSUAL SHOOT GROWTH PATTERN IN A TROPICAL TREE,OREOPANAX (ARALIACEAE)

The tropical tree Oreopanax shows a number of characters usually considered as adaptations to a temperate climate combined with typically tropical features. This evergreen tree grows in flushes and forms “resting buds” between successive flushes. Because of the lack of marked seasons in the tree's habitat, the growth cycle shows almost no correlation with external factors. The terminal resting bud appears only after the rest period; new leaves within the bud are formed only during bud growth and bud break which last 10-14 weeks vs. 2-3 weeks for taxa in the temperate zone. Abscisic acid seems not to be involved in the induction of the rest period.     

Apical Dominanace in Xanthium strumarium: A DISCUSSION IN RELATION TO CURRENT HYPOTHESES OF CORRELATIVE INHIBITION

The influence of the spectral distribution of illumination onthe gibberellin, cytokinin, auxin, and abscisic acid levelsand the correlation with the degree of branching in Xanthiumstrumarium is presented and discussed. Gibberellins do not appearto play a major role in apical dominance but may be importantfor bud extension following the initial release from dominance.The cytokinin level was much higher in inhibited buds than inreleased buds. It is suggested that the cytokinins present wereprobably not able to participate in bud growth because of anauxin-induced accumulation of abscisic acid in the buds themselves.The concentration of abscisic acid as measured by bioassay andgas-liquid chromatography was between 50 and 250 times thatoccurring in all other plants parts examined. This level felldramatically following release from apical dominance by decapitation.The results are discussed in relation to current hypothesesof apical dominance.