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.     

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     

Axillary Bud Formation in Two Isogenic Lines of Tomato Showing Different Degrees of Apical Dominance

Grafting experiments have been carried out in which rootstocksof the cultivar Craigella were paired with scions of an isogenicline Craigella Lateral Suppressor (ls ls) and vice versa, andthe levels of hormones in the roots and shoots of the graftedplants examined. The roots of Craigella plants differed from those of LateralSuppressor in that they contained a higher proportion of a cytokininthat co-chromatographed with N⁶ - (²—isopentenyl) adenosine.Reciprocal grafts did not lead to any qualitative or quantitativechanges in the cytokinins in the roots of either line. GraftingLateral Suppressor scions on Craigella rootstocks led to anincrease in the IAA content of the apical region and the ABAcontent of the stem tissue immediately below it, but when Craigellascions were grafted on Lateral Suppressor rootstocks there wereno changes in the level of either hormone. Cytokinins applied to the leaf axils of Lateral Suppressor plantsresulted in lateral bud initiation in the axils above the pointof treatment but not if the plants were also given a short periodof far-red light at the end of the photoperiod. Cytokinins wereineffective in initiating lateral buds in grafted Lateral Suppressorscions. It is suggested that root-produced cytokinins influence lateralbud outgrowth indirectly by way of their effect on the levelsof IAA and ABA in the shoot. Lycopersicon esculentum Mill., tomato, apical dominance, growth regulation, indol-3yl acetic acid, abscisic acid, cytokinins     

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     

Effect of Gibberellic Acid on the Distribution of Products of Photosynthesis in Sunflower

Single leaves on growing sunflower plants were allowed to assimilate¹⁴CO₂. Gibberellic acid was applied to the same leaf or to theterminal bud or the roots, and the distribution of assimilated¹⁴C was determined at intervals of 1–96 h. Gibberellicacid had no significant effect on initial distribution of ¹⁴Cduring the period of rapid export from the leaf, but enhancedre-export from the roots after translocation from the leaf hadvirtually ceased. Most of the ¹⁴C exported from the roots accumulatedin the shoot tip. The site of application of the hormone wasof relatively minor importance. Wherever it was applied themajor effect was enhancement of movement from the roots to theshoot tip. Application to the terminal bud was most effectivein this respect. There was no evidence that gibberellic aciddirectly affected the transport system, but the data supportthe hypothesis that it increases the strength of the sink inthe shoot tip. Helianthus annuus L., sunflower, assimilate transport, gibberellic acid, phloem transport     

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     

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; )     

Influence of Position and Number of Nodal Roots on Outgrowth of Axillary Buds and Development of Branches in Trifolium repens (L.)

The implications of the presence of a root, either at the parentnode or at neighbour nodes, on branch formation of Trifoliumrepens (white clover) was investigated. Plants were freely rootedor rooting was restricted to every sixth or every twelfth nodealong the parent axis. The absence of a root at the parent nodehad little influence on the probability of the subtending axillarybud forming a branch but, on average, delayed the outgrowthof the bud. The probability that an axillary bud, emerging froma non-rooted parent node, developed to a lateral branch (branchwith elongated internodes) decreased with decreasing proximityof the parent node to a rooted node. Lateral branches emergingfrom non-rooted parent nodes which were two nodes distal toa rooted node had a higher rate of node appearance, a greatermean internode length and area per leaf, and were more branchedthan lateral branches emerging from other non-rooted parentnodes. The dry mass of each single root and of branches grownat rooted parent nodes were significantly higher in plants withrestricted rooting than in freely rooted plants. Restrictionin the number of rooted nodes per plant increased the numberof inflorescences. It is concluded that the whole plant responseto restricted root formation was continuous growth of the parentaxis and compensatory growth of the branch at the rooted node.In general, growth was slow for axillary buds whose developmentwas dependent on the basipetal movement or cross-transport withinthe stolons of resources exported from roots. Trifolium repens (L.); white clover; axillary bud outgrowth; branch development; clonal growth; nodal root     

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     

加拿大金露梅离体培养与快繁体系的建立

以加拿大金露梅嫩芽、叶片为外植体进行试验,通过观察确定嫩芽为初代培养的外植体。运用L₉(3⁴)正交试验筛选出最适合的腋芽初代培养、芽苗继代增殖及组培苗生根的最佳培养基,从而为金雨点建立了一套“腋芽诱导—继代增殖—生根培养”的快速繁殖体系。结果表明,诱导腋芽的分化培养基为MS+6-BA 2 mg·L^-1+NAA 0.1 mg·L^-1,其中MS、6-BA和NAA均为诱导的主要因子,影响顺序为MS＞6-BA＞NAA,诱导率达96.33%;继代增殖培养中激素6-BA是影响加拿大金露梅芽增殖生长的主要激素,差异极显著（p=0.000 1）,并且以浓度为2.0 mg·L^-1的增殖效果最好,确定最佳培养基为MS+6-BA 2.0 mg·L^-1+NAA 0.6 mg·L^-1+KT 0.2 mg·L^-1,半月增殖倍数达6.12;对生根培养3种激素（KT、NAA、IBA）进行方差分析, KT和NAA的影响均达到了显著水平(p=0.000 1; 0.001 0),是影响生根的主导因子,而IBA的p值为0.424 5,因此可以忽略其影响,在诱导时确定用NAA和KT两种激素。之后对生根数量、生根率进行多重比较表明最终确定生根培养基为MS+NAA 0.1 mg·L^-1+KT 1.0 mg·L^-1,生根数为8.63条,生根率为95.33%。     

Epicormic Bud Development in Quercus robur L. Studies of Endogenous IAA, ABA, IAA Polar Transport and Water Potential in Cambial Tissues10

Seasonal measurements of IAA,³ made using GC-MS, ⁴ indicatedthat in Q. robur the spring initiation of cambial activity andonset of visible bud outgrowth in the canopy is preceded byan increase in cambial region IAA. The effects of notch-girdlescut into the bole indicated that IAA in the cambial region laterwas present in separate physiological pools, with only the polar-transportedfraction affecting epicormic bud outgrowth. The stage in thespring when the epicormic buds grew out coincided with an increaseboth in cambial region IAA and in the capacity of cambial explantsfor IAA polar transport. Thus the stimulus needed by the epicormicbuds to overcome inhibition by polar-transported IAA appearedto be self-generated. The observed effects of exogenous hormoneson epicormic bud outgrowth from stem explants indicated thatthis stimulus might be cytokinin. The seasonal changes detectedin cambial region ABA³ were consistent with a role for stress-inducedABA in the induction of epicormic bud dormancy after canopydevelopment during the summer. No consistent effects of standthinning on cambial region IAA, ABA, water potentials or watercontents were detected, although polar transport of exogenousIAA by cambial region explants removed in the spring was reducedby thinning. Key words: Epicormic buds, cambium, hormones     

Haploid Plantlet Formation from Female Gametophytes of Ephedra foliata Boiss. in vitro

Female gametophytes (at the archegonial stage) excised fromyoung ovules of Ephedra foliata Boiss, were cultured on a basalmedium (Murnshige and Skoog's combinations of major and minorsalts, Iron source, vitamins, myo-inositol along with 2 percent sucrose and 10 per cent coconut milk) under aseptic conditions.Growth and morphogenetic responses of the explants to auxinswere compared at different concentrations and a study of theirinteractions with cytokinins has also been made. At 2 mg 1^–1,2, 4-D induced profuse callusing which subsequently producedroots. NAA at 4 mg 1^–1 was optimal for callus growth androoting. Combinations of 2,4-D and kinetin were more effectivein inducing roots and shoot buds than those of 2,4-D and benzylamino-purine (BAP). Addition of BAP (0.05 mg ^1–1) to themedium containing optimal concentrations of NAA resulted information of a large number of roots. Kinetin induced only rootingin the presence of 4 mg 1^–1 NAA. A high concentrationof BAP (8 mg 1^–1), stimulated shoot bud formation. Forthe further development of shoot buds, neither auxin nor cytokininwas needed. Cytological observations revealed the presence ofhaploid number of chromosomes, i.e. seven. Ephedra foliata, tissue culture, callus, regeneration, 2,4-dichlorophenoxyacetic acid, naphthalene acetic acid, kinetin, benzyl amino-purine     

Involvement of Calcium in Adventitious Bud Initiation in Torenia Stem Segments

In Torenia stem segments cultured in vitro, active meristematicdivisions are induced in the epidermis by treatment with cytokinin,resulting in the formation of adventitious buds. Applicationof the calcium ionophore A23187 [GenBank] was found to induce meristematicdivisions in the absence of cytokinin. The induction by A23187 [GenBank] was inhibited by simultaneous addition of auxin, but not byanti-cytokinin. A two hour pre-treatment with A23187 [GenBank] was alsoeffective, but only when it was applied to the explants justafter their excision from mother plants. The A23187 [GenBank] -inducedmeristematic zones developed into dome-shaped structures, butnot into complete adventitious buds. Complete elimination ofcalcium from the culture medium caused 50% inhibition of A23187 [GenBank] -and/or cytokinin-induced initiation of meristematic divisions.When the explants were preincubated with EGTA and then culturedon a Ca-free medium containing EGTA, cytokinin failed to inducebud initiation. Similar inhibition was also obtained by lanthanum,a calcium antagonist, by verapamil, a calcium channel inhibitor,and by trifluoperazine and chlorpromazine, calmodulin inhibitors.These results support the idea that adventitious bud initiationinduced by cytokinin in Torenia stem segments may be mediated,at least partially, by an increase in the level of intracellularCa²⁺. ¹Bioscience Research Center, Mitsui Petrochemical IndustriesLtd., Waki-cho, Kuga-gun, Yamaguchi 740, Japan. (Received May 9, 1985; Accepted October 5, 1985)     

The Role of Glucose on Flower Bud Formation in Thin-Layer Tissue 12Nicotiana tabacum L.

The effect of glucose on flower bud formation was studied inthin-layer tissue cultures of epidermal strips from flower stalksof Nicotiana tabacum L. cv. Samsun. A minimum concentration of 30 mol m^–3 glucose in the MS-mediumcontaining 1.0 mmol m^–3 of both NAA and BA was necessaryfor flower bud formation. With 150 mol m^–3 glucose a minimumstay of 10 d was required for optimal flower bud formation. Withholding glucose for a limited period at different time intervalsafter the onset of culture caused a delay in flower bud formationand did not affect previous development on glucose. The resultsindicated that competence for flower bud initiation is not restrictedto the early stage of culture. The process may start at anytime later at the appropriate glucose concentration. However,for both optimal initiation and further development of flowerbuds the presence of a metabolizable sugar is required. Incubationof the tissue on glucose is associated with higher respirationrate. Key words: Flower formation, Glucose, mannitol, Nicotiana tabacum, Respiration, tissue culture     

Organogenesis in the Cultured Female Gametophyte of Ephedra foliata

The female gametophyte of Ephedra foliata was used as an explantfor the production of haploids as it is composed of haploidcells, all of the same genotype. The regeneration of roots wasdependent upon the presence of NAA, while BAP had a modifyingeffect. At lower concentrations (0.05 parts 10^–6 and 3.5parts 10^–6) BAP enhanced the root promotion of NAA (0.05–4.0parts 10^–6). At higher concentrations of BAP (1–6parts 10^–6), roots and shoot buds were formed. Kinetinat 4.0 parts 10–6 with 0.5 parts 10–6 2, 4-D wasoptimal for shoot bud production in explants at the archegonialstage and 2, 4-D at 2.0 parts 10–6 with 0.5 parts 10–6kinetin was optimal for root formation. Cells of the callusand root tip had the haploid number of chromosomes, n = 7. Meristemoidswere located on the surface or embedded in the callus tissue.The deep seated meristemoids organized only root primordia,but the peripheral ones gave rise to root as well as shoot budprimordia. Initially, there was no vascular connection betweenthe shoot-bud and the callus. This was established later. Key words: Ephedra, Female gametophyte, Haploid, Tissue culture     

Tuberization in Potato at High Temperatures: Gibberellin Content and Transport from Buds

Warm temperatures (35°C day/30°C night) which inhibittuberization in potato (Solanum tuberosum L., cv. Sebago) increasedgibberellin activity in crude extracts from buds, but not frommature leaves, as determined by the lettuce hypocotyl bioassay.Changes in the growth of tubers and stolons indicate the occurrenceof basipetal movement of GA₃ applied to the terminal bud ora mature leaf. ¹⁴C labelling from GA₃ or mevalonic acid injectedjust below the terminal bud was recovered in the lower shoot,stolons and tubers, but the amount transported was greater atcool temperatures (20/15°C). It is concluded that high temperaturespromote the synthesis of gibberellin in the buds rather thantransport to the stolons. Solanum tuberosum L., potato, tuberization, gibberellin     

CHEMICAL CONTROL OF ADVENTITIOUS ORGAN FORMATION IN LACTUCA SATIVA EXPLANTS

Both kinetin and adenine promote bud initiation in excised cotyledons of Lactuca sativa. Controls lacking these substances form abundant roots but have never formed buds. Indoleacetic acid and certain mineral salts are also necessary for regeneration of shoots. Although bud growth from cotyledons is extensive on a medium containing both indoleacetic acid and kinetin, excised roots display a low propensity toward bud formation and typically develop callus tissue with roots. Growth of hypocotyl sections is intermediate with respect to bud formation. Shoot initiation in lettuce thus varies with the region of the seedling as well as with the culture medium.     

Differentiation of Shoot Buds in vitro in Tissue 1Sisymbrium irio L.

Shoot bud formation was induced in the stem callus of Sisymbriumirio L., a Cruciferous plant. The callus was established onMurashige and Skoog medium with IAA (1?0 mg l^–1) and kinetin(0?5 mg l^–1). The effect of three purines (kinetin, 6-benzylaminopurine,and 6-methylaminopurine) incorporated singly along with IAAin MS medium was investigated. It was found that kinetin orMAP (3–5 mg l^–1) along with IAA (0?5 mg l^–1)were the most effective in inducing shoot bud formation. Adeninesulphate (10 mg l^–1) with kinetin (1?0 mg l^–1) alsoinduced bud differentiation. The morphogenetic potential of the callus to differentiate shootbuds was seemingly lost in 2 year old callus cultures. However,on successively subculturing on a regeneration medium shootbuds differentiated and the number of buds formed improved onfurther subculture. Two types of meristematic outgrowths were recognized: (i) arisingfrom superficial cells and (ii) arising from deep-seated cellsin the vicinity of tracheidal elements. However, both typesformed meristematic nodules on the surface of which shoot budsdifferentiated. Some embryoids were also recognized arisingsuperficially.     

Regeneration in Streptocarpus Leaf Discs and its Regulation by Temperature and Growth Substances

The formation of adventitious buds and roots in leaf discs of Streptocarpus x bybridus‘Constant Nymph’ were both stimulated by relatively low temperatures (12 and 18°C) applied to isolated discs or to the growing plants before leaf harvest. Auxins also promoted both bud and root formation, the optimum concentration for rooting always being one to two orders of magnitude higher than the optimum for budding. Cytokinins had only a small stimulatory effect on bud formation. At higher concentrations it was inhibitory and even counteracted the stimulatory effect of auxin on bud formation. As usual, root formation was inhibited by cytokinin. GA₃ inhibited both bud and root formation but the inhibition was reversible by auxin. In presence of optimum auxin levels abscisic acid enhanced bud formation. It had little effect on root formation except for an inhibition at high concentrations. The effects of exogenous auxin and cytokinin suggest that Streptocarpus leaves have a high and non-limiting level of endogenous cytokinin with auxin as the limiting factor for both root and bud formation. This would also explain the exceptionally high regeneration ability of this plant.     

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)