Alternating Cytokinins in Multiplication Media Stimulates in Vitro Shoot Growth and Rooting of Eucalyptus globulus Labill.

Shoots of Eucalyptus globulus Labill. cultured on shoot multiplicationmedia containing, on alternate subcultures, 6-benzylaminopurine(BAP) or 6-furfurylaminopurine (kinetin), showed better growththan cultures in which either of the cytokinins was used continuously,or both were used in an equimolar mixture. When BAP was usedcontinuously in the medium (i.e. in every subculture), shootsmultiplied but remained stunted and leaves became red and abscised.Kinetin or 6-dimethylallyaminopurine (2iP) used continuouslyin the medium induced very low multiplication but the shootsdid not become red nor did the leaves abscise. Shoots takenfrom multiplication medium containing BAP and placed on rootingmedium with 10 µM indole butyric acid (IBA) produced fewroots and often died while on the rooting medium. In contrast,shoots from the multiplication medium containing kinetin producedmore roots and remained healthy during the passage on the rootingmedium.Copyright 1994, 1999 Academic Press Eucalyptus globulus, Tasmanian bluegum, cytokinins, micropropagation, in vitro rooting     

The Uptake of Cytokinins by Protoplasts and Root Sections of Brassica campestris

The effect of cytokinins was studied on the incorporation of ¹⁴C-labelled precursors into the nucleic acid fraction of protoplasts isolated from callus or roots of Brassica campestris. Protoplasts from callus and roots took up ¹⁴C-uridine from the incubation medium and incorporated this precursor into the ribonucleic acid fraction during the experimental period of 16 h. Low concentrations of kinetin (10^?8-5 × 10^?6M) did not stimulate the incorporation, and kinetin inhibited this process at higher concentrations (5 × 10^?5M). This result led to an investigation on the uptake of cytokinins by protoplasts of roots. In contrast to a rapid uptake of radio-actively labelled adenine and uridine. protoplasts from roots took up only small amounts of labelled kinetin. zeatin, zeatin riboside and zeatin nucleotides from the incubation medium. Root sections took up far more adenine and kinetin than protoplasts from roots. The ratio between the amount of kinetin taken up and applied was much higher for the sections than for protoplasts, indicating that intact root cells took up kinetin far more rapidly than protoplasts. It is suggested that the plasmalemma and cell wall play an essential role in the uptake of cytokinins or that the differences in the uptake rates are related to differences between the rates of metabolism of cytokinins in root sections and in protoplasts.     

Light cytokinin interactions in shoot formation in epicotyl cuttings of Troyer citrange cultured in vitro

Ilumination did not affect the pathway of shoot regeneration at the cut edges of epicotyl explants of Troyer citrange (Moreira-Dias et al. 2000, 2001), but signigficantly affected the number of developed shoots and the response to exogenous cytokinins. Shoot regeneration at the apical end occurred through a direct organogenic pathway without callus formation. For explants incubated in the light, this regeneration did not require cytokinin addendum, but the number of shoots formed was significantly increased by benzyl adenine, but not by zeatin or kinetin. Incubation in the dark almost suppressed shoot formation at the apical end. The addition of benzyl adenine or kinetin, but not of zeatin, restored shoot formation in the dark to the value obtained in the light. At the basal end of the explants shoot regeneration occurred through an indirect organogenic pathway after the formation of a primary callus. In explants incubated in the light, callus formation and shoot growth was supported by a low (0.5–1 mg l⁻¹) benzyl adenine concentration and by zeatin. Kinetin did not support callus growth. Shoot formation was higher in the presence of benzyl adenine (0.5–1 mg l⁻¹) than of zeatin, but was inhibited by a high (5 mg l⁻¹) benzyl adenine concentration. Incubation in the dark increased callus growth and shoot formation at the basal cut as compared to explants incubated in the light. The three cytokinins tested supported callus growth and shoot formation in the dark, zeatin being the most effective and kinetin the least. In terms of number of shoots developed, the optimum cytokinin addendum depended on the pathway of organogenesis and the conditions of incubation. The maximum number of shoots developed at the apical end was obtained when the incubation was performed in the light in the presence of benzyl adenine. At the basal end, the optimal conditions were incubation in the dark in the presence of zeatin. It was not always possible to define an optimal cytokinin concentration as the curve concentration/response varied from experiment to experiment, which seemed unrelated to the endogenous cytokinin concentration in the explants.     

Influence des racines sur le développement végétatif ou floral des bourgeons cotylédonaires chez le Scrofularia arguta: role possible des cytokinines

Influence of roots on the vegetative or floral development of cotyledonary buds of Scrofularia arguta Sol.: A possible cytokinin role. This study shows that the presence of “nonabsorbing roots” insures a vegetative development of cotyledonary buds cultured in vitro whereas buds growing without roots produce flowers early. In the same way, roots suppress floral expression of axillary meristems of the same cotyledonary buds and induce these buds to vegetative functioning. Various trophic modifications in the culture medium are ineffective on non-rooted buds as also are gibberellin As and adenine. On the contrary, several cytokinins (kinetin, benzyladenine and zeatin) exert the same influence as roots. These results suggest that roots regulate meristematic functioning through cytokinins.     

Age-related Changes in Stomatal Response to Cytokinins and Abscisic Acid

Kinetin and zeatin(100 mmol m^–3)reversald the ABA-mediated(100mmol ^m-2)closure of stomata of young maize leaves but did notaffect stomatal apertures of these leaves when applied alone.As leaves aged, kinetin or zeatin alone promoted increased stomatalapertures, while abscisic acid (ABA) applied alone had a reducedeffect on stomata. Even with older leaves, cytokinins reversadthe effect of ABA on stomata. Maize, stomata, abscisic acid, kineusc, zeatin, Zea mays     

A tracheid-differentiation factor from pine needles

Exogenous indol-3yl-acetic acid (IAA), alone and together with several cytokinins, was ineffective in promoting the complete differentiation into tracheids of cambial derivatives of Pinus contorta Dougl.; IAA alone promoted cambial cell division and primary-wall growth in cambial derivatives throughout the stem's length. In contrast, a single pair of needles on a stem cutting in light promoted neither cambial cell division nor primary-wall growth in cambial derivatives but did promote complete differentiation of cambial cells into tracheids; tracheids differentiated only near the junction of the foliated short shoot with the stem. Clear inter-and intracellular differences in the extent of tracheid differentiation occurred in response to a single needle pair and have suggested the hypothesis that a specific tracheid-differentiation factor regulates the differentiation of cells into proto-, meta-, or secondary-xylem tracheary elements through an interaction with IAA.Abbreviations IAA indol-3yl acetic acid - K kinetin - BAP 6-benzylaminopurine - Z zeatin - ZR zeatin riboside - FAA formalin: acetic acid: ethanol: water (10:5:50:35, by vol.)     

Organogenesis in leafy spurge (Euphorbia esula L.)

Summary All parts of leafy spurge seedlings can be regenerated when isolated and placed onto B5 medium. One-centimeter isolated hypocotyl segments were tested successfully for their usefulness as a bioassay system by comparing the response of auxins, herbicides, and cytokinins. Indole-3-acetic acid (IAA) was the most effective auxin to stimulate root formation. IAA was effective whether the hypocotyl segments remained on the same medium up to 60 days, or the segments were transferred to basal media after 2 or 5 days (pulse treatment). Pulse treatments with the other auxins resulted in stimulation of root formation; continuous or 5-day pulses of higher concentrations of indole-3-butyric acid,α-naphthaleneacetic acid and especially 2,4-dichlorophenoxyacetic acid and picloram formed excessive callus instead of roots. Picloram did not stimulate root formation, whether the treatment was continuous or pulse-treated. No roots formed with continuous picloram at 0.1 mg/liter or greater, but transfer to basal media did result in root and shoot formation at about 50% of the number formed on the controls. Lesser picloram concentrations had no effect. Shoots formed readily on untreated (control) segments, but continuous treatment with all three cytokinins, kinetin, zeatin, and zeatin riboside, increased the numbers of shoots about equally. Root formation was inhibited by the cytokinins at the higher concentrations (0.1 to 0.2 mg/liter). With the exception of a 5-day pulse of 0.04 mg/liter IAA, the auxins did not stimulate shoot formation, but generally inhibited shoot formation, even in pulse-treated cultures.     

Effect of cytokinins on <Emphasis Type="BoldItalic">in vitro</Emphasis> development of autotrophism and acclimatization of <Emphasis Type="Italic">Annona glabra</Emphasis> L.

The role of cytokinins in the differentiation of the photosynthetic apparatus in micropropagated plants and their effect on the plant’s ability to transition from a heterotrophic to an autotrophic condition during acclimatization was investigated. Annona glabra L. shoots were cultured on woody plant medium supplemented with sucrose and different cytokinins to evaluate leaf tissue for chloroplast development, chloroplast numbers, photosynthetic pigmentation, total photosynthetic potential, and soluble sugar content. Plants were transferred to the rooting medium in the presence or absence of sucrose and then acclimatized. Kinetin and benzyladenine (BAP) stimulated chloroplast differentiation. Inclusion of zeatin in the medium induced the formation of greater numbers of chloroplasts in the leaves, while plants cultivated in the presence of only kinetin and BAP demonstrated greater chlorophyll a and carotenoid content. The use of kinetin and BAP during in vitro culture promoted accumulation of dry matter during the acclimatization phase, especially in plants rooted under autotrophic conditions (without sucrose). Kinetin and BAP promoted development of more leaf area and greater plant survival rates in plant acclimatization on both autotrophic and heterotrophic media. The inhibitory effects of thidiazuron on the differentiation of chloroplasts, accumulation of chlorophyll a, and photosynthetic potential were examined.     

Patterns of morphogenesis from cotyledon explants of pigeonpea

Summary Cotyledons excised from seedlings of Cajanus cajan (pigeonpea) were grown on media containing cytokinins (6-benzyladenine, zeatin, and zeatin riboside) and an allied compound, thidiazuron. With the exception of zeatin riboside, initial response in terms of induction of organized structures was very high. However, subsequent regeneration of shoots from cotyledon explants was very poor. Anatomical studies on the regenerating explants were undertaken to study the pattern of morphogenesis. Cytokinins and thidiazuron induced divisions in the epidermal and sub-epidermal cell layers leading to the formation of primary protrusions on the surface. This was followed by the development of foci of high meristematic activity either on the surface or within the primary protrusions. These foci differentiated into embryo-like structures or shoot meristem-like structures. Mostly aberrant shoots, with poorly developed apical meristems, regenerated from these structures.     

Possible Regulatory Roles of Cytokinins : NADH Oxidation by Peroxidase and a Copper Interaction

Apparently free-base cytokinins can interact with cupric ions in a specific manner. Oxidation of NADH by a horseradish peroxidase system was strongly promoted by such cytokinins provided cupric ions were present. Oxidation was promoted by 5 micromolar kinetin, zeatin, 6-benzylaminopurine (BA), or 6-(Δ²-isopentenylamino)purine (2iP) but not by adenine, 6-methylaminopurine or 6,6-dimethylaminopurine. The 6-methylaminopurine promoted oxidation at 500 micromolar but adenine and 6,6-dimethylaminopurine did not. Activity of the free-base purines correlated well with their activity in cell-division assays. However, addition of methoxymethyl-, cyclohexyl-, or tetrahydropyranyl- at N-9 of BA or of ribosyl- at N-9 of BA, 2iP, kinetin, or zeatin eliminated activity in the peroxidase system. In a nonenzymic system containing cupric ions, all of the bases, including adenine, inhibited the Cu²⁺ -stimulated oxidation of ascorbic acid. As in the peroxidase system, the N-9 derivatives were inactive. The cytokinin promotion of NADH oxidation by peroxidase may result from an interaction of the hormones with copper, with peroxidase conferring a specificity similar to the cytokinin specificity observed in growth and development.     

Influence of Growth Regulators on Shoot Proliferation in Quercus suber L.

Procedures have been developed to standardize the multiplicationstage during mature cork-oak (Quercus suber L.) micropropagation.Axillary and terminal buds were established on Gresshoff andDoy basal medium containing 1 mg I^–1 of 6-benzylaminopurine(BAP). Initiation of cultures was possible all over the year.The effects of BAP, Z, IBA, 1AA and NAA and various nutrientformulae on shoot growth and proliferation was investigated.BAP was more suitable than zeatin. Shoot proliferation and elongationwere strongly improved by the combination BAP/IAA in the presenceof low salt media, like Gresshoff and Doy or Woody Plant medium.Both rates were significantly increased when a double-phaseculture system was used. Shoots have been multiplied for 1 yearat the rate of three to four-fold every 4 weeks without anydecline of vigour. Rooting was achieved by briefly dipping thebasal ends of in vitro regenerated shoots in an IBA concentratedsolution. The results here reported constitute a promising steptowards large scale in vitro propagation of a species in whichconventional vegetative propagation by cuttings is very difficult. Auxins, browning, cytokinins, cork-oak, forestry, multiplication, Quercus suber L., re-multiplication, re-invigoration, two-phase medium     

The Growth of Shoot Apices and Inflorescences of Carex flacca Schreb. in Aseptic Culture

The vegetative apex and young inflorescence of Carex flaccahave been grown in aseptic culture for several weeks on a definedmedium. Explants comprised the apical dome and the three youngestleaf primordia, and the young inflorescence complete with bracts,excised shortly after the initiation of the lateral spikes.Some growth occurred on the basal medium which contained inorganicsalts, sucrose, and vitamins, but growth was increased and thelife span extended by the addition of certain other compounds.The most effective additive was gibberellic acid, which, however,resulted in precocious differentiation of the meristematic tissuesand the differentiation of abnormal xylem. These deleteriouseffects of gibberellic acid were counteracted by the additionof kinetin. This substance did not otherwise affect vegetativeapices but it resulted in a further increase in growth and lifespan of inflorescences.     

Changes in hormonal balance and meristematic activity in primary root tips on the slowly rotating clinostat and their effect on the development of the rapeseed root system

The morphometry of the root system, the meristematic activity and the level of indole-3-acetic acid (IAA), abscisic acid (ABA) and zeatin in the primary root tips of rapeseed seedlings were analyzed as functions of time on a slowly rotating clinostat (1 rpm) or in the vertical controls (1 rpm). The fresh weight of the root system was 30% higher throughout the growth period (25 days) in clinorotated seedlings. Morphometric analysis showed that the increase in biomass on the clinostat was due to greater primary root growth, earlier initiation and greater elongation of the secondary roots, which could be observed even in 5-day-old seedlings. However, after 15 days, the growth of the primary root slowed on the clinostat, whereas secondary roots still grew faster in clinorotated plants than in the controls. At this time, the secondary roots began to be initiated closer to the root tip on the clinostat than in the control. Analysis of the meristematic activity and determination of the levels in IAA, ABA and zeatin in the primary root tips demonstrated that after 5 days on the clinostat, the increased length of the primary root could be the consequence of higher meristematic activity and coincided with an increase in both IAA and ABA concentrations. After 15 days on the clinostat, a marked increase in IAA, ABA and zeatin, which probably reached supraoptimal levels, seems to cause a progressive disturbance of the meristematic cells, inducing a decrease of primary root growth between 15 and 25 days. These modifications in the hormonal balance and the perturbation of the meristematic activity on the clinostat were followed by a loss of apical dominance, which was responsible for the early initiation of secondary roots, the greater elongation of the root system and the emergence of the lateral roots near the tip of the primary root.     

Changes in the Chlorophyll Contents of Leaves and in Levels of Cytokinins in Root Exudates during Ripening of Rice Cultivars Nipponbare and Akenohoshi

Changes in fluxes of cytokinins in exudates transported viathe xylem from roots of rice plants cvs. Nipponbare (a standardJapanese cultivar) and Akenohoshi (a slowly senescing cultivar)were measured by mass spectrometry with deuterium-labeled standards.The fluxes of zeatin (Z), trans-ribosylzeatin (trans-RZ), N⁶-isopentenyladenine(iP), and "conjugated Z" (Z in the hydrolysates of highly polarfractions) decreased from heading to the late ripening stagein both cultivars. At the late ripening stage, iP and Z couldno longer be detected, while the flux of N⁶-isopentenyladenosine(iPA) increased slightly. In Akenohoshi, conjugated Z was thepredominant cytokinin from heading to the middle of the ripeningstage. The flux of each of the cytokinins in Akenohoshi washigher than that in Nipponbare at every time point, with theexception of the flux of iPA just after heading. The total concentrationof cytokinins in the xylem exudate of Akenohoshi was higherthan that of Nipponbare after the middle of ripening stage.The chlorophyll content of the third leaves, which were senescingrapidly, was significantly correlated with the flux of totalcytokinins per plant or per unit leaf area. These results suggestthat the larger amounts of cytokinins, in particular conjugatedZ, transported from the roots to the shoots caused the slowsenescence of leaves in Akenohoshi during the ripening stage. (Received May 9, 1994; Accepted July 1, 1995)     

The effect of cytokinins on nitrate reductase activity

Cytokinins in addition to nitrate induce nitrate reductase activity (NRA) in some plants. Effects of cytokinins onNRA was investigated in stem pith parenchyma of kale, intact wheat and barley seedlings and isolated cucumber cotyledons. The most profound effect onNRA was found in barley and wheat seedlings.NRA in seedlings sprayed with 100 μM 6-benzylaminopurine (BAP) for three subsequent days was increased in leaves and decreased in roots. These changes were further enhanced in seedlings grown in nutrient solution lacking nitrate:NRA in wheat and barley leaves was increased by 57% and 202%, respectively, in plants supplied with nitrate theNRA increase was not significant: in wheat and barley leaves by 22% and 9%, respectively. Similar effect of BAP and kinetin was found in kale stem parenchyma and cucumber cotyledons. The cytokinin kinetin or BAP alone increasedNRA about twice in kale and three times in cucumber. Addition of nitrate to the medium enhanced the effect of kinetin in kale discs, but the two effects were not additive. Additive effect of nitrate and BAP onNRA was found in cucumber cotyledons in light. In general NRA was more affected by cytokinins in intact seedlings of wheat and barley as compared to explanted tissue of kale and cucumber, and lack of nitrogen made their effect more expressive.     

Adventitious Shoot Regeneration in Carnation (Dianthus caryophyllus) from Axillary Bud Explants

Adventitious shoots were regenerated from axillary bud explantsof 15 carnation cultivars. The use of leaf and stem explantswas not successful, largely due to explant senescence in thepresence of benzyladenine, kinetin and, to a lesser extent,zeatin. For axillary bud explants, a suitable optimum adventitiousregeneration medium contained Murashige and Skoog basal mediumsolidified with Gelrite and supplemented with 15 µm benzyladenineand 0.5 µM a-napthaleneacetic acid. Adventitious primordiaarose from the cut basal end of bud explants erupting as individualshoots after 2–3 weeks incubation. The axillary bud sizeand the time between subcultures of source material influencedthe production of adventitious shoots. Transfer of regeneratedshoots onto a medium solidified with agar minimized visiblesigns of vitrification. Regenerated shoots could be easily rooted,transferred to glasshouse conditions and grown to flowering. Vitrification, tissue culture, cut flowers, Dianthus caryophyllus L., carnation, cytokinins, explant     

The Inhibition of Growth by Gravitropic Stimulation in Darkness in Agravitropic Primary Roots of Zea and the Role of Calcium

The primary roots of the "Golden Cross Bantam 70" cultivar ofZea mays are agravitropic in darkness and their orthogravitropismis light-dependent. Analysis of the agravitropic roots providesimportant information about the mechanism of orthogravitropism.However, the underlying mechanism of the agravitropic responsein darkness is unknown. We found that the growth of intact primaryroots was inhibited by gravitropic stimulation (i.e., changingthe orientation of the roots from vertical to horizontal) indarkness, but that of detipped roots was not. The role of calciumin this gravistimulation-dependent inhibition of growth wasinvestigated using apical 5-mm segments of the primary roots.The gravistimulation-dependent inhibition of growth was preventedby applying 10 mM MES-KOH buffer at pH 6.0 to the root cap.By contrast, the application of 0.1–1 mM buffer at pH6.0 and 10 mM buffer at pH 4.5–5.0 allowed the gravistimulation-dependentinhibition of growth. Furthermore, when the buffer of 10 mM(pH 6.0) contained 1–5 mM CaCl₂, the gravistimulation-dependentinhibition of growth was apparent. By contrast, when weak (1mM) buffer at pH 6.0 or 10 mM buffer at pH 4.5 contained 5 mMEGTA, no gravistimulation-dependent inhibition of growth wasobserved. Thus, the gravistimulation-dependent inhibition ofgrowth in darkness seemed to be mediated by an increase in thelevel of free Ca²⁺ in the root tip. These results suggest thatfree Ca²⁺ in the apoplast of the root tip plays an importantrole in the agravitropic response in darkness as well as inorthogravitropism under light of the roots of this cultivarof Zea mays. (Received March 21, 1994; Accepted July 25, 1994)     

Biological activity of cytokinins derived from Ortho- and Meta-Hydroxybenzyladenine

To determine the structure-activity relationships of natural aromatic cytokinins, the activity of 6-benzylaminopurine (BAP) and its hydroxylated derivatives was compared in three bioassays based on stimulation of tobacco callus growth, retention of chlorophyll in excised wheat leaves, and dark induction of betacyanin synthesis in Amaranthus cotyledons. The aromatic cytokinins 6-(2-hydroxybenzylamino)purine (ortho-topolin) and 6-(3-hydroxybenzylamino)purine (meta-topolin), their 9-ribosides and 9-glucosides, were synthesized by the condensation of 6-chloropurine and its 9-glycosides with the appropriate hydroxybenzylamine. The activity of free bases, 9-ribosides and 9-glucosides was compared with that of BAP, trans-zeatin and their 9-glycosides. Hydroxylation of the benzyl ring in the meta position increased the activity of BAP and its riboside in tobacco callus and chlorophyll retention bioassays, whereas ortho-hydroxylation decreased the activity. In contrast, in the Amaranthus bioassay meta-hydroxylation of BAP substantially decreased its activity. Ribosylation at position 9 had no significant effect on the activity of zeatin, BAP and both topolins. The activity of 9-glucosides of all cytokinins tested was near zero. The biological activity of meta-topolin and its riboside is comparable to that of the most active isoprenoid cytokinin, zeatin, in tobacco callus growth and senescence bioassays. The results establish the existence of a family of endogenous aromatic cytokinins centered around the highly active compound, meta-topolin. We also report here an improved chlorophyll retention bioassay based on incubation of 2.5 cm long detached wheat leaf segments in microtiter plate wells containing 150 µl of cytokinin solution. The consumption of cytokinin to be tested is 0.1 µmol per assay only. The amount as small as 1.5 pmol of substance can be estimated using this biotest.     

Auxin Transport in Roots: VI. MOVEMENT OF IAA THROUGH DIFFERENT ZONES OF ZEA ROOTS

The movement of IAA through 6-mm segments excised 1 mm, 7 mm,and 13 mm behind the apex of the primary root of Zea mays seedlingshas been investigated at temperatures between 10 and 25°C. In all segments, and at all temperatures, the movement of IAAwas polarized acropetally, more IAA being found in apical receiverblocks than in basal ones after transport periods of up to 24h. The amounts of IAA which moved acropetally through a segmentdecreased as the segment was taken at an increasing distancebehind the root apex. Similarly, at least after transport periodsof 8 h, more IAA moved basipetally through the apical segmentthan through the basal ones. At 10°C the velocity of acropetal movement was similar inall three segments, but the acropetbut the acropetal flux wasgreatest in the apical segment and smallest in the most basalone. The same situation appears to exist at the other temperatures. The flux and velocity of the acropetal movement of IAA througha 6-mm segment taken 7 mm behind the apex of the root were similarto those previously reported for the acropetal movement througha 12-mm segment excised 1 mm behind the apex. The smaller amountsof IAA which move acropetally through longer root segments aretherefore attributable to a limitation of the flux in the mostbasal regions of the segment.     

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