Inhibitory effects of 2,3,5-triiodobenzoic Acid on ion absorption, respiration, and carbon metabolism in excised barley roots

The ability of 2,3,5-triiodobenzoic acid (TIBA) to alter ion absorption, respiration, carbon metabolism, and the permeability of the cell membranes of excised barley roots has been examined. Roots pretreated in either H₂O, KCl, or TIBA followed by treatment in KCl, TIBA, or KCl and TIBA demonstrated that inhibition of ion uptake due to TIBA was reversible. These studies also suggest that ions already accumulated within the vacuole remain sequestered after the addition of TIBA, whereas cytoplasmic ions leak out into the external medium. A 20-minute lag period was present prior to the onset of inhibition of O₂ consumption by TIBA. A b-type cytochrome from corn that is apparently associated with the plasmalemma and possibly involved in respiration or ion uptake, or both, was unaffected by TIBA. The addition of TIBA to treatment solutions resulted in the synthesis and accumulation of ethanol. Analysis of organic acids showed that only the malate concentration was affected by treatment with TIBA. A reduction of 26% was noted for malate in the presence of 2 micromolar TIBA. These combined results suggest that the inhibitory action of TIBA in barley roots involves an alteration of mitochondrial respiration and not a direct depolarization of the plasmalemma.     

Inhibition of respiration and ion uptake by 2,3,5-triiodobenzoic Acid in excised barley roots

The addition of 1 micromolar 2,3,5-triiodobenzoic acid (TIBA) to solutions containing KCl resulted in the inhibition of K and Cl uptake in excised barley roots. The effectiveness of TIBA as an inhibitor increased as the pH of the treatment solution decreased and approached the pK_a of TIBA. A lag period of approximately 20 minutes existed prior to the onset of TIBA induced inhibition of ion uptake. Respiratory activity was also inhibited by TIBA. The data suggest that in this material, TIBA functions by entering the cytoplasm and inhibiting metabolism. Comparisons made on the effect of added Ca, showed that at pH 5.7 and higher, Ca had no effect on ion uptake whereas at lower pH values the presence of Ca enhanced uptake by offsetting the deleterious effects of H⁺.     

Auxin-Promoted Transport of Metabolites in Stems of Phaseolus vulgaris L.: EFFECTS REMOTE FROM THE SITE OF HORMONE APPLICATION

Phloem transport in stems of Phaseolus vulgaris was found tobe sensitive to treatment with the auxin transport inhibitor,2,3,5-triidobenzoic acid (TIBA). The response was dependenton the concentration of TIBA applied. A concentration of TIBA(0?5% in lanolin) which did not interfere with normal phloemtransport proved inhibitory to both basipetal transport of IAAand the acropetal component of IAA-promoted metabolite transport.In contrast, both acropetal IAA transport and basipetal IAA-promotedmetabolite transport were unaffected by TIBA treatment. Theinhibitory effect of TIBA on acropetal IAA-promoted transportwas overcome by providing IAA below the point of TIBA application.Both acropetal and basipetal IAA-promoted transport in stemsegments were unaccompanied by any corresponding changes inthe accumulation of [¹⁴C]sucrose by the segments.     

Trijodbenzoesäure und die Stoffleitung bei höheren Pflanzen

Summary The effect of 2,3,5-triiodobenzoic acid (TIBA) on the translocation of various substances within etiolated pea plants was tested by applying the substances to different places on the decapitated plants and measuring the effect of the substances on the growth of lateral buds after placing a lanolin ring containing TIBA around the stem between the place of application of the substance and the buds. In control experiments the TIBA-ring was placed in such a way, that TIBA and the other substance reached the bud from opposite directions.TIBA blocked the basipetal translocation of indole-3-acetic acid, -4-chlorophenoxyisobutyric acid and -(1-naphthylmethylsulfid) propionic acid, it did not block the acropetal translocation of sucrose, potassium nitrate and indole-3-acetic acid. It did howevers block the acropetal translocation of native inhibitors (correlation inhibitors) extracted from pea plants. It is concluded that TIBA is a general blocker of the energy requiring translocation of many substances in plants. Moreover TIBA produces various different effects.Intensity of translocation of TIBA was equal in both directions, acropetal and basipetal. Application of TIBA to more distal points of the stem may cause greater effects because of a faster migration through younger tissues into the stem.Mit 2 Textabbildungen.     

Developmental changes in the secondary xylem ofAcer rubrum induced by various auxins and 2,3,5-tri-iodobenzoic acid

Summary TIBA has been applied laterally to actively growing stems of uprightAcer rubrum seedlings. The frequency of initiation of tracheary elements is reduced and a complete ring of tension wood is developed in the stem locally below the TIBA application site. Rings of tension wood were never formed above the TIBA treatment site. In regard to anatomy, lignin distribution and peroxidase activity, the tension wood fibers formed as a result of TIBA treatment are identical to those which can be induced by bending.In the region of the stem above the site of TIBA application there is a particularly strong alteration in the development of tracheary elements.Application of IAA, NAA, or 2,4-D to the TIBA treatment site suppresses the capacity of TIBA to induce the development of tension wood and at the same time generally increases the frequency of initiation of tracheary elements.The effect of auxin alone on theAcer rubrum system has been studied. The secondary xylem formed during treatment with auxins (especially 2,4-D and NAA) at the stated concentrations is generally characterized by large groups of tracheary elements with a conspicuous angular outline in transverse section.The evidence suggests that auxins are involved in the regulatory systems which bring about the orderly development of the secondary xylem in arborescent angiosperms.This material was included in a doctoral thesis submitted by P. R.Morey to the graduate school of Yale University, New Haven.     

Nod factors and tri-iodobenzoic acid stimulate mycorrhizal colonization and affect carbohydrate partitioning in mycorrhizal roots of Lablab purpureus

Roots of Lablab purpureus (L.) Sweet were treated with tri -iodobenzoic acid (TIBA), kinetin or with nodulation factors (Nod factors) purified from Rhizobium sp. NGR234 and grown in the presence of a mycorrhizal inoculum ( Glomus mosseae (Nicol. & Gerd.) Gerdemann & Trappe. Colonization by the mycorrhizal fungus was increased from <30% to c . 65% of root length when roots were treated with these growth regulators. Moreover, treatment of mycorrhizal L. purpureus roots with Nod factors or TIBA strongly induced sporocarp formation of Glomus mosseae . In parallel, the pool size of the fungal disaccharide trehalose was significantly affected in roots treated with TIBA and Nod factors alone, and with TIBA combined with all effectors, and increased from 0·06 mg g⁻¹ d. wt in control roots to up to 1·7 mg g⁻¹ d. wt (TIBA+kinetin). Conversely, the sucrose pool decreased from 5% d. wt to less than a half in roots treated with Nod factors. Activities of trehalase were significantly enhanced in mycorrhizal roots by the treatment with Nod factors or TIBA. When Nod factors and TIBA were added in combination, these activities were strongly enhanced suggesting synergism between these growth regulators.     

Inhibition of IAA-induced ethylene production in etiolated mung bean hypocotyl segments by 2,3,5-triiodobenzoic acid and 2-(p-chlorophenoxy)-2-methyl propionic acid

The effect of two auxin antagonists, 2,3,5-triiodobenzoic acid (TIBA) and 2-( p -chlorophenoxy)-2-methyl propionic acid (CMPA) on IAA-induced ethylene production in etiolated mung bean hypocotyl ( Vigna radiata L. Rwilcz cv. Berken) segments was studied. Both TIBA and CMPA inhibited IAA-induced ethylene production and CO₂ production at concentrations from 0.001 m M to 0.1 m M and 0.01 m M to 1.0 m M , respectively. The optimum concentration for inhibition of ethylene production by TIBA was 0.05 m M and CMPA was 0.5 m M . At the optimum concentration of TIBA and CMPA, there was a significant decrease in IAA-induced ethylene production without a decrease in respiration rates below control levels. After 18 h, mung bean hypocotyl segments treated with 0.05 m M TIBA for 6 h or 0.5 m M CMPA for 8 h showed a maximum inhibition of IAA-induced ethylene production. Treatments longer than 8 h caused no further inhibition. The uptake of [¹⁴C]-naphthaleneacetic acid by mung bean segments was greatly reduced by the addition of either TIBA (0.05m M ) or CMPA (0.5 m M ) to the incubation media. The results of treatment sequences showed that TIBA needed to be applied prior to IAA in order to inhibit IAA-induced ethylene production, but CMPA caused the same inhibitory effect whether applied before or after IAA treatment. These findings provide evidence that TIBA inhibits auxin-induced ethylene production in etiolated mung bean hypocotyl segments by blocking auxin movement into the tissue whereas CMPA may work on both auxin transport and action.     

Effect of Gibberellic Acid, 2,3,5-Triiodobenzoic Acid and Indole Acetic Acid on Growth and Development of Impatiens balsamina during Different Photoperiods

This paper deals with the effect of 100 mg/1 each of GA₃ TIBA and IAA singly and in combination with each other on stem elongation, development of lateral branches and floral bud initiation in Impatiens balsamina plants exposed to 8-, 16- and 24-h photoperiods. GA₃ enhances stem elongation, the enhancing effect decreasing with IAA as well as with TIBA during 8-h but increasing during 16- and 24-h photoperiods. It decreases the number of lateral branches, the decrease being greatest during 16-, less during 8- and the least during 24-h photoperiods. The time taken for floral buds to initiate with and length of branches during 16-h photoperiods. During 8-h photoperiods, IAA delays the initiation of floral buds, while GA₃ hastens it when used together with TIBA or IAA or both. GA₃ increases the number of floral buds on the main axis but decreases it on lateral branches, while TIBA decreases the number on the main axis but increases it on lateral branches. IAA reduces the number of floral buds on the main axis only when used alone, but on both the main axis as well as on lateral branches when used together with GA₃ and TIBA. Floral buds were not produced on lateral branches when plants were treated with GA₃, TIBA and IAA all together. GA₃ and TIBA induced floral buds even under non-inductive photoperiods, the number of buds and reproductive nodes being less in TIBA- than in GA₃-treated plants during 24-h photoperiods. The time taken for floral buds to initiate with GA₃ and TIBA during noninductive photoperiods is much longer than that during 8-h inductive photoperiods with or without GA₃ or TIBA application. IAA completely inhibits the GA₃- and TIBA-caused induction during 24-h, but only delays it and reduces the number of reproductive nodes and floral buds during 16-h photoperiods.     

Morphogenese und Stoffwechsel höherer Pflanzen unter dem Einfluß einiger Herbizide und Growth Retardants

Summary Effects of TIBA, 2,4-D, Flurenol and CCC upon growth, root formation, membrane permeability, content of nucleic acids and stability of the chromatin were investigated. The four substances showed little or no effect on growth of isolated plant segments, but TIBA, 2,4-D and CCC caused 25–30% inhibition of growth of whole pea seedlings even at low concentrations. Root formation is inhibited by TIBA, Flurenol and 2,4-D, but not by CCC. At concentrations >10^-4mol/l all the substances reduced the permeability of the plasma lemma, at lower concentrations only CCC and Flurenol still reduced permeability of the plasma lemma. The ratio RNA/DNA was decreased by TIBA, 2,4-D and Flurenol but it was increased by CCC. The Tm-value of isolated pea-chromatin was lowered by treatment with CCC and elevated by treatment with TIBA, 2,4-D and Flurenol can decrease or increase the Tm of isolated chromatin depending on their concentration. The results have shown that even very low concentrations of herbicides and growth retardants are able to induce metabolic alterations with partly unknown consequences.     

Influence of 2,3,5-triiodobenzoic acid on the transport and metabolism of IAA in lupin hypocotyls

The influence of 2,3,5-triiodobenzoic acid (TIBA) on the transport and metabolism of indolyl-3-acetic acid (IAA) was studied in etiolated lupin (Lupinus albus L) hypocotyls. Double isotope-labeled IAA [(5-³H)-IAA plus (1-¹⁴C)-IAA] was applied to the cut surface of decapitated seedlings. This confirmed that the species mobilized was unaltered IAA and permitted us to measure the in vivo decarboxylation of applied IAA. A pretreatment with TIBA applied to the cut surface produced a partial or drastic inhibition in the basipetal IAA movement at 0.5 or 100 M, respectively. Since TIBA inhibits auxin polar transport by interfering with the efflux carrier, the above results suggest that 100 M TIBA is sufficient to saturate the binding sites in the transporting cells. Compared to the control plants, in vivo decarboxylation of IAA was enhanced in 0.5 M TIBA-treated plants, while no decarboxylation was detected after treatment with 100 M TIBA. The in vitro decarboxylation of (1-¹⁴C)-IAA catalyzed by purified peroxidase was moderately activated by 100 M and unaffected by 0.5 M TIBA. The paradoxical effect of TIBA in vivo vs in vitro assays suggests that the in vivo effect of TIBA on IAA oxidation might be the consequence of the action of TIBA on the auxin transport system. Thus, transport reduction by 0.5 M TIBA caused a temporary accumulation of IAA in that apical region of the hypocotyl which has the highest capacity to decarboxylate IAA. In the presence of 100 M TIBA, a concentration which presumably saturates the efflux carriers, most of the added IAA can be expected to be located in the transporting cells where, according to the present data, IAA decarboxylation cannot take place.     

A comparison between 3,5-diiodo-4-hydroxybenzoic acid and 2,3,5-triiodobenzoic acid. II. Effects on uptake and efflux of IAA in maize roots

An explanation is sought for the inhibition of maize root growth and gravireaction brought about by treatment with 3,5-diiodo-4-hydroxybenzoic acid (DIHB). The effects of DIHB and 2,3,5-triiodobenzoic acid (TIBA) on the uptake and efflux of [³H]-indol-3yl-acetic acid (IAA) were tested using segments prepared from the elongation zone (2 to 7 mm region) of maize (Zea mays L. cv. LG11) roots. The uptake of [³H]-IAA (21 nM) by root segments incubated in buffered solutions (pH 5.0) was measured over a 5-min time-course. No significant effect of DIHB at 100 μM was observed, whereas TIBA at 10 μM slightly stimulated the uptake of [³H]-IAA. This experiment was repeated with the addition of non-radioactive IAA (total IAA concentration 1.0 μM). Up to 3 min DIHB (100 μM) had no significant effect, but thereafter a slight stimulation of IAA net uptake was observed. Treatment with TIBA (10 μM) stimulated the accumulation of IAA in the segments. The effects of DIHB (10, 50, 100 μM) and TIBA (10 and 50 μM) on the efflux of [³H]-IAA from segments that had been pretreated in [³H]-IAA (22 nM) were then tested. Treatment with DIHB or TIBA at pH 5.0 inhibited IAA efflux; the inhibition by TIBA was more marked than that produced by DIHB. This experiment was repeated using DIHB (10, 50, 100 μM) buffered at pH 6.0, and an inhibition of IAA efflux was again observed. Both DIHB (10 μM) and TIBA (10 μM) inhibited the binding of [³H]-NPA to a 5000–48000 g membrane fraction prepared from whole maize roots. The effects of the two substances were similar: 40% inhibition of specific binding by DIHB and 41% inhibition by TIBA. This indicates that DIHB, like TIBA, binds to the N-1-naphthyl-phthalamic acid-sensitive carrier for IAA efflux. It is concluded that DIHB, like TIBA, inhibits IAA transport at the level of efflux. The similarity between DIHB and TIBA as regards chemical structure and their inhibitory effects on IAA efflux and NPA binding strongly suggest that they act on the same carrier for IAA efflux across the plasmalemma.     

1-N-naphthylphthalamic acid and 2,3,5-triiodobenzoic acid

Summary Auxin transport in corn coleoptile sections was inhibited by 2,3,5-triiodobenzoic acid (TIBA) as well as by 1-N-naphthylphthalamic acid (NPA); this inhibition was effected within 1 min of application.A particulate cell fraction-presumably plasma-membrane vesicles-specifically binds NPA and properties of these binding sites were studied using ³H-NPA and a pelletting technique. The saturation kinetics of the physiological NPA effect, i.e. the inhibition of auxin transport, is similar to that of the specific in-vitro NPA binding. Half saturation of the inhibitory effect was found with about 5×10^-7 M TIBA and with 10^-7 M NPA. Both substances also decreased the speed of movement of auxin pulses within coleoptile sections.NPA dissociates from its binding site when the particulate cell material is centrifuged through an NPA-free cushion. The NPA that is washed from its binding site can be used in another binding test without any apparent change and is chromatographically unaltered. Therefore, the NPA binding is probably reversible and non-covalent. Inhibition of auxin transport by TIBA or NPA could also be reversed when the coleoptile sections were washed in buffer.The movement of ¹³¹I-TIBA in corn coleoptiles appears to be polar in a basipetal direction. Higher concentrations of indoleacetic acid or TIBA inhibited this polar movement, suggesting that TIBA moves in the same channels as auxin. With ³H-NPA, however, no polar transport could be detected. Together with the in-vitro binding results, these data indicate that TIBA acts directly at the auxin receptor while NPA has a different receptor site.The effect of TIBA and NPA on elongation, with or without auxin, is neglegible in comparison to their effects on auxin transport.     

PIS1, a negative regulator of the action of auxin transport inhibitors in Arabidopsis thaliana

In order to clarify the mechanism underlying the polar auxin transport system, the pis1 mutant in Arabidopsis thaliana that is hypersensitive to N -1-naphthylphthalamic acid (NPA), an auxin transport inhibitor was isolated and characterized. Whereas the pis1 mutant is normally sensitive to phytohormones, auxins, cytokinin and ethylene precursor, this mutant is hypersensitive to NPA over the broad spectrum of its effects such as growth of seedlings, root elongation, root gravitropism, root phototropism and root curling. This result indicates that the pis1 mutant is specifically affected in the polar auxin transport system. This result also defines a genetic factor controlling both gravitropism and phototropism, and strongly indicates the involvement of auxin transport during both tropic responses. NPA, 2,3,5-triiodobenzoic acid (TIBA) and 9-hydroxyfluorene-9-carboxylic acid (HFCA) represent different classes of auxin transport inhibitors. The pis1 mutation conferred hypersensitivity to both NPA and TIBA but not to HFCA. These results show the genetic separation of the actions of NPA/TIBA and of HFCA. The PIS1 gene product might be specifically involved in the response pathway of NPA/TIBA, leading to interference with auxin-efflux carriers, and might act as a negative regulator of the action of NPA/TIBA.     

Tiba inhibition of <Emphasis Type="Italic">in vitro</Emphasis> organogenesis in excised tobacco leaf explants

Summary Triiodobenzoic acid (TIBA), an anti-auxin, was found to inhibit both shoot and root formation in cultured excised leaf explants of tobacco (Nicotiana tabacum L.). The shoot formation (SF) medium used required only exogenous cytokinin (N⁶-benzyladenine) and the root formation (RF) medium required both auxin (indole-3-butyric acid) and cytokinin (kinetin). By transferring the explants from SF or RF media to SF or RF media with TIBA (4.0×10⁻⁵ M), respectively or vice versa, at different times in culture, it was found that TIBA inhibition was at the time of meristemoid formation and after determination of organogenesis. This indicates that TIBA interfered with endogenous auxin involvement in organized cell division.     

A comparison between 3,5-diiodo-4-hydroxybenzoic acid and 2,3,5-triiodobenzoic acid. I. Effects on growth and gravireaction of maize roots

A comparison between the effects of DIHB and TIBA on growth and gravireaction of 15 mm primary maize ( Zea mays L. cv. LG 11) roots is presented. Intact roots were pretreated in the dark for 1 h with buffered solutions (pH 5.0 or 6.0) containing DIHB (10, 50, 100 μ M ). The plantlets were then maintained either vertically or horizontally in the dark or the light, and growth and gravireaction were recorded using a macrophotographic technique. Pretreatment with DIHB slightly inhibited growth and delayed gravireaction. These effects were most marked with DIHB at 100 μ M and were enhanced when DIHB was applied at pH 5.0. Similar effects were observed in roots pretreated with TIBA, but at a lower concentration (1 μ M ). The similarities between DIHB and TIBA as regards both chemical structure and the inhibition of gravireaction and growth, lead us to suggest that a major mode of action of DIHB, like TIBA, is the inhibition of indol-3yl-acetic acid transport.     

Hormonal regulation of the leaf blade movement of Drosera capensis

Several Drosera species show a bending of the leaf blade as a slow reaction to a prey. In Drosera capensis L. this bending is enhanced by a simultaneous application of IAA either to the prey or to the leaf tip, and IAA alone can induce a curvature of the leaf. This curvature is always to the upper side of the leaf independent of the side of IAA application. PCIB (1 m M ), and TIBA (0.1 m M ) inhibit the bending reversibly. The inhibition by ABA (1 m M ) is not reversible. A TIBA barrier between the prey and the tip of the leaf reduces the bending reaction, whereas application of TIBA to the basal part of the leaf has no effect. In the former case 35% of the leaves showed a strong bending just on the apical side of the TIBA barrier. It is concluded that the bending is a consequence of an internal auxin stream from the tip of the leaf to the bending point, induced by the prey.     

Developmental changes in the secondary xylem ofAcer rubrum induced by gibberellic acid,various auxins and 2,3,5-tri-iodobenzoic acid

Summary The effect of GA on the development of the secondary xylem ofAcer rubrum was studied. GA was applied to seedlings (1) separately, (2) simultaneously with TIBA, and (3) simultaneously with TIBA and an auxin. GA alone is without effect on the development of the secondary xylem. In seedlings treated with TIBA-GA or TIBA-GA-auxin, the differentiation of the xylem elements is in general similar to that of seedlings treated with TIBA or TIBA-auxin respectively. GA however, does stimulate cambial activity in a localized region of the stem if the endogenous rate of cambial division is low.The following abbreviations will be used TIBA (2,3,5-tri-iodobenzoic acid) - IAA (indole-3-acetic acid) - GA (gibberellic acid) - NAA (naphthaleneacetic acid) - 2,4-D (2,4-dichlorophenoxyacetic acid) This material was included in a doctoral thesis submitted by P. R.Morey to the graduate school of Yale University, New Haven.     

Auxin transport in intact pea seedlings (Pisum sativum L.): The inhibition of transport by 2,3,5-triiodobenzoic acid

Summary The application of 2,3,5-triiodobenzoic acid (TIBA, 10 mg·g^-1 in lanolin) to the stem of intact pea seedlings (Pisum sativum L.) inhibited the basipetal transport of ¹⁴C from indoleacetic acid-1-¹⁴C (IAA-1-¹⁴C) applied to the apical bud, but not the transport of ¹⁴C in the phloem following the application of IAA-1-¹⁴C or sucrose-¹⁴C to mature foliage leaves. It was concluded that fundamentally different mechanisms of auxin transport operate in these two pathways.When TIBA was applied at the same time as, or 3.0 h after, the application of IAA-1-¹⁴C to the apical bud, ¹⁴C accumulated in the TIBA-treated and higher internodes; when TIBA was applied 24.0 h before the IAA-1-¹⁴C, transport in the stem above the TIBA-treated internode was considerably reduced. TIBA treatments did not consistently influence the total recovery of ¹⁴C, or the conversion of free IAA to indoleaspartic acid (IAAsp). These results are discussed in relation to the possible mechanism by which TIBA inhibits auxin transport,.Attention is drawn to the need for more detailed studies of the role of the phloem in the transport of endogenous auxin in the intact plant.Abbreviations TIBA 2,3,5-triiodobenzoic acid - IAAsp indoleaspartic acid     

Interaction of Auxin-TIBA in Lycopersicon esculentum

[5-³H] indoleacetic acid (IAA) was applied to the apical budof young tomato plants (Lycopersicon esculentum Mill.) treatedor not with 2,3,5-triiodobenzoic acid (TIBA). Chromatographicanalysis showed that treatment with TIBA increased the quantityof breakdown products in the apical 1.5 mm segment of the stem.Autoradiographs of ultra-thin sections of this segment wereprepared after treatment with glutaraldehyde. The inhibitionof polar auxin transport by TIBA caused an increase in the densityof labelling of all the cellular types in the shoot apex. TheTIBA treatment provoked a modification of the structure of theshoot apex in which the greatest increases in density of labellingwere detected in the superficial tunical layer and in the pithmeristem. The increase in radioactivity of the superficial tunicallayer could be explained by the presence of polyphenols in thevacuoles. For the pith meristem, the TIBA treatment intensifiedthe high labelling previously observed at this level in thecontrol plants. This could indicate a role for auxin in cellularelongation. It could also point to the importance of the pithmeristem in the functioning of the shoot apex. Key words: [³H] IAA, Lycopersicon esculentum, TIBA     

Triiodobenzoic acid, an auxin polar transport inhibitor, suppresses somatic embryo formation and postembryonic shoot/root development in Eleutherococcus senticosus

The effect of auxin polar transport inhibitor on somatic embryo development and postembryonic growth in Siberian ginseng (Eleutherococcus senticosus) was examined. In the presence of 2,3,5-triiodobenzoic acid (TIBA), an auxin polar transport inhibitor, embryo formation from embryogenic cells was suppressed, while cell division was not affected. When globular embryos at different stages were transferred onto medium containing TIBA, development of axial and bilateral polarity was suppressed in a stagespecific manner. In abnormal embryos induced by TIBA, further development of shoot and root apical meristems and vascular differentiation was also suppressed. Thus, abnormal development of embryos induced by inhibition of auxin polar transport resulted in plantlets without shoots and roots.