Effect of Inversion on Growth and Movement of Indole-3-acetic Acid in Coleoptiles

The effect of a 180° displacement from the normal vertical orientation on longitudinal growth and on the acropetal and basipetal movement of ¹⁴C-IAA was investigated in Avena sativa L. and Zea mays L. coleoptile sections. Inversion inhibits growth in intact sections (apex not removed) and in decapitated sections supplied apically with donor blocks containing auxin. Under aerobic conditions, inversion inhibits basipetal auxin movement and promotes acropetal auxin movement, whereas under anaerobic conditions, it does not influence the movement of auxin in either direction. Inversion retards the basipetal movement of the peak of a 30-minute pulse of auxin in corn.

The inversion-induced inhibition of basipetal auxin movement is not explained by an effect of gravity on production, uptake, destruction, exit from sections, retention in tissue, or purely physical movement of auxin. It is concluded that inversion (a) inhibits basipetal transport, the component of auxin movement that is metabolically dependent, and as a result (b) inhibits growth and (c) promotes acropetal auxin movement.

     

Movement and Endogenous Levels of Abscisic Acid during Water-Stress-induced Abscission in Cotton Seedlings

In an effort to investigate possible involvement of abscisic acid (ABA) in foliar abscission processes, its movement and endogenous levels were examined in cotyledons taken from cotton seedlings (Gossypium hirsutum L.) subjected to varying degrees of water deficit, a condition which initiates leaf abscission. Using a pulse-labeling technique to avoid complications of uptake and exit from the tissue, ABA-1-¹⁴C movement was observed in both basipetal and acropetal directions in cotyledonary petioles taken from well watered, stressed, and rewatered plants. The label distribution patterns obtained after 1 and 3 hours of transport under all situations of water supply were diffusive in nature and did not change when tested under anaerobic conditions. The transport capacity of the petioles ranged from 3.6 to 14.4% ABA-1-¹⁴C transported per hour at estimated velocities of 0 to 2 millimeters per hour. Comparison of basipetal and acropetal movement indicated a lack of polarity under all conditions tested. These low transport capacities and slow velocities of movement, when compared to the active transport systems associated with auxin movement, as well as the lack of anaerobic effects and polarity, suggest that ABA movement in cotton cotyledonary petiole sections is facilitated by passive diffusion. Increases in free and bound ABA in the lamina with increased water stress did not correlate with patterns of cotyledonary abscission. Thus, no evidence was found to suggest that ABA is directly involved in stress-induced abscission processes.     

Morphogenesis in Selaginella: II. Auxin Transport in the Root (Rhizophore)

The rhizophore of Selaginella willdenovii Baker develops from the ventral angle meristem. The morphological nature of this organ has been in dispute. The purpose of this investigation was to obtain physiological evidence to support the contention that the rhizophore is a root and not a shoot. This was accomplished by studying the movement of ³H-indoleacetic acid and ¹⁴C-indoleacetic acid in Selaginella rhizophores. In 6-millimeter tissue segments, twice as much radioactivity accumulated in acropetal receivers as in basipetal. During 1 hour of transport in intact roots auxin traveled twice as far in the acropetal direction as basipetal. A significant amount of radioactivity transported in the tissue was found to co-chromatograph with cold indoleacetic acid. Decarboxylation accounted for 10% loss of activity from donors. The data provide sufficient physiological evidence that this organ is morphogenetically a root.     

Polar transport of kinetin in tissues of radish

Polar transport of kinetin-8-¹⁴C occurred in segments of petioles, hypocotyls, and roots of radish (Raphanus sativus L.). The polarity was basipetal in petioles and hypocotyls and acropetal in roots. In segments excised from seedlings with fully expanded cotyledons, indole-3-acetic acid was required for polarity to develop. In hypocotyl segments isolated at this stage, basipetal and acropetal movements were equal during the first 12 hours of auxin treatment after which time acropetal movement declined. Pretreatment with auxin eliminated this delay in the appearance of polarity. In hypocotyl segments excised from seedlings with expanding cotyledons, exogenous auxin was unnecessary for polarity. Potassium cyanide abolished polarity at both stages of growth by allowing increased acropetal movement. The rate of accumulation of kinetin in receiver blocks was greater than the in vivo increase in cytokinin content of developing radish roots.     

Basipetal and Acropetal Auxin Transport in Relation with Temperature

In stem sections of lentil seedlings, there is a typical polar movement of IAA labelled with ¹⁴C. The degree of polarity, expressed as the ratio of basipetal to acropetal transport, was (25°C) 7.6. A decrease (from 25° to 15°C) and an increase (from 25° to 30°C) of temperature cause a reduction of the IAA uptake by the sections and a decrease of both the basipetal and the acropetal translocation of IAA. Results suggest that the basipetal as well as the acropetal movement of auxin, are dependent of a metabolical component which is discussed.     

Maintenance of polarity of auxin movement by basipetal transport

The polar, basipetal transport of indoleacetic acid helps to maintain polarity of auxin movement in coleoptiles of Avena sativa L. by opposing acropetal diffusion. This conclusion is supported by 3 different kinds of experiments. In all 3 experiments, sections took up ¹⁴C carboxyl-labeled indole-3-acetic acid anaerobically, and the distribution of auxin within all sections was similar at the end of uptake.

[List: see text]

     

Auxin transport: a new synthetic inhibitor

The new synthetic plant growth regulator DPX1840 (3,3a-dihydro-2-(p-methoxyphenyl)-8H-pyrazolo [5,1-a] isoindol-8-one) was examined for its effects on auxin transport. At a concentration of 0.5 mm in the receiver agar cylinders DPX1840 significantly inhibited the basipetal transport of naphthaleneacetic acid-1-¹⁴C in stem sections of Vigna sinensis Endl., Pisum sativum L., Phaseolus vulgaris L., Glycine max L., Helianthus annuus L., Gossypium hirsutum L., and Zea mays L. without significantly reducing total auxin uptake or recovery. The time sequence of the effect varied with the plant species. A similar inhibition of the basipetal movement of indoleacetic acid-1-¹⁴C was observed in intact seedlings of Phaseolus vulgaris L. In contrast to basipetal auxin transport DPX1840 had no significant effect on the acropetal movement of indoleacetic acid-1-¹⁴C in stem sections of Gossypium hirsutum L. Qualitatively the effect of DPX1840 on basipetal auxin transport was similar to that of other known auxin transport inhibitors. Quantitative differences, however, suggested the following order of activity: Naptalam>morphactin[unk]DPX1840>2,3,5-triiodobenzoic acid.     

Movement of Indoleacetic Acid in Coleoptiles of Avena sativa L. II. Suspension of Polarity by Total Inhibition of the Basipetal Transport

Acropetal and basipetal movement of indole-3-acetic acid through coleoptiles of Avena sativa L. was studied. Sections 10-mm long were supplied with either apical or basal sources containing C(14) carboxyl-labeled indoleacetic acid (10(-5)m). Anaerobic conditions inhibit metabolically dependent movement (transport) thus reducing basipetal but not acropetal movement. Total inhibition of basipetal transport abolishes the polarity of auxin uptake and movement. The nonpolar movement that remains in anaerobic sections is free diffusion with an average diffusion coefficient of approximately 1 x 10(-4) mm(2) per second. During an 8-hour diffusion, at least the first millimeter of the section comes to equilibrium at approximately the same concentration as the donor.Acropetal movement is probably by diffusion and is accompanied by an aerobic immobilization of indoleacetic acid that increases more than proportionally to concentration. Anaerobic conditions totally prevent this immobilization and reduce acropetal uptake but not the amount of indoleacetic acid moving into the upper parts of the section; there is, therefore, no evidence for acropetal transport.Polarity of auxin movement in aerobic coleoptile sections is achieved by strict basipetal transport of auxin. The basipetal transport may intensify the polarity by recycling auxin that is moving acropetally.     

Polar Movement of Indole-3-acetic Acid-C in Roots of Lens and Phaseolus

A critical review of the few papers on IAA-¹⁴C movement in roots revealed apparent contradictions, as well as flaws in experimental design that would be apt to cause artifacts. The movement of ¹⁴C from IAA-¹⁴C was studied in sections of Lens and Phaseolus roots, using a system 20 or more times as sensitive as any previously used. To make sure that our results with roots could be compared validly with published work on petioles and stems, we used the same techniques as we had earlier used for shoot structures. The results with Lens were similar in many ways to those for shoots: net movement into receiver blocks was very strongly polar, followed a linear course for several hours, and showed a velocity of the same order of magnitude as in shoots (and, in fact, very close in absolute value to that found in Coleus stem cylinders). Also, as with shoots, all the radioactivity in receiver blocks ran to the R_F of IAA. The time-course of loss of counts from donor blocks was similar to that found in shoots. The 2 most striking differences from shoots were 1) the very low percentage of added ¹⁴C that was moved into the receivers (about one-tenth of the values for bean petioles), and 2) the fact that the polar movement was acropetal in roots, rather than basipetal as in shoots. Results with Phaseolus roots were similar to those for Lens, although an additional complication with Phaseolus roots was the indication of a transitory stage of weak basipetal polarity in the first few hours after excising the section. This stage was followed in a few hours by a stronger acropetal polarity.     

Does the Induction of Flowering by Photoperiod Change the Polarity or Other Characteristics of Indole-3-acetic Acid Transport in Petioles for the Short Day Plant,Xanthium?

To test the hypothesis that photoinduction acts by changing the ability of the plant to transport hormones, rather than by changing the ability of organs to synthesize them, the transport of carboxy-labeled indole-3-acetic acid was measured in the short day plant Xanthium pensylvanicum. Plants grown under noninductive conditions were matched for developmental stage, then assigned by a mathematically random method to either short day or noninductive conditions of “short day + light break.” After the plants had been subjected to one to seven cycles, the movement of auxin was followed through sections cut from the middle of petioles of various ages. Photoinduction, even with as many as seven cycles, had no effect on auxin movement in either the basipetal or acropetal direction. Auxin movement in vegetative Xanthium was similar to that in Coleus and Phaseolus: strongly polar in a basipetal direction through younger petioles, but with polarity declining with increasing petiole age and concomitant decreasing elongation.     

Transport of indoleacetic acid in intact roots of Phaseolus coccineus

Summary Indoleacetic acid (IAA)-5-³H (2×10^-9) was applied to intact roots of Phaseolus coccineus seedlings at the apex or 2 cm above the apex, and the movement of IAA-³H and its metabolites traced by sectioning and chromatography. Basipetal movement of label occurred for 2 cm or less, declining exponentially, and the amount increased with time. Acropetal transport from above the apex showed quantitatively less movement of radioactivity. After a 6h treatment period a decline of label occurred in the first 0.5cm, below which there was a long distance movement of small amounts of label, mainly in IAA, towards the apex where the label concentrated by a factor of approximately 2. Short-distance basipetal movement consisted of about equal amounts of IAA and metabolites, and only metabolites were found in areas more basipetal than 2cm. Label from solutions of sucrose-¹⁴C and ³H₂O followed the same general pattern of movement as label from IAA-³H, except that acropetal movement of water showed a steady decrease in the amount of label as the distance from the area of application increased. The short distance basipetal transport of label with the breakdown of IAA-³H indicates that the extent of basipetal movement was limited by catabolic processes. The acropetal pattern of IAA-³H movement with the concentration of the transported material close to the apex, is possibly the result of transport in the phloem.     

Effects of Cations on Hormone Transport in Primary Roots of Zea mays

We examined the influence of aluminum and calcium (and certain other cations) on hormone transport in corn roots. When aluminum was applied unilaterally to the caps of 15 mm apical root sections the roots curved strongly away from the aluminum. When aluminum was applied unilaterally to the cap and ³H-indole-3-acetic acid was applied to the basal cut surface twice as much radioactivity (assumed to be IAA) accumulated on the concave side of the curved root as on the convex side. Auxin transport in the apical region of intact roots was preferentially basipetal, with a polarity (basipetal transport divided by acropetal transport) of 6.3. In decapped 5 mm apical root segments, auxin transport was acropetally polar (polarity = 0.63). Application of aluminum to the root cap strongly promoted acropetal transport of auxin reducing polarity from 6.3 to 2.1. Application of calcium to the root cap enhanced basipetal movement of auxin, increasing polarity from 6.3 to 7.6. Application of the calcium chelator, ethylene-glycol-bis-(β-aminoethylether)-N,N,N′, N′-tetraacetic acid, greatly decreased basipetal auxin movement, reducing polarity from 6.3 to 3.7. Transport of label after application of tritiated abscisic acid showed no polarity and was not affected by calcium or aluminum. The results indicate that the root cap is particularly important in maintaining basipetal polarity of auxin transport in primary roots of corn. The induction of root curvature by unilateral application of aluminum or calcium to root caps is likely to result from localized effects of these ions on auxin transport. The findings are discussed relative to the possible role of calcium redistribution in the gravitropic curvature of roots and the possibility of calmodulin involvement in the action of calcium and aluminum on auxin transport.     

Maintenance of polar auxin transport in Zea coleoptiles by anaerobic metabolism

Summary The basipetal movement of IAA in 5-mm Zea coleoptile segments is drastically reduced under anaerobic conditions, but it remains greater than acropetal movement which is closely similar in the presence and absence of oxygen. The polarity of IAA movement has thus been confirmed in Zea coleoptile segments which have been deprived of oxygen. This net polar flux is dependent upon anaerobic metabolism since it is abolished in the presence of the metabolic inhibitiors sodium fluoride and iodoacetic acid.Acropetal movement of IAA is unaffected by the presence of sodium fluoride in air or anaerobic conditions. Uptake of IAA from a basal donor is not affected by sodium fluoride in air, but under anaerobic conditions the inhibitor decreased uptake by approximately 13%.Under anaerobic conditions both inhibitors reduce basipetal movement of IAA to the level of acropetal movement, and both decrease the total uptake of IAA from an apical donor by up to 30–45%. Under aerobic conditions sodium fluoride has no marked effect upon either the uptake of IAA from an apical donor or the basipetal movement of IAA by the segments. On the other hand, iodoacetic acid greatly decreased the uptake of IAA by the segments in air, but the same fraction of the total IAA taken up was recovered in the receiving block in the presence and absence of the inhibitor.This research was supported by Grant Number 83/6 to Professor M. B. Wilkins from the U. K. Agricultural Research Council.     

Auxin Transport in Roots: V. EFFECTS OF TEMPERATURE ON THE MOVEMENT OF IAA IN ZEA ROOTS

The effects of temperature on the polar movement of IAA through6-mm and 12-mm segments of Zea mays roots have been investigatedover the range from 1 to 50°C. At all temperatures an acropetal polar movement of IAA predominated,although at low temperatures and at 50°C the 6-mm segmentsshowed a transient basipetal polarity, before the persistentacropetal polarity developed. At 1°C the differences betweenacropetal and basipetal movement of IAA were less distinct thanat the other temperatures. There is, however, a marked metabolically-dependentacropetal movement of IAA through the tissues at 1°C, becausewhen the segments were deprived of oxygen the acropetal movementwas severely reduced while the basipetal movement was reducedto a smaller extent. At 1°C and at 5°C there was alwaysa persistent basipetal polarity of IAA movement through 6-mmand 12-mm segments under anaerobic conditions. The velocity of acropetal movement (mm h^–1) was the samethrough the 6-mm and the 12-mm segments and was markedly affectedby temperature. It increased from 1°C to a maximum valueof 8 mm h^–1 at 31°C and then decreased again at 40and 50°C. The velocity of basipetal movement could be assessedonly at 1 and 5°C at which temperatures it was greater thanthe velocity of acropetal movement, and virtually independentof segment length. The acropetal flux of IAA (cpm h^–1) was much less through12-mm segments than through 6-mm segments. For both lengthsof segment, however, the flux showed a complex relationshipwith ambient temperature, increasing from 1°C to a maximumat 10–15°C, declining to a minimum value at 31°Cand then rising again at 40 and 50°C. The basipetal fluxof IAA could be astimated only at 1 and 5°C at which itwas very much smaller than the acropetal flux. The amount of IAA in the receiver blocks increased linearlywith time at the lower temperatures. At temperatures withinthe range 15°C to about 31°C, however, the amount ofIAA in the receiver blocks began to decline if the transportperiods exceeded a certain length. The time at which this declinein the IAA in the receiver block began was related to the ambienttemperature. Chromatographic analysis indicated one radioactive substancein receiver blocks at the apical end of segments supplied withIAA-1-¹⁴C at the basal end after transport periods of 6 h at25°C, and 72 h at 5°C. The Rf of this substance wasclosely similar to that of the radioactive IAA supplied in thedonor blocks.     

Evidence for Three Different Systems of Movement of Indoleacetic Acid in Intact Roots of Phaseolus coccineus

Indoleacetic acid (IAA)-5-³H (2 × 10⁻⁹M) was applied to intact roots of Phaseolus coccineus seedlings, at the apex or 2 cm above the apex, at various pHs and in the presence of Cu²⁺ and NaCl. The transport of label in the roots was then examined after 6 h by cutting the roots into 1 mm sections above and below the zone of treatment. Basipetal movement from 2 cm above the apex was unafected by pH, Cu²⁺ or NaCl. Acropetal movement from the same area decreased with increasing pH from 5.4 to 8.0, probably due to an effect of pH on the entry of IAA into the cells. pH had no effect on sucrose transport. Cu²⁺ also inhibited acropetal movement but NaCl had no effect. Basipetal movement of label from the apex was reduced by Cu²⁺ and increasing pH, but not as much as with acropetal movement, and increased by the presence of NaCl. These facts are interpreted as showing 3 different systems of IAA movement in intact roots: basipetal from 2 cm up the root in some extracellular physical system; acropetal from 2 cm up the root, and basipetal from the apex, in a metabolically dependent intracellular system, but in different tissues of the root. It is proposed that endogenous IAA not only moves into the root from the stem but is also synthesized in the root apex, and moves basipetally for a short distance to the root growing zone in a separate system from the IAA descending from the stem.     

Basipetally polarised transport of [3H]gibberellin A1 and [14C]gibberellin A3, and acropetal polarity of [14C]indole-3-acetic acid transport,in stelar tissues of Phaseolus coccineus roots

Summary Movement of both [³H]GA₁ and [¹⁴C]GA₃ through root segments from P. coccineus seedlings was basipetally polarised. The basipetal/acropetal ratio of radioactivity from [³H]GA₁ in agar receiver blocks was 9.2 for apical, elongating segments, and 4.0 for more basal, non-elongating segments. Polarity of gibberellin transport was restricted to the stele, and absent from cortical tissues. Transport of [¹⁴C]IAA through root segments to agar receivers was preferentially acropetal, particularly so in the stele. Despite the existence of basipetal polarity of gibberellin transport in the root, [³H]GA₁ injected into cotyledons moved into and acropetally along the seedling root.     

Transport of 14C-lableled indoleacetic acid in Vicia root segments

IAA transport in Vicia root segments was investigated for comparisonwith that in intact roots. Lanolin paste (1-mm-wide ring) oragar blocks (3?3?1.5mm), both containing IAA-2-¹⁴C were appliedto the surface or a cut end of the root segments, respectively;transported ¹⁴C was collected in receiver agar blocks placedon the cut end of the segments. When lanolin paste was appliedto 5-mm segments, basipetal transport of IAA predominated overacropetal transport. When agar blocks were applied to 1- and2-mm segments, the same was true; in longer segments (3 and5 mm long), however, basipetal movement occurred predominantlyat first but was surpassed by acropetal movement after 2–3hr. Among the segments tested (regions 2–4, 4–6and 8–10 mm from the tip), the most apical one showedthe distinctest predominancy of basipetal movement. The velocitiesof the acropetal and basipetal movement of the ¹⁴C were estimatedat 3–3.8 and 8–12 mm/hr, respectively. Autoradiographicstudy and the experiment in which wire was inserted longitudinallythrough the central part of the segments showed that basipetalmovement occurred mainly through the outer part of the rootsand acropetal movement mainly through the central cylinder.The present results were compatible with those obtained previouslywith intact roots. Some properties of polar movement, such asits specificity, inhibition by TIBA, and dependency on terneprature are described. (Received March 22, 1978; )     

Transport of Kinetin-814C in Petioles

Several differences in the translocation pattern of radioactive kinetin in plant petioles were determined. Radioactivity from kinetin-8-¹⁴C (Kn*) moved from donor agar blocks through petioles of bean and cocklebur but not of cotton. There was no difference in basipetal or acropetal movement of radioactivity from Kn* in cocklebnr petioles, but there was in bean petioles. In bean petioles this movement was preferentially basipetal, but it was influenced by the age of the petiole and by the presence of added indoleactic acid. The combination treatment accelerated the basipetal movement of radioactivity from Kn* in young bean petioles and not in old ones. All data is based on radioactivity translocated into receiver agar blocks which were assayed individually in a liquid scintillation spectrometer. The results show that plant species, direction of transport, age of tissue, and presence of IAA can all influence the translocation of Kn* in petioles.     

Light stimulation of cold acclimation: production of a translocatable promoter

The light stimulation of cold acclimation of Hedera helix L. var. Thorndale has been shown to result in the production of translocatable promoters of hardiness. Movement of the promoters from an illuminated donor portion to a darkened receptor portion was demonstrated. The majority of transport was acropetal through the phloem and to a much lesser degree basipetal through the xylem. In the early stages of hardening, transport was strictly acropetal. It is suggested that acropetal transport is under the influence of a mobilizing center located in the apex of the plant. Mobilization of the promoters of hardiness was induced by applications of ⁶N-benzyladenine. Attempts to characterize the light-generated promoters through fixation of ¹⁴CO₂ and subsequent translocation of ¹⁴C-labeled compounds from the illuminated donor to the darkened receptor indicated that the translocatable promoting material was either some component of the Dowex 1 fraction or sucrose. Furthermore, the hardiness of leaves was significantly increased by sucrose solutions but not by equi-molar solutions of glucose, galactose or mannitol.     

Influence of 2,3,5-Triiodobenzoic Acid and 1-N-Naphthylphthalamic Acid on Indoleacetic Acid Transport in Carnation Cuttings: Relationship with Rooting

³H-IAA transport in excised sections of carnation cuttings was studied by using two receiver systems for recovery of transported radioactivity: agar blocks (A) and wells containing a buffer solution (B). When receivers were periodically renewed, transport continued for up to 8 h and ceased before 24 h. If receivers were not renewed, IAA transport decreased drastically due to immobilization in the base of the sections. TIBA was as effective as NPA in inhibiting the basipetal transport irrespective of the application site (the basal or the apical side of sections). The polarity of IAA transport was determined by measuring the polar ratio (basipetal/acropetal) and the inhibition caused by TIBA or NPA. The polar ratio varied with receiver, whereas the inhibition by TIBA or NPA was similar. Distribution of immobilized radioactivity along the sections after a transport period of 24 h showed that the application of TIBA to the apical side or NPA to the basal side of sections, increased the radioactivity in zones further from the application site, which agrees with a basipetal and acropetal movement of TIBA and NPA, respectively. The existence of a slow acropetal movement of the inhibitor was confirmed by using ³H-NPA. From the results obtained, a methodological approach is proposed to measure the variations in polar auxin transport. This method was used to investigate whether the variations in rooting observed during the cold storage of cuttings might be related to changes in polar auxin transport. As the storage period increased, a decrease in intensity and polarity of auxin transport occurred, which was accompanied by a delay in the formation and growth of adventitious roots, confirming the involvement of polar auxin transport in supplying the auxin for rooting. Received April 19, 1999; accepted December 2, 1999