Geotropic curvature of decapitated Avena coleoptiles after application of tips of maize roots,tips of Avena coleoptiles,indoleacetic acid,or abscisic acid

Isolated Avena coleoptiles were decapitated at different distances from the tip and then placed horizontally, after which the geotropic curvature was measured. No geotropic curvature could be detected during the first 3 h. Later, upward curvature occurred which was found to depend inversely on the length of the decapitated tips. When the tips of maize roots or Avena coleoptiles were placed on the cut surface of decapitated Avena coleoptiles, the coleoptiles showed a significantly stronger upward curvature as compared to controls which had been provided with agar blocks on the cut surface. The same upward curvature was found with decapitated coleoptiles provided with agar blocks containing 10^-6 or 10^-7 M indoleacetic acid (IAA). After application of abscisic acid (ABA) at concentrations of 10^-6 and 10^-8 M to the decapitated coleoptiles, the curvature observed was not different from that of the controls; at higher concentrations of ABA the curvature was found to be lower than that of the controls. It is concluded that root tips secrete a substance which may replace the effect of IAA in coleoptiles. The results are discussed in view of the validity of the Cholodny-Went hypothesis for the geotropic reaction of roots.Abbreviations ABA abscisic acid - IAA 3-indoleacetic acid     

Tryptophan-dependent indoleacetic-acid biosynthesis from indole,demonstrated by double-labelling experiments

Summary ³H-serine+¹⁴C-indole were administered to tips of sterily-grown pea seedlings and of non-sterile oat coleoptiles. The Try and IAA produced were extracted and purified by paper chromatography, and their ³H/¹⁴C ratios were determined. The ³H/¹⁴C ratio of IAA was lower than the ³H/¹⁴C ratio of Try. However, the same decrease of the IAA ³H/¹⁴C ratio was found when ³H, ¹⁴C-Try was supplied instead of ³H-serine+¹⁴C-indole. This result supports the view that Try is the native IAA precursor and that no significant bypass from indole to IAA exists in the plant material used.Abbreviations IAA indole-3-acetic acid - IPyA indole-3-pyruvic acid - Try tryptophan     

Interactions between Plants and Epiphytic Bacteria Regarding Their Auxin Metabolism

More “diffusible” auxin is received from nonsterile than from sterile corn coleoptile tips. An artificial reinfection of sterile coleoptiles with epiphytic, IAA-producing bacteria strains does, a superinfection of nonsterile coleoptiles does not increase the auxin amount. The difference between sterile and nonsterile tips persists if diffusion from the coleoptile surface is excluded by covering the surface with a paraffin layer. The greater the distance from the apex, the higher becomes the superiority of nonsterile tips. An artificial bacterial contamination of the contact face between tip and receiver agar block, or addition of glucose and tryptophan to the agar block, do not influence the received auxin amount. Consequently the additional, bacteria-produced auxin delivered by the nonsterile tip is not produced at the cut surface or in the agar but is present in the tissues of the coleoptile tip.     

TRANSPORT OF IAA AND ACC IN FLORAL ORGANS OF IPOMOEA NIL (CONVOLVULACEAE)

The involvement of the stamens as transporters of plant growth regulators in flowers was examined by measuring the movement of ¹⁴C-indole-3-acetic acid (IAA) and ^l4C-l-aminocyclopropane-1-carboxylic acid (ACC) through floral organs of Ipomoea nil. During the transport of ¹⁴C-IAA through isolated filament segments, the polar accumulation of ¹⁴C-IAA in receiver blocks increased with time during filament development, which correlated with polar efflux rates at older stages of filament development. An inhibitor of polar IAA transport, 2,3,5-triiodobenzoic acid, disrupted the polarity of auxin transport by reducing the movement of ¹⁴C- IAA from filaments into receiver blocks. Transport of both ¹⁴C-IAA and ^l4C-ACC through filaments into other floral organs also was monitored in isolated flower buds in the laboratory and intact buds in the greenhouse. In isolated and intact buds 21 hr before anthesis, substantially higher levels of isotope were recovered in corolla tissue when ¹⁴C-ACC was transported through the filaments than when ¹⁴C-IAA was transported from the filaments. In isolated buds, substantial levels of both isotopes accumulated in the pistil (69 hr and 45 hr before anthesis), but minimal amounts were observed in receptacle and calyx tissues (69 hr to 21 hr before anthesis). In intact buds, high levels of both isotopes were recovered in receptacle, calyx, and pistil tissues (69 hr to 21 hr before anthesis). The results from this study support the hypothesis that Ipomoea stamens are transporters for ACC and IAA to regulate ethylene production in the corolla and other floral tissues.     

The transport of radiolabeled indoleacetic acid and its conjugates in nodal stem segments of Phaseolus vulgaris L.

The transport of radiolabeled indoleacetic acid (IAA), and some of its conjugates, was investigated in nodal stem segments of Phaseolus vulgaris L. Donor agar blocks containing either [2-acetyl-¹⁴C]-IAA; [2-acetyl-¹⁴C]-indole-3-acetyl-L-aspartate (IAAsp); [2-acetyl-¹⁴C]-indole-3-acetyl-L-glycine (IAGly); or [2-acetyl-¹⁴C]-indole-3-acetyl-L-alanine (IAAla) were placed on either the apical or basal cut surface of stem segments each bearing an axillary bud at the midline. In some experiments, a receiver block was placed on the end opposite to the donor. After transport was terminated, the segments were divided into five equal sections plus the bud, and the radioactivity of donors, receivers and each part of the stem segment was counted.For all four substances tested, the amount of ¹⁴C transported to the axillary bud from the base was the same or greater than that from the apical end. After basipetal transport, the distribution of ¹⁴C in the segment declined sharply from apex to base. The inverse was true for acropetal transport. Transport for the three IAA conjugates did not differ substantially from each other.The IAA transport inhibitor, N-1-naphthylphthalamic acid (NPA), inhibited basipetal ¹⁴C-IAA transport to the base of the stem segment but did not alter substantially the amount of ¹⁴C-IAA recovered from the bud. Transport of ¹⁴C-IAA from the apical end to all parts of the stem segment declined when the base of the section was treated with nonradioactive IAA. Taken together with data presented in the accompanying article [Tamas et al. (1989) Plant Growth Regul 8: 165–183], these results suggest that the transport of IAA plays a role in axillary bud growth regulation, but its effect does not depend on the accumulation of IAA in the axillary bud itself.     

Gravitropic Responses of Partially Decapitated Corn Coleoptiles with and without Applied [C]Indoleacetic Acid

The curvature of corn seedling (Zea mays L. Mo17 × B73) coleoptiles which had been half-decapitated and supplied with [¹⁴C]indoleacetic acid (IAA) (3.2 micromolar, 51 milliCuries per millimole) was determined during a 3-hour period of gravitational stimulation. Curvature of such half-decapitated coleoptiles was found to be similar in rate and extent to that of intact coleoptiles responding to gravity. Gravitational stimulation was accomplished by reorienting seedlings to a horizontal position, either up or down with respect to the removed half of the coleoptile tips.

The first set of experiments involved placing aluminum foil barriers along one of the two cut surfaces to restrict the movement of IAA into tissues. The initiation and extent of curvature of these half-decapitated coleoptiles was dependent upon the orientation of the removed half-tip and the accompanying barrier. The distribution of radioactivity from [¹⁴C] IAA after 3 hours indicated that the specific lateral movement of label was also dependent upon orientation of the removed half-tip of the coleoptile. A specific movement to the lower side of approximately 14% of the total recovered radioactivity was found in coleoptiles in which the [¹⁴C]IAA was supplied across a transverse cut surface. In contrast, specific movement of only 4% was found for application across a longitudinal cut surface.

A second series of experiments was conducted using 1.0 and 3.2 micromolar [¹⁴C]IAA (51 milliCuries per millimole) supplied to half-decapitated coleoptiles without inserted barriers. The 3.2 micromolar concentration adequately replaced the removed coleoptile half-tips in terms of straight growth, but it did not result in as much curvature as shown by coleoptiles of intact seedlings. The 1 micromolar concentration was not adequate to replace the removed half-tip in straight growth, but resulted in gravitropic curvature nearly as great as that produced by the higher concentration.

The data presented here suggest that strong auxin gradients are not produced in response to gravity stimulation based on the recovered radioactivity from [¹⁴C]IAA. However, it is evident that auxin is required for the development of normal gravitropic responses. It is possible, therefore, that an important early role of this movement is not to cause a large stimulation of growth on the lower side but to decrease growth on the upper side of a gravitropically responding coleoptile.

     

IAA-Induced Growth Responses of Decapitated Corn Seedlings: Indications of Two Apparent Adaptations with a Possible Role in Gravitropism

The vertical growth responses of corn seedlings (Zea mays L. Mo17 × B73) were determined over an 8-hour period. When seedlings were decapitated 3 millimeters from the coleoptile's tip and supplied with indole-3-acetic acid (IAA) in 1.5% agar blocks, the response was dependent both on time and IAA concentration. The dose-response curves changed in shape and magnitude depending on the total time of IAA application. High concentrations (>3.2 × 10⁻⁶ molar) initially produced high relative growth rates that decreased back to the intact rate (0.03 millimeter per hour per millimeter) after 3 hours. Low concentrations (<1.0 × 10⁻⁶ molar), or agar blocks without IAA, resulted in a rapid decrease from the intact rate to a level that stabilized at 0.01 millimeter per hour per millimeter until the growth rate began to recover after 3 to 4 hours. Intermediate concentrations produced responses similar to that of the intact organ, though some features of these responses were unique.

The coleoptile curvature in response to gravity depended upon whether the coleoptiles were intact, decapitated, or decapitated and supplied with IAA. Coleoptiles decapitated and not supplied wth IAA showed little or no curvature for 3 hours after decapitation. By this time an adaptation, evoked by the low IAA level, had developed and the coleoptiles began to curve steadily. When 1.0 or 3.2 × 10⁻⁶ molar IAA was supplied, curvature was initiated within the first 30 minutes and reached a maximum rate before decreasing and stopping after 3 to 4 hours. The sequence of events in response to these concentrations was similar to the intact sequence but the curvature rate was reduced to one-third to one-half. A model for the autotropic response involving an auxin concentration-dependent, growth-modulating mechanism capable of two modes of adaptation is described.

     

Translocation of Indole-3-acetic Acid-1'-C and Tryptophan-1-C in Seedlings of Phaseolus coccineus L. and Zea mays L

Indole-3-acetic acid-1′-¹⁴C (IAA-¹⁴C) and tryptophan-1-¹⁴C injected in small amounts into cotyledons of Phaseolus coccineus L. seedlings were found to be translocated acropetally into the epicotyls and young shoots. Similarly IAA-¹⁴C was translocated acropetally into coleoptiles of Zea mays following injection into the endosperms. Labeled metabolites of the injected compounds were also extractable from shoot tissue. However, evidence that IAA-¹⁴C itself was translocated acropetally was obtained by collection in agar blocks applied to cut surfaces of coleoptiles of injected seedlings. The acropetal translocation in Phaseolus was shown not to occur in the transpiration stream but in living tissue. Cotyledons of Phaseolus coccineus and Phaseolus vulgaris contain extensive vascular tissue.     

Indoleacetic Acid biosynthesis in Avena coleoptile tips and excised bean shoots

Avena coleoptiles did not elongate when incubated with tryptophan under sterile conditions. Indole, anthranilic acid, and tryptamine promoted elongation. Under the same conditions, the tissue converted tryptophan-¹⁴C to IAA-¹⁴C. More IAA-¹⁴C was produced from indole-¹⁴C than from tryptophan-¹⁴C; however, the free tryptophan content of the tissue was also greatly increased by the indole treatment. Tryptophan-¹⁴C was readily taken up by the tissue but was mainly incorporated into protein and did not increase the free tryptophan level. When bean shoots were labeled with tryptophan-¹⁴C or indole-¹⁴C, the label incorporation into IAA-¹⁴C was very nearly the same. In this tissue the free tryptophan level in the tryptophan-¹⁴C and indole-¹⁴C treatments was also about equal. These results suggest that failure of exogenously supplied tryptophan to promote the elongation of Avena coleoptiles is a result of its predominant incorporation into protein and consequent unavailability for conversion to IAA.     

Adventitious root formation in relation to irradiance and auxin supply

High irradiance during treatment of mung bean cuttings favours root formation in response to supplied auxin, whether the latter is IAA or IBA. On the other hand it is inhibitory towards root formation in the absence of supplied auxin. Light promotes the uptake of¹⁴C-IAA into cuttings and its upward movement into the leaves. When¹⁴C-IAA is applied to leaves of cuttings high irradiance favours movement of radioactivity into the epicotyl and hypocotyl. This movement is also enhanced by concomitant supply of IBA to the base of the cuttings. The irradiance under which stock plants are raised also affects the extent of root formation on cuttings. When cuttings are held in darkness without a supply of exogenous auxin they root best if prepared from seedlings raised under high irradiance. However, transport of¹⁴C-IAA out of leaves of cuttings is favoured when cuttings are prepared from seedlings grown under low irradiance. These observations are discussed in relation to auxin transport, photodestruction and, possibly, metabolism.     

Studies on the movement of indole auxins in willow (Salix viminalis L.)

Summary Auxin activity was detected in honeydew obtained from the aphid Tuberolachnus salignus (Gmelin) feeding on willow (Salix viminalis). Active uptake of ¹⁴C-indolyl-3-acetic acid (IAA) into the sieve tubes was demonstrated by irrigating the cambial surface of willow bark with ¹⁴C-IAA solution and assaying aphid stylet exudate. When, however, ¹⁴C-IAA was applied to the peridermal tissues of the bark or to a mature leaf most of the radioactivity (collected in honeydew or stylet exudate) co-chromatographed with indolyl-3-acetyl-aspartic acid (IAAsp). The presence of IAAsp in honeydew was not affected by extraction procedure or by aphid metabolism. Honeydew obtained from willow treated with ¹⁴C-tryptophan contained only ¹⁴C-tryptophan. When ¹⁴C-IAA was applied in agar to the cut end of willow segments the radioactivity was found to move in a basipetally polar manner. The direction of movement of radioactivity in the sieve tubes, however, was found to be influenced by the proximity of the roots. Nevertheless, there was evidence that endogenous auxin in the sieve tubes does move in a predominantly basipetal direction.     

A METHOD FOR OBTAINING AXENIC ALGAL CULTURES USING THE ANTIBIOTIC CEFOTAXIME WITH EMPHASIS ON CLADOPHOROPSIS MEMBRANACEA (CHLOROPHYTA)1

Axenic cultures of the tropical green seaweed Cladophoropsis membranacea (C. Agardh) Boergesen were obtained by cutting 2-mm apical tips from fast-growing unialgal filaments and incubating them in 1/2PES containing 100 μg · mL^?1 cefotaxime. After 1 week, apical tips were cut from the newly grown plantlets, washed through a series of sterile drops of seawater, and incubated in sterile 1/2PES. Plantlets were screened for the presence of bacteria by incubating droplets of the culture medium on peptone agar plates and by examining DAPI-stained filaments. Ninety to one hundred percent of the plantlets obtained with this treatment were axenic. Cefotaxime was also effective against cyanobacteria but of only limited value in rhodophytes.     

Bound Form Indole-3-acetic Acid Synthesis in Tumorous and Nontumorous Species of Nicotiana

The synthesis of H₂O-soluble and NaOH-hydrolyzable bound forms of indole-3-acetic acid (IAA) in petiole slices of Nicotiana glauca, Nicotiana langsdorffii, and their tumorous and nontumorous hybrids in the presence of exogenous ¹⁴C-IAA was investigated. The synthesis of conjugates progressively increased during 6 hours of incubation in ¹⁴C-IAA. The results showed that the rate of synthesis of IAA conjugates was higher in tumorous hybrids supplied exogenous IAA than in the parental species similarly supplied, and the rate of synthesis was higher in amphidiploid tumor plants than in a nontumorous mutant. It was also found that after 10 to 12 hours of incubation, 45% of the IAA taken up by F1 hybrids was in conjugated form whereas only 10 to 25% of the IAA taken up by a nontumorous mutant, N. langsdorffii, or N. glauca was conjugated. An F1 hybrid and an amphidiploid hybrid were found equally efficient in conjugating exogenously supplied IAA. It is postulated on the basis of these and other findings that IAA conjugates play an important role in tumorigenesis in Nicotiana.     

Auxin Transport in Zea mays L. Coleoptiles I. Influence of Gravity on the Transport of Indoleacetic Acid-2-C

¹⁴C-methylene labeled IAA was used to determine the influence of reorientation with respect to gravity on auxin transport in Zea mays L. coleoptile segments. It was observed that inversion of the segments leads to a decrease in the capacity to transport ¹⁴C-IAA basipetally, as well as, in certain instances, the linear velocity of that transport. Segments were also reoriented horizontally, and the transport velocity and capacity of the upper and lower tissue halves compared with vertical halves. There was no significant change in the velocity, but the transport capacity of lower halves was higher than that of the vertical halves, which in turn was higher than the capacity of the horizontal upper halves. It is suggested that the geocurvature of horizontally placed coleoptiles may be caused primarily by the effect of reorientation on auxin transport.     

The biosynthesis and translocation of 14C-IAA in Ricinus communis

The biosynthesis of ¹⁴C-IAA from ¹⁴C-tryptophan applied to abraded leaves of Ricinus communis and its subsequent export through the phloem were studied. Phloem sap was collected at intervals from incisions made in the stem below the IAA fed leaf. Any upward movement of label through the phloem or downward movement of phloem mobile compounds from leaves above the treated one were restricted by bark-ringing the plants.TLC and HPLC analyses of the collected sap indicate that some conversion of ¹⁴C-tryptophan to ¹⁴C-IAA had occurred. Subsequent GC-MS analysis of the HPLC purified samples of phloem sap revealed high levels of endogenous IAA transported from the fed leaf. The high ratio of unlabelled/labelled IAA in the phloem sap makes unequivocal confirmation by GC-MS of the predicted biosynthesis of ¹⁴C-IAA impossible. It is postulated that IAA is synthesised from tryptophan in mature leaves and exported to developing sink tissues with the flow of photoassimilates in the phloem.     

Red light causes a reduction in IAA levels at the apical tip by inhibiting de novo biosynthesis from tryptophan in maize coleoptiles

When maize coleoptiles were unilaterally exposed to red light (7.9 μmol m⁻²s⁻¹ for 5 min), 3 h after treatment IAA levels in coleoptiles decreased in all regions, from top to basal, with levels about 60% of dark controls. Localized irradiation in the 5 mm top zone was sufficient to cause the same extent of IAA reduction in the tips to that in the tips of whole irradiated shoots. When coleoptiles were treated with N-1-naphthylphthalamic acid (NPA), an accumulation of IAA in the tip and a decrease of diffusible IAA from tips were simultaneously detected. IAA accumulation in red-light treated coleoptiles by NPA was much lower than that of dark controls. NPA treatment did not affect the content of conjugated IAA in either dark or light treated coleoptile tips. When ¹³C₁₁ ¹⁵N₂-tryptophan (Trp) was applied to the top of coleoptiles, substantial amounts of stable isotope were incorporated into free IAA in dark and red-light treated coleoptile tips. The ratio of incorporation was slightly lower in red-light treated coleoptile tips than that in dark controls. The label could not be detected in conjugated IAA. The rate of basipetal transport of IAA was about 10 mm h⁻¹ and the velocity was not affected by red light. These results strongly suggest that red light does not affect the rates of conversion of free IAA to the conjugate form or of the basipetal transport, but just reduces the IAA level in the tips, probably inhibited by IAA biosynthesis from Trp in this region.Electronic Supplementary Material Supplementary material is available to authorised users in the online version of this article at .     

Hormonal Relations in the Phototropic Response: III. The Movement of C-labeled and Endogenous Indoleacetic Acid in Phototropically Stimulated Zea Coleoptiles

The effect of phototropic stimulation of Zea coleoptile tips on the distribution of both endogenous indoleacetic acid (IAA) and applied C¹⁴-labeled IAA was determined. The tips rested on bisected agar blocks. More IAA was found in the blocks under the shaded side of the coleoptile tips than those under the irradiated side. However, no significant difference was observed between the total amounts of IAA, endogenous or labeled, in the irradiated and shaded sides of the experimental system. In addition, less endogenous auxin was found in the shaded tissues than in their irradiated counterparts. It is suggested that phototropism following unilateral irradiation with first positive radiant densities might be a consequence of lateral inequalities in the ability of the irradiated and shaded tissues to transport auxin basipetally.     

Relationship Between Metabolism and the Lateral Transport of IAA in Corn Coleoptiles

The lateral movement of IAA in coleoptiles of Zea mays has been investigated under aerobic and anaerobic conditions. The IAA-1-¹⁴C was supplied asymmetrically to the apical end of the segment. The results were as follows: A) In air more ¹⁴C was found in the lower half of horizontal segments supplied with an upper donor than in the half opposite the donor in vertical segments. The enhanced lateral movement of ¹⁴C in geotropically stimulated segments of corn coleoptiles under aerobic conditions has thus been confirmed. B) This increased lateral movement of ¹⁴C in geotropically stimulated segments is greatly reduced, but is not completely abolished, under anaerobic conditions. C) The lateral movement of ¹⁴C in vertical segments is significantly less under anaerobic conditions than in air. D) Under anaerobic conditions, the lateral movement of ¹⁴C in horizontal segments can be reduced to the level found in vertical segments by pre-soaking the tissue in a 1 mm solution of the metabolic inhibitor sodium fluoride for 2 hours. The inhibitor has no effect on lateral movement of ¹⁴C in vertical anaerobic segments. E) In air, sodium fluoride has no effect on the lateral movement of ¹⁴C in either vertical or horizontal segments.     

Effect of ethylene on the uptake, distribution, and metabolism of indoleacetic Acid-1-C and -2-C and naphthaleneacetic Acid-1-C

The effect of ethylene on the uptake, distribution, and metabolism of indoleacetic acid (IAA)-1-¹⁴C, IAA-2-¹⁴C, and naphthaleneacetic acid (NAA)-1-¹⁴C in cotton stem sections (Gossypium hirsutum L., var. Stoneville 213) was studied. Stem sections excised from plants pretreated with ethylene for 15 hours transported significantly less ¹⁴C-IAA and ¹⁴C-NAA than control sections. Concomitant features of the reduction of ¹⁴C-IAA transport were an increase in decarboxylation and a trend toward a reduction in total uptake. With ¹⁴C-NAA, however, total uptake was significantly increased, and decarboxylation was unaffected.     

Gibberellins and geotropism in Zea mays coleoptiles

Summary Diffusible gibberellins were obtainable in agar from excised 4 mm tips of etiolated coleoptiles of Zea mays. Placing the tips in a horizontal position increased the total yield of gibberellins by approximately five times. With horizontal tips, the ratio of gibberellin activity recovered from lower and upper halves, expressed as a percentage of total yield, was 80.76:19.24 (lower:upper).