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  • 1
    Electronic Resource
    Electronic Resource
    Reevaluation of the role of auxin binding site II (1994)
    Springer
    Journal of plant growth regulation 13 (1994), S. 79-85 
    Details
    ISSN: 1435-8107
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Binding of 1-naphthylacetic acid (1-NAA) was assayed in microsomal membranes from Zea mays coleoptiles and from hypocotyls of Cucurbita pepo. Auxin binding site II was differentiated from site I binding by using phenylacetic acid (PAA) to saturate site I binding capacity. The amount of type-II binding sites, per gram original fresh weight, was 34 pmol with Zea and 6.4 pmol with Cucurbita. When maize membranes were separated by dextran gradient centrifugation, auxin binding site II migrated coincident with tonoplast marker enzymes. The physiologically active auxin 4-chloroindoleacetic acid (4-Cl-IAA) competed very poorly with 1-NAA binding to both site I and site II. This result suggests that sites I and II are not involved in the regulation of growth. When comparing isolated outer epidermis with intact coleoptile of Zea, similar amounts and ratios of site I and site II binding activities were observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00210951
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  • 2
    Electronic Resource
    Electronic Resource
    1-N-naphthylphthalamic acid and 2,3,5-triiodobenzoic acid (1973)
    Springer
    Planta 109 (1973), S. 337-352 
    Details
    ISSN: 1432-2048
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00387102
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  • 3
    Electronic Resource
    Electronic Resource
    Lateral electrical potential following asymmetric auxin application to maize coleoptiles (1978)
    Springer
    Planta 140 (1978), S. 31-35 
    Details
    ISSN: 1432-2048
    Keywords: Auxin ; Coleoptiles ; Electrical Potential ; Zea
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Following asymmetric application of indoleacetic acid to maize (Zea mays L.) coleoptiles the early time course of changes in lateral electrical potential was externally monitored with static-drop electrodes. First, an early negative potential change of ca.-1 mV was measured at the surface on the side of a strong auxin application. This negative auxin effect ended after ca. 15 min and was followed by a strong and lasting auxin stimulation of a positive lateral potential up to +12 mV at the auxin-treated side. The initial auxin effect appeared to depend on the size of the step-up in auxin concentration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00389376
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  • 4
    Electronic Resource
    Electronic Resource
    In-vitro auxin transport in membrane vesicles from maize coleoptiles (1987)
    Springer
    Planta 172 (1987), S. 285-287 
    Details
    ISSN: 1432-2048
    Keywords: Auxin transport ; Coleoptile ; Membrane vesicles ; Phytotropin ; Zea (auxin transport)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract When membrane vesicles from maize (Zea mays L.) coleoptiles are extracted at high buffer strength, a pH-driven, saturable association of [14C] indole-3-acetic acid is found, similar to the in-vitro auxin-transport system previously described for Cucurbita hypocotyls. The phytotropins naphthylphthalamic acid and pyrenoylbenzoic acid increase net uptake, pressumably by inhibiting the auxin-efflux carrier.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00394599
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  • 5
    Electronic Resource
    Electronic Resource
    Amyloplasts are necessary for full gravitropic sensitivity in roots of Arabidopsis thaliana (1989)
    Springer
    Planta 177 (1989), S. 198-206 
    Details
    ISSN: 1432-2048
    Keywords: Amyloplast ; Arabidopsis ; Gravitropism ; Gravity ; Mutant (gravitropism) ; Plastid and graviperception ; Starch and graviperception ; Statolith
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The observation that a starchless mutant (TC7) of Arabidopsis thaliana (L.) Heynh. is gravitropic (T. Caspar and B.G. Pickard, 1989, Planta 177, 185–197) raises questions about the hypothesis that starch and amyloplasts play a role in gravity perception. We compared the kinetics of gravitropism in this starchless mutant and the wild-type (WT). Wild-type roots are more responsive to gravity than TC7 roots as judged by several parameters: (1) Vertically grown TC7 roots were not as oriented with respect to the gravity vector as WT roots. (2) In the time course of curvature after gravistimulation, curvature in TC7 roots was delayed and reduced compared to WT roots. (3) TC7 roots curved less than WT roots following a single, short (induction) period of gravistimulation, and WT, but not TC7, roots curved in response to a 1-min period of horizontal exposure. (4) Wild-type roots curved much more than TC7 roots in response to intermittent stimulation (repeated short periods of horizontal exposure); WT roots curved in response to 10 s of stimulation or less, but TC7 roots required 2 min of stimulation to produce a curvature. The growth rates were equal for both genotypes. We conclude that WT roots are more sensitive to gravity than TC7 roots. Starch is not required for gravity perception in TC7 roots, but is necessary for full sensitivity; thus it is likely that amyloplasts function as statoliths in WT Arabidopsis roots. Furthermore, since centrifugation studies using low gravitational forces indicated that starchless plastids are relatively dense and are the most movable component in TC7 columella cells, the starchless plastids may also function as statoliths.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00392808
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  • 6
    Electronic Resource
    Electronic Resource
    Effect of gravity and centrifugal acceleration on auxin transport in corn coleoptiles (1969)
    Springer
    Planta 88 (1969), S. 233-243 
    Details
    ISSN: 1432-2048
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Inversion of corn coleoptile sections resulted in a 10–20% inhibition of basipetal transport of 3-indoleacetic acid (IAA) and a more pronounced inhibition (20–50%) of the transport of 1-naphthaleneacetic acid (NAA). The effect of inversion on basipetal NAA transport was compared in wild-type corn and in the amylomaize mutant which contains smaller and slower sedimenting amyloplasts: the gravity induced inhibition was higher in the wild type coleoptiles (27% versus 9%). In wild type the inhibitory effect on basipetal NAA transport appeared within less than 30 min after inversion; then the effect remained relatively constant over at least 2 hr of transport. When the sections were returned to the upright position the transport rate increased, reaching the level of upright controls within 30 min. An effect of gravity on lateral transport of NAA was also demonstrated and shown to be expressed within 10 min after placing the tissue horizontally. When basipetal transport was tested in the direction of gravity and/or centrifugal acceleration, auxin movement incrased with increasing acceleration. Transport against centrifugal acceleration (10 x g) was less than transport of control sections (inverted at 1 x g). The results agree with the hypothesis that starch statoliths act by a pressure mechanism on the membrane transport system of auxin.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00385066
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  • 7
    Electronic Resource
    Electronic Resource
    Some aspects of geotropism in coleoptiles (1970)
    Springer
    Planta 94 (1970), S. 333-354 
    Details
    ISSN: 1432-2048
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Auxin transport was studied in coleoptile sections that were stimulated geotropically. The early time course of auxin-transport asymmetry was measured. An initial phase in which more IAA was delivered into the receptor for the upper half was found after 5 min of horizontal exposure. After about 15 min this was followed by the expected known asymmetry in which more auxin flows in the lower side of the coleoptile. Upon return of the coleoptile to a vertical position, this asymmetry disappeared within 30 min. Earlier correlations of geosensitivity of the auxin transport system with sedimentation of amyloplasts in comparisons of wild type corn and an amylomaize mutant were confirmed and extended. It was also shown that, in contrast to the geotropic effect, phototropically induced lateral auxin asymmetry was not significantly different in wild type and amylomaize. Eleven other single-gene endosperm starch mutants of corn were compared to their corresponding normals. In all pairs, if a difference in geosensitivity of lateral auxin transport was present, it was correlated with a parallel difference in amyloplast sedimentation: e.g., sugary 1 (“67”) had an amyloplast asymmetry index of 0.32 and a 13% gravity effect on auxin transport; the paired wild-type had both a greater amyloplast asymmetry (0.61) and a greater gravity effect on transport (23%). Correlations between gravity effects on auxin transport and amyloplasts were also shown in comparisons of apical and basal sections of corn, oat and Sorghum coleoptiles. Further results, confirming the increased effect of centrifugal acceleration greater than 1xg on lateral auxin transport and on curvature, are in agreement with the hypothesis that the pressure exerted by amyloplasts, acting as statoliths, locally stimulates the auxin transport system in the individual cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00385765
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  • 8
    Electronic Resource
    Electronic Resource
    Auxin movement in corn coleoptiles (1968)
    Springer
    Planta 82 (1968), S. 123-144 
    Details
    ISSN: 1432-2048
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Movement of radioactive auxins was analysed in corn coleoptile sections. The results support the idea that processes involved in the transport of indoleacetic acid (IAA) are specific for growth-promoting auxins. Inhibition of IAA transport by triiodobenzoic acid is caused by a reversible block of the exit; the auxin held back remains in the transport pool. The observed increase in immobilization may be a secondary effect caused by the increased concentration of free IAA in the tissue. Auxin molecules are most likely transported by anon-covalent mechanism. IAA and naphthaleneacetic acid (NAA) move through the cell and exit as free molecules. A search for a transient auxin complex, chaseable as required for any transport carrier intermediate, yielded negative results. No18O was lost from NAA labeled with18O in the carboxyl group during transport of the auxin through coleoptile tissue. After application of IAA to auxin-depleted tissue, the transport rate undergoes oscillations with a period length of ca. 25 min. The movement of the auxin 2.4-dichlorophenoxyacetic acid which is usually sluggish, increased several times if some IAA was added. Auxin, thus, stimulates its own transport. A model is discussed in which auxin-binding to the plasma membrane and reversible changes of membrane conformation may provide a basis for active secretion and for the observed cooperativity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01305716
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  • 9
    Electronic Resource
    Electronic Resource
    Heterogeneity of auxin-accumulating membrane vesicles from Cucurbita and Zea: a possible reflection of cell polarity (1989)
    Springer
    Planta 177 (1989), S. 304-311 
    Details
    ISSN: 1432-2048
    Keywords: Auxin transport ; Cucurbita (auxin transport) ; Membrane vesicle ; Polarity (auxin transport) ; Zea (auxin transport)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract When microsomes from hypocotyls of Cucurbita pepo L. or coleoptiles of Zea mays L. were centrifuged on dextran-sucrose gradients a heterogeneity of auxin-accumulating vesicles was observed. Vesicles from the top part of the gradient showed saturable, specific accumulation of indole-3-acetic acid with only a small stimulation by phytotropins, and with very few binding sites for 1-N-naphthylphthalamic acid. In the vesicles from the lower part of the gradient, net accumulation of indole-3-acetic acid could be strongly increased by addition of phytotropins; binding of 1-N-naphthylphthalamic acid was high in this region. After two-phase partitioning, both kinds of vesicles were found in the upper-phase membrane fraction considered to be purified plasma membrane. The hypothesis is discussed that vesicles can be separated from the apical and basal parts of the cell's plasmalemma.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00403587
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  • 10
    Electronic Resource
    Electronic Resource
    Auxin transport in membrane vesicles from Cucurbita pepo L. (1983)
    Springer
    Planta 157 (1983), S. 193-201 
    Details
    ISSN: 1432-2048
    Keywords: Auxin transport ; Chemiosmotic theory ; Cucurbita ; pH gradient and auxin transport ; Plasma membrane ; Symport (IAA-/H+) ; Transport (cellular, auxin) ; Vesicles, sealed
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Association of 14C-labelled indole-3-acetic acid (IAA) with membrane particles from zucchini (Cucurbita pepo L.) hypocotyls — previously described as “site III binding” (M. Jacobs and R. Hertel, 1978, Planta 142, 1–10) — is reinterpreted as a carrier-mediated uptake into closed and sealed vesicles driven by a pH gradient. Accumulation of the radioactive auxin is saturable, sensitive to the protonophore, carbonyl cyanide p-trifluoromethoxyphenyl hydrazone (FCCP), and to nigericin, and requires a pH gradient across the membranes with proton concentration greater outside than inside. The pH gradient decays within 1–2 h at 4°C and can be restored by re-equilibration of the particle preparation at more alkaline pH followed by return to more acidic medium. Osmotic shock and sonication release the IAA from the vesicles. 1-N-naphthylphthalamic acid (NPA) and 2,3,5-triiodobenzoic acid (TIBA), both inhibitors of auxin transport in vivo, increase the amount of net IAA accumulation in the vesicles, presumably by blocking efflux. Analogs of NPA less active or inactive in vivo are respectively less active or inactive in vitro. It is proposed that these membrane particles are outside-out plasma membrane vesicles, and that they perform the essential functions of auxin transport according to the chemiosmotic theory, with a specific, saturable proton symport uptake and an export anion carrier which is inhibited by NPA and TIBA.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00405182
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