Effects of light and low temperature on the reciprocal style curvature of Flexistylous Alpinia Species (Zingiberaceae)

The style curvature (flexistyly) of Alpinia species in ginger family is a unique plant organ movement because the style of each flower curves twice during its 1-day anthesis and styles of two phenotypes of each Alpinia species in the same population synchronously curve in opposite directions at the same time. In this study, we investigated the effects of low temperature and light conditions on these reciprocal style movements. Our results indicate that low temperature cannot change the direction of each curvature movement, but can slow down these movements and decrease the curve degrees. Light did not affect the upward curvature of the cataflexistylous morph, but the degrees of downward curvature decreased in darkness. For the anaflexistylous morph, the downward curvature only occurred in darkness, but curved directly upward in light condition; after the first (downward) curvature, the second (upward) movement only occurred in light, but did not occur if styles maintained in darkness. These results suggest that low temperature does not stimulate style curvature; light is the necessary condition for the upward movement of the anaflexistylous morph. The stimuli that induced curvature movements in the two morphs were different. Both two curvatures of the cataflexistylous style and downward movement of the anaflexistylous style were controlled via an endogenous program, while the upward movement of the anaflexistylous style was controlled by light.     

光对马来良姜花柱运动和花药开裂的影响

以马来良姜(Alpinia mutica)花柱为研究对象,研究光对花柱卷曲运动和花药开裂的影响.结果表明下垂型花柱的两次运动在光下和暗处都能进行,花药的开裂也不受光照影响.上举型花柱的第一次运动在暗处时向下进行,在光下时向上进行;暗处的花药不开裂,光下的花药开裂.第二次运动的方向和幅度取决于第一次运动期间的光照条件,第一次运动在暗处时,若第二次也在暗处,第二次运动不会发生且花药不开裂;若在光处,花柱向上运动.第一次运动在光下时,第二次运动无论光下或暗处,都向下运动.本研究表明,在不同光照条件下,两种表型的花柱与花药状态的组合使柱头接触不到同花的花粉,从而保证了雌雄异位与雌雄异熟.尽管两种表型的花柱运动和花药开裂行为相似,却受不同的机制调控.     

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     

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.     

Similar behavior,different mechanisms: the research of the style bending of <Emphasis Type="Italic">Alpinia</Emphasis> species

The styles of the plants of genus Alpinia show a similar bending behavior. Each species has two types—hyper-type and cata-type. The styles of hyper-type bend downward first, and then bend upward second. The styles of cata-type also bend twice, but the bending direction is opposite to hyper-type. We tested the effects of light, IAA, and NPA on the style movement of Alpinia oxyphylla and Alpinia galanga, and analyzed the IAA distribution in their styles. We found that the effects of light were similar for the two species, but the two types of each species responded differently. The first style bending of hyper-type was downward when it was in dark, and was upward when in light; the second bending was upward if in light, and did not move if in dark. The two bendings of cata-type showed no obvious difference between in dark and in light. Effects of IAA and NPA were different for two species. For A. galanga, neither IAA nor NPA had obvious effects on the style bending. For A. oxyphylla, IAA enhanced the second bending of hyper-type and the two bendings of cata-type. NPA enhanced the second bending of hyper-type and the first bendings of cata-type, and significantly inhibited the second bending of cata-type. The results of IAA immunolocalization indicated that IAA was symmetrical in the styles of A. galanga both before the first bending and before the second bending in two types. However, in A. oxyphylla, IAA asymmetry was found in two types. Therefore, we hypothesize that the mechanisms of the style bending of Alpinia plants are different, not only between two types of each species, but also among species.     

Inhibition of polar calcium movement and gravitropism in roots treated with auxin-transport inhibitors

Primary roots of maize (Zea mays L.) and pea (Pisum sativum L.) exhibit strong positive gravitropism. In both species, gravistimulation induces polar movement of calcium across the root tip from the upper side to the lower side. Roots of onion (Allium cepa L.) are not responsive to gravity and gravistimulation induces little or no polar movement of calcium across the root tip. Treatment of maize or pea roots with inhibitors of auxin transport (morphactin, naphthylphthalamic acid, 2,3,5-triiodobenzoic acid) prevents both gravitropism and gravity-induced polar movement of calcium across the root tip. The results indicate that calcium movement and auxin movement are closely linked in roots and that gravity-induced redistribution of calcium across the root cap may play an important role in the development of gravitropic curvature.Abbreviations 9-HFCA 9-hydroxyfluorenecarboxylic acid - NPA naphthylphthalamic acid - TIBA 2,3,5-triiodobenzoic acid - IAA indole-3-acetic acid     

Auxin Transport Inhibitors and the Rooting of Hypocotyl Cuttings from Etiolated Mung-bean Vigna radiata (L.) Wilczek Seedlings

The auxin transport inhibitors 2, 3, 5-triiodobenzoic acid (TIBA)and naphthylphthalamic acid (NPA) inhibited adventitious rootformation (ARF) induced by indol-3-butyric acid (IBA) on cuttingsfrom etiolated mung-bean seedlings floated on solutions of thegrowth regulators. The concentrations of TIBA and NPA requiredfor a 25 per cent reduction in ARF with 10 µM IBA wereestimated by linear interpolation to be 11.3 µm and 0.42µM respectively. NPA is a particularly potent inhibitorof IBA-induced ARF. The inhibitory effect of either compoundwas reversible by higher concentrations of IBA. NPA had no effectwhen applied after the auxin treatment. The inhibitory effects of TIBA or NPA could not be explainedby effects on the uptake or metabolism of [2-^14C]IAA. Consideringthis and other evidence, it is suggested that NPA and possiblyTIBA are acting as specific antagonists of auxin in the inductionof ARF. Vigna radiata (L.), mung-bean, root induction, hypocotyl cuttings, auxin inhibitors, indol-3-butyric acid, 2,3,5-triiodobenzoic acid, naphthylphthalamic acid, auxin uptake, auxin metabolism, adventitious roots     

两种姜科花柱卷曲性植物柱头的位置与其可授性的关系

花柱卷曲性是一种见于姜科山姜属(Alpinia)和砂仁属(Amomum)植物中的独特的性二态现象, 具有这一性系统的植物, 其居群包括上举型和下垂型两种表型, 所有个体的雌雄性别功能在时间和空间上分离。本研究通过操控授粉和花粉管生长两项实验, 探讨花柱卷曲性植物个体两性功能的隔离方式及其适应意义。云南草蔻(Alpinia blepharocalyx)操控授粉实验表明, 自花花粉对其异交率影响不显著(P > 0.05), 但可能由于自花花粉沉降导致胚珠贴现进而引起近交衰退, 操控条件下每果结籽数显著减少(P < 0.01)。云南草蔻和红豆蔻(Alpinia galanga)花粉管生长实验都显示无论对两种表型进行怎样的授粉处理, 花粉粒萌发和花粉管生长的速率仅在柱头处于可授位置时表现出最大值, 与自交和异交授粉方式无关; 上举型植株上午花粉囊虽未裂但其内花粉已成熟。研究结果表明即使不考虑花柱运动, 山姜属植物也具有异型雌雄异熟的特性。这一结果证实了花柱卷曲运动机制是通过互补式雌雄异位和异型雌雄异熟相结合形成的花部二态性, 异型雌雄异熟促进了异交, 而花柱运动的功能可能在于避免雌雄干扰。     

Effect of Cyclanilide on Auxin Activity

Cyclanilide is a plant growth regulator that is registered for use in cotton at different stages of growth, to either suppress vegetative growth (in combination with mepiquat chloride) or accelerate senescence (enhance defoliation and boll opening, used in combination with ethephon). This research was conducted to study the mechanism of action of cyclanilide: its potential interaction with auxin (IAA) transport and signaling in plants. The activity of cyclanilide was compared with the activity of the auxin transport inhibitors NPA and TIBA. Movement of [³H]IAA was inhibited in etiolated corn coleoptiles by 10 μM cyclanilide, NPA, and TIBA, which demonstrated that cyclanilide affected polar auxin transport. Although NPA inhibited [³H]IAA efflux from cells in etiolated zucchini hypocotyls, cyclanilide had no effect. NPA did not inhibit the influx of IAA into cells in etiolated zucchini hypocotyls, whereas cyclanilide inhibited uptake 25 and 31% at 10 and 100 μM, respectively. Also, NPA inhibited the gravitropic response in tomato roots (85% at 1 μM) more than cyclanilide (30% at 1 μM). Although NPA inhibited tomato root growth (30% at 1 μM), cyclanilide stimulated root growth (165% of control at 5 μM). To further characterize cyclanilide action, plasma membrane fractions from etiolated zucchini hypocotyls were obtained and the binding of NPA, IAA, and cyclanilide studied. Cyclanilide inhibited the binding of [³H]NPA and [³H]IAA with an IC₅₀ of 50 μM for both. NPA did not affect the binding of IAA, nor did IAA affect the binding of NPA. Kinetic analysis indicated that cyclanilide is a noncompetitive inhibitor of both NPA and IAA binding, with inhibition constants (K _i) of 40 and 2.3 μM, respectively. These data demonstrated that cyclanilide interacts with auxin-regulated processes via a mechanism that is distinct from other auxin transport inhibitors. This research identifies a possible mechanism of action for cyclanilide when used as a plant growth regulator.     

The action of specific inhibitors of auxin transport on uptake of auxin and binding of N-1-naphthylphthalamic acid to a membrane site in maize coleoptiles

Using both 1-mm segments of corn (Zea mays L.) coleoptiles and a preparation of membranes isolated from the same source, we have compared the effectiveness of several inhibitors of geotropism and polar transport in stimulating uptake of auxin (indole-3-acetic acid, IAA) into the tissue and in competing with N-1-naphthylphthalamic acid (NPA) for a membrane-bound site. Low concentrations of 2,3,5-triiodobenzoic acid (TIBA), NPA, 2-chloro-9-hydroxyfluorene-9-carboxylic acid (morphactin), and fluorescein, eosin, and mercurochrome all stimulated net uptake of [³H]IAA by corn coleoptile tissues while higher concentrations reduced the uptake of both [³H]IAA and another lipophilic weak acid, [¹⁴C]benzoic acid. Since low concentrations of fluorescein and its derivatives competed for the same membrane-bound site in vitro as did morphactin and NPA, the basis for both the specific stimulation of auxin accumulation and the inhibition of polar auxin transport by all these compounds may be their ability to interfere with the carrier-mediated efflux of auxin anions from cells. At higher concentrations, the decrease in accumulation of weak acids was nonspecific and thus may be the result of acidification of the cytoplasm and a general decrease in the driving force for uptake of the weak acids. Triiodobenzoic acid was an exception. Low concentration of TIBA (0.1–1 M) were much less effective than NPA in competing for the NPA receptor in vitro, but little different from NPA in ability to stimulate auxin uptake. One possibility is that TIBA, a substance which is polarly transported, may compete with auxin for the polar transport site while NPA, morphactin, and the fluorescein derivatives may render this site inactive.Abbreviations C1-NPA 2,3,4,5-tetrachloro-N-1-naphthylphthalamic acid - IAA indole-3-acetic acid - -NAA -naphthaleneacetic acid - -NAA -naphthalenacetic acid - NPA N-1-naphthylphthalamic acid - TIBA 2,3,5-triiodobenzoic acid     

Auxin-Growth Relationships in Maize Coleoptiles and Pea Internodes and Control by Auxin of the Tissue Sensitivity to Auxin

Growth of a zone of maize (Zea mays L.) coleoptiles and pea (Pisum sativum L.) internodes was greatly suppressed when the organ was decapitated or ringed at an upper position with the auxin transport inhibitor N-1-naphthylphthalamic acid (NPA) mixed with lanolin. The transport of apically applied ³H-labeled indole-3-acetic acid (IAA) was similarly inhibited by NPA. The growth suppressed by NPA or decapitation was restored by the IAA mixed with lanolin and applied directly to the zone, and the maximal capacity to respond to IAA did not change after NPA treatment, although it declined slightly after decapitation. The growth rate at IAA saturation was greater than the rate in intact, nontreated plants. It was concluded that growth is limited and controlled by auxin supplied from the apical region. In maize coleoptiles the sensitivity to IAA increased more than 3 times when the auxin level was reduced over a few hours with NPA treatment. This result, together with our previous result that the maximal capacity to respond to IAA declines in pea internodes when the IAA level is enhanced for a few hours, indicates that the IAA concentration-response relationship is subject to relatively slow adaptive regulation by IAA itself. The spontaneous growth recovery observed in decapitated maize coleoptiles was prevented by an NPA ring placed at an upper position of the stump, supporting the view that recovery is due to regenerated auxin-producing activity. The sensitivity increase also appeared to participate in an early recovery phase, causing a growth rate greater than in intact plants.     

Exploring the role of auxin in the androgynophore movement in Passiflora

The flowers of the species belonging to the genus Passiflorashow a range of features that are thought to have arisen as adaptations to different pollinators. Some Passiflora species belonging to the subgenus Decaloba sect. Xerogona, show touch-sensitive motile androgynophores. We tested the role of auxin polar transport in the modulation of the androgynophore movement by applying auxin (IAA) or an inhibitor of auxin polar transport (NPA) in the flowers. We recorded the movement of the androgynophore during mechano-stimulation and analyzed the duration, speed, and the angle formed by the androgynophore before and after the movement, and found that both IAA and NPA increase the amplitude of the movement in P. sanguinolenta. We hypothesize that auxin might have a role in modulating the fitness of these Decaloba species to different pollination syndromes and demonstrate that an interspecific hybrid between insect- and hummingbird-pollinated Xerogona species present a heterosis effect on the speed of the androgynophore movement.     

Ethylene Interacts with Auxin in Regulating Developmental Attenuation of Gravitropism in Flax Root

Previous research shows that gravity-sensing in flax (Linum usitatissimum) root is initiated during seed imbibition and precedes root emergence. In this study we investigated the developmental attenuation of flax root gravitropism post-germination and the involvement of ethylene. Gravity response deteriorated significantly from 3 to 11?h after root emergence, which occurred at around 19?h after imbibition (that is, from “age” 22 to 30?h). Although the root elongation rate increased from 22 to 30?h, the gravitropic curving rate declined steadily. Older roots were able to tolerate higher levels of exogenous IAA before inhibition of elongation and gravitropism occurred. The age-dependent effect of IAA on root growth and gravitropism suggests that young roots are more sensitive to auxin and respond to a smaller vertical auxin gradient than older roots upon horizontal gravistimulation. The ethylene synthesis inhibitor AVG (2-aminoethoxyvinyl glycine, 10?μM) or ethylene action inhibitor Ag⁺ (10?μM) stimulated gravitropic curvature of 30?h roots by 24 and 32%, respectively, but had no effect on 22?h roots, suggesting that as roots age, ethylene begins to play a role in root gravitropism. The auxin transport inhibitor NPA (N-naphthylphthalamic acid, 50?μM) reduced gravitropic curvature of 30?h roots by 24% but had no effect on 22?h roots. On the other hand, treating roots simultaneously with the auxin transport inhibitor and ethylene synthesis or action inhibitor stimulated gravitropic curvature of 30?h roots but not 22?h roots. Taken together, these data indicate that as roots develop, their weakened gravity response is due to decreased auxin sensitivity and possibly auxin transport regulated by ethylene.     

A saturable site responsible for polar transport of indole-3-acetic acid in sections of maize coleoptiles

The velocity of transport and shape of a pulse of radioactive indole-3-acetic acid (IAA) applied to a section of maize (Zea mays L.) coleoptile depends strongly on the concentration of nonradioactive auxin in which the section has been incubated before, during, and after the radioactive pulse. A pulse of [³H]IAA disperses slowly in sections incubated in buffer (pH 6) alone; but when 0.5–5 M IAA is included, the pulse achieves its maximum velocity of about 2 cm h^-1. At still higher IAA concentrations in the medium, a transition occurs from a discrete, downwardly migrating pulse to a slowly advancing profile. Specificity of IAA in the latter effect is indicated by the observation that benzoic acid, which is taken up to an even greater extent than IAA, does not inhibit movement of [³H]IAA. These results fully substantiate the hypothesis that auxin transport consists of a saturable flux of auxin anions (A^-) in parallel with a nonsaturable flux of undissociated IAA (HA), with both fluxes operating down their respective concentration gradients. When the anion site saturates, the movement of [³H]IAA is nonpolar and dominated by the diffusion of HA. Saturating polar transport also results in greater cellular accumulation of auxin, indicating that the same site mediates the cellular efflux of A^-. The transport inhibitors napthylphthalamic acid and 2,3,5-triiodobenzoic acid specifically block the polar A^- component of auxin transport without affecting the nonsaturable component. The transport can be saturated at any point during its passage through the section, indicating that the carriers are distributed throughout the tissue, most likely in the plasmalemma of each cell.Abbreviations A^- auxin anion - HA undissociated auxin - IAA indole-3-acetic acid - NPA N-1-napthylphthalamic acid - TIBA 2,3,5-triiodobenzoic acid     

The Promotion of the Immobilization of Auxin in Avena Coleoptiles by Triiodobenzoie Acid

A study was made of the inhibition of auxin transport in Avena coleopliles by 2, 3, 5-triiodobenzoic acid (TIBA), using carboxyl labelled ¹⁴C indole-3-acetic acid (IAA). A transport period of 1 hour followed by an export period of 2 hours was used routinely. Treatment with TIBA resulted in increased radioactivity remaining in the coleoptile sections after the export period. This radioactivity was distributed throughout the length of the coleoptile. The increase in radioactivity was shown to be due to an increase in the amount of IAA immobilized. The action of TIBA in inhibiting auxin transport is achieved by the promotion of the immobilization of IAA.     

Genetic Analysis of the Effects of Polar Auxin Transport Inhibitors on Root Growth in Arabidopsis thaliana

Polar auxin transport inhibitors, including N-1-naphthylphthalamicacid (NPA) and 2,3,5-triiodobenzoic acid (TIBA), have variouseffects on physiological and developmental events, such as theelongation and tropism of roots and stems, in higher plants.We isolated NPA-resistant mutants of Arabidopsis thaliana, withmutations designated pir1 and pir2, that were also resistantto TIBA. The mutations specifically affected the root-elongationprocess, and they were shown ultimately to be allelic to aux1and ein2, respectively, which are known as mutations that affectresponses to phytohormones. The mechanism of action of auxintransport inhibitors was investigated with these mutants, inrelation to the effects of ethylene, auxin, and the polar transportof auxin. With respect to the inhibition of root elongationin A. thaliana, we demonstrated that (1) the background levelof ethylene intensifies the effects of auxin transport inhibitors,(2) auxin transport inhibitors might act also via an inhibitorypathway that does not involve ethylene, auxin, or the polartransport of auxin, (3) the hypothesis that the inhibitory effectof NPA on root elongation is due to high-level accumulationof auxin as a result of blockage of auxin transport is not applicableto A. thaliana, and (4) in contrast to NPA, TIBA itself hasa weak auxin-like inhibitory effect. (Received April 12, 1996; Accepted September 2, 1996)     

Changes in starch and inositol 1,4,5-trisphosphate levels and auxin transport are interrelated in graviresponding oat (Avena sativa) shoots

This study was conducted to unravel a mechanism for the gravitropic curvature response in oat (Avena sativa) shoot pulvini. For this purpose, we examined the downward movement of starch-filled chloroplast gravisensors, differential changes in inositol 1,4,5-trisphosphate (IP(3)) levels, transport of indole-3-acetic acid (IAA) and gravitropic curvature. Upon gravistimulation, the ratio for IAA levels in lower halves versus those in upper halves (L/U) increased from 1.0 at 0 h and reached a maximum value of 1.45 at 8 h. When shoots were grown in the dark for 10 d, to deplete starch in the chloroplast, the gravity-induced L/U of IAA was reduced to 1.0. N-naphthylphthalamic acid (NPA) and 2,3,5-triiodobenzoic acid (TIBA), both auxin transport inhibitors, significantly reduced the amount of gravitropic curvature and gravity-induced lateral IAA transport, but did not reduce the gravity-induced late change in the L/U ratio of IP(3) levels. U73122, a specific phospholipase C (PLC) inhibitor, decreased gravity-induced curvature. Because U73122 reduced the ratio of L/U of IAA imposed by gravistimulation, it is clear that IAA transport is correlated with changes in IP(3) levels upon gravistimulation. These results indicate that gravistimulation-induced differential lateral IAA transport may result from the onset of graviperception in the chloroplast gravisensors coupled with gravity-induced asymmetric changes in IP(3) levels in oat shoot pulvini.     

Auxin activity of substituted benzoic acids and their effect on polar auxin transport

Six dichloro-, 3 trichloro-, 2 triiodo-, and 3 heterosubstituted benzoic acids (amiben, dinoben, dicamba), and N-1-naphthylphthalamic acid have been tested for effects on growth and on polar auxin transport. Growth activity with and without kinetin was measured by effects on fresh and dry weights of 30-day cultures of fresh tobacco pith. Transport inhibition was measured by following uptake and output of IAA-2-¹⁴C through 10 mm bean epicotyl sections. The distribution of callus growth on vascularized tobacco stem segments was also observed. Avena first internode extension assays established the relative activities: dicamba > amiben > dinoben suggested by pith growth results. Growth effects of active compounds were similar with and without kinetin, except that amiben was less active with kinetin, while 2,3,6-trichlorobenzoic acid was more active with kinetin than alone. The weak auxin activity of NPA was confirmed. Transport experiments showed that NPA was the most inhibitory compound tested, followed by TIBA. Other compounds tested were at least 300 times less inhibitory to IAA transport. The best growth promoters were the least inhibitory to transport, and the most effective transport inhibitors were at best poor auxins. It is suggested that the weak auxin and auxin synergistic activity of TIBA (and perhaps 2,3-dichlorobenzoic acid) in extension growth tests arises from its inhibition of transport of endogenous or added auxin out of the sections, rather than from its intrinsic auxin activity. Chemically induced apolar callus growth on vascularized tobacco stem explants can arise from inhibition of native auxin transport, apolar growth stimulation by auxinic action of the test compound, or both.     

THE TIMING OF AND EFFECT OF TEMPERATURE ON AUXIN-INDUCED HYPONASTIC CURVATURE OF THE BEAN PRIMARY LEAF BLADE

Detailed examination of the hyponastic curvature of the primary bean leaf blade in response to indoleacetic acid (IAA) shows that curvature begins within 15 min after application and increases to a maximal rate at 20 to 30 min. A second application of IAA results in a second curvature maximum when applied 1.5 hr or more after the first. Washing experiments indicate IAA uptake is largely complete by about 20 min after application, suggesting the return to planar form is accompanied by the uptake and passage of a wave of IAA through the responding cells. The rate of curvature decreases as the temperature is lowered, particularly below 14 C; at low concentrations (10^–4 m) the rate of response to 2,4-dichlorophenoxyacetic acid and 2,4,5-trichlorophenoxypropionic acid is slower than that for IAA and naphthaleneacetic acid. These differences are proposed to reflect the involvement of the polar auxin transport system in the response. The leaves of bean seedlings exposed to 4 C develop hyponastic curvatures when returned to normal growth temperature; 5 min treatment is sufficient to induce this response, and with longer treatments, greater curvatures are obtained. This curvature is inhibited by application of 2,3,5-triiodobenzoic acid (TIBA) to the undersurface of the leaf at the beginning of the cold treatment. The results are consistent with a model of planar plageotropic growth regulation in the leaf blade in which auxin produced by cells in the upper portion of the blade is transported by the polar transport system through cells in the lower portion that are growth limited by auxin supply. The hyponastic and epinastic effects caused by exogenous application of auxin or TIBA and of cold treatments are considered to result from changes in this auxin supply.