Effect of indoleacetic acid,abscisic acid,root tips and coleoptile tips on growth and curvature of maize roots

The effect of externally applied indoleacetic acid (IAA) and abscisic acid (ABA) on the growth of roots of Zea mays L. was measured. Donor blocks of agar with IAA or ABA were placed laterally on the roots and root curvature was measured. When IAA was applied to vertical roots, a curvature directed toward the donor block was observed. This curvature corresponded to a growth inhibition at the side of the root where the donor was applied. When IAA was applied to horizontal roots from the upper side, normal geotropic downward bending was delayed or totally inhibited. The extent of retardation and the inhibition of curvature were found to depend on the concentration of IAA in the donor block. ABA neither induced curvature in vertical roots nor inhibited geotropic curvature in horizontal roots; thus the growth of roots was not inhibited by ABA. However, when, instead of donor blocks, root tips or coleoptile tips were placed onto vertical roots, a curvature of the roots was observed.Abbreviations ABA abscisic acid - IAA 3-indoleacetic acid     

The lateral transport of IAA in intact coleoptiles of Avena sativa L. and Zea mays L. during geotropic stimulation

Summary Movement of IAA was studied in excised coleoptile apices and whole seedlings of Zea mays L. and Avena sativa L. during geotropic stimulation. A micropipette technique permitted the application of [5-³H]IAA at predetermined points on the coleoptiles with minimal tissue damage.When [5-³H]IAA was applied to the upper side of a horizontal excised Zea coleoptile, about 60% of the recoverable radioactivity had moved into the lower half after 2 h. In contrast, when application was made to the lower side of a horizontal excised coleoptile, only 4% of the radioactivity migrated to the upper half. There was, thus, a net downward movement of 56%. Similar patterns of distribution were found for radioactivity in both the tissue and the basal receiver blocks. In horizontal shoot tissues of intact Zea seedlings a net downward movement of about 30% of the recoverable radioactivity occurred after 1 h of geotropic stimulation. Comparable experiments with Avena indicated a net downward movement of 6–12% in excised apices of coleoptiles and in the intact shoot. In both Zea and Avena chromatographic analyses of tissue and receiver blocks indicated that the movement of radioactivity reflected that of IAA.In Zea coleoptiles, the lateral migration of radioactivity after 2 h was 3 to 4 times greater in the apical tissues than in the basal tissues. A significant net downward movement of radioactivity was detected after 10 min of geotropic stimulation in the extreme apex of Zea coleoptiles but not in the more basal regions.These experiments show that downward lateral transport of IAA occurs in intact shoots of Zea and Avena seedlings upon geotropic stimulation. Lateral transport of IAA had previously been demonstrated only in sub-apical segments of Zea coleoptiles.     

IAA transport during the phototropic responses of intact Zea and Avena coleoptiles

Summary Transport of indolyl-3-acetic acid (IAA) was studied during the phototropic responses of intact shoots and detached coleoptiles of Zea mays L. and Avena sativa L. The use of a high specific activity [5-³H]IAA and glass micropipettes enabled asymmetric application of the IAA to be made to individual coleoptiles with minimal tissue damage.A unilateral stimulus of 2.59×10^-11 einstein cm^-2 of blue light, probably in the dose range of the first positive phototropic response, caused significant net lateral movement of radioactivity from [5-³H]IAA away from the illuminated side of intact shoots and detached coleoptile apices of both Avena and Zea. The magnitude of the net lateral movement was 15.3% in Zea seedlings and 12.3% in Avena seedlings. Chromatographic analyses indicated that the movement of radioactivity reflected that of IAA. A phototropic stimulus of 1.24×10^-7 einstein cm^-2, which was probably in the second positive dose range, caused significant lateral movement of radioactivity in intact shoots and detached coleoptiles of Zea but not of Avena.In intact Zea seedlings, neither phototropic dosage affected the longitudinal transport of IAA. In intact Avena seedlings, first positive stimulation inhibited longitudinal transport only when the IAA was applied to the illuminated side of the coleoptile, but second positive stimulation inhibited basipetal movement of IAA regardless of the side of application.Exposing the intact seedlings to red light before phototropic stimulation abolished lateral transport after a first positive stimulus in Zea and in Avena.Phototropic stimulation can thus induce a lateral transport of IAA towards the shaded side of the coleoptiles of both Zea and Avena seedlings, and can affect longitudinal movement of IAA in the coleoptile of Avena. However, since phototropic curvature was observed under certain conditions in the absence of either of these effects, the extent to which they are involved in the induction of asymmetric growth in a stimulated coleoptile has yet to be resolved.     

Levels of indole-3-acetic acid in intact and decapitated coleoptiles as determined by a specific and highly sensitive solid-phase enzyme immunoassay

A specific solid-phase enzyme immunoassay for the detection of as little as 3–4 pg of indole-3-acetic acid (IAA) is described. The assay involves minimal procedural efforts and requires only standard laboratory equipment. Up to 50 samples in triplicate, processed simultaneously, can be assayed and evaluated in 2.5 h. As little as 1 mg oat coleoptile tissue is sufficient for a quantitative IAA analysis and little or no extract purification is necessary. Using this assay, levels of IAA have been determined in coleoptiles of maize and oat. The distribution of IAA within single coleoptiles was quantitated and the production of IAA during the regeneration of the physiological tip in Avena coleoptiles was investigated. The changes in levels of IAA and other major phytohormones were quantitated during the growth of oat coleoptiles.Abbreviations ABA abscisic acid - BHT butylated hydroxytoluene - BSA bovine serum albumin - IAA indole-3-acetic acid - TBS Trishydroxymethylaminomethane buffered saline Part 21 in the series Use of Immunoassay in Plant Science     

The role of the apex in the phototropic curvature of Avena coleoptiles: positive curvature under conditions of continuous illumination

The differential growth causing second positive phototropic curvature in intact, black-capped and decapitated Avena coleoptiles has been measured. In all cases the curvature is brought about by a cessation in growth of the illuminated side. The fact that shading the apex does not significantly alter the initial steps of differential growth means that the subapical zones can perceive and respond to unilateral illumination. Decapitation significantly reduces coleoptile growth, especially in the most apical zone. However, the fact that differential growth is still evident in the other zones of decapitated coleoptiles within 30 min of unilateral illumination requires one to conclude that the apex cannot be controlling the differential growth in those basal zones.     

Revision of the theory of phototropism in plants: a new interpretation of a classical experiment

Went's classical experiment on the diffusion of auxin activity from unilaterally illuminated oat coleoptile tips (Went 1928), was repeated as precisely as possible. In agreement with Went's data with theAvena curvature assay, the agar blocks from the illuminated side of oat (Avena sativa L. cv. Victory) coleoptile tips had, on an average, 38% of the auxin activity of those from the shaded side. However, determination of the absolute amounts of indole-3-acetic acid (IAA) in the agar blocks, using a physicochemical assay following purification, showed that the IAA was evenly distributed in the blocks from the illuminated and shaded sides. In the blocks from the shaded and dark-control halves the amounts of IAA were 2.5 times higher than the auxin activity measured by theAvena curvature test, and in those from the illuminated half even 7 times higher. Chromatography of the diffusates prior to theAvena curvature test demonstrated that the amounts of two growth inhibitors, especially of the more polar one, were significantly higher in the agar blocks from the illuminated side than in those from the shaded side and the dark control. These results show that the basic experiment from which the Cholodny-Went theory was derived, does not justify this theory. The data rather indicate that phototropism is caused by the light-induced, local accumulation of growth inhibitors against a background of even auxin distribution, the diffusion of auxin being unaffected.Abbreviation IAA indole-3-acetic acid     

Phototropic stimulation does not induce unequal distribution of indole-3-acetic acid in maize coleoptiles

Distribution of endogenous diffusible auxin into agar blocks from phototropically stimulated maize coleoptile tips was studied using a bioassay and a physicochemical assay, to clarify whether phototropism in maize coleoptiles involves a lateral gradient in the amount of auxin. At 50 min after the onset of phototropic stimulation, when the phototropic response was still developing, direct assay of the blocks with the Avena curvature test showed that the auxin activity in the blocks from the shaded half-tips was twice that of the lighted side, at both the first and second positive phototropic curvatures. However, physicochemical determination following purification showed that the amount of indole-3-acetic acid (IAA) was evenly distributed in the blocks from lighted and shaded coleoptile half-tips at both the first and second positive phototropic curvatures. The even distribution of the IAA was also confirmed with the Avena curvature test following purification by HPLC. These results indicate that phototropism in maize coleoptiles is not caused by a lateral gradient of IAA itself and thus cannot be described by the Cholodny-Went theory. Furthermore, the lower auxin activity in the blocks from the lighted half-tips suggests the presence of inhibitor(s) interfering with the action of auxin and their significant diffusion from unilaterally illuminated coleoptile tips.     

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 .     

Regulation of Growth in Avena (Oat) Stem Segments by Gibberellic Acid and Abscisic Acid

The purpose of this study was to analyze the nature of the interaction between gibberellic acid (GA₃) and abscisic acid (ABA) in the regulation of growth in excised Avena (oat) stem segments. Growth, compared to sucrose controls, was inhibited by ABA in the range of 10^?4 to 10^?6M. GA₃-promoted growth was also inhibited by ABA in the same concentration range. A Lineweaver-Burk analysis of the interaction between GA₃ and ABA indicated that ABA acts in a non-competitive fashion with GA₃. This same result was obtained previously with GA₃-indoleacetic acid (IAA) and GA₃-kinetin interactions with Avena stem sections. Our results indicate that ABA can inhibit GA₃-promoted growth within physiological concentrations, and that it is probably acting at a different physiological site from that for GA₃.     

The Geoelectric Effect in Plant Shoots: III. DEPENDENCE UPON AUXIN CONCENTRATION GRADIENTS AND AEROBIC METABOLISM

The development of the geoelectric effect has been followedin Zea coleoptiles with a flowing-solution electrode system,and its dependence upon auxin concentration gradients and aerobicmetabolism assessed. A symmetrical source of IAA can effectively replace the coleoptiletip in allowing the geo-electric potential to occur. The diffusatefrom coleoptile tips, when applied asymmetrically to the apexof a vertical decapitated coleoptile, generates a potentialdifference across the coleoptile indistinguishable from thatinduced by the asymmetrical application of IAA. Asymmetricalapplication of IAA to vertical Avena and Zea coleoptiles andHelianthus hypocotyls induces closely similar responses. Neither the geoelectric effect nor a geotropic response developswhen intact Zea coleoptiles are placed horizontally after beingdeprived of oxygen, but they both occur when an aerobic atmosphereis restored. The lateral potential difference induced by theasymmetrical application of IAA to the apex of a vertical coleoptiledoes not occur under anoxic conditions. With a static-drop electrode system and a decapitated Zea coleoptile,a potential difference develops immediately after reorientationof the coleoptile into the horizontal position, and attainsa maximum value after about 10 min. This potential differencecan be further increased by the asymmetrical application ofIAA to the lower half of the apical cut surface of the coleoptile. Our data support the view that both the geoelectric potentialand the geotropic response are due to the IAA concentrationgradient which arises from the lateral transport of this substancefrom the upper to the lower half of the horizontal shoot. Theyalso bear out our previous conclusions that the ‘geoelectricpotential’ observed with static-drop electrodes and anintact shoot, is the resultant of two processes. The first isa physical phenomenon arising in the electrodes, or betweenthe electrodes and the plant tissue, and the second arises inthe living tissues of the shoot as the result of gravity-inducedchanges in auxin distribution.     

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.

     

Gibberellic acid induces cytoplasmic acidification in maize coleoptiles

Indole-3-acetic acid (IAA), fusicoccin and weak acids all lower the cytoplasmic pH (pH_i) and induce elongation growth of maize (Zea mays L.) coleoptiles. Gibberellic acid (GA₃) also induces elongation growth and we have used confocal laser scanning microscopy to study the effects of GA₃ on pH_i employing the pH-indicator dyes, 2,7-bis(2-carboxyethyl)-5-(and-6) carboxyfluorescein and carboxy-semi-naphthorhodafluor-1. We confirm that GA₃ induces growth significantly in light-grown but only slightly or not at all in dark-grown coleoptiles. The growth induced by IAA treatment was similar in light- and dark-grown coleoptiles. The pH_i decreased by up to 0.6 units during the first 7 min of GA₃ or IAA treatment of both light- and dark-grown coleoptiles. Gibberellic acid inhibited IAA-induced growth of dark-grown coleoptiles. Hence, in dark-grown coleoptiles GA₃ may activate either directly or indirectly reactions that interfere with the signalling pathway leading to elongation growth. The possible role of pH_i in growth is discussed.Abbreviations ABA abscisic acid - AM acetoxymethyl ester - BCECF 2,7-bis(2-carboxyethyl)-5-(and-6) carboxyfluorescein - [Ca²⁺]_i cytoplasmic free calcium - GA_(n) gibberellin A_(n) - GA₃ gibberellic acid - IAA indole-3-acetic acid - PGR plant growth regulator - pH_i cytoplasmic pH - Pipes piperazine-N,N-bis[2-ethanesulfonic acid] - Snarf-1 carboxy-semi-naphthorhodafluor-1 We thank Dr R. King (CSIRO, Canberra) for providing the GA₁ and T. Phillips for processing the photographic material. H.R. Irving was supported by an Australian Research Council Research Fellowship and the work was supported by an Australian Research Council grant.     

Studies on the action of abscisic acid on IAA-induced rapid growth of Avena coleoptile segments

Summary A linear displacement transducer has been used to monitor the growth of a column of Avena coleoptile segments in flowing solution. IAA at 10^-5M in phosphate buffer of pH7 promotes growth after a latent period of 10.9 min, the initial maximum growth rate occurring after 25 min. Simultaneous treatment with 10^-5 M ABA does not affect either the latent period or the initial maximum growth rate in response to the IAA treatment, but subsequently gives rise to an inhibition of growth detectable after 30 min. In contrast, pretreatment with ABA for 100 min increases the duration of the latent period and reduces the initial maximum growth rate. Removal of the ABA rapidly relieves the inhibition of IAA-induced growth but a growth rate comparable to that of material treated only with IAA is never attained. Studies using 2-[¹⁴C]ABA and 1-[¹⁴C]IAA suggest that the latent period before ABA inhibition of growth is detectable is not due to a lag in ABA uptake, and that ABA is not acting by reducing IAA uptake.     

The Effects of Externally Applied 3-indolylacetic Acid on Phototropic Induction and Response in the Coleoptile of Avena

The effects of intermittent immersion of Avena seedlings insolutions of IAA on the response of the coleoptiles to unilateralillumination in the region of that producing the second positivecurvature were studied by means of automatic time-lapse photographywhich enabled the growth-rate and curvature to be recorded simultaneously. Phototropic induction occurred even after the coleoptiles hadabsorbed sufficient IAA from a 10^-4 M. solution to raise theirrate of elongation to about twice the normal value. Phototropiccurvature, which had been temporarily inhibited by a curvaturein the opposite direction induced by the IAA, became evidentas soon as this curvature had ceased to operate. In coleoptiles, supplied with IAA after the commencement ofa phototropic curvature, the response was temporarily suppressed.It was resumed as soon as the effects of the exogenous IAA haddisappeared. The ability of the coleoptiles to produce a slight phototropicresponse persisted even when their growth-rate had been greatlyreduced by previous removal of the endosperm. Increasing thegrowth-rate by supplying the starved seedlings with IAA or sucrose,separately or together, failed to increase the response. Decapitation did not prevent phototropic induction, but delayedthe onset of the response. Application of IAA by intermittentimmersion in a 0.1 mg./l. solution, after the decapitated coleoptileshad been exposed to unilateral illumination, increased the rateof growth but reduced the response. The results suggest that in these experiments phototropic inductionwas not mediated by any direct action of light on the displacement,inactivation, or rate of synthesis of an endogenous auxin. Theyare in agreement with the hypothesis that the stimulus causedan asymmetrical distribution of a co-factor of auxin.     

Fusicoccin-induced growth and hydrogen ion excretion of Avena coleoptiles: Relation to auxin responses

Summary The fungal toxin fusicoccin (FC) induces both rapid cell elongation and H⁺-excretion in Avena coleoptiles. The rates for both responses are greater with FC than with optimal auxin, and in both cases the lag after addition of the hormone is less with FC. This provides additional support for the acid-growth theory. The FC responses resemble the auxin responses in that they are inhibited by a range of metabolic inhibitors, but the responses differ in three ways. First auxin, but not FC, requires continual protein synthesis for its action. The auxin-induced H⁺-excretion is inhibited by water stress or by low external pH, while the FC-induced H⁺-excretion is much less sensitive to either. It is concluded that auxin-induced and FC-induced H⁺-excretion may occur via different mechanisms.Abbreviations FC fusicoccin - DNP dinitrophenol - CCCP carbonylcyanide m-chlorophenylhydrazone - CHl cycloheximide - IAA indoleacetic acid     

Modalités de l'inhibition de la croissance et de la synthèse des acides nucléiques des plantules de blé par l'acide abscissique

The growth of wheat seedlings (Triticum sativum) is inhibited by abscisic acid (ABA). The inhibition increases with the concentration of ABA (from 10^-6M to 5 × 10^-5M) and is stronger in the case of coleoptiles and first leaves than in roots. In contrast, naphthaleneacetic acid (ANA), at 10^-5M, exerts its greatest inhibitory effect on the roots. The inhibitory effect of ABA on coleoptiles can be partially overcome by kinetin and to a much smaller degree by gibberellic acid. Neither of these two compounds, at 10^-5M, had any effect on the ABA-induced inhibition of root growth. The RNA and DNA contents per plant organ are considerably reduced after treatment of the seedlings with ABA, particularly in the coleoptiles and the first leaves. The incorporation of uracil-2-¹⁴C and uridine T (G) into RNA of treated seedlings is reduced in the case of coleoptiles and first leaves, but considerably enhanced in roots. The mechanism of the action of ABA is discussed in the light of these results.     

Investigations on the Nature of the Auxin-Wave in the Cambial Region of Pine Stems : Validation of IAA as the Auxin Component by the Avena Coleoptile Curvature Assay and by Gas Chromatography-Mass Spectrometry-Selected Ion Monitoring

The major auxin of Scots pine (Pinus silvestris L.) which is transported basipetally into agar strips from the cambial region of the stem was quantified by the Went Avena coleoptile curvature assay before and after reversed phase C₁₈ high performance liquid chromatography (HPLC), and then identified by full spectrum gas chromatography-mass spectrometry (GC-MS) as indole-3-acetic acid (IAA). The IAA was subsequently quantified by GC-MS-selected ion monitoring (SIM) using an internal standard of [¹³C]-(C₆)-IAA. The amount of IAA collected into 22-millimeter long agar strips during 10 minutes of contact with the stem cambial region was estimated by GC-MS-SIM and the Went bioassay to be 2.3 and 2.1 nanograms per strip, respectively. The GC-MS technique thus confirmed the results obtained by the Went curvature assay. The Avena curvature assay revealed the presence of at least one other, more polar (based on HPLC retention time) auxin that diffused into the agar strips with the IAA. Its bioactivity was only 5% of the IAA fraction. Its HPLC retention time was earlier than IAA-glucoside, IAA-aspartate, or IAA-glycine, but the same as IAA-inositol. No significant amounts of inhibitors or synergists of IAA activity on the Avena assay were found in extracts corresponding to one or five strips of agar. Thus, the direct bioassay of the agar strips immediately after their removal from the cambial region of P. silvestris stem sections reflects the concentration of the native IAA. For both P. silvestris and lodgepole pine (Pinus contorta) a wavelike pattern of auxin stimulation of Avena curvature was found in agar strips exposed for only 10 minutes to the basal ends of an axial series of 6-millimeter long sections from the cambial region of the stem. This wavelike pattern was subsequently confirmed for P. contorta both by Avena curvature assay and by GC-MS-SIM of HPLC fractions at the retention time of [³H]IAA. The wavelike pattern of auxin diffusing from the cambial region of Pinus has thus been determined to consist primarily of IAA and this pattern has now been quantitated using both the Went Avena curvature assay and GC-MS-SIM with [¹³C]-C₆-IAA as an internal standard.     

Transport and metabolism of [214-C]abscisic acid in maize root

The tips of intact maize (cv. LG 11) roots, maintained vertically, were pretreated with a droplet of buffer solution or a bead of anion exchange resin, both containing [2¹⁴-C]abscisic acid (ABA). A significant basipetal ABA movement was observed and two metabolites of ABA (possibly phaseic acid and dihydrophaseic acid) were found. ABA pretreatment enhanced the gravireaction of 10 mm apical root segments kept both in the dark and in the light. The possibility that ABA could be one of the endogenous growth inhibitors produced or released by the cap cells is discussed.Abbreviations ABA abscisic acid - 3,3-DGA 3,3-dimethyl-glutaric acid - DPA dihydrophaseic acid - PA phaseic acid - GCMS gas chromatography-mass spectrometry     

Growth of Avena coleoptiles and pH drop of protoplast suspensions induced by chlorinated indoleacetic acids

Several indoleacetic acids, substituted in the benzene ring, were compared in the Avena straight growth bioassay. 4-Chloroindoleacetic acid, a naturally occurring plant hormone, is one of the strongest hormones in this bioassay. With an optimum at 10^-6 mol l^-1, it is more active than indoleacetic acid, 2,4-dichlorphenoxyacetic acid and naphthaleneacetic acid. 5-Chloro- and 6-chloroindoleacetic acids are very strong auxins as well. Other derivatives tested have a lower activity. 5,7-Dichloro- and 5-hydroxyindoleacetic acids have very low auxin activity at 10^-4 mol l^-1 and may be anti-auxins. Some of the derivatives were compared for their effect on pH decline in stem protoplast suspensions of Helianthus annuus L. and Pisum sativum L. The change of pH occurs without a lag period or with only a very short one. Derivatives which are very active in the Avena straight growth assay cause a larger pH decline than indoleacetic acid, while inactive derivatives cause effectively no pH decline.Abbreviations IAA Indoleacetic acid - 4-Cl-IAA 4-chloroindoleacetic acid - 5,7-Cl₂-IAA etc 5,7-dichloroindoleacetic acid     

Effect of morphactin on certain plant growth substances in bean roots

The effect of morphactin (methyl-2-chloro-9-hydroxyfluorene-9-carboxylate) on the content of several plant growth substances in bean roots was determined. Beans (Phaseolus vulgaris L. cv. Spartan) were soaked in aqueous solutions of morphactin, 1 x 10^-4, 1 x 10^-5, and 1 x 10^-6M and grown in moist vermiculite. As controls were used beans grown in water-moistened vermiculite either intact or having the root tips removed (decapped). The roots, morphactin-treated, controls, and the decapped ones were analyzed for indol-3-yl acetic acid (IAA), indol-3-yl acrylic acid (IAcA), indol-3-yl pyruvic acid (IPyA), indol-3-yl lactic acid (1LA), abscisic acid (ABA), gibberellins GA₁, GA₃, GA₄, and GA₉ using gas-liquid chromatographic methods. Morphactin, while affecting the geotropical responses, changed also the growth substance content of roots. IAA, ABA, GA₁, and GA₉ contents decreased, IPyA, IAeA, GA₃, and GA₄ contents were not affected and ILA content increased slightly with increasing dosages of morphactin. Growth substance pattern of decapped roots resembled that of the roots treated with the highest dose, 1 x 10^-4M, of morphactin.