Root Growth Inhibitors from Root Cap and Root Meristem of Zea mays L.

A micro-assay based on the growth inhibition of root segmentsof the seminal roots of Zea mays has been used to investigatethe root-growth-inhibiting substances in root caps and meristemsrespectively of the roots of Zea mays. This micro-assay is sensitiveto 50 pg of IAA or less. Paper chromatography of the acid fractionof methanolic extracts shows the presence of one main inhibitorin root caps and a different main inhibitor in root meristems.Neither is IAA, whose presence in meristems is sometimes indicatedby small inhibitions (or stimulations) at the characteristicRf of IAA. A Commelina leaf-epidermis assay shows the presenceof one stomata-closing ABA-like substance in root caps and onein meristems, one corresponding in Rf to the main root-growthinhibitor from the root cap. The implications of these findingsfor the geotropic responses of roots is briefly discussed.     

Metabolism of Some Indole Auxins in Excised Tomato Roots

Indolylacetylaspartic acid (IAAsp) and possibly indolylacetylglutamicacid (IAG) are formed by exposure of excised tomato roots toIAA. Little ‘free’ IAA accumulates in the tissue.An unidentified substance reacting pink with nitricnitrite reagentis also formed. These substances are metabolized when IAA-treatedroots are transferred to auxin-free medium. IAAsp and IAA aresimilarly inhibitory to the growth of excised tomato roots.Excised tomato roots do not interconvert IAA and IAN. IAN-feedingleads to IAN accumulation and the appearance of indolylcarboxylicacid (ICA); transference to auxin-free medium causes a declinein the IAN activity but the ICA spot persists. The inhibitoryactivity of IAN is not due to its conversion to ICA. Excisedtomato and wheat roots respond very differently to externall-tryptophane but in neither case is there evidence of the conversionof tryptophane to ethyl acetate-soluble auxins.     

Identification of 3-Hydroxy-2-indolone-3-acetylaspartic Acid as a New Indole-3-acetic Acid Metabolite in Vicia Roots

A new indole-3-acetic acid (IAA) metabolite in the root of Viciafaba L. cv. Chukyo was identified as 3-hydroxy-2-indolone-3-acetylasparticacid, with the simpler name of dioxindole-3-acetylaspartic acid,by comparison with the authentic sample. Formation of dioxindole-3-aceticacid conjugates seems to be a major route of IAA metabolismin Vicia roots. (Received October 22, 1985; Accepted January 7, 1986)     

Lateral Root Development in Attached and Excised Roots of Zea mays L. Cultivated in the Presence or Absence of Indol-3-yl Acetic Acid

The initiation of lateral root primordia and their subsequentemergence as secondary roots have been examined in attachedand excised roots of Zea mays grown in the presence or absenceof indol-3-yl acetic acid (IAA). Exposure to IAA enhanced anlageinception in both batches of roots. In the attached roots, theIAA-induced stimulation of primordium initiation was followedby a similar increase in lateral emergence. IAA treatment, however,had no effect on the number of laterals produced, per centimetreof root, in the excised primaries. Thus, exposure to IAA didnot directly enhance lateral emergence in the attached rootsnor did it stimulate such emergence in the excised ones. Nocorrelation was found between proliferative activity in themeristem at the apex of the primary or the rate of root elongationon the one hand, and either the number of primordia initiated,or the number of laterals produced, per centimetre of primary,on the other. Zea mays, maize, root, primordium, lateral, indol-3-yl acetic acid, meristematic activity     

Transport of shoot- and cotyledon-applied indole-3-acetic acid to Vicia faba root

To clarify the participation of indole-3-acetic acid (IAA) originatingfrom the shoot in root growth regulation and the mechanism ofIAA translocation from shoot to root, the movement of ¹⁴C-IAAwhich was applied to the epicotyl or the cotyledon of Viciafaba seedlings was investigated. The radioactivity of IAA appliedto the cotyledon moved faster to the root tip than that appliedto the epicotyl. On the basis of the effect of 2,3,5-triiodobenzoic acid on IAAmovement, a comparison with ¹⁴C-glucose movement and autoradiographicexamination, the nature of IAA movement was concluded to bepolar transport from the epicotyl to the basal part of the roots,while IAA movement from the epicotyl to the cotyledon, fromthe basal part of roots to the apical part, and from the cotyledonto the epicotyl and to the root took place in the phloem. Theradioactivity from ¹⁴C-IAA applied to the cotyledon accumulatedin lateral root primordia and vascular bundles. These factssuggest that IAA produced in cotyledons may participate in theregulation of Vicia root development. (Received December 21, 1979; )     

Some Effects of Indol-3-yl Acetic Acid on Lateral Root Development in Attached and Excised Roots of Pisum sativum L.

The effect of continuous exposure to indol-3-yl acetic acid(IAA) on primordium initiation and their subsequent emergenceas lateral roots was determined in excised and attached rootsof Pisum sativum. IAA was found to stimulate the number of primordiainitiated per centimetre of attached or excised primary. Similarly,lateral emergence in terms of the number produced per centimetreof primary was promoted in the presence of IAA. This stimulationof lateral emergence even took place in excised roots whichwere 1 cm in length at the onset of culture and which neverproduced secondary roots over a 6-d culture period when grownin the absence of auxin. These effects of IAA on lateral rootdevelopment have been considered in relation to the concurrentchanges which take place in proliferative activity in the apicalmeristem of the primary root during exposure to auxin. Pisum sativum, garden pea, anlage, primordium, emerged lateral, cell proliferation, indol-3-yl acetic acid     

Stimulation of indoleacetic acid production in a <Emphasis Type="Italic">Rhizobium</Emphasis> isolate of <Emphasis Type="Italic">Vigna mungo</Emphasis> by root nodule phenolic acids

The influence of endogenous root nodules phenolic acids on indoleacetic acid (IAA) production by its symbiont (Rhizobium) was examined. The root nodules contain higher amount of IAA and phenolic acids than non-nodulated roots. Presence of IAA metabolizing enzymes, IAA oxidase, peroxidase, and polyphenol oxidase indicate the metabolism of IAA in the nodules and roots. Three most abundant endogenous root nodule phenolic acids (protocatechuic acid, 4-hydroxybenzaldehyde and p-coumaric acid) have been identified and their effects on IAA production by the symbiont have been studied in l-tryptophan supplemented yeast extract basal medium. Protocatechuic acid (1.5 μg ml⁻¹) showed maximum stimulation (2.15-fold over control) of IAA production in rhizobial culture. These results indicate that the phenolic acids present in the nodule might serve as a stimulator for IAA production by the symbiont (Rhizobium). Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. An erratum to this article can be found at     

The Involvement of Indole-3-Acetic Acid Produced by Bradyrhizobium elkanii in Nodule Formation

IAA-deficient mutants T10, T27 and TN3 were isolated from B.elkanii USDA 31 by spontaneous and/or N-methyl-N'-nitro-N-nitrosoguanidine(NTG) mutageneses. Inoculation with these mutants significantlyreduced the nodule number on soybean roots when compared tothat of the parent strain. Furthermore, exogenous IAA applicationrestored the nodule number of soybeans inoculated with TN3 tothe original level. (Received July 18, 1994; Accepted September 13, 1994)     

Inoculation with Azospirillum lipoferum Affects Growth and Gibberellin Status of Corn Seedling Roots

Maize (Zea mays L., hybrid Cargill 147) seedlings, grown inaseptic conditions, were inoculated with three strains of Azospirillumlipoferum (Al op 33, Al iaa 320, and ATCC 29708) or culturedin different concentrations of indol-3-acetic acid (IAA) orgibberellin A₃ (GA₃). After 48 h, root length, root surfacearea, root dry weight, and shoot dry weight were measured inall treatments. Gibberellin content was evaluated in selectedroots of control and Azospirillum inoculated seedlings by gaschromatography-mass spectrometry-selected ion monitoring withthe use of deuterated gibberellins as internal standards. Thethree strains of A. lipoferum, IAA (2 ng ml^–1), and GA₃(40 to 400 pg ml^–1) significantly enhanced root growth.Improvement of root hair growth and density was obtained mainlywith A. lipoferum strain Al op 33 and GA₃ 40 pg ml^–1.GA₃ was identified by gas chromatography-mass spectrometry (byboth, full scan and selected ion monitoring) in a free acidfraction from roots of the seedlings inoculated with A. lipoferum.In the roots of the non inoculated seedlings GA₃ was found afterhydrolysis of a fraction expected to contain glucosyl conjugates. (Received April 26, 1993; Accepted September 27, 1993)     

The Effect of the Conversion of Indolebutyric Acid into Indoleacetic Acid on Root Formation on Microcuttings of Malus

The uptake and metabolism of tritiated indolebutyric acid (IBA)and indoleacetic acid (IAA) were related to root regenerationon stem bases of apple (Malus cv "Jork") shootlets culturedin vitro. The major part of the auxins taken up from the mediumwas located in the bottom 1 mm of the stem basis, the locationwhere the roots emerge. In this part of the shoot about 4% ofthe accumulated IBA-³H remained in the free acid. Analysis onnormal phase TLC followed by reversed phase HPLC revealed thatabout 1% of the IBA-metabolites co-chromatographed with standardIAA. Incubation of shoots on medium with IAA led also to anIAA^int content of about 1% of the amount absorbed. IAA was notconverted into IBA. A medium concentration of 3.2 µM IAAor IBA induced maximum root formation of 9 and 13 roots pershoot, respectively. The IAA^int content in the stem base was0.5 µmol per kg FW after 5 days regardless of the auxinsource. Incubation on medium with IBA led to an IBA^int concentrationof 3.4 µmol per kg FW. IBA may exert its action partlyvia conversion into IAA. However, the fact that IBA inducedmore roots than IAA suggests that IBA itself is also active,or modulates the activity of IAA. The partition of absorbed auxin over active free auxin acidand individual conjugates was not directly related to root formation.At inductive and non-inductive auxin concentrations no shiftin the ratio of free auxin acids to total absorbed auxin wasobserved during root formation. (Received March 4, 1992; Accepted May 25, 1992)     

Automated Recording of Lettuce Root Elongation as Affected by Auxin and Acid pH in A New Rhizometer with Minimum Mechanical Contact to Roots

The elongation of many lettuce roots was separately recordedat the same time by a new rhizometer with minimum mechanicalcontact to root tips. The apparatus was operated by a microcomputersystem interfaced with field-effect transistor circuits. Elongationresponses of intact seedling roots (ISR), decotylized seedlingroots (DSR) and excised apical roots (EXR) to different concentrationsof H⁺ and IAA were compared. A pH 4-induced acid growth wasobserved only in DER and EXR, whereas a pH 3-induced one wasobserved in all roots. Duration of pH 3-induced elongation wasshorter in ISR than in DSR and EXR. Growth curves suggested that ISR is more susceptible to acid-injurythan EXR. The maximum acid growth was obtained at pH 2.5 inEXR which is comparable to thick roots of maize [Edwards andScott (1974) Planta 119: 27]. Indole-3-acetic acid showed growthinhibition at concentrations higher than 10^–8 M whichis comparable to other reports on thick roots. It is concludedthat fine lettuce roots have the same magnitude of sensitivityto external concentration of H⁺ and IAA as thick roots. It isalso suggested that root excision or decotylization makes rootsless susceptible to acid-injury, resulting in greater acid-growthof EXR. Further characteristics and application of the new rhizometerare discussed. (Received March 19, 1986; Accepted September 8, 1986)     

Production and metabolism of indole acetic acid in roots and root nodules of Phaseolus mungo

The mature root nodules of Phaseolus mungo (L.), a leguminous pulse, contain higher amount of indole acetic acid (IAA) than non-nodulated roots. The tryptophan pool present in the mature nodule and young roots might serve as a precursor for the IAA production. Presence of IAA metabolising enzymes – IAA oxidase and peroxidase – indicate the metabolism of IAA in the nodules and roots. In culture, the symbiont, isolated from the nodules, produced a high amount of IAA, when tryptophan was supplied in the medium as a precursor. The symbiont preferred l-isomer over the dl- or d-isomer of tryptophan for IAA production.The important physiological implication of the IAA production in the legume-Rhizobium symbiosis is discussed.     

Effects of Growth Hormone Application on the Secondary Growth of Roots and Stems in Picea sitchensis (Bong.) Carr

Indol-3-ylacetic acid (IAA), gibberellin A3 (GA) and 6 benzylaminopurine(BAP) were applied factorially each at 3x10^–2 M in lanolinto the roots and stems of Sitka spruce seedlings and the activityof the two secondary meristems, the vascular cambium and phellogen,and of the parenchymatous tissues between them, was examined.All the treatments, with the exception of GA produced a localizedstimulation of radial growth at the point of application andthere was a similarity in the response of the various tissuesin both the root and stem. Radial growth of the xylem was notsignificantly affected in the roots whereas in the stems BAPand IAA stimulated growth. In the phloem BAP produced significantstimulation in both roots and stems and IAA stimulated growthin the roots. Growth of the parenchyma and periderm externalto the phloem was also strongly stimulated by both BAP, andIAA in roots and stems. In roots and stems the application of BAP altered the derivativesproduced by the vascular cambium, resulting in the productionof large multiseriate rays in the xylem, and giving rise toan overall increase in the proportion of ray tissue. Picea sitchensis (Bong.) Carr, Sitka spruce, secondary growth, xylem, phloem, periderm, wood rays, Indol-3-ylacetic acid, gibberellin A3, 6 benzylaminopurine, growth hormones     

Effects of Indol-3yl Acetic Acid on the Citrate-Condensing Reaction by Preparations of Root and Shoot Tissue

Preparations of citrate condensing enzyme (citrate oxaloacetate-lyase(CoA-acetylating) E. C. 4. 1. 3. 7) from root and shoot tissueof 5-day-old bean seedlings (Phaseolus vulgaris L., var. Burpee'sStringless Greenpod) had different activities, expressed asreaction rate per unit of fresh tissue. Activity per mg proteinwas increased when protein concentrations of the preparationswere reduced by dilution. Addition of indol-3yl acetic acid(IAA) enhanced activity of both root and shoot preparations.The effect was optimal at a concentration of 1.25x10^-4 M andthe enzyme was inhibited at 1.25x10^-3 M. Enhanement was greaterin root than in shoot preparations and in mixtures of equalamounts of each prepartion activity was intermediate betweenthose of the separte enzymes in absence of IAA but in its presenceapproached that of the shoot preparation. Apparent citrate synthesis in vivi was increased in shoots by application of IAA but therewas no such effect in roots.     

A Comparative Study of the Effects of Some Growth Regulators on the Biochemistry of Oryza sativa L.

A comparative study was made on the effects of indol-3yl-aceticacid (IAA), maleic hydrazide (MH), naphthalene acetic acid (NAA),and gibberellic acid (GA) at a concentration of 1o^-1 mg I^-1,on the growth and metabolism of Oryza sativa L., cv. Bhasamanik.All the growth substances excepting NAA caused promotion ofroot elongation and increased the number of roots formed buthad very little effect on shoot growth. NAA was found to havea retarding effect on the general growth of the plant, but alsoincreased the number of roots formed. At the concentration used IAA caused enhanced protein synthesisin parallel with increased root growth. However, with MH nosuch direct relationship could be observed between root growthand protein synthesis at the early stage, but stimulation ofroot growth was directly related to increased protein synthesisat the later stage. Despite the adverse effect of NAA on thegrowth of the plant, protein synthesis was not affected. Infact a general increase in the protein content of the plantwas observed. In plants treated with GA increased sugar contentand enhanced protein synthesis were noted. The levels of free amino acids were found to be affected markedlyby the application of the growth regulators. With NAA treatmentan accumulation of asparagine in the shoot and with GA an increasein the level of alanine in the root were noted. Aspartic aciddecreased in the roots, but increased in the shoots of treatedplants. Glutamic acid was lower in plants treated with IAA,MH, and NAA, while treatment with GA increased it in the shootat the tillering stage. In the shoots of IAA-, MH-, and NAA-treatedplants an increase in the quantity of serine was noted whereasunder the action of GA both serine and glycine decreased.     

Phytohormones,Rhizobium mutants, and nodulation in legumes. IV. Auxin metabolites in pea root nodules

High specific activity [³H]indole-3-acetic acid (IAA) was applied directly to root nodules of intact pea plants. After 24 h, radioactivity was detected in all plant tissues. In nodule and root tissue, only 2–3% of³H remained as IAA, and analysis by thin layer chromatography suggested that indole-3-acetyl-L-aspartic acid (IAAsp) was a major metabolite. The occurrence of IAAsp in pea root and nodule tissue was confirmed unequivocally by gas chromatography-mass spectrometry (GC-MS). The following endogenous indole compounds were also unequivocally identified in pea root nodules by GC-MS: IAA, indole-3-pyruvic acid, indole-3-lactic acid, indole-3-propionic acid, indole-3-butyric acid, and indole-3-carboxylic acid. Evidence of the occurrence of indole-3-methanol was also obtained. With the exception of IAA and indole-3-propionic acid, these compounds have not previously been unequivocally identified in a higher plant tissue.     

Pseudomonas fluorescens CHA0 can kill subterranean termite Odontotermes obesus by inhibiting cytochrome c oxidase of the termite respiratory chain

In the rhizosphere and their interaction with plants rhizobia encounter many different plant compounds, including phytohormones like auxins. Moreover, some rhizobial strains are capable of producing the auxin, indole-3-acetic acid (IAA). However, the role of IAA for the bacterial partner in the legume– Rhizobium symbiosis is not known. To identify the effect of IAA on rhizobial gene expression, a transposon (mTn 5gusA - oriV ) mutant library of Rhizobium etli , enriched for mutants that show differential gene expression under microaerobiosis and/or addition of nodule extracts as compared with control conditions, was screened for altered gene expression upon IAA addition. Four genes were found to be regulated by IAA. These genes appear to be involved in plant signal processing, motility or attachment to plant roots, clearly demonstrating a distinct role for IAA in legume– Rhizobium interactions.     

Plant-derived smoke solutions stimulate the growth of Lycopersicon esculentum roots in vitro

Aqueous extracts of smoke, derived from Themeda triandra, a fire-climax grass, and Passerina vulgaris, a fynbos plant, stimulated the growth of primary root sections of tomato roots in suspension culture. The optimal dilution for both extracts was 1:2000. Several of the fractions obtained from TLC separation of the Themeda and the Passerina extracts significantly promoted primary root growth. The auxins naphthaleneacetic acid (NAA), indolebutyric acid (IBA) and indoleacetic acid (IAA) were found to stimulate the growth of the primary root axis, with IAA and NAA significantly promoting lateral root number. Similarly, the naturally occurring cytokinins, zeatin and its derivatives (zeatin-O-glucoside; dihydrozeatin and zeatin riboside) stimulated primary root length. Zeatin and dihydrozeatin promoted secondary root growth, but only at very low concentrations.     

Indoleacetic acid synthesis in sterile roots of Phaseolus coccineus

Excised root tips from sterile Phaseolus coccineus L. seedlingswere incubated in sterile L-tryptophan-³H. Ethanol extractsof the roots were separated by thin-layer chromatography, andthe IAA area was eluted and run again in a different solventsystem. The presence of labeled IAA was detected using threedifferent solvent pair systems. (Received July 11, 1972; )     

Effectiveness of Lotus Root Nodules: III. EFFECT OF COMBINED NITROGEN ON NODULE EFFECTIVENESS AND FLAVOLAN SYNTHESIS IN PLANT ROOTS

When grown in a nutrient solution containing combined nitrogen(NH₄NO₃), Lotus pedunculatus and L. tenuis seedlings inoculatedwith a fast-growing strain of Rhizoblum (NZP2037) did neitherdevelop root nodules nor develop flavolans in their roots. Incontrast, the roots of nodulated seedlings growing in a nitrogen-freenutrient solution contained flavolans. Flavolan synthesis coincidedwith root nodule development on these plants. When added as a single dose, high concentrations of NH₄NO₃ (5and 10 mg N per plant) stimulated the growth of L. pedunculatusplants but suppressed nodulation and nitrogen fixation. In contrastthe continued supply of a low concentration of NH₄NO₃ (1?0 mgN d^–1 per plant) stimulated nitrogen fixation by up to500%. This large increase in nitrogen fixation was associatedwith a large increase in nodule fresh weight per plant, a doublingof nodule nitrogenase activity, and a lowering of the flavolancontent of the plant roots. The close relationship between nitrogendeficiency, nodule development, and flavolan synthesis in L.pedunculatus meant that it was not possible (by nitrogen pretreatmentof plants) to alter the ineffective nodule response of a Rhizobiumstrain (NZP2213) sensitive to the flavolan present in the rootsof this plant.