Studies on the Geotropism of Roots:II.THE EFFECTS OF THE AUXIN ANTAGONIST {alpha}-(I-NAPHTHYLMETHYLSULPHIDE)PROPIONIC ACID (NMSP) AND ITS INTERACTIONS WITH APPLIED AUXINS

Previous experiments on the effects of auxins on the geotropicresponses of seedling pea roots (Audus and Brownbridge, 1957)have been extended using the ‘anti-auxin’ -(I-naphthylmethylsulphide)propionicacid (NMSP) alone and in combination with indole-3-acetic acid(IAA) and 2:4-dichlorophenoxyacetic acid (2:4-D). NMSP action differs from that of the auxins in that it reducesthe rate of curvature progressively as the concentration isincreased, irrespective of whether the overall extension growthof the roots is being stimulated (10 and 30 p.p.m.) or inhibited(100 p.p.m.). Correspondingly the reaction time is lengthenedby 25–50 per cent. in all concentrations. Studies of responsesin mixtures of growth-stimulating concentrations of NMSP (30p.p.m.) and growth-inhibiting concentrations of IAA (10^–8)and 2:4-D (3 x 10^–8) show that auxins and ‘antiauxins’are mutually antagonistic in most, if not all, their actionson growth and curvature. The results suggest that the anti-auxin NMSP may stimulate rootgrowth and inhibit curvature by interfering with the synthesisor distribution of a natural endogenous inhibitor, which isnot IAA. NMSP inhibition of root growth in high concentrationsmust, however, be exerted independently of this natural inhibitor.The mutual antagonisms shown between the auxins and NMSP arebest explained in terms of an interference with access to thegrowth centres; competitive action at the growth centres themselvesseems not to be involved.     

Growth-regulator Interactions in the Growth of the Shoot System of Avena sativa Seedlings: I. THE GROWTH OF THE FIRST INTERNODE

1. Segments, 3.5 mm. long, cut from the first internode of Avenasativa seedlings grown in complete darkness respond to bothauxins and gibberellic acid by accelerated extension. 2. The optimum concentration of indole-3-acetic acid (IAA) is10 p.p.m. and of gibberellic acid (GA) is 0.1 p.p.m. 3. The degree of stimulation relative to the growth of controlsegments is affected by the inclusion in the segement of thenode between the internode and coleoptile. Thus the gibberellineffect is greatly increased while the IAA effect is decreased.The optimal concentrations are not affected by inclusion ofthe node. 4. These results can best be explained in terms of the supplyby the node tissue of an endogenous auxin which is necessaryfor the expression of GA action. 5. Numerous factorial experiments demonstrated that there isno detectable interaction between applied IAA and GA in thepromotion of first-internode extension. This implies that thepostulated endogenous auxin which synergized GAA action in (4)is either an active form of IAA produced only in the node tissueor is a completely different auxin. 6. No synergism of growth-promotive action can be detected betweenGA and the two synthetic auxins I-naphthylacetic acid and 2,4-dichlorophenoxyaceticacid. 7. p-chlorophenoxy-iso-butyric acid (PCIB) anc 2,4,6-trichlorophenoxyaceticacid (2,4,6-T) act as weak auxins and thus antagonize competitivelythe promotive action of GA. 8. The anti-auxin -(I-naphythyl-methyl-sulphide)propionic acid(NMSP) antagonizes competitively the promotive action of bothIAA and GA. 9. The facts under (5)–(8) suggest that auxins and GAare acting at the same growth-promotion centres and may competefor them. 10. Growth inhibitions are induced by high concentrations ofPCIB, 2,4,6-T and NMSP. The inhibitions produced by PCIB and2,4,6-T are both synergized by supra-optimal concentrationsof IAA while that of NMSP is synergized by supra-optimal concentrationsof both IAA and GA. This similarity of the effects of IAA andGA suggests that their inhibition actions also are of a closelysimilar nature.     

Effects of indoleacetic, p-chlorophenoxyisobutyric and 2,4,6-trichlorophenoxyacetic acids on three phases of rooting in Azukia cuttings

In adventitious root formation of disbudded epicotyl cuttingstaken from light-grown, 5-day-old Azukia angularis seedlings,indoleacetic acid (IAA), 1 x 10^–4 M, applied during thefirst day showed no effect, but enhanced the effect of IAA,1 x 10^–4 M, applied during the second day. Treatment duringthe second day promoted rooting by about 70%, and a combinationof treatments for the first and second days promoted rootingsome 200%. p-Chlorophenoxyisobutyric acid (PCIB), 3 x 10^–4M, and2,4,6-trichlorophenoxyacetic acid (2,4,6-T), 2 x 10^–44M, applied the first day also enhanced the effect of IAA, 2x 10^–4 M, applied the second day. When applied the second day, PCIB, 2 x 10^–4M, increasedthe number of root primordia or clusters of small cells, butnot die number of protruded roots. Formation of the cell clusterwas inhibited by 2,4,6-T, 3 x 10^–4M, applied the secondday. Rooting processes in Azukia cuttings seem to include at leastthree phases: the first phase is induced not only by IAA butalso by PCIB or 2,4,6-T, the second phase is induced by IAAor PCIB and the diird phase depends specifically on IAA. (Received October 28, 1970; )     

Mineral nutrition and auxin-induced growth of Triticum coleoptile sections

A revised method has been described for assaying auxin by thegrowth of Triticum coleoptile sections. With additions of Ca(NO₃)₂10^–4 and MgSO₄ 10^–5 mol liter^–1 the sensitivityand accuracy have been increased. This is mainly due to Ca.The coleoptiles obviously suffer from Ca-deficiency. The importanceof a strict time schedule for manipulations is emphasiced. Theduration of the tests is limited to 6 hr.Indole-3-acetic acidcan be determined in concentrations down to 10^–9mol liter^–1;from 10^–10 to 10^–9mol liter^–1 the log-logrelation between concentration and growth is linear. Above 10^–7mol liter^–1 elongation takes place under an abnormal increasein elastic extension, indicating that growth is limited by someunknown wallstabilizing factor. The interrelation between auxin,an anti-auxin and Ca are discussed. (Received May 8, 1973; )     

Somatic Embryogenesis and Its Hormonal Regulation in Tissue Cultures of Freesia refracta

Somatic embryogenesis can be induced in tissue cultures of Freesiarefracta either directly from the epidermal cells of explants,or indirectly via intervening callus. These two pathways ofsomatic embryogenesis can be controlled and regulated by varyingthe combinations and levels of exogenous hormones. When younginflorescence segments were cultured in vitro on modified N₄(MN₄) medium supplemented with 2 mg l^–1 indoleacetic acid(IAA) and 3 mg l^–1 6-benzylaminopurine (BAP), some ofthe epidermal cells began to exhibit the features of embryogeniccells. These cells produced embryoids and developed into newplants through direct somatic embryogenesis. If the same explantswere placed on Murashige and Skoog's (MS) medium containing2 mg l^–1 IAA, 05 mg l^–1 BAP and 05 mg l^–1naphthaleneacetic acid (NAA), pale-yellow translucent nodularcalluses appeared on the surface of the explants. When thiskind of callus was transferred to MN6 medium with 2 mg l^–1IAA and 3 mg l^–1 BAP, embryoids formed which further developedinto plantlets. The regenerated plants were morphologicallynormal and possessed the normal diploid chromosome number of2n = 22. A similar result has also been obtained with youngleaf explants of this plant. The early segmentations of embryogeniccells and the development of embryoids were studied using histologicaland scanning electron microscopic techniques, and the resultshave been discussed in association with the ontogeny and originof the embryoids. Freesia refracta Klatt, somatic embryogenesis, plant regeneration, exogenous hormones     

The Effect of Inorganic Nutrients on the Hormonal Requirements of Normal, Habituated, and Crown-gall Tissue 4

The addition of Braun and Wood's inorganic supplements (845mg l^–1 KCl, 1800 mgl^–1 NaNO₃, 300 mg l^–1 NaH₂PO₄.2H₂O,790 mg l^–1 (NH₄)₂SO₄) to White's medium caused markedincreases in the growth of normal tissues of Helianthus annuus,Nicotiana rustica, Daucus carota, and Vinca rosea and crown-galltumour tissues of H. annuus. However, no evidence was obtainedwhich suggested that the presence of these extra salts markedlyinfluenced the essential requirements of normal callus for auxinsand kinetin. In contrast their presence significantly influencedthe hormonal requirements of certain habituated cultures ofH. annuus and V. rosea. These habituated cultures had specificauxin requirements on White's medium while either an auxin orkinetin was sufficient on high-salts medium. These results arediscussed in relation to previous reports which suggested thatthe biosyntheses of auxins and other growth factors in normaland crown-gall cultures are specifically activated by certaininorganic ions.     

Identification and oligosaccharide structure analysis of rhodopsin glycoforms containing galactose and sialic acid

The N-linked oligosaccharides of frog (Rana pipiens) rhodopsinwere analysed by sequential exoglycosidase digestion and gelfiltration chromatography, following reductive tritiation. Inaddition, selected tryptic glycopeptides obtained from frogretinal rod outer segment membranes were examined by electrospraymass spectrometry (ES-MS), fast atom bombardment mass spectrometry(FAB-MS), amino acid sequence and composition analysis, andcarbohydrate composition analysis. The amino acid sequence datademonstrated that the glycopeptides were derived from rhodopsinand confirmed the presence of twoN-glycosylation sites, at residuesAsn² and Asn¹⁵. The predominant glycan (60% of total) had thestructure GlcNAcß1–2Man1–3(Man1–6)Manß1–4GlcNAcß1–4GlcNAc-(Asn),with the remaining structures containing 1–3 additionalhexose residues, as reported previously for bovine rhodopsin.Unlike bovine rhodopsin, however, a sizable fraction of thetotal giycans of frog rhodopsin also contained sialic acid (NeuAc),with the sialylated oligosaccharides being present exclusivelyat the Asn² site. FAB-MS analysis of oligosaccharides releasedfrom the Asn² site gave, among other signals, an abundant quasimolecularion corresponding to a glycan of composition NeuAc₁Hex₆HexNAc₃(where Hex is hexose and HexNAc is N-acetylhexosamine), consistentwith a hybrid structure. The potential biological implicationsof these results are discussed in the context of rod outer segmentmembrane renewal. glycoforms oligosaccharide structure rhodopsin     

Abscisic Acid and Apical Dominance in Phaseolus coccineus L. The Role of Tissue Age

Abscisic acid (ABA) applied to the decapitated second internodeof runner bean plants enhanced outgrowth of lateral buds onlywhen internode stumps were no longer elongating. Applied toelongating internodes of slightly younger plants, ABA causesinhibition of bud outgrowth. Together with 10^–4 M indol-3-ylacetic acid (IAA), ABA stimulated internode elongation and interactedadditively in the inhibition of bud outgrowth. A mixture of10^–5 M ABA and 10^–6 M gibberellic acid (GA₃ ) causedsimilar effects on internode growth as IAA + ABA, but was mutuallyantagonistic in effect on growth of the lateral buds. Abscisic acid, apical dominance, gibberellic acid, indol-3yl acetic acid, Phaseolus coccineus, bean     

Effects of Auxin and Gibberellin on Elongation of Young Hyphae in Neurospora crassa

IAA, 2,4-D and GA₃ promoted the elongation of young hyphae inNeurospora crassa at the optimum concentrations of 10^–6,10^–6 and 10^–4 M, respectively. The effects of IAAand GA₃ were additive. (Received June 17, 1983; Accepted December 22, 1983)     

Factors affecting the Abscission of Reproductive Organs in Yellow Lupms (Lupinus luteus L.): II. THE EFFECTS OF GROWTH SUBSTANCES, DEFOLIATION, AND REMOVAL OF LATERAL GROWTH

Abscission of flowers in Lupinus luteus L. (var. Weiko II) withoutgrowth of ovaries is followed by abscission of small pods (15–20mm. long). Normally flower abscission is much more pronouncedthan pod abscission. Abscission was delayed on plants from which laterals or theirterminal and axifliary buds were removed. Flower abscissionwas not affected, but pod abscission increased as a result ofdefoliation. When flowers at the base of the main inflorescence were replacedby auxins and anti-auxins flower abscission was induced in eitheran auxin pattern in which most of the flowers near the siteof application dropped, and pods developed on the apical whorls,or an anti-auxin pattern in which pods developed on basal whorlsnear the site of application but not higher up. The anti-auxinpattern was similar to the pattern of abscission normally inducedby developing pods on basal whorls. -Naphthylacetic acid (NAA) was much more effective in inducingabscission than ß-indolylacetic acid (IAA). 2:3:5-triiodobenzoicacid (TIBA), NAA, and IAA applied in mixtures at various concentrationsacted mainly antagonistically, i.e. the abscission-inducingeffect of NAA and LAA was depressed in basal whorls, and inapical whorls the effect of TIBA was less prevalent. Consequentlythe effect of the mixtures on the total number of pods was aboutequal to that of the most active component by itself. All growth substances seemed to move much more efficiently inacropetal direction than in basipetal direction in the flowerstalk. Transport in lateral direction was very limited. The effect of growth substances applied on laterals was enhancedby defoliating the main 8tem. The influence of assimilates on flower and pod abscission andtransport of growth substances is discussed.     

Total and Polar Lipid Biosynthesis during Crotalaria juncea Linn. Pollen Tube Growth: Effect of Gibberellic Acid, Indoleacetic Acid and (2-Chloroethyl)-phosphonic Acid

Gibberellic acid (GA₃) at 58 µM, indoleacetic acid (IAA)at 29 µM, and (2-chloroethyl) phosphonic acid (Ethephon)at 70 µM promoted pollen tube growth in Crotalaria junceapollen suspension cultures both in water and basal medium. GA₃stimulated [ l-¹⁴C]acetate incorporation into total lipids inboth media, whereas IAA enhanced incorporation in water culturesonly. On the contrary, Ethephon reduced the label in total lipidswhen supplemented in basal medium. Based on [l-¹⁴C lacetateincorporation into different phospho- and glycolipids, it isproposed that these growth regulators have a definite role inthe biosynthesis of lipid components of the membranes.     

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)     

Effect of Some Known Growth Regulators on Growth and Fertility in Male Clones of the Moss Microdus brasiliensis (Dub.) Ther.

Among the auxins (IAA, 2,4-D, NAA and NOA) LAA proves inhibitoryfor antheridial formation. The rest promote this response, andNAA is most effective. Cytokinin (2iP) stimulates vegetativegrowth as well as antheridial formation, but the effect is morepronounced on the former. Interaction of kinetin and IAA provesbetter for antheridial production as compared to IAA alone.Gibberellic acid enhances gametangial induction as well as vegetativegrowth at lower levels (10^–8–10^–8 mol dm^–3).With abscisic acid both the responses are markedly reduced.Anti-auxins and cycocel promote antheridial production and vegetativegrowth. Testosterone is more potent than progesterone in promotingantheridial formation and vegetative growth. Key words: Fertility, growth hormones, moss     

Distribution of Radioactivity from Exogenously Supplied [1-14C]Indol-3-yl-acetic Acid and [3, 4-3H (N)] Gibberellin A, in Geotropically-stimulated Picea abies (L.) Karst. Roots

The distribution of exogenously-supplied radioactive labelledindol-3-yl-acetic acid (IAA) and gibberellin A₁ (GA₁) in geotropicallystimulated roots of Norway spruce (Picea abies (L.) Karst.)has been demonstrated. Seedlings were positioned with theirroot tips in 2.1 x 10^–6 M [¹⁴C]IAA or 1.3 x 10^–8m ³H-GA₁ for 4 and 20 h, respectively. After geotropic stimulationfor 90 min in the horizontal position the root tips were cutlongitudinally in 50 µm thick sections, using a freeze-microtome.The radioactivity in the ¹⁴C-IAA treated roots occurred in higherconcentration in the lower than in the upper halves (ratio 1.25:1). A similar trend was observed in the [³H]GA₁-treated rootswhere the ratio lower: upper halves was 2.04: 1. The ratio ofradioactivity in right and left halves of vertical roots wasapproximately the same in roots supplied with [¹⁴C]IAA and [³H]GA₁(1.09: 1). The supplied radioactive compounds were analysed chromatographicallyafter extraction in methanol of 6 mm apical root segments. Onlya small fraction (7–8 per cent) of the supplied [¹⁴C]IAAwas revealed unchanged in the segments. The major part of thechromatographed, labelled compound has not been identified,but on basis of its R_F value it is suggested that it may beindol-3-acetyl-aspartic acid (IAAasp). The chromatographic analysis of the [³H]GA,-treated segmentsshowed that only small fractions of this gibberellin has beenconverted to other compounds. These results have been discussed and correlated with knowledgeof plant growth regulators and their participation in root geotropism. Picea abies, spruce, geotropism, gibberellin A₁, indol-3-yl-acetic acid, growth regulators, redistribution in roots     

Comparative Studies of Acid Glycosidases from Three Legumes

The major isoenzymes of -mannosidase (EC 3.2.1.24 [EC] ) and ß-galactosidase(ECf 3.2.1.23 [EC] ) have been separated from cotyledons of gardenpea, Pisum sativum L. (Vicieae), chick pea, Cicer arietinumL. (Cicereae), and cowpea, Vigna unguiculata (L.) Walp. (Phaseoleae).Some of their properties have been determined, including pHoptima, K_m values for p-nitrophenyl glycosidc substrates, andthe effects of several inhibitors. Swainsonine, an indolizidinealkaloid, was the most effective inhibitor of mannosidase 1,with I₃₀ values of 5.6 x 10^–8 M (cowpea), 1x 10^–7M (chick pea) and 2.9 x 19^–7 M (pea). The most effectiveinhibitor of ß-galactosidase 2 from all sources wasD-galactonic acid-1,4-lactonwe (-lactone), with K_i values rangingbetween 3.0 and 3.9x 10^–3 M. An inhibitor of the E. coliß-galactosidose, p-aminophenyl thio-ß-D-galactopyranoside,did not inhibit any of the legume ß-galctosidases;rather it enhanced the activites of the enzymes from chick peaand cowpea cotyledons. Etiolated hull and seed tissues frompea pods developing in darkness contained similar acid glycosidaseactivities to normal green tissues, thus the chloroplast isan unlikely location for ß-galactosidase 2. The majorß-galactosidasesdetected with an indigogenic substrate (5-bromo-4-chloro-3-indoxyl-ß-D-galactopyranoside)following gel electrophoresis of extracts from pea hull, seedcoats and cotyledons appeared to be different from ß-galactosidase2. Acid glycosidase, cotyledon, isoenzyme, -lactone, legume, swainsonine     

The influence of temperature and light on the upper limit of Microcystis aeruginosa production in a hypertrophic reservoir

Primary production was measured for 7 years, using the in situ¹⁴C-method in hypertrophic Hartbeespoort Dam, South Africa,to examine the influence of light and water temperature on theupper limit of Microcystis aeruginosa production. Water temperaturesvaried from 11 to >25°C and chlorophyll concentrationsreached 6500 mg m^–3. The maximum volumetric rate of production(A_max) was 12->8800 mg C m^–3 h^–1 with areal productions(A) of 69->3300 mg C m^–2 h^–1 for euphotic zonedepths of <0.5–8.4 m. The intrinsic parameters of phytoplanktonproduction (, A_max/B, I_k) indicated that the phytoplankton populationwas adapted to high light levels. Both A_max/B and I_k were correlatedwith temperature. Under optimal conditions, , the theoreticalupper limit of A, was calculated to be 2.8 g Cm^–2 h^–1,while the measured rate was 2.5 g Cm^–2 h^–1. Measuredareal rates exceeding were overestimated due to methodologicalproblems when working with Microcystis scums. Light and watertemperature interacted to yield high production rates: watertemperature through its direct effect on photosynthetic ratesand indirectly in the formation of diurnal mixed layers; lightindirectly through water temperature and directly through itsattenuation and induction of light-adapted physiology in Microcystis.     

Effect of Indoleacetic Acid on Growth and Dinitrogen Fixation in Cyanobacteria

The effect of IAA on growth, dinitrogen fixation, and heterocystsfrequency of Anabaena PCC 7119 and Nodularia sp. have been investigated.Concentrations of IAA ranging from 10^–10 to 10^–4M did not change the growth of Anabaena PCC 7119. Concentrationshigher than 10^–4 M were inhibitory. Similar results werefound in Nodularia sp. although in this case the inhibitoryeffect appeared with 10^–5M of IAA. Neither the nitrogenaseactivity nor the heterocysts frequency were enhanced by IAAtreatment. (Received June 17, 1986; Accepted January 22, 1987)     

Nitrate Effects on Pre-emergence Growth and Emergence Percentage of Wheat (Triticum aestivum L.) from Different Sowing Depths

The effects of a range of applied nitrate (NO₃^–) concentrations(0–20 mol m3) on germination and emergence percentageof Triticum aestivum L. cv. Otane were examined at 30, 60, 90and 120 mm sowing depths. Germination percentage was not affectedby either sowing depth or applied NO₃^– concentration whereasemergence percentage decreased with increased sowing depth regardlessof applied NO₃^– concentration. Nitrate did not affectemergence percentage at 30 mm sowing depth, but at 60 to 120mm depth, emergence percentage decreased sharply with an increasedapplied NO₃^– concentration of 0 to 1·0 mol m^–3then decreased only slightly with further increases in appliedNO₃^– of about 5·0 mol m^–3. Root and shoot growth, NO₃^– accumulation and nitrate reductaseactivity (NRA) of plants supplied with 0, 1·0 and 1·0mol m^–3 NO₃^– at a sowing depth of 60 mm were measuredprior to emergence. The coleoptile of all seedlings opened withinthe substrate. Prior to emergence from the substrate, shootextension growth was unaffected by additional NO₃^– butshoot fr. wt. and dry wt. were both greater at 1·0 and1·0 mol m^–3 NO₃^– than with zero NO₃^–.Root dry wt. was unaffected by NO₃^–. Nitrate concentrationand NRA in root and shoot were always low without NO₃^–.At 1·0 and 10 mol m3 NO₃^–, NO₃^– accumulatedin the root and shoot to concentrations substantially greaterthan that applied and caused the induction of NRA. Regardlessof the applied NO₃^– concentration, seedlings which failedto emerge still had substantial seed reserves one month afterplanting. Coleoptile length was substantially less for seedlingswhich did not emerge than for seedlings which emerged, but wasnot affected by NO₃^–. It is proposed that (a) decreasedemergence percentage with increased sowing depth was due tothe emergence of leaf I from the coleoptile within the substrateand (b) decreased emergence percentage with additional NO₃^–was due to the increased expansion of leaf 1 within the substrateresulting in greater folding and damage of the leaf. Key words: Triticum aestivwn L., nitrate, sowing depth, seedling growth, seedling emergence     

Growth Substance Interactions during Uptake by Mesocotyl Segments of Zea mays L.

The effects of various growth substances on the ‘metabolic’uptake of indol-3yl-acetic acid (IAA) by Zea mesocotyl segmentswas investigated using methods of fluorescence spectroscopyand radioactivity assay. 2, 4-Dichlorophenoxyacetic acid (2,4-D) and -(I-naphthylmethylthio)propionic acid (NMSP) exertedno discernible effects on IAA uptake, whereas N-I-naphthylphthalmicacid (NPA) stimulated uptake to some degree. Low concentrationsof 2,3,5-tri-iodobenzoic acid (TIBA) promoted the uptake oflow IAA concentrations, while higher concentrations were decidedlyinhibitory. 2,4-Dinitrophenol (DNP), ioxynil, and bromoxynilalso induced marked inhibition presumably by preventing oxidativephosphorylation. The uptake interactions between these compoundswere examined in relation to concentration and time. In no casewas there evidence of competitive interaction. The inhibitoryeffects of TIBA on IAA uptake were considerably greater thanthose of DNP. SH-enzyme protectors such as BAL and cysteinedid not relieve these inhibitions. The absorption of TIBA-¹³¹Iwas completely unaffected by any concentration of IAA tested.Chromatographic and radio-autographic analysis revealed no detectableproducts of IAA-I-¹⁴C metabolism or degradation in maize mesocotyltissue during the 6-h experimental period and this was not alteredby TIBA treatment. Respiratory decarboxylation of IAA-I-¹⁴Cwas found to be negligible and unaffected by TIBA.