Studies in Plant Growth Hormones: V. CHROMATOGRAPHY OF HORMONES IN EXCISED AND INTACT ROOTS OF TOMATO SEEDLINGS

1. An examination has been made of the hormones present in extractsof excised roots and intact seedling roots of tomato. Acid andneutral ether-soluble fractions and the ether-insoluble aqueousfraction were chromatographed, and the chromatograms assayedusing oat coleoptile sections. 2. The pattern of hormone activity in excised roots differedlittle from that in seedling roots. 3. On chromatograms of the aqueous fraction developed in isopropanol/ammonia, growth promotion occurred at the position of 3-indolylaceticacid (IAA, Rf 0·5) and sometimes at the position of 3-indolylacetonitrile(IAN, Rf 0·8). When the IAA zone was eluted off the paperand rechromatographed, it formed the IAN zone and another zoneof promotion at Rf 0·1–0·2. 4. When the aqueous fraction was developed in n-butanol/ammonia,promotion occurred at the position of IAA (Rf 0·15),at Rf 0·5, and at the position of IAN (Rf 0-85). Thesezones have been called X, Y, and Z respectively. They were alsoformed when the IAA zone in wopropanol/ammonia was rechromatographedin ammoniacal n-butanol. It is shown that X and Y are interconvertible,and that each can form Z on rechromatography; also, there issome evidence that Z can form X and Y. When Z was separatedinto ether-soluble (acid and neutral) and ether-insoluble fractionswith sodium bicarbonate solution and chromatographed in iiopropanol/ammonia,growth resulted at the position of Z in the neutral and aqueousfractions, but in the acid fraction it occurred at Rf 0·24–O·35.Comparison with other chromatograms indicates that this lastzone does not occur in the aqueous fraction but has been formedas a result of extraction with sodium bicarbonate solution. 5. The zones found in the aqueous fraction also occurred insmall quantities in acid and neutral ethereal fractions in anumber of experiments. 6. The ethereal fractions gave no chromogenic reactions withferric chloride/ perchloric acid, nitrous/nitric acid, or p-dimethylaminobenzaldehyde(MeAB). In the aqueous fraction only MeAB gave a reaction (yellow)which showed any consistent correlation with biological activity.A yellow colour with this reagent is not a characteristic chromogenicreaction of indole compounds. It is suggested that a non-indolehormone system may be operating in tomato roots.     

Growth and Dormancy in Lunularia cruciata (L.) Dum.: I. RESUMPTION OF GROWTH AND ITS CONTINUATION

Lunularia cruciata may become dormant at three stages in itslife history: mature thallus, gemma, and spore. The resumptionof growth and its continuation in various conditions have beenstudied in thalli and gemmae. Air-dry, mature thalli of theIsrael strain, planted on a suitable medium, produce adventitiousbranches ventrally from the region immediately posterior tothe existing meristem, which itself fails to resume growth.When dormant gemmae are taken from the gemma-cup, however, theexisting apical cells and meristems simply recommence growing,so that the new growth is continuous with the old. Except inthe case of mature thalli aroused from dormancy, apical dominanceis pronounced, and branching occurs only by bifurcation. Thisdominance can be broken by applying sucrose solution to thegrowing tips—possibly a plasmolytic effect. The growth in area of freshly planted gemmae accelerates forabout 25 days before its relative rate slows to any great extent.During the first half of this period, growth is due exclusivelyto the expansion of existing cells, but subsequently cell numbersincrease rapidly from the 8–10,000 present in the dormantgemma. Cell numbers were estimated by using a modified macerationtechnique, in which chelation followed prolonged fixation. Lunularia grows successfully at quite low light intensities.Of the mineral nutrient deficienccs investigated, lack of Plimits growth most severely, although N-deficiency also restrictsit to a very low level. Gemma-cup production appears to be unaffected by light intensity,at least within levels permitting growth. There is, however,a large temperature effect, cup production decreasing markedlyabove 12° C.     

Growth Substances in the Roots of Vicia faba

An investigation has been made into the growth regulators presentin ethanol extracts of the seedling roots of Vicia faba afterseparation on paper partition chromatograms, using segmentsof Avena coleoptiles and mesocotyls and of Pisum sativum.rootsas biological assay material. Acetonitrile purification shows the presence of at least threeauxins running in isobutanol: methanol: water, at Rfs of 0–0·25,0·4–0·6, and 0·65–0·95;the latter may represent two different auxins. A similar, butclearer, picture is shown by the ether-soluble acid fraction.Here an auxin at Rf 0–0·25 also stimulates rootgrowth and could be ‘accelerator ’. A second atRf 0–0·25 is an indole compound which inhibitsroot growth and does not seem to be be IAA. A third at Rf 0·8–1·0is also a root-growth inhibitor and gives no indole reaction.The ‘inhibitor ß’ complex was demonstrated(Rf 0·65–0·85) together with a number ofother inhibitors at lower Rf value. The ether-soluble neutral component also contains auxins orauxin precursors. The water-soluble, ether-insoluble fraction contains four readilyinterconvertible substances with auxin properties. They allappear to inhibit root growth and give no indole reaction.     

Studies in Plant Growth Hormones: IV. CHROMATOGRAPHY OF HORMONES AND HORMONE PRECURSORS IN CABBAGE

1. Acid and neutral ethereal fractions and the non-ether-solubleaqueous fraction of an extract of cabbage leaves were chromatographed,and the chromatc-grams assayed using oat coleoptile sections. 2. In the aqueous fraction an acidic precursor of 3-indolylacetonitrile(IAN) was found. When chromatographed in isopropanol/ammonia,the precursor travelled at the position of 3-indolylacetic acid(IAA), but in n-butanol/ammonia it was much closer to the starting-line.IAN is liberated from the precursor under conditions of alkalinehydrolysis including ammoniacal chromatography, and is alsoliberated by heat. Precursor and IAN zones promoted coleoptilegrowth, but the former when sprayed with ferric chloride/perchloricacid or nitrous/nitric acid gave a yellow colour showing thatthere was no free IAN on this part of the chromatogram. Hypothesesto account for this activity are discussed. 3. A neutral inhibitor was present in the aqueous fraction.It is volatile, ether-soluble, and is thought to have been liberatedfrom a water-soluble substance. 4. The neutral fraction, chromatographed in isopropanol/ammonia,contained IAN and a growth promoter at Rf o–o·1:thelatter stimulates cress root growth above that in water. Thispromoter could be formed from a precursor in the aqueous fractionby heat treatment followed by shaking with sodium bicarbonatesolution. It is suggested that this neutral hormone is the accelerator-of Bennet-Clark and Kefford. The data of these workers are analysedto show that this interpretation is consistent with their results. 5. The acid fraction contained IAN but no IAA. The former isthought not to have been liberated from the precursor in thisfraction but to have entered into it from the neutral fractionduring separation with sodium bicarbonate solution. AlthoughIAA may have been absent from the plant material, it is possiblethat any present was destroyed during the process of extraction. 6. Evidence is presented that there are other growth promoterspresent at low concentration in the extract in addition to thosealready mentioned.     

Growth and Dormancy in Lunularia cruciata (L.) Dum: V. THE CONTROL OF GROWTH BY A NATCRAL, ENDOGENOUS INHIBITOR

The production of an endogenous growth inhibitor by Lunulariahas been demonstrated in tests with diffusates from gemmae andthalli. Increased growth made by bisected gemmae compared withintact controls suggests that self-inhibition also occurs andpoints to the growing tip as the locus of inhibitor production.More inhibitor is produced in short-day (optimum growth) thanin long-day (dormancy inducing) conditions, but even in shortdays the growth of thalli depends on conditions allowing theinhibitor to diffuse away. Thalli prevented from doing thisby resting the apical 2 mm on non-wettable cover slips stoppedgrowth and showed morphological changes of incipient dormancy.Some of the ecological implications of these tests are discussed.     

Studies on the Geotropism of Roots: III. EFFECTS OF GEOTROPIC STIMULATION ON GROWTH-SUBSTANCE CONCENTRATIONS IN VICIA FABA ROOT TIPS

The auxins contained in 5-mm. tips of horizontal Vicia fabaroots have been compared with those in tips of vertical rootsafter cold ethanol extraction, paper-chromatographic separation,and Avena mesocotyl bioassay. At about the time curvature commencesin horizontal roots there is a marked increase in the contentof an auxin corresponding to ‘AP(ii)’ of pea roots(Rf 0.35–0.65 in isobutanol/methanol/water). There areindications that this is not due to its release from an inactivebound state but that it is either synthesized de novo or maybe converted from another auxin corresponding to ‘AP(iii)’of pea roots (Rf 0.75–1.0). The literature dealing with the auxins of geotropically stimulatedorgans is reassessed and it is concluded that, with the exceptionof the Avena coleoptile, there is very little evidence favouringa simple transport redistribution of auxin under gravity; themajority of the data favour an effect of gravity on auxin metabolism.     

Factors Affecting Growth and Aggregate Dissociation in Batch Suspension Cultures of Datura innoxia (Miller)

Growth kinetics of Datura innoxia batch suspension cultureswen monitored by a Klett-turbidimetric technique. While cultured. wt varied linearly with Klett units, f. wt and packed cellvolume did not. Turbidimetrically determined doubling timeswere highly reproducible. The method proved to be useful inthe determination of acutely lethal conantrations of a seriesof anti-metabolites. In certain circumstances, aggregate dissociation in batch suspensioncultures of D. innoxia was found to be coupled to growth rate.Suspensions maintained with 10^–5 M 2,4-D exhibited a relativelyslow growth rate with a high degree of aggregate dissociation:10^–4 M 2,4-D promoted a maximum growth rate, but dramaticallysuppressed aggregate dissociation. At 10^–5 M 2,4-D, themitotic index of smaller-aggregate fractions was greater thanthe mitotic index of the large-aggregate fraction. At 10^–5M 2,4-D the converse was observed. Supraoptimal 2,4-D concentrationsthus enhanced both aggregate dissociation and the growth ofsmaller aggregates. When present in concentrations promoting optimal growth. malicand succinic acids caused a decrease in aggregate dissociation.Casein hydrolysate dramatically enhanced growth, but did notaffect aggregate dissociation to the same degree as 2,4-D orthe Krebs cycle organic acids. Suggestions are made concerningmedium composition to be used in future mutant selection schemesusing D. innoxia. Datura innoxia (Miller), suspension culture, growth kinetics, mitotic index, 2,4-dichorophenoxy acetic acid     

Responses of Marchantia in Aseptic Culture to Well-known Auxins and Antiauxins

Responses of young thalli of Marchantia nepalensis to ten well-knownauxins and antiauxins in aseptic culture are described. Effectsof one concentration of an auxin or an antiauxin were studiedin both liquid and solid cultures. The normal growth of inoculated thalli was inhibited but callus-liketissue was produced on them by the highest concentration (I.Omg./I.) of almost all the growth substances except MH, TIBA,and 2, 4^–DNP. At a later period callus-like tissue producedby IAA, IBA, and IPA differentiated into new thalli but thatproduced by NAA, NOA, 2,4^–D, and TCPA only did so on beingtransferred to control medium. At lower concentrations inoculated thalli developed normallybut they were soon overgrown by daughter thalli. No protonemalphase comparable to that of mosses could be observed in thedevelopmental stage of a regenerating thallus. The early stageis characterized by a stable filamentous structure, normallyconsisting of two to three cells. Filamentous structures ofvarying number of cells were however produced in some treatments. Profuse rhizoids were produced by the highest concentrationof NOA, 2,4^–D, TCPA, IBA, and IPA. Certain growth substancesinhibited the formation of tuberculate but not of smooth rhizoidsin liquid but not in solid cultures. Also tuberculate rhizoidswith feebly developed pegs were produced in certain liquid culturesonly and even in control liquid culture. More gemma-cups wereproduced in liquid cultures. Germinated gemmae with rhizoidswere invariably present in solid but not in corresponding liquidcultures. Germinated gemmae within gemma-cups were frequentlyfound. The significance of these results is discussed.     

Growth and Dormancy in Lunularia cruciata (L.) Dum.: IV. LIGHT AND TEMPERATURE CONTROL OF RHIZOID FORMATION IN GEMMAE

The first sign of initiation of growth in dormant gemmae ofL. cruciata is the formation of rhizoids. Gemmae in the cupcannot ‘germinate‘ until exposed to substrate conditionsallowing the outward diffusion of a growth inhibitor. Rhizoidproduction depends on temperature and light. With long lightperiods rhizoids are formed over a wide range of temperatures.Transference to darkness after 2 h white light causes about50 per cent of gemmae to produce rhizoids, and these are formedonly between 20 and 25 °C. Outside these temperature limitsthe percentage of gemmae with rhizoids soon drops to zero. Althoughrhizoid production is prevented in total darkness, gemmae remainalive for well over 6 months. Red light for as little as 5 spromoted, and far-red light inhibited, rhizoid formation inthe dark. Coumarin and indol-3yl-acetic acid can substitutefor light and partly reverse the effect of far-red irradiation.     

14C2H4: Distribution of 14C-labeled tissue metabolites in pea seedlings

The ¹⁴C-metabolite distribution pattern following ¹⁴C₂H₄ metabolismin intact pea seedlings (Pisum sativum L.) was determined undervarious conditions. After a 24 hr exposure to ¹⁴C₂H₄, the majorityof ¹⁴C-metabolites were water-soluble (60–70%) with lesseramounts in the protein (10–15%), lipid (1%), and insoluble(1–2%) fractions. Ion exchange chromatography of the water-solublecomponents into basic, neutral, and acidic fractions revealeda 50 : 40 : 10 distribution, respectively. Chromatography ofthe neutral fraction revealed two regions of radioactivity (Rf=0.38)and 0.63 which did not cochromatograph with twenty-two knownsugars or neutral metabolites. Chromatograms of the basic fractioncontained 3 regions of radioactivity. Similar distribution patternswere noted when ¹⁴C₂H₄ exposure was followed by a 6 hr air chaseor when 5% CO₂, an antagonist of ethylene action, was presentduring the exposure. Marked differences in the ¹⁴C-metabolite distribution patternswere obtained when ¹⁴CO₂ was substituted for ¹⁴C₂H₄. These resultsindicate that the metabolic pathway involved in ethylene metabolismis different from that involved in intermediary carbon metabolism. ¹ Contribution No. 2338 from Central Research and DevelopmentDepartment, Experimental Station, E. I. du Pont de Nemours andCompany, Wilmington, Delaware. (Received June 28, 1976; )     

Changes of Cell Wall Composition and Polymer Size in Primary Roots of Cotton Seedlings Under High Salinity

The aim of this study was to investigate changes in cell wallchemical composition and polymer size in the root tip of intactcotton seedlings (Gossypium hirsutum L. cv. Acala SJ-2) grownin saline environments, in order to relate the interaction betweenhigh salinity and root growth to possible changes in cell wallmetabolism. Cotton seedlings were grown in modified Hoagland nutrient solutionwith various combinations of NaCl and CaCl₂. Cell walls werefractionated into four fractions (pectin, hemicellulose 1 and2, cellulose), and analysed for their total sugar content, neutralsugar composition and size of polysaccharides. At 1 mol m^–3Ca, 150 mol m^–3 NaCl resulted in a significant increasein the cell wall uronic acid content, but a reduction in cellulosecontent on a per unit dry weight basis. Supplemental Ca overcamethe inhibitory effect of high Na on cellulose content. The neutralsugar composition of the cell wall fractions showed no majorchanges caused by varied Na/Ca ratios. Determinations of polysaccharidepolymer size showed that high Na at 1 mol m^–3 Ca led toan increase in the amount of polysaccharides of intermediatemolecular size and a decrease in that of small size in the hemicellulose1 fraction, indicating a possible inhibition of polysaccharidedegradation by high Na. This change was not observed in the10 mol m^–3 Ca treatments. The results reveal a relationshipbetween the effects of high salinity on root growth and cellwall metabolism, particularly in regard to cellulose biosynthesis Key words: Gossypium hirsutum, salinity, root, cell wall     

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     

Effect of Spermidine and Methylglyoxal-bis (Guanyl-hydrazone) (MGBG) on In Vitro Pollen Germination and Tube Growth in Catharanthus roseus

Incorporation of polyamine-spermidine into the nutrient mediumat 10^–6 and 10^–5 M concentrations stimulates pollen-tubegrowth in vitro in Catharanthus roseus L. G. Don. MGBG, an inhibitorof spermidine biosynthesis, at 0.5 x 10^–3 and 1 x 10^–3M concentrations reduced the percentage of germination as wellas tube growth and at a concentration of 1.5 x 10^–3 Mgermination was totally inhibited. Pollen grains incubated inthe medium containing 1.5 x 10^–3 M MGBG, when transferredto a fresh medium with 10^–5 M spermidine, resulted in80% germination recovery, along with considerable tube growth.Experiments with actinomycin-D indicate that stimulation ofpollen-tube growth by spermidine may involve de novo synthesisof protein. Catharanthus roseus, pollen germination, tube growth, spermidine, MGBG, inhibition, actinomycin-D     

Size-fractionated chlorophyll a biomass and picophytoplankton cell density along a longitudinal axis of a temperate estuary (Southampton Water)

Size-fractionated chlorophyll a biomass and picophytoplanktoncell number distributions were investigated along a longitudinalaxis of Southampton Water estuary during autumn. Chlorophylla concentration in the >5µm and the 1–5 µmsize fractions was highest midway down the estuary, and decreasedboth in the landward and seaward directions. In contrast, chlorophylla biomass in the 0.2–1 µm size fraction showed nodecline towards the seaward end of the estuary. In agreementwith this observation, phycoerythrin-containing picocyanobacteriacell concentration showed a positive exponential-like relationshipwith salinity and eukaryotic picophytoplankton were also highestat high salinities. Expressed as a percentage of total, chlorophylla standing stock in both the 1–5 µ.m (4.4–28.7%)and the 0.2–1 µm size fractions (1.7–8.6%)was inversely correlated with total chlorophyll a concentration.Both these two fractions made a greater input to the total phaeopigmentconcentration than to the total pool of active chlorophyll a.     

Involvement of cellulose synthesis in actions of gibberellin and kinetin on cell expansion. Gibberellin-coumarin and kinetin-coumarin interactions on stem elongation

In azuki bean (Azukia angularis = Vignia angularis) epicotylsections, 5 ? 10^–4 M coumarin inhibited the incorporationof radioactivity from [U^–14C]glucose into the cellulosefraction by 35% in the absence of indole-3-acetic acid (IAA)and by 40% in the presence of 1 ? 10^–4 M IAA. There wasno inhibitory effect on the incorporation of radioactivity intothe other fractions. Coumarin at 5 ? 10^–4 M reversed thepromoting effect of 1 ? 10^–5 M gibberellin A₃ (GA) andthe inhibitory effect of 1 ? 10^–5 M kinetin on IAA-inducedelongation of sections with no significant effects on IAA-inducedelongation. Neither GA nor kinetin had any appreciable effectson cellulose synthesis. No inhibition of cellulose syntheiswas observed with 1 ? 10^–3 M colchichine, which has beenreported to have effects similar to those of coumarin on GA-or kinetin-affected stem elongation. Coumarin at 5 ? 10^–4M was ineffectual in breaking up wall microtubules, while adisrupting effect on wall microtubules was clearly demonstratedwith 3 ? 10^–4M colchicine. From these results, the possible involvement of cellulose synthesisin cell expansion controlled by GA or kinetin was suggested. (Received August 3, 1973; )     

Ion Transport and the Effects of Acetic Acid in White Clover: I. PHOSPHATE ABSORPTION

Dunlop, J., Knighton, M. V. and White, D. W. R. 1988. Ion transportand the effects of acetic acid in white clover. I. Phosphateabsorption.—J. exp. Bot. 39: 79–88. The effect of acetic acid on phosphate absorption by white clovertissue has been examined. At 1·0 mol m³ acetic acid phosphateabsorption by roots of intact plants was stimulated by 36% (P< 0.001). At 5.0 and 10 mol m^–3 acetic acid there wasmarked inhibition of absorption by both suspension culturesof cells and the roots of intact plants. The inhibition waspH dependent with decreasing pH causing increased inhibition.Acetic acid caused changes in the membrane electropotential(E) with concentrations of 2·0 mol m^–3 or lesscausing persistent polarization whereas at 5·0 mol m^–3and higher concentrations the polarization was followed by agreater depolarization. Intracellular pH as measured by thefluorescence of fluorescein was lowered by acetic acid. Calculationsindicate that for white clover roots the proton motive force(pmf) appears to provide sufficient energy for phosphate absorption.It is proposed that acetic acid influences phosphate absorptionthrough its dependence on proton cotransport and that changesin J E affect the rate of phosphate absorption because of thedependence of the pmf on E. Key words: Phosphate absorption, intracellular pH, acetic acid, proton motive force, Trifolium repens, membrane electropotential     

Differential Effects of the Substituted Pyridazinone Herbicide Sandoz 9785 on Lipid Composition and Biosynthesis in Photosynthetic and Non-Photosynthetic Marine Microalgae: II. FATTY ACID COMPOSITION

The effect of the substituted pyridazinone, 4-chloro-5-(dimethylamino)-2-phenyl-3(2H)-pyridazinone(Sandoz 9785), on fatty acid synthesis in two photosyntheticspecies (Chroomonas salina and Nannochloropsis oculata) andone non-photosynthetic species (Crypthecodiniun cohnii) of marinemicroalgae were examined. Effects were more obvious in C. salinathan in C. cohnii or N. oculata. In C. cohnii the relative distributionamongst polyunsaturated fatty acids (PUFA) of radioactivityincorporated from ¹⁴C-acetate was not influenced by the herbicideto any great extent and no major changes in the fatty acid compositionof lipid fractions were observed. In C. salina, Sandoz 9785reduced the proportions of radioactivity recovered in 20: 5(n–3) and 22: 6 (n–3) of the phospholipid fraction.The distribution pattern of radioactivity in the fatty acidsof monogalactosyldiacylglycerol (MGDG) in this species was notgreatly affected by the herbicide whereas its presence significantlyreduced the proportions recovered in 18: 4 and 20: 1 in digalactosyldiacylglycerol(DGDG). The level of 20: 5 (n–3) in DGDG of C. salinawas increased from 4.0 to 19.8% by growing the algae in thepresence of Sandoz 9785. The only notable effect of the herbicideon the synthesis of PUFA in N. oculata was a reduction from18.3% to 11.3% of the proportion of radioactivity recoveredin 20: 5 in phospholipids. The herbicide had no effect on thedistribution of radioactivity in PUFA of galactolipids or onthe fatty acid composition of lipid fractions. The results arediscussed in relation to the potential role of galactolipidsand phospholipids as substrates for desaturations involved inthe formation of long chain PUFA in marine microalgae. Key words: Microalgae, herbicide, fatty acids     

Growth and Dormancy in Lunularia cruciata (L.) Dum.: III. THE WAVELENGTHS OF LIGHT EFFECTIVE IN PHOTOPERIODIC CONTROL

Growth and dormancy in Lunularia are controlled by daylength,short-day promoting active growth, long-day or light-break treatmentinducing dormancy. Light-breaks of red light are highly effectivein inducing dormancy, while irradiation with other wavebandsis much less inhibitory to growth. Far-red light given afterred irradiation causes substantial reversal of the red-lighteffect, suggesting strongly that phytochrome is involved inthe photoperiodic response mechanism of Lunularia. However,even short(15 sec.) exposures to far-red light alone cause significantgrowth inhibition, and it is considered possible that far-redirradiation also leads to the formation of some of the P 730form of phytochrome.     

Comparison of the Disruption of Mitosis and Cell Plate Formation in Oat Roots by DCPA, Colchicine and Propham

Holmsen, J. D. and Hess, F. D. 1985. Comparison of the disruptionof mitosis and cell plate formation in oat roots by DCPA, colchicineand propham.—J. exp. Bot. 36: 1504–1513. Concentrationsof DCPA, propham and colchicine were selected to cause from0% to greater than 60% inhibition of oat (Avena sativa L. ‘Victory’)root growth after 24 h exposure. Root growth progressively declinedas concentrations were raised from 1·0 to 5·6mmol m^–3 DCPA, 1·0–5·0 mmol m^–3propham, and 50–500 mmol m^–3 colchicine. In additionto inhibiting root growth each mitotic disrupter caused theroot tips to swell to an extent dependent upon concentration.All three compounds effectively disrupted mitosis at concentrationsthat caused less than maximal root growth inhibition. Mitoticdisruption was manifest as a reduction in the number of normalmitotic figures and an increase in the number of condensed prophase,multipolar and anaphase bridge division figures. The frequencyof each type of division figure was different for each of thethree compounds. DCPA disrupted mitosis more effectively whencompared with propham and colchicine at concentrations whichcaused the same amount of root growth inhibition. Each mitoticdisrupter also induced the formation of aberrant cell walls.DCPA was the most effective at disrupting cell plate formation,whereas colchicine was least effective. These data suggest thatthe mechanism of action of DCPA is distinct from the mechanismof colchicine or propham Key words: Avena sativa L., mitotic disruption, DCPA, colchicine, propham