Indole-3-acetic Acid Transport Research Articles

Polar Calcium Flux in Sunflower Hypocotyl Segments

Calcium flux in sunflower (Helianthus annuus L. cv Russian mammoth) hypocotyl was measured with a Ca(2+) electrode as the increase or decrease in Ca(2+) in an aqueous solution (10 micromolar CaCl(2)) in contact with either the basal or apical end of 20 millimeter segments. Ca(2+) efflux was significantly higher at the apical end compared with the basal end; this apparent polarity was maintained even when the segments were inverted. No significant difference was observed in the cation exchange capacity of apical and basal cell walls that could explain the difference in Ca(2+) efflux at opposite ends of the hypocotyl segment. The presence of exogenous indoleacetic acid (IAA) in the segment medium resulted in the promotion of both Ca(2+) efflux and segment elongation. However, osmotic inhibition of the IAA-induced elongation did not result in inhibiting the IAA-induced Ca(2+) efflux. Ca(2+) efflux was inhibited by cyanide. Lowering the temperature from 25 degrees C also caused the gradual reduction of Ca(2+) efflux; at 5 degrees C the hypocotyl segments showed a net absorption of Ca(2+) from the segment medium. These findings support the suggestion that: (a) the observed Ca(2+) efflux in hypocotyl segments is probably the manifestation of the system which maintains the transmembrane Ca(2+) gradient at the cellular level. (b) The acropetal polarity of Ca(2+) efflux may be the result of the involvement of Ca(2+) in the basipetal transport of IAA.

Auxinlike Activity and Metabolism of Mefluidide in Corn (Zea mays) and Soybean (Glycine max) Tissue

Mefluidide {N-[2,4-dimethyl-5-[[(trifluoromethyl) sulfonyl] amino] phenyl] acetamide} was evaluated for effects on corn [Zea mays(L.) ‘Pioneer 3535’] coleoptile elongation. Mefluidide at 10-8M, 10-7M, and 10-6M stimulated elongation approximately equal to growth stimulations with 10-6M indoleacetic acid (IAA). Polar transport of14C-IAA from donor agar blocks through corn coleoptiles and into receiver agar blocks after 12 h was increased 246% by 10-4M mefluidide and inhibited 82% by 10-3M mefluidide. Mefluidide-related chemicals (10-4M) lacking a trifluoromethyl-sulfonyl-amino chain at the 1-position of the phenyl ring did not alter14C-IAA transport. IAA transport was increased 97% when the acetamide chain at the 5-position was absent and 255% when the methyl in the 4-position was absent, and it decreased 65% when the methyl at the 2-position was absent. Polar transport of14C-IAA through soybean [Glycine max(L.) Merr. ‘Williams’] hypocotyls was not altered by 10-4M mefluidide; however, 10-3M mefluidide increased IAA transport 116%. After 6 h, corn coleoptiles metabolized 14% of the mefluidide absorbed and soybean metabolized 54% of the mefluidide absorbed from14C-mefluidide solutions (10-6M). Differences in the rate of metabolism of mefluidide in meristematic tissue of corn and soybean may explain differences in mefluidide effects on auxin transport in corn and soybean.

Investigations on the Mechanism of the Brassinosteroid Response

A brassinosteroid treatment of light-grown first internode sections of Phaseolus vulgaris results in an increased bending response following unilateral indole-3-acetic acid (IAA) application. Reverse isotope dilution analysis shows that this increased response is not due to an increase in the concentration of applied IAA in the tissue or a change in the amount of IAA conjugated. Treatment with the brassinosteroid also does not affect the rate of IAA transport as measured using the agar block method. These results indicate that even though brassinosteroid potentiates auxin action, it does not have a direct effect on IAA uptake, metabolism, or cell to cell transport.

Uptake and polar transport of indoleacetic acid in moss rhizoids

Rhizoids of the moss Funaria liygrometrica Sibth. (L.) accumulate auxin in a manner similar to whole protonctnata. In the base of rhizoids auxin accumulation is always higher than in the tip. Auxin is transported in rhizoids from the tip to the base. The auxin transport is strictly polar. This can be explained by the different pattern of auxin accumulation in tip and base of rhizoids which represents a good model for the chemiosmotic hypothesis of polar auxin transport. The involvement of such a polar transport in moss development is discussed.

Possible hormonal modes of action of three apple thinning agents

Thinning-experiments were carried out with carbaryl, ethephon (CEPA) and the amide of naphthaleneacetic acid (NAAm) in the apple cultivars ‘Golden Delicious’ and ‘King of the Pippins’. In order to get more information on the possible hormonal modes of action of these substances, fruit treated with thinning-agents were analysed for ethylene (C 2H 4), diffusable and extractable indoleacetic acid (IAA), abscisic acid (ABA) and gibberellin-like substances (GA s), and compared with water-treated controls. It is thought that the observed reduction in IAA transport is a major factor in the mode of action of all 3 thinning-agents investigated. Auxin transport may be affected directly by the chemicals or via a shift in the mobilizing ability of the treated fruits. The role of other hormones investigated is briefly discussed.

Transport of 14 C-indoleacetic Acid in the Hepatic Marchantia polymorpha

Tracer experiments using exogenous 14C-indoleacetic acid showed that its transport is localized in the midrib cells of Marchantia polymorpha vege- tative thalli. Transport occurs both acropetally and basipetally at approximately the same velocity, but basipetal transport is significantly greater in intensity. In- terference with energy-yielding metabolism due to anaerobic conditions, iodoacetic acid or sodium fluoride reduced basipetal transport by 40-50%. Disruption of cel- lular integrity via centrifugation or cytochalasin B reduced basipetal transport by 30-40%. IAA transport in M. polymorpha gametophytes is essentially the same as in vegetative axes of flowering plants with respect to all parameters compared. The presence of naturally occurring auxin in gametophytic tissue of Marchantia poly- morpha has been demonstrated by both chemical methods and bioassays. As early as 1956, an endogenous compound was isolated from thalli that gave positive results with the Avena curvature test (La Rue & Narayanaswami 1957). Schneider et al. (1967) isolated an Erlich and Salkowski-positive ethanol-soluble compound with an Rf corresponding to indoleacetic acid (IAA). La Rue and Narayanaswami (1957) also present evidence for the localized synthesis of auxin in the apical region of the thallus, and Maravolo (1976) dem- onstrated that IAA was the major transport form in Marchantia. Endogenous growth regulators exert correlative action over developmental processes in bryophytes analogous to their action in tracheophytes. Their correlative activity is dependent upon absolute concentrations, gradients, differential rates of synthesis, inacti- vation and the direction and intensity of transport. The polar distribution of auxin in Marchantia polymorpha assumes an important regulatory role in apical dominance, gem- mae-cup formation and rhizoid initiation through its influence on the balance between cell division and elongation (Maravolo & Voth 1966; Binns & Maravolo 1972; Davidonis & Munroe 1972; Rota & Maravolo 1975). Hebant (1970) and Scheirer (1977) demonstrated that some bryophytes possess spe- cialized cells within the midrib tissue with morphological characteristics of phloem sieve tube cells. Translocation of auxin in Marchantia is conducted in a similar transport system. This transport is strictly basipetal, and was adversely affected by triiodobenzoic acid, cinnamic acid and ethylene, all inhibitors of polar transport in tracheophytes (Maravolo 1976). The present investigation derives from the latter and investigates the nature of several aspects of the auxin transport mechanism in Marchantia.

Effect of Auxin on Acropetal Auxin Transport in Roots of Corn

Acropetal [(14)C]indoleacetic acid (IAA) transport was investigated in roots of corn. At least 40 to 50% of this movement is dependent on activities in the root apex. Selective excision of various populations of cells comprising the root apex, e.g. the root cap, quiescent center, or proximal meristem show that the proximal meristem is the critical region in the apex with regard to influencing IAA movement. The quiescent center has no influence and the root cap has only a minor effect. Excision and replacement of the proximal meristem with an exogenous supply of 10(-8) to 10(-9) molar IAA prevents the reduction in acropetal IAA transport which would normally occur in the absence of this meristem. Substituting 10(-9) molar IAA for the excised root cap brings about a significant increase in the amount of IAA moved acropetally, as compared to intact roots with the root cap still in place. From this and previous work, it is concluded that IAA synthesis occurring in the proximal meristem stimulates the movement of IAA from the basal to apical end of the root.

Existence of a fast component of IAA transport in scrofularia arguta sol. and in lycopersicum esculentum mill

The basipetal mobility of [ 14C] indoleacetic acid (IAA) was followed in intact Scrofularia arguta and Lycopersicum esculentum plants cultured in vitro. The tracer was given to a young leaf. The radioactivity of plant fragments and of agar medium was measured at different times. In both species, the tracers moved according to 2 modalities characterized by their velocities. The first one is classical (mean velocity # 1 cm/h). The velocity of the second modality is much higher (at least 780 cm/h) and fewer molecules are translocated. In the 2 cases, a great part of the radioactivity is IAA, even when the tracers are extracted from the agar medium.

Myo-Inositol Esters of Indole-3-acetic Acid as Seed Auxin Precursors of Zea mays L.

Indole-3-acetyl-myo-inositol esters constitute 30% of the low molecular weight derivatives of indole-3-acetic acid (IAA) in seeds of Zea mays. [(14)C]Indole-3-acetyl-myo-inositol was applied to a cut in the endosperm of the seed and found to be transported from endosperm to shoot at 400 times the rate of transport of free IAA. The rate of transport of indole-3-acetyl-myo-inositol from endosperm to shoot was 6.3 picomoles per shoot per hour and thus adequate to serve as the seed auxin precursor for the free IAA diffusing downward from the shoot tip. Indole-3-acetyl-myo-inositol is the first seed auxin precursor to be identified.Application of either [(14)C]IAA or (14)C-indole-3-acetyl-myo-inositol ester to the endosperm results in both free and esterified [(14)C]IAA in the seedling shoot. Esterification of free IAA and hydrolysis of indole-3-acetyl-myo-inositol occurred in the shoot and not the endosperm yielding ratios of ester to free IAA which approximate the ratios of ester to free IAA normally found in corn shoot tissue. This proves, for the first time, that esterified IAA and free IAA are interconvertible in the growing shoot. Since free IAA may be limiting for plant growth, knowledge that the free hormone is in "equilibrium" with its conjugates suggests new methods for the control of plant growth.

Inhibition of Polar Indole-3-acetic Acid Transport by Cycloheximide

Cycloheximide inhibits polar indoleacetic acid transport in midrib tissues of leaves of citrus (Citrus sinensis [L.] Osbeck) and poplar (Populus deltoides Bartr.) as measured by the donor-receiver agar cylinder technique. It appears that the mechanism of auxin transport inhibition by cycloheximide consists in arresting protein synthesis and not in the disruption of energy flow. The interpretation of the data takes into account the involvement of either a carrier protein or auxin-induced proton excretion in auxin transport.

Effect of ethylene on auxin transport and metabolism in midrib sections in relation to leaf abscission of woody plants

Abstract The relationship between ethylene‐induced leaf abscission and ethylene‐induced inhibition of auxin transport in midrib sections of the leaf blade of Citrus sinensis L. Osbeck, Populus deltoides Bart, and Eucalyptus camaldulensis Dehn. was studied. These species differed greatly in their abscission response to ethylene. The kinetic trend of abscission resembled that of the inhibition of auxin transport in all three species. It is suggested that one of the main actions of ethylene in the leaf blade is to inhibit auxin transport in the veinal tissues, thus reducing the amount of auxin transported from the leaf blade to the abscission zone.Ethylene inhibited transport of both IAA (indole‐3‐acetic acid) and NAA (α‐naphthaleneacetic acid) in the midrib sections. However, while ethylene enhanced the conjugation of IAA with aspartic acid and glucose in the apical (absorbing) segment of the midrib sections, it had little effect on the conjugation of NAA. The data indicate that auxin destruction through conjugation does not play a major role in the inhibition of auxin transport by ethylene.

Physiological Evaluation of the Nutritional Autonomy of a Hornwort Sporophyte

The nutritional relationship between sporophytes and parent gametophytes of Phaeoceros laevis (L.) Prosk. was studied by (1) radioactive tracers to follow glucose uptake, CO2 fixation, and indoleacetic acid transport; (2) enzyme histochemistry to test for enhanced actvity in specialized transfer cells at the sporophyte-gametophyte interface; and (3) polarography to determine photosynthetic and respiratory rates. Based on fresh weight, sporophytes photosynthesize at almost twice the rate of gametophytes. The carbon fixed by photosynthetic sporophytes is sufficient for self-maintenance but not for sustained growth. Higher relative respiratory rates account for the observed nutritional reliance of sporophytes upon gametophytes. Enhanced enzymatic activity in transfer cells is correlated with net carbon transfer from gametophyte thalli. Mobilization of gametophyte reserves may be influenced by basipetally transported auxin from the sporophyte meristem. Labeled carbon accumulates in the intercalary meristem and in spores following uptake.

Measurement of the Cytoplasmic pH in Nitella translucens

A comparison has been made between the use of two types of pH microelectrode and the weak acid method for determining the cytoplasmic pH of Nitella translucens at an external pH of 6. There was good agreement between the value obtained with glass pH microelectrodes (7.54 +/- 0.15 se) and that obtained using the weak acid 5,5-dimethyloxazolidine-2,4-dione (7.42 +/- 0.07 se). Plastic-insulated antimony microelectrodes gave a significantly lower value (6.74 +/- 0.15 se) possibly due to disruption of the insulation by the cell wall. The addition of 1 mM NaN(3) rapidly reduced the pH recorded by the glass pH microelectrodes to about 5.3. A smaller change was observed using the weak acid method. The relevance of this observation to recent work on indoleacetic acid transport is discussed.

The specificity of carrier-mediated auxin transport by suspension-cultured crown gall cells

1. The specificity of the auxin transport system of suspension-cultured crown gall cells from Parthenocissus tricuspidata Planch- is examined with regard to 2,4-Dichlorophenoxyacetic acid (2,4 D), l-Naphthylacetic acid (NAA) and Benzoic acid (BA) as well as for indole-3-acetic acid (IAA). - 2. All four weak acids can be accumulated by the cells from a medium more acidic than the cytoplasm. This is by virtue of non-specific passive diffusion of their lipid-soluble protonated forms down a concentration gradient. The corresponding anionic species are much less permeant. The extent of the accumulation is dependent on the pH difference that is maintained by the cells between their cytoplasm and the incubation medium. Studies of the concentration dependence of BA and NAA net uptake at a series of external pHs suggest that an acidification of the cytoplasm can be eventually brought about by the entry of weak acid into the cells. - 3. The uptake of 2,4 D, as well as that of IAA, has a saturable carrier-mediated component in addition to the passive diffusion of the undissociated acid. These saturable components probably represent anion uptake and appear to be mediated by a common carrier. The kinetic studies provided no evidence for the participation of carriers in the transport of BA or NAA. - 4. It was shown that the efflux of 2,4 D also has a carrier-mediated component and it is suggested that both the influx and efflux of IAA and 2,4 D occur on a common carrier. - 5. The inhibitor of polar auxin transport, 2,3,5-triiodobenzoic acid (TIBA), stimulates the net uptake of IAA by inhibiting carrier-mediated efflux of IAA from the cells. However, TIBA could not be demonstrated to have a significant effect on 2,4 D transport and any perturbation that occurs is very small in comparison with its effect on IAA movement. To account for this, the proposed common carrier could exhibit some difference in its internal binding characteristics betweend 2,4 D and IAA. An alternative explanation is that a second carrier is present, which mediates IAA efflux only, and which is inhibited by TIBA. - 6. TIBA has no significant effect on the transport of either BA or NAA, except to bring about an inhibition of net uptake, and a corresponding stimulation of efflux, when it is present at concentrations sufficient to acidify the cytoplasm. -7. The crown gall cells are compared to intact plant tissues capable of polar auxin transport with regard to the specificities exhibited for the transport of the auxins IAA, 2,4 D and NAA and the non-auxin BA.

Auxin Transport Inhibitors. II. 2-(1-Pyrenol)Benzoic Acid, a Potent Inhibitor of Polar Auxin Transport

2-(1-Pyrenoyl)benzoic acid is shown to be a highly active inhibitor of auxin transport by its ability to prevent the polar transport of indoleacetic acid in bean petioles. It is comparable in activity to other known auxin transport inhibitors, and also affects apical dominance and the geotropic and phototropic responses.

Auxin Transport Inhibitors

Fluoresceins are shown to be effective inhibitors of indoleacetic acid transport as measured by the receiver agar block technique, eosin having the same order of activity as 2,3,5-triiodobenzoic acid and N-1-naphthylphthalamic acid, with fluorescein less effective. It is suggested that many of their characteristic effects on plants, especially those which involve auxin, are at least partially due to their effects on auxin transport.

Hormonal Regulation of Pedicel Abscission in Begonia Flower Buds

AbstractIn order to analyse the hormonal regulation of flower bud shedding in Begonia, levels of indoleacetic acid (IAA), abscisic acid (ABA) and ethylene were determined in buds and pedicels. The translocation and metabolism of 14C‐labeled IAA in pedicel segments were also studied.In a monoecious Begonia fuchsioides hybrid, abscising male flower buds contain about 1% of the IAA present in non‐abscising female flowers. In a male Begonia davisii hybrid, the seasonal variation in bud drop coincides with changes in the IAA content of the buds, while also the release of IAA from the bud to the pedicel is hampered.Abscission zones of these pedicels always contain abscission promoting ethylene concentrations. The tissue is prevented from responding with abscission by IAA from the flower buds. The buds also contain ABA but without influencing abscission considerably.Pretreatment with ethylene or ABA does not affect IAA transport in pedicel segments. The rate of this transport is 4–6 mm × h–1:; the capacity increases with the transverse area. In young segments, IAA is decarboxylated and also otherwise metabolized.

Rhythmic Differences in the Basipetal Movement of Indoleacetic Acid between Separated Upper and Lower Halves of Geotropically Stimulated Corn Coleoptiles

Rhythmic fluctuation in the basipetal movement of auxin occurs in corn (Zea mays) coleoptiles oriented either in the vertical or in the horizontal position. This periodicity of transport rate varies from region to region in a horizontal coleoptile. Between an upper and lower half coleoptile (with respect to gravity), the comparable regions in the coleoptile do not exhibit similar periods. The velocity of transport also varies from region to region along a geostimulated coleoptile. In the upper half coleoptile, the velocities are 29 millimeters per hour (tip), 8 millimeters per hour (mid), and 30 millimeters per hour (base); in the lower, 41 millimeters per hour (tip), 12 millimeters per hour (mid) and 12 millimeters per hour (base).During the first 24 minutes of transport, there is a reduction of basipetal movement of (14)C-indoleacetic acid in the lower half coleoptile. This may be causally related to the initial downward geotropic curvature in oat and corn coleoptiles reported by others. However, about 30 minutes after donor removal a significant reduction of basipetal transport of indoleacetic acid occurs in the upper half coleoptiles.

Rhythmicity in the Basipetal Transport of Indoleacetic Acid through Coleoptiles

(14)C-Indoleacetic acid was applied to coleoptiles of corn (Zea mays) and oat (Avena sativa). The coleoptiles were detached from the endosperms at 6-minute intervals after indoleacetic acid application, and the radioactivity was determined in successive 2-millimeter regions. The rate (per cent per minute) of basipetal transport of indoleacetic acid is periodic in various regions of the coleoptile, with a period of about 20 minutes. The possible relation of this cyclic phenomenon to other rhythmic processes of similar periodicities is discussed. A distinct acropetal transport (against the concentration gradient) from the subapical region to the apical 2-millimeter region of the coleoptile was detected.The velocity of indoleacetic acid transport differs in different regions of the coleoptile. Within an entire coleoptile the velocity can be divided into three classes for corn, 41 millimeters per hour (apical), 13 millimeters per hour (mid), and 34 millimeters per hour (base), and 2 classes for oats, 28 millimeters per hour (apical) and 14 millimeters per hour (remainder). An inverse relationship between the velocity of indoleacetic acid transport, and the growth rate of the coleoptile is discussed. Corn coleoptiles exceed oat coleoptiles both in rate and in velocity of IAA transport.

The Regulation of Abscission and IAA by Senescence Factor and Abscisic Acid

The effects of the endogenous “senescence factor” (SF) and synthetic (±)-abscisic acid (ABA) on basipetal transport of indoleacetic acid (IAA) in Coleus blumei Benth. were studied. When used to pretreat explant petioles, both SF and ABA accelerated abscission and decreased basipetal movement of IAA through petiolar sections but had no effect on acropetal movement, which was negligible in all experiments. SF decreased the intensity but not the velocity of the basipetal movement of IAA. Pretreatment with either SF or ABA decreased the free IAA and increased the IAA-aspartate extractable from the sections. The results support the hypothesis that SF and ABA hasten abscission by lowering the amounts of IAA transport in the tissue. Known properties of SF are similar to those of ABA. Efforts are under way to elucidate the chemical identity of SF.