IAA Treatment Research Articles

IAA Inhibition of in vitro Flowering of the Short-Day Plant Streptocarpus nobilis. An Effect on Maintenance of Induction

Summary Leaf explants from photoperiodically induced plants of the short-day plant Streptocarpus nobilis (C. B. Clarke) developed adventitious flower buds when cultured in non-inductive photo-periods. The degree of in vitro flowering correlated quantitatively with the number of short days received by the donor plant. The discrete states of induction, generated in response to various cycles of short days, were stable and served to assay the influence of IAA on the expression of the induced state in vitro . IAA was a very potent inhibitor of the expression of the induced state. In non-inductive photoperiods, IAA (5×10 −6 M) increased bud production three-fold and completely inhibited flower formation on explants of photoinduced leaves. In short days flowering was not inhibited by IAA and although IAA-mediated bud production was lower than in night-breaks IAA treatment resulted in an increased production of flower buds. Inhibition of flowering by IAA was due to degradation of the induced state in non-inductive photo-periods. Mechanisms by which IAA could modulate the expression of the photoperiodically induced flowering signal are discussed.

Rooting, growth and ethylene evolution of pea cuttings in response to chloroindole auxins

In pea cuttings (Pisum sativum L. cv. Alaska) we measured shoot and root growth and ethylene production in response to 4‐chloroindole‐3‐acetic acid (4‐CI‐IAA) or 4,6‐dichloroindole‐3‐acetic acid (4,6‐Cl2‐IAA). Leafy cuttings treated basally with either of the chlorinated auxins in high concentrations showed permanent epinasty, loss of apical growth and dominance resulting in the outgrowth of laterals from the lower‐most axillary bud. The naturally occurring 4‐CI‐IAA was a better root promoter than the synthetic 4,6‐Cl2‐IAA which inhibited rooting. Both chloroindole auxins induced very high ethylene evolution, which lasted much longer than the ethylene evolution after IAA treatment.

Changes in CTP:cholinephosphate cytidylyltransferase protein levels in pea stems treated with indole-3-acetic acid

Indole-3-acetic (IAA) reduced the activity of CTP:cholinephosphate cytidylyltransferase in pea (Pisum sativum) stems by an average of 45% compared to controls 1 hr after treatment. An enzyme-linked immunosorbent assay (ELISA) was developed to measure the changes in enzyme protein levels after IAA treatment. The levels of cytidylyltransferase protein were found to be reduced significantly but only by 5 %.

Rooting of Sweet Potato Stem Cuttings under CO2-enriched Environment and with IAA Treatment

Abstract Stem cuttings of sweet potato (Ipomoea batatas L. ‘Georgia Jet’) with intact apex and leaves were cultured in water or in different concentrations of IAA and were maintained in controlled-environment chambers at 350, 675, or 1000 ppm CO2. The temperature was 20°C during a 14-hr day and 14° during a 10-hr dark period. The photosynthetic photon flux density was 550 μmol s-1m-2 (27.7 mol m-2 day-1). Elevated CO2 concentrations stimulated the production of roots in the presence of IAA, and this effect was more pronounced at 675 ppm than at 1000 ppm CO2 atmosphere.

Effects of osmotic concentrations and IAA on the rapid shortening of the cortex in the main pulvinus ofMinosa pudica

In 0.8 M mannitol solution, no rapid shortening was recorded, while normal action potential was recorded. This result suggests that motive force of rapid shortening is an elastic stretch of the cell wall caused by the turgor pressure, and that osmotic concentration of motor cell is 0.6–0.7 M. IAA increased the rapid shortening, recovery rate and Cl−-efflux. The magnitudes of rapid shortening in IAA were 3–10 times as large as those in APW. The mean and maximum values of the rapid shortening in IAA were 87.0±2.2μm and 207 μm, respectively, or 1.6 and 3.9% of the whole length of motor tissue. When the large rapid shortening occurred, the large recovery rate was observed. These results suggest that both mechanisms, expulsion and re-entry of cell sap, are enhanced by IAA treatment. IAA-induced hyperpolarization was observed with a short time lag, which suggests that IAA enhances the electrogenic ion pump.

A quantitative stereological analysis of the effect of indoleacetic acid on the dictyosomes in pea stem epidermal cells

A quantitative analysis of electron micrographs showed that IAA treatment caused an initial rapid increase in the amount of dictyosome material in pea stem epidermal cells. The increase was detected within 15 minutes of auxin presentation and reached a maximum around 30 minutes. This was followed by a decrease, presumably due to an increased utilization of the organelle. The decrease involved a fall in the amount of dictyosome-derived vesicles and in the actual number of dictyosomes. The results are discussed in relation to similar observations on expanding cells of monocotyledonous plants.

Inhibition of IAA‐induced ethylene production in etiolated mung bean hypocotyl segments by 2,3,5‐triiodobenzoic acid and 2‐(p‐chlorophenoxy)‐2‐methyl propionic acid

The effect of two auxin antagonists, 2,3,5‐triiodobenzoic acid (TIBA) and 2‐(p‐chlorophenoxy)‐2‐methyl propionic acid (CMPA) on IAA‐induced ethylene production in etiolated mung bean hypocotyl (Vigna radiata L. Rwilcz cv. Berken) segments was studied. Both TIBA and CMPA inhibited IAA‐induced ethylene production and CO2 production at concentrations from 0.001 mM to 0.1 mM and 0.01 mM to 1.0 mM, respectively. The optimum concentration for inhibition of ethylene production by TIBA was 0.05 mM and CMPA was 0.5 mM. At the optimum concentration of TIBA and CMPA, there was a significant decrease in IAA‐induced ethylene production without a decrease in respiration rates below control levels. After 18 h, mung bean hypocotyl segments treated with 0.05 mM TIBA for 6 h or 0.5 mM CMPA for 8 h showed a maximum inhibition of IAA‐induced ethylene production. Treatments longer than 8 h caused no further inhibition. The uptake of [14C]‐naphthaleneacetic acid by mung bean segments was greatly reduced by the addition of either TIBA (0.05mM) or CMPA (0.5 mM) to the incubation media. The results of treatment sequences showed that TIBA needed to be applied prior to IAA in order to inhibit IAA‐induced ethylene production, but CMPA caused the same inhibitory effect whether applied before or after IAA treatment. These findings provide evidence that TIBA inhibits auxin‐induced ethylene production in etiolated mung bean hypocotyl segments by blocking auxin movement into the tissue whereas CMPA may work on both auxin transport and action.

Ultrastructure and autoradiography of dormant and activated parenchyma ofHelianthus tuberosus

Parenchyma cells of dormant tubers ofHelianthus tuberosus L. cv. OB1 (Jerusalem artichoke) contain a very low amount of hormones, therefore they respond to 2,4-D or IAA treatment by dividing and synthesizing RNA, DNA, and polyamines.

Matromorphy in Pisum sativum L.

The possibility of obtaining instant pure breeding lines by matromorph seed development in Pisum sativum L. has been investigated. Two types of maternal parents, namely, homozygous for the recessive marker genes and heterozygous for the dominant marker genes were pollinated with Lathyrus odoratus and the 'P174' variety of Pisum sativum L. carrying dominant markers. For both pollinators, induction of matromorphy by prickle pollination, irradiated pollen and IAA treatment was examined. Promising matromorphs were identified in the M1 generation which were studied in the M2 generation for assessing their genetic status with respect to homozygosis. The success of pod set varied from zero to 28% with a varying number of matromorphic seeds following different treatments. The possible mechanisms for matromorphic origin have been discussed. The evidence presented herein favours induction of matromorphy in peas for the production of homozygous stocks. In addition, the recovery of double recessive seed markers of the maternal parents along with plant markers from the paternals has prospective implications in plant breeding as an alternative tool to recurrent back crossing.

Gibberellin-induced ethylene production and its effect on cowpea epicotyl elongation

The effect of gibberellin A1 (GA1) on production of ethylene by cowpea (Vigna sinensis cv Blackeye pea no. 5) epicotyl explants and its relationship to epicotyl elongation was investigated. The explants were placed upright in water and incubated in sealed culture tubes or in large jars. GA, and IAA in ethanol solution were injected into the subapical tissues of the decapitated epicotyls. Cowpea epicotyl explants elongated after GA but not after IAA treatment, and they were very sensitive to exogenous ethylene. As little as 0.14 μ1/1 ethylene reduced significantly GA1-induced epicotyl elongation.

Further examination of the effects of IAA and anoxia on the growth rate and the spatially separate electrogenic ion pumps in bean hypocotyl

Abstract. Measurements of Vps and Vpx were made on Vigna sesquipedalis hypocotyls in a stream of air or nitrogen during and after the application of IAA in an aerosol added to the gas stream. The lAA‐induced hyperpolarization of Vps and increase in growth rate in air was maintained for at least half an hour after the 50‐min IAA treatment was terminated. Changing from air to O2‐free gas stream in the presence of IAA aerosol depolarized Vps and Vpx, and then reduced growth rate, to the same extent as in hypocotyls in which IAA and O2 supply were terminated simultaneously. Under anoxic conditions, application of an IAA N2‐aerosol had no effect on Vps. Vpx or growth rate.

Relationship between cell number, cell size and fruit size of seeded fruits of tomato (Lycopersicon esculentum Mill.), and those induced parthenocarpically by the application of plant growth regulators

Application of GA3, IAA or 4-CPA to tomato ovaries induced the development of parthenocarpic fruit, which showed different growth rates. In the pericarp cell division and cell enlargement was affected differentially. GA3-induced fruits had considerably less but larger cells than seeded control fruits, IAA treatment resulted in the same number of cells but these were smaller and 4-CPA treatment induced fruits with about 20% more cells. Reduction in cell number had a similar effect on final fruit size as diminution of cell size. A reduction in the number of cell division centres (area around vascular bundles) as well as changes in the degree of endoploidy are possible reasons for the observed reductions in cell numbers. Hormonal causes for the different number and size of pericarp cells after the various treatments are discussed.

Environmental and growth regulator effects on heterophylly and growth of Proserpinaca intermedia (Haloragaceae)

Effects of five growth regulators GA 3, AMO-1618, ABA, IAA and kinetin on growth and leaf development of aerial forms of Proserpinaca intermedia Mack. were investigated. Plants were cultured in different photoperiods (8, 10, 12, 14 and 16 h light) and at different temperatures (15 and 27°C) for 35 days. Untreated plants maintained in photoperiods of 14 h and greater at 27°C grew erect, produced lanceolate-serrate leaves and flowered. Plants subjected to shorter photoperiods grew prostrate, developed small dissected leaves and remained vegetative. Leaf form and growth habit were modified by low temperature. Plants cultured at 15°C grew prostrate and developed dissected leaves regardless of photoperiod. ABA, IAA or kinetin treatments had no effect on growth or leaf form. GA 3 application to plants cultured under short days induced a growth habit and leaf form similar to that observed in plants cultured under long days. Low temperature induced prostrate growth and resulting dissected leaf formation was counteracted by GA 3 application. Plants which were made gibberellin deficient following application of AMO-1618 produced dissected leaves under long days (14 h). It is concluded that the morphological changes observed in Proserpinaca are caused by changes in endogenous hormonal levels. Their action is initiated by photoperiod through phytochrome and is modulated by temperature.

Beziehungen zwischen Indolessigsäure-induziertem Wachstum und dem Steringehalt der Plasmamembran-Fraktion bei Avena-Koleoptilen

Summary After etiolated Avena coleoptiles have been incubated either for 1 h or 20 h in buffered 10-4 or 10-5 MIAA, the plasma membrane fraction was isolated by means of homogenization and centrifugation on a linear sucrose gradient of 15-45 % (w/w). Centrifugation concentrated plasma membrane material in the sucrose gradient fractions of 33-37 %. This material was identified by electron microscopy and with the aid of marker enzymes. After extraction of the plasma membrane fraction, cholesterol, campesterol, stigmasterol, and sitosterol could be detected in the purified extract by means of gc-ms-analysis. Quantitative determinations of the sterols contained in the plasma membrane after IAA-treatment revealed that, in comparison to the untreated control, 10-5 M IAA applied 1 h before analysis leads to an increased concentration (11-24 %) of the four identified sterols, whereas incubation for 20 h in 10-4 M IAA shows a weaker promotive effect (2-15 %); in fact, the concentration of sitosterol deereases. As it is well known that sterols can influence microviscosity and permeability in biomembranes, it may be concluded from the above-mentioned results that a relationship exists between the primary action of the tested auxin and the sterol composition of the plasma membrane. However, these alterations in the sterol concentration observed in extracts of complete membranes are rather small; but with regard to this observation, it must be taken into consideration (ORCI et al. 1980) that the distribution of sterols in membranes is not homogeneous. Thus, it might be possible that sterol concentrations underwent strongly localized alterations after IAA treatment of the plasma membrane. These locations could be situated near transport proteins or ATPases responsible for proton pumping. It seems reasonable to believe that many effects observed after steroid treatment of plants may be attributable to the interrelation of auxins and sterols at the membrane level.

Les rythmes saisonniers: le point de vue d'un biologiste moléculaire

SummaryCircannual rhythms modulate numerous physiological functions as well as the pattern of certain circadian rhythms (CR), independently from developmental processes. Organisms are endowed with a complex temporal organization. It comprises high frequency oscillations (or fluctuations), circadian rhythms (as shown by chloroplast ultrastructure in Acetabularia, plate 1) and circannual rhythms.The effects of the environmental factors may qualitatively and quantitatively depend on the time at which they act on the plant. Auxin (IAA) might be a mediator of their action. It has been shown that a short IAA treatment affects the chloroplast ultrastructure and that the effect varies with the time of the day (plate 2).Many functions and many structures undergo changes during the course of development. CR themselves follow an ontogenetic evolution. Ultrastructure reveals that chloroplasts may be «young», «mature» or «old» and devoted to storage (plate 3). Changes in a parameter of the CR of the Hill reaction constitute a developmental evolution.Photoperiodism is a special case of morphogenesis. CR play a key role in their mechanism (see also Queiroz, this Colloquium). Moreover, the induced state is reflected both in the CR pattern and chloroplast ultrastructure. Three models have been proposed to account for photoperiodism—the first one being of Bünning (See Pittendrigh, 1972). All three involve the circadian organization.Circannual rhythms might constitute a mechanism involving at the same time endogenous circannual variations and a response to environmental factors, itself modulated by a CR (also endogenous). However, certain authors hypothetize that, to some extent at least, circannual rhythms might depend upon geophysical factors.

Relations polyphenols‐croissance: Lignification et limitation de croissance chez Lycopersicum esculentum

Abstract Polyphenols and growth – Lignification and limitation of growth in Lycopersicum esculentum.When fed with quinic acid, young tomato seedlings (Lycopersicum esculentum Mill. cv. St. Pierre) exhibited reduced growth and marked changes in cell wall composition: cellulose concentrations decreased whereas those of lignin increased. Exogenously supplied growth substances (IAA, GA3) affected both the size of the plants and the lignification process: IAA treatments resembled quinic acid induced modifications with regard to both size and lignification: GA3 applied to quinate treated plants counteracted the effects of this compound by reducing the lignin content and improving the growth. The possible effect of abnormal lignification as a limiting factor in cell growth is supported by the characterization of lignins in tissues different from xylem.

Auxin autotrophy and hyperauxinity of Eriophyes induced Zizyphus stem galls in Culture

Summary In contrast to Zizyphus normal stem tissue, the gall tissue was able to grow on HIS medium free of auxin and kinetin.With DL-tryptophan, both the tissues showed optimum growth at 5 mg/l, but the growth response of gall tissue was much higher.The optimal concentration of NAA and IAA was 10 mg/l for growth of both normal and gall tissues. In vivo , and in vitro grown gall tissues showed higher auxin contents as compared to normal tissues.The endogenous auxin level in both gall and normal tissues was highest in in vivo tissues, followed by DL-tryptophan, N AA, and IAA treatments in decreasing order.

Role of ascorbic acid in auxin induced cell elongation

Cytochemical detection of ascorbic acid in cultured root tips of Zea mays shows that dividing cells accumulate ascorbic acid in the cytoplasm. The localization pattern alters in the root tip as the cells begin to elongate. In elongating cells ascorbic acid is distinctly localized on cell walls. Ascorbic acid content per cell increases with the onset of cell elongation. Fully elongated cells contain fivefold more ascorbic acid than meristematic cells. Cytophotometric analysis reveals a sharp and positive correlation (r = +0.93) between percentage increase in content of ascorbic acid per cell and corresponding increase in cell size at different phases of cell elongation. IAA treatment to the roots raises the content of ascorbic acid per cell with a parallel increase in size of cell. Involvement of ascorbic acid in IAA induced cell elongation is discussed.

Spikelet Abscission in Guineagrass as Influenced by Auxin and Gibberellin1

Seed production of guineagrass (Panicum maximum Jacq.), an important pasture and forage crop in the tropics, is hindered by its heavy loss of seeds through spikelet abscission. A method whereby abscission could be delayed or arrested would be a great aid in seed harvest of this and other Panicum species.Auxin and gibberellin at three concentrations (10‐3, 5✕10‐3 and 10‐2M) were applied to the inflorescences of two experimental genotypes (PM285 and 68s‐5‐2) when the panicle was three‐fourths emerged from the flag leaf to inhibit spikelet abscission. Growth chamber and field experiments were conducted.Response was dependent on plant genotype and growth regulator concentration. In the growth chamber, panicle branch explants were inserted into semisolid agar solutions of growth regulators. The most responsive auxin treatment inhibited abscission by 32%. In the field, aqueous sprays of growth regulators were app.lied to entire inflorescences. The most responsive auxin treatment inhibited abscission by 40%, The two genotypes responded differently to IAA treatment with 68s‐5‐2 exhibiting significantly less abscission than PM285. Gibberellin treatments either stimulated abscission or had no influence under the conditions tested.Histological sections of pedicels of the genotype 68s‐5‐2 were made to follow the development of the abscission zone with and without applied auxin. The abscission zone exhibited no readily observable morphologlc or histologic response to auxin.

The effect of kinetin and auxin on the chloroplast structure and chlorophyll content in wheat coleoptiles

Kinetin and auxin when applied to excised segments of wheat coleoptiles bring about changes in chloroplast structure and chlorophyll content of parenchymatous cells. Auxin (IAA) alone at a concentration of 10-5M stimulated the elongation (growth), but the chloroplast membrane system was less developed and the chlorophyll content was lowest in comparison with control and other variants. Kinetin (KIN) exhibited various effects depending on the concentration used. 10-6M KIN somehow stimulated the elongation and enhanced the amount of grana coming to one chloroplast section, but the individual grana were relatively small and the chlorophyll content a little higher than in the control. On the other hand 10-5M KIN which did not promote the elongation of wheat coleoptiles, had the maximum stimulatory effect on the chloroplast membrane system, especially on the occurrence of large grana, and the chlorophyll content was highest in comparison with the other variants. The occurrence of starch grains in chloroplasts was lower than in the other variants. The effect of a joint treatment of KIN and IAA did not exceed that of KIN (10-5M) alone. Thus the development of chloroplasts and the accumulation of chlorophyll in wheat coleoptiles are stimulated by the concentration of KIN which does not promote the elongation of coleoptiles.