Avena Coleoptiles Research Articles

Effect of fluorophenylalanine on indole-3-acetic acid oxidation in Avena coleoptiles

Effects of the amino acid analog D,L-p-fluorophenylalanine on auxin oxidizing activity from <i>Avena saliva</i> cv. Clintford have been examined. Incubation of etiolated <i>Avena</i> coleoptile apices with D,L-p-fluorophenylalanine, previously reported to promote elongation and depress phenolic metabolism, lowers auxin oxidizing activity. Temperature and pH profiles demonstrated that depression of oxidizing activity by D,L-p-fluorophenylalanine occurs over a relatively wide range. Incubation of coleoptiles in media containing L-phenylalanine alone or L-phenylalanine combined with D,L-p-fluorophenylalanine result in oxidizing activities which are, respectively, slightly higher than or restored to control levels. Thus, dark incubation of coleoptiles with D,L-p-fluorophenylalanine results in auxin oxidizing activity which differs from that of control and other treatment groups. Oxidizing activity from D,L-p-fluorophenylalanine pretreated coleoptiles has a Michaelis constant (70 µM) and a maximum velocity (0.200) which are consistently lower than the control constants. These findings provide further clarification of the effects of D,L-p-fluorophenylalanine, on coleoptile elongation and auxin oxidizing activity in etiolated <i>Avena</i> coleoptiles.

Scanning electron microscope studies of Avena coleoptiles during primary leaf emergence

A scanning electron microscope study of the fine structure of coleoptiles of <em>Avena sativa</em> L. cv. Clintford has revealed information about the relationship between aspects of coleoptilar structure and the emergence of the primary leaf. Stomata are located on the lateral sides of the coleoptile and arch across the apex. The location of the stomata and associated vascular tissue may play a role in the splitting of the coleoptile pore and influence the manner in which the primary leaf emerges. Details of the surface fine structure of the coleoptile pore, its associated cells, stomata and guard cells are presented.

Photogravitropic equilibrium in Avena coleoptiles: fluence rate-response relationships and dependence on dark adaptation and clinostating.

Phototropism of Avena coleoptiles was measured in response to blue-light irradiation lasting between 2 and 24 h. During this time the coleoptiles established a bending angle of photogravitropic equilibrium that was dependent on the time of irradiation and also on the pretreatment in light or darkness prior to stimulation. The absolute threshold for the photogravitropic equilibrium in response to blue light was 10(-8) micromol m(-2) s(-1). Photon fluence rate-response curves, which were generated after several hours of dark adaptation, had a characteristic shape with a prominent optimum in the middle of the dynamic range. Curves which were generated without prior dark adaptation displayed no such optimum. Clinostating dark-adapted coleoptiles caused an increase of sensitivity and responsiveness during a 2-h period of unilateral irradiation. The advantages and the drawbacks of long-term irradiation experiments for the investigation of phototropism and the generation of action spectra are discussed.

Hypoxic induction of anoxia tolerance in Avena coleoptiles

Summary Seedlings of Avena sativa were subjected to 24 h anoxic stress after 24 h hypoxic-pretreatment (H-PT). The H-PT increased 4.5-fold the survivability of the anoxia in coleoptiles of the seedlings compared to that of non-pretreated (N-PT) seedlings. During pretreatment periods, alcohol dehydrogenase (ADH, EC 1.1.1.1) and pyruvate decarboxylase (PDC, EC 4.1.1.1) activities in the coleoptiles became 4.1- and 3.9-fold greater respectively than those of N-PT seedlings. After the onset of anoxic stress, ADH and PDC activities in all coleoptiles increased, but their activities in the H-PT coleoptiles remained much greater than those in the N-PT coleoptiles, and the average production rate of ethanol for the initial 6 h was 3.1 and 1.4 μmol g −1 fresh weight h −1 for the H-PT and N-PT coleoptiles, respectively. Coleoptiles of the seedlings lost ATP rapidly under anoxic stress; however, the decrease in ATP was much slower in the H-PT coleoptiles than in the N-PT coleoptiles. These results suggest that the H-PT may improve the subsequent tolerance of anoxia in Avena coleoptiles due to maintenance of ATP levels with rapid induction of ethanolic fermentation. The present results are consistent with the results that were found in roots of several plants, suggesting that the mechanism in hypoxic acclimation to anoxia implicated in their roots may act in Avena coleoptiles.

Auxin-induced elongation of short maize coleoptile segments is supported by 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one.

Endogenous extractable factors associated with auxin action in plant tissues were investigated, especially their effects on elongation of 1-mm coleoptile segments of maize (Zea mays L.), in the presence of saturating 10 microM indole-3-acetic acid (IAA). The relative growth response, to auxin alone, was much smaller in segments shorter than 2-3 mm compared to 10-mm segments. Fusicoccin-induced elongation, however, was less affected by shortening the segments. A reduced auxin response may result from the depletion through cut surfaces of a substance required for IAA-mediated growth. Sucrose, phenolics like flavonoids, and vitamins were ruled out as the causal factors. A partially purified methanol extract of maize coleoptiles supported longterm, auxin-controlled elongation. The active material was also found among substances bleeding from scrubbed maize coleoptiles. The active factor from maize was further purified by HPLC and characterised by the UV spectrum and its pH shift. This factor was identified as 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA) by mass spectroscopy. Activity tests confirmed that pure DIMBOA from other sources sustained auxin-induced elongation of short maize coleoptile segments. However, DIMBOA only partially restored the activity lost from short segments. This indicates that an additional factor, other than DIMBOA, is required. Extracts from Avena or Cucurbita did not contain the factor DIMBOA; it was active on maize elongation, but not on Avena coleoptiles or Cucurbita hypocotyls. This narrow specificity and the lack of DIMBOA action in short-term tests with maize indicate that DIMBOA is not the general auxin cofactor but may specifically "spare" the co-auxin in maize.

Synthesis and biological activities of 4-chloroindole-3-acetic acid and its esters.

4-Chloroindole-3-acetic acid (4-Cl-IAA) and its esters were synthesized from 2-chloro-6-nitrotoluene as the starting material. The biological activities of 4-CI-IAA and its esters were determined by four bioassays. Except for the tert-butyl ester, 4-Cl-IAA and its esters had stronger elongation activity toward Avena coleoptiles than had indole-3-acetic acid. The biological activities of the methyl, ethyl and allyl esters were as strong as the activity of the free acid. All the esters, except for the tert-butyl, inhibited Chinese cabbage hypocotyl growth more than the free acid did, and all the esters induced severe swelling and formation of numerous lateral roots in black gram seedlings even at a low concentration. Furthermore, adventitious root formation was strongly promoted in Serissa japonica cuttings by all the esters. The root formation-promoting activities of the ethyl and allyl esters were about three times the value for indole-3-butyric acid which is used to promote and accelerate root formation in plant cuttings.

Plant growth inhibitors involved phototropism of Avena coleoptiles.

Plant growth inhibitors involved phototropism of Avena coleoptiles.

32 Plant growth inhibitors involved in phototropism of Avena coleoptiles.

32 Plant growth inhibitors involved in phototropism of Avena coleoptiles.

Gravitropic responses of the Avena coleoptile in space and on clinostats. III. Hypogravity effects on coleoptile curvatures

The precise description of the gravitropic curvature response of plants is often difficult due to the presence of gravity when the response is recorded. Therefore, unambiguous results on the gravitropic reactions in differents segments of coleoptiles, the participation of auxin transport in the curvature development and the reactions to hypogravity stimulations can only be achieved in weightlessness. To answer these questions, curvatures of Avena coleoptiles at different distances from the apex were studied after transverse, hypogravity stimulations. The experiments were conducted in Spacelab on the Shuttle in earth orbit.Test plants were cultivated on 1.0 g‐centrifuges in Spacelab. The stimulation accelerations, were between 0.1 and 1.0 g, and duration varied between 2 and 130 min. All plant responses were recorded in weightlessness by a video cassette recorder for analysis.The gravitropic curvature started almost simultaneously in apical segments, and occurred later in the basal ones. After maximum response, the curvature in the top segments showed a clear autotropic reaction, that was not seen in the basal segments. Initial wrong‐way curvatures were recorded in the basal part of the coleoptiles at several g‐levels.The further down along the coleoptile, the later the occurrence of the maximum gravitropic curvature of each segment. For example, after a stimulus of 25 g min the maxima appeared to travel down the coleoptile with a speed of about 50 mm h−1 in the upper and 20 mm h−1 in the lower part of the coleoptiles. It is concluded that the basipetal auxin transport can contribute only marginally to the gravitropic curvature pattern due to its much lower transport rate. Local reactions control the curvature pattern in each segment (even if the basipetal auxin transport must add to the reactions).Extrapolations from stimulus response data curves allowed some determinations of threshold stimulation times for different segments along the coleoptiles. Data for the individual segments along the coleoptiles were not at variance with the reciprocity law.

Gravitropic responses of the Avena coleoptile in space and on clinostats. IV. The clinostat as a substitute for space experiments

Gravitropic responses of the Avena coleoptile in space and on clinostats. IV. The clinostat as a substitute for space experiments

Structural studies on monofluorinated derivatives of the phytohormone indole-3-acetic acid (auxin)

As part of the molecular recognition studies on the phytohormone indole-3-acetic acid (IAA) a series of fluorinated IAA's has been examined. The phenyl ring substitution at positions 4, 5, 6 and 7 resulted in four compounds, which were analyzed. Structure–activity correlation includes the analysis of their molecular conformations, based on the X-ray diffraction and computational chemistry results, and bioactivity determinations in the Avena coleoptile and the Pisum sativum stem straight-growth tests, lipophilicity and UV absorbance. The conformations of monofluorinated IAA's and a free hormone are defined by rotations about two bonds: one describes the relative orientation of a side chain towards the indole plane and the second the orientation of the carboxylic group. The results of X-ray structure analysis revealed the folded shape of the molecules in all compounds studied. Molecular mechanics and dynamics located the folded conformation as the local minimum, but failed to detect the planar conformation as one of the local minima, which according to ab initio results on IAA and 4-CI-IAA could also be possible. Crystal data at 295 K for 4-F-IAA and at 297 K for 5-F-IAA, and at 100 K for 6-F-IAA and 7-F-IAA using Mo Kα radiation (λ = 0.71073 Å) and Cu Kα (λ = 1.5418 Å, for 7-F-IAA), are as follows: 4-F-IAA, C10H8NO2F, Mr = 193.18, monoclinic, C2/c, a = 17.294 (5), b = 13.875 (4), c = 7.442 (4) Å, β = 103.88 (6)°, V = 1734 (1) Å3, Z = 8, Dx = 1.480 g cm−3, μ = 1.1 cm−1, F(000) = 800, R = 0.043, wR = 0.044 for 823 symmetry-independent [I ≥ 3σ(I)] reflections; 5-F-IAA, C10H8NO2F, monoclinic, P21/c, a = 19.284 (5), b = 5.083 (4), c = 9.939 (4) Å, β = 117.28 (6)°, V = 865.9 (1) Å3, Z = 4, Dx = 1.482 g cm−3, μ = 1.1 cm−1, F(000) = 400, R = 0.062, wR = 0.057 for 729 symmetry-independent [I ≥ 3σ(I)] reflections; 6-F-IAA, C10H8NO2F, monoclinic, P21/a, a = 9.360 (1), b = 5.167 (4), c = 17.751 (4) Å, β = 93.75 (1)°, V = 856.7 (8) Å3, Z = 4, Dx = 1.498 g cm−3, μ = 1.1 cm−1, F(000) = 400, R = 0.048, wR = 0.048 for 1032 symmetry-independent [I ≥ 2σ(I)] reflections; 7-F-IAA, C10H8NO2F, monoclinic, P21/a, a = 9.935 (5), b = 5.0059 (4), c = 17.610 (1) Å, β = 102.13 (1)°, V = 856.3 (1) Å3, Z = 4, Dx = 1.498 g cm−3, μ = 9.8 cm−1 (Cu Kα, F(000) = 400, R = 0.035, wR = 0.040 for 1504 symmetry-independent [I ≥ 2σ(I)] reflections.

Calcium chloride and calcium bromide in allium test, Lemna test and their effect upon peroxydases in Avena coleoptiles

Calcium chloride and calcium bromide in allium test, Lemna test and their effect upon peroxydases in Avena coleoptiles

Gravitropic responses of the Avena coleoptile in space and on clinostats. II. Is reciprocity valid?

Gravitropic responses of the Avena coleoptile in space and on clinostats. II. Is reciprocity valid?

Gravitropic responses of the Avena coleoptile in space and on clinostats.I. Gravitropic response thresholds

Gravitropic responses of the Avena coleoptile in space and on clinostats.I. Gravitropic response thresholds

Gravitropic responses of the Avena coleoptile in space and on clinostats. I. Gravitropic response thresholds

We conducted a series of gravitropic experiments on Avena coleoptiles in the weightlessness environment of Spacelab. The purpose was to test the threshold stimulus, reciprocity rule and autotropic reactions to a range of g-force stimulations of different intensities and durations The tests avoided the potentially complicating effects of earth's gravity and the interference from clinostat ambiguities. Using slow-speed centrifuges, coleoptiles received transversal accelerations in the hypogravity range between 0.l and 1.0 g over periods that ranged from 2 to 130 min. All responses that occurred in weightlessness were compared to clinostat experiments on earth using the same apparatus. Characteristic gravitropistic response patterns of Atuena were not substantially different from those observed in ground-based experiments. Gravitropic presentation times were extrapolated. The threshold at 1.0 g was less than 1 min (shortest stimulation time 2 min), in agreement with values obtained on the ground. The least stimulus tested, 0.1 g for 130 min, produced a significant response. Therefore the absolute threshold for a gravitropic response is less than 0.1 g.

Light-induced increase in the contents of ferulic and diferulic acids in cell walls of Avena coleoptiles: its relationship to growth inhibition by light

Light-induced increase in the contents of ferulic and diferulic acids in cell walls of Avena coleoptiles: its relationship to growth inhibition by light

The Role of Transpiration in Phototropism of the Avena Coleoptile: Evidence of Stomatal Control of the Phototropic Response

The hypothesis that phototropism is caused by the effect of light on transpiration seemed at variance with the observation that Avena coleoptiles respond phototropically while submerged in water. Further investigations, however, provided evidence that phototropism of submerged coleoptiles may be caused by the light-induced promotion of stomatal guttation. Evidence of guttation by submerged coleoptiles was provided by measuring tritium accumulation in a water jacket surrounding the coleoptile when tritiated water (THO) was supplied to the roots. It was shown that the application of nail polish to the coleoptiles induced almost immediate guttation from the stomata. This response, measured quantitatively by image analysis, occurred predominantly on the irradiated side of coleoptiles previously stimulated phototropically with blue light while submerged in water, and was much reduced and more uniformly distributed when the phototropic response had been eliminated by saturating the water with CO2. Small curvatures exhibited by coleoptiles kept in the dark at high humidity were almost invariably towards the side from which guttation occurred from the apical (hydathode) stomata. Application of petroleum jelly (Vaseline) to the stomata on the illuminated side of coleoptiles stimulated phototropically in moist air induced a negative curvature in the apical half of the coleoptile and reduced the positive curvature in the basal half. In contrast, vaseline applied to the middle of one of the broad sides of the coleoptile, where no stomata occur, had relatively little effect. These results are consistent with the hypothesis that phototropism of the Avena coleoptile is caused by light-induced loss of water from the stomata. It is also postulated that the mechanism is essentially the same whether water is lost by transpiration or guttation.

An Investigation of Aryloxyphenoxypropionate Antagonism of Auxin-Type Herbicide Action on Proton-Efflux

Interactions between MCPA and diclofop-methyl, clopyralid and quizalofop-ethyl, and 2,4-D with fluazifop-acid and -butyl were examined in detail in a proton-efflux assay using etiolated coleoptile tissue from Avena sativa L. The aryloxyphenoxypropionic acid/esters alone were inactive but significantly inhibited synthetic auxin-induced proton-efflux in mixtures at physiologically relevant concentrations. Computer-assisted dose-response analysis revealed that these graminicides reduced both the amplitude of synthetic auxin-induced response and the relative receptor affinity toward the auxin-type herbicides, without significantly altering the "switch-like" nature of the auxin control mechanism. These findings suggest that the aryloxyphenoxypropionic acid/esters interfere directly with the processes controlling proton-efflux in the Avena coleoptile and act as competitive inhibitors of synthetic auxin-receptor binding, which in light of their lack of auxin activity suggests an anti-auxin role. Moreover, enantiomeric studies imply that the auxin receptor shows some stereospecificity for the herbicidally active R(+)-enantiomer. These observations are discussed in relation to recent findings on auxin binding in sensitive tissues and it is suggested that the basis of antagonism may reside at the receptor level.

Enzymatic Hydrolysis of 4-O and 6-O-Indol-3-Ylacetyl-β-D-Glucose in Plant Tissues

The activity of the enzyme catalyzing the hydrolysis of IAA glucose conjugates has been studied in vegetative tissues of plants. We have demonstrated the presence of this enzyme in sprouts of oat ( Avena sativa L.), potato tubers ( Solanum tuberosum L.) and sprouts of bean ( Phaseolus vulgaris L.). 4-O and 6-O-IAA glucose esters caused the stimulation of Avena coleoptiles growth in elongation tests. This fact points to enzymatic hydrolysis of IAGlucose isomers as a process yielding free IAA and glucose. We have also found activity of two enzymes catalyzing the hydrolysis of IAA glucose esters in potato tubers. The enzyme specifically hydrolysing 6-O(4-O)-IAGlucose was partially purified using fractionation by PEG 6000, followed by ion-exchange, hydrophobic interaction and gel filtration chromatography. The enzyme has a molecular weight of 32 kDa, it shows a very similar activity over the range pH 6–9. The affinity of the enzyme for 6-O(4-O)-IAGlucose is in milimolar range, K m =10 milimolar. The presence of enzymes hydrolysing of IAA glucose conjugates in storage plant tissues may have physiological significance in regulating of free auxin level.

Auxin-induced growth of Avena coleoptiles involves two mechanisms with different pH optima.

Although rapid auxin-induced growth of coleoptile sections can persist for at least 18 hours, acid-induced growth lasts for a much shorter period of time. Three theories have been proposed to explain this difference in persistence. To distinguish between these theories, the pH dependence for auxin-induced growth of oat (Avena sativa L.) coleoptiles has been determined early and late in the elongation process. Coleoptile sections from which the outer epidermis was removed to facilitate buffer entry were incubated, with or without 10 micromolar indoleacetic acid, in 20 millimolar buffers at pH 4.5 to 7.0 to maintain a fixed wall pH. During the first 1 to 2 hours after addition of auxin, elongation occurs by acid-induced extension (i.e. the pH optimum is <5 and the elongation varies inversely with the solution pH). Auxin causes no additional elongation because the buffers prevent further changes in wall pH. After 60 to 90 minutes, a second mechanism of auxin-induced growth, whose pH optimum is 5.5 to 6.0, predominates. It is proposed that rapid growth responses to changes in auxin concentration are mediated by auxin-induced changes in wall pH, whereas the prolonged, steady-state growth rate is controlled by a second, auxin-mediated process whose pH optimum is less acidic.