Phytohormone production by three strains of <Emphasis Type="Italic">Bradyrhizobium japonicum</Emphasis> and possible physiological and technological implications

The aim of this work was to evaluate phytohormone biosynthesis, siderophores production, and phosphate solubilization in three strains (E109, USDA110, and SEMIA5080) of Bradyrhizobium japonicum, most commonly used for inoculation of soybean and nonlegumes in USA, Canada, and South America. Siderophore production and phosphate solubilization were evaluated in selective culture conditions, which had negative results. Indole-3-acetic acid (IAA), gibberellic acid (GA₃), and abscisic acid (ABA) production were analyzed by gas chromatography–mass spectrometry (GC-MS). Ethylene and zeatin biosynthesis were determined by GS–flame ionization detection and high-performance liquid chromatography (HPLC-UV), respectively. IAA, zeatin, and GA₃ were found in all three strains; however, their levels were significantly higher (p < 0.01) in SEMIA5080 (3.8 μg ml⁻¹), USDA110 (2.5 μg ml⁻¹), and E109 (0.87 μg ml⁻¹), respectively. ABA biosynthesis was detected only in USDA110 (0.019 μg ml⁻¹). Ethylene was found in all three strains, with highest production rate (18.1 ng ml⁻¹ h⁻¹) in E109 cultured in yeast extract mannitol medium plus l-methionine. This is the first report of IAA, GA₃, zeatin, ethylene, and ABA production by B. japonicum in pure cultures, using quantitative physicochemical methodology. The three strains have differential capability to produce the five major phytohormones and this fact may have an important technological implication for inoculant formulation.     

Indole-3-Acetic Acid Control on Acidic Oat Cell Wall Peroxidases

Incubation of oat coleoptile segments with 40 μm indoleacetic acid (IAA) induced a decrease of 35–60% in peroxidase activity at the cell wall compartment. Treatment with IAA also produced a similar decrease in the oxidation of NADH and IAA at the cell wall. Isoelectric focusing of ionic, covalent, and intercellular wall peroxidase fractions showed that acidic isoforms (pI 4.0–5.5) were reduced preferentially by IAA treatment. Marked differences were found between acidic and basic wall isoperoxidases in relation to their efficacy in the oxidation of IAA. A peroxidase fraction containing acidic isoforms oxidized IAA with a V _max/s_0.5 value of 2.4 × 10⁻² min⁻¹· g fw⁻¹, 4.0 times higher than that obtained for basic peroxidase isoforms (0.6 × 10⁻² min⁻¹· g fw⁻¹). In contrast, basic isoforms were more efficient than acidic isoperoxidases in the oxidation of coniferyl alcohol or ferulic acid with H₂O₂ (5.6 and 2.1 times, respectively). The levels of diferulate and lignin in the walls of oat coleoptile segments were not altered by treatment with IAA. The decrease in cell wall peroxidase activity by IAA was related more to reduced oxidative degradation of the hormone than to covalent cell wall cross-linking. Received November 1, 1998; accepted December 14, 1998     

Proline accumulation induced by weak acids and IAA in coleoptiles of wheat seedlings

Proline accumulation in coleoptiles of wheat seedlings or in excised coleoptile segments incubated under shaking for a 24 h period was studied. There was no increase of proline content of coleoptiles after incubation of the seedlings in 5 mM citric acid (a relatively strong and slowly penetrating organic acid) in a pH range from 4.5 to 7.0 and only a slight increase of proline content after incubation in phosphate buffer at pH 7.0 to 7.5 duo to the higher osmotic concentration of phosphate buffer in this pH range. Quite different results were obtained with seedlings incubated in 10 mM acetic acid, a weak and easily penetrating organic acid. With increasing proton concentrations, proline accumulation increased. Application of 400 mM mannitol or higher concentrations of IAA (more than 10⁻⁵M) additionally increased proline accumulation in the presence of 10 mM acetic acid in the pH range from 6.0 to 7.5 in which acetic acid alone was loss effective. It is suggested that a decrease of cytosolic pH causes stress—induced proline accumulation.     

The effect of indole-3-Acetic acid on ethylene formation in wheat seedlings

Isoperoxidase B 1 isolated from winter wheat (Triticum aestivum L., cv. Jubilar) seedlings was shown to catalyze ethylene formation from α-keto, γ-methylmercaptobutyric acid (KMBA). In the presence of Mn²⁺, indole-3-acetic acid (IAA), andp-coumaric acid, the kinetics by isoperoxidase B 1 catalyzed conversion of KMBA into ethylene and other products was similar to that of IAA oxidation. The reaction rate was therefore controlled by IAA through its electrondonating properties. Exogenous IAA induced ethylene formation in the segments of etiolated wheat coleoptiles. IAA-induced ethylene production was enhanced by L-methionine and mitomycin C. Aminoethoxy-analogue of rhizobitoxine, ferulic acid, sodium benzoate, cycloheximide and actinomyoin D exhibited significant inhibitory effects. These data indicate that the overall reaction mechanism in coleoptile segments involves RNA and protein synthesis. The site of IAA action is not specific; 2,4-dichlorophenoxyacetic, α-naphthylacetic and indole-3-butyric acids, respectively, possessed comparable inductive effect as IAA. Indole-3-propionic acid, indole, L-tryptophan and glucobrassicin had only low inductive efficiency, and moreover indole and L-tryptophan slowed down IAA-induced ethylene formation.     

Effect of temperature on the dose–response curves for auxin-induced elongation growth in maize coleoptile segments

The dose–response curves for IAA-induced growth in maize coleoptile segments were studied as a function of time and temperature. In addition, the kinetics of growth rate responses at some auxin concentrations and temperatures was also compared. It was found that the dose–response curves for IAA-induced elongation growth were, independently of time and temperature, bell-shaped with an optimal concentration at 10⁻⁵ M IAA. The kinetics of IAA-induced growth rate responses depended on IAA concentration and temperature, and could be separated into two phases (biphasic reaction). The first phase (very rapid) was followed by a long lasting one (second phase), which began about 30 min after auxin addition. For coleoptile segments incubated at 30°C, the amplitudes of the first and second phase were significantly higher, when compared with 25°C, at all IAA concentrations studied. However, when coleoptile segments were incubated at 20°C, the elongation growth of coleoptile segments treated with suboptimal IAA concentrations was diminished, mainly as a result of both phases reduction. In conclusion, we propose that the shape of the dose–response curves for IAA-induced growth in maize coleoptile segments is connected with biphasic kinetic of growth rate response.     

High-frequency plant regeneration from coleoptile tissue of indica rice (Oryza sativa L.)

Summary An efficient method was established for high-frequency embryogenic callus induction and plant regeneration from 3-,4-, 5- and 7-d-old coleoptile segments of Indica rice (Oryza sativa L. cv. Kasturi), Compact and friable callus developed from the cut ends and also on the entire length of the coleoptile segments cultured on Murashige and Skoog (MS) basal medium (1962) supplemented with 2,4-dichlorophenoxyacetic acid (2,4-D, 4.50–18.0 μM), kinetin (2.32 μM) and sucrose (3%, w/v). High frequency embryogenic callus induction and somatic embryo development was achieved when embryogenic calluses were transferred to MS medium supplemented with 2.25 μM 2,4-D, 2.32 μM kinetin, 490 μM L-tryptophan and 3% (w/v) sucrose. Plant regeneration was achieved by transferring clumps of embryogenic callus onto MS medium containing 2.85 μM indole-3-acetic acid (IAA), 17.77 μM 6-benzylaminopurine (BA) and 3% (w/v) sucrose. Histological observations of embryogenic calluses revealed the presence of somatic embryos and also plant regeneration via multiple shoot bud formation. Three, 4- and 5-d-old coleoptile segments showed a significantly (P<0.05) higher frequency of plant regeneration and mean number of plantlets per explant in comparison to 7-d-old coleoptile segments. The highest frequency (73.5%) of plant regeneration and mean number of plantlets (11.9±1.0) was obtained from 4-d-old coleoptile segments. Regenerated shoots were rooted on MS basal medium containing 4.92 μM indole-3-butyric acid (IBA) and plants were successfully transferred to soil and grown to maturity.     

Cooperation of Ethylene and Auxin in the Growth Regulation of Rice Coleoptile Segments

Elongation of coleoptile segments, having or not having a tip,excised from rice (Oryza sativa L. cv. Sasanishiki) seedlingswas promoted by exogenous ethylene above 0.3 µl l^–1as well as by IAA above 0.1 µM. Ethylene production ofdecapitated segments was stimulated by IAA above 1.0µM,and this was strongly inhibited by 1.0 µM AVG. AVG inhibitedthe IAA-stimulated elongation of the decapitated segment witha 4 h lag period, and this was completely recovered by ethyleneapplied at the concentration of 0.03 µl l^–1, whichhad no effect on elongation without exogenous IAA. The effectsof IAA and ethylene on elongation were additive. These factsshow that ethylene produced in response to IAA promotes ricecoleoptile elongation in concert with IAA, probably by prolongingthe possible duration of the IAA-stimulated elongation, butthat they act independently of each other. Moreover, AVG stronglyinhibited the endogenous growth of coleoptile segments withtips and this effect was nullified by the exogenous applicationof 0.03 µl l^–1 ethylene. These data imply that theelongation of intact rice coleoptiles may be regulated cooperativelyby endogenous ethylene and auxin in the same manner as foundin the IAA-stimulated elongation of the decapitated coleoptilesegments. Key words: oryza sativa, Ethylene, Auxin, Coleoptile growth     

Effect of thiosulphinates contained in garlic extract on growth, proton fluxes and membrane potential in maize (Zea mays L.) coleoptile segments

The effect of thiosulphinates contained in garlic extract (GE) on endogenous growth, growth in the presence of either indoleacetic acid (IAA) or fusicoccin (FC), and proton extrusion in maize coleoptile segments were studied. In addition, membrane potential changes at some GE dilutions and the protective effect of dithiothreitol (DTT) against GE toxicity were also determined. It was found that GE at almost all dilutions studied, when added to the incubation medium inhibited endogenous growth as well as growth in the presence of either IAA or FC. Simultaneous measurements of growth and external pH indicated that the administration of GE resulted in a complex change in the pH of the external medium; after an initial transient acidification, pH increased and reached the maximal value followed by a gradual decrease of medium pH. When IAA or FC was added after preincubation of the segments in the presence of GE the changes in medium pH were not significantly different from these obtained with GE only. If the coleoptile segments were first preincubated with GE and subsequently GE was removed, the addition of IAA induced strong growth and medium acidification. Dithiothreitol added together with GE neutralized the toxic effect of GE on growth of coleoptile segments incubated in the presence of IAA. The addition of GE to the control medium caused a depolarization of the membrane potential, the value of witch depended on GE dilution. These results indicate that the toxic effect of GE on growth of plant cells might be caused by disruption of the catalytic function of the plasma membrane H⁺-ATPase on formation of the disulfide bonds.     

Inhibition of galectin-3 mediated cellular interactions by pectic polysaccharides from dietary sources

Pectic polysaccharides from dietary sources such as Decalepis hamiltonii—swallow root (SRPP), Hemidesmus indicus (HPP), Nigella sativa—black cumin (BCPP), Andrographis serpyllifolia—(APP), Zingiber officinale—ginger (GRPP) and, citrus pectin (CPP) were examined for galectin inhibitory activity. Inhibition of (a) galectin-3 of MDA-MB-231 cells induced hemagglutination of red blood cells; (b) galectin-3 mediated interaction between normal/metastatic human buccal cells (NBC)/(MBC) and; (c) invasion of MDA-MB-231 and MBC in the invasive chamber was assessed. Results indicated that SRPP inhibited hemagglutination at Minimum Inhibitory Concentration (MIC) of 1.86 μg ml⁻¹ equivalent of carbohydrate as apposed to those of BCPP (130 μg ml⁻¹), APP (40 μg ml⁻¹), HPP (40 μg ml⁻¹) and CPP (25 μg ml⁻¹). GRPP even at concentration >1–6 mg ml⁻¹ did not inhibit agglutination. Also SRPP showed ∼15 and 2 fold potent anti hemagglutination activity relative to that of galectin-3 specific sugars—galactose (MIC-27.1 μg ml⁻¹) and lactose (MIC-4.16 μg ml⁻¹) respectively. Further, SRPP at 10 μg ml⁻¹ inhibited agglutination of NBC by galectin-3 of MDA-MB-231 cells. Modified swallow root pectic polysaccharide (MSRPP) of 50 kDa retained anti hemagglutination activity (MIC of 1.03 μg ml⁻¹) and inhibited MDA-MB-231 and MBC invasion by 73 and 50% with an IC₅₀ of 136 and 200 μg ml⁻¹ respectively. Both SRPP and MSRPP induced apoptosis up to 80% at 100 μg ml⁻¹ concentration by activating ∼2 and 8 folds of Caspase-3 activity. Sugar composition analysis and its correlation with the galectin inhibitory property indicated that pectic polysaccharides with higher arabinose and galactose content—arabinogalactan inhibited hemagglutination significantly.     

Action of red light on indole-3-acetic-acid status and growth in coleoptiles of etiolated maize seedlings

Brief irradiation of intact etiolated seedlings of maize (Zea mays L.) with red light (R; 30 W cm^-2, 10 min) reduces the amounts of diffusible and free (solvent-extractable) indole-3-acetic acid (IAA) obtainable from excised coleoptile tips. The effect is transient, the lowest level (30% of the dark control) occurring at about 3 h after irradiation. The free-IAA content of the whole coleoptile and the diffusible-IAA yield from the base of the same organ are similarly reduced, whereas the conjugated-IAA content of the coleoptile is not affected. These results support the view that R inhibits the production of IAA at the coleoptile tip. It is further shown that R inhibits biosynthesis of [³H]IAA from [³H]tryptophan supplied to the coleoptile tip. The shapes of the fluence-response curves obtained for the reduction of the diffusible-IAA yield by R and far-red light (FR) indicate the participation of two photoreactive systems. One has thresholds at 10^-3 W s cm² of R, five orders of magnitude less than the minimum required for the appearance of spectrophotometrically measurable far-red-absorbing form of phytochrome (Pfr) in vivo, and 10^-1 W s cm^-2 of FR; its response is linear to the logarithm of fluence exceeding five orders of magnitude. The other system is seen above 10² W s cm^-2 as an increase in the slope of the fluenceresponse curve; its response is FR reversible and related to the Pfr level of total photoreversible phytochrome. Both systems inhibit biosynthesis of IAA from tryptophan. Elongation of the coleoptile is stimulated by R; the stimulation is most apparent in the apical region, and is saturated with a fluence at which bo detectable pfr is formed. Farred light can also saturate this response. Since the endogenous IAA concentration in the coleoptile appears not to be in the inhibitory range, it is concluded that the stimulation of coleoptile elongation is not the result of changes in free-IAA levels.Abbreviations FR far-red light - IAA indole-3-acetic acid - Pfr phytochrome in the far-red-absorbing form - Pr phytochrome in the red-absorbing form - R red light     

Regulation of auxin transport in pea (Pisum sativum L.) by phenylacetic acid: effects on the components of transmembrane transport of indol-3yl-acetic acid

Phenylacetic acid (PAA), a naturally-occurring acidic plant growth substance, was readily taken up by pea (Pisum sativum L. cv. Alderman) stem segments from buffered external solutions by a pH-dependent, non-mediated diffusion. Net uptake from a 0.2 M solution at pH 4.5 proceeded at a constant rate for at least 60 min and, up to approx. 100 M, the rate of uptake was directly proportional to the external concentration of the compound. The net rate of uptake of PAA was not affected by the inclusion of indol-3yl-acetic acid (IAA) in the uptake medium (up to approx. 30 M) and, unlike the net uptake of IAA, was not stimulated by N-1-naphthylphthalamic acid (NPA) or 2,3,5-triiodobenzoic acid. At an external concentration of 0.2 M and pH 4.5, the net rate of uptake of PAA was about twice that of IAA. It was concluded that the uptake of PAA did not involve the participation of carriers and that PAA was not a transported substrate for the carriers involved in the uptake and polar transport of IAA. Nevertheless, the inclusion of 3–100 M unlabelled PAA in the external medium greatly stimulated the uptake by pea stem segments of [1-¹⁴C]IAA (external concentration 0.2 M). It was concluded that whilst PAA was not a transported substrate for the NPA-sensitive IAA efflux carrier, it interacted with this carrier to inhibit IAA efflux from cells. Over the concentration range 3–100 M, PAA progressively reduced the stimulatory effect of NPA on IAA uptake, indicating that PAA also inhibited carrier-mediated uptake of IAA. The consequences of these observations for the regulation of polar auxin transport are discussed.Abbreviations IAA indol-3yl-acetic acid - DMO 5,5-dimethyloxazolidine-2,4-dione - NPA N-1-naphthylphthalamic acid - PAA phenylacetic acid - TIBA 2,3,5-triiodobenzoic acid     

Promotion of elongation and acid invertase activity in Phaseolus vulgaris L. internode segments by phenylacetic acid

Phenylacetic acid (PAA) significantly stimulated the elongation of isolated Phaseolus vulgaris internodal segments and prevented the decline in acid invertase specific activity observed in segments incubated in the absence of growth substances. Unlike IAA, which stimulated both elongation and invertase activity over a very wide range of concentrations (<10^-4 - 1 mol.m^-3; optimum 10^-2 mol.m^-3), the response to PAA was restricted to a much narrower range of concentrations (3 × 10^-2 - 1 mol.m^-3; optimum ca. 1–2 × 10^-1mol.m^-3). At the optimum concentration of PAA, the stimulation of both responses was about 63–75% of that induced by the optimum concentration of IAA. The differences in the concentration range and magnitude of the responses to IAA and PAA were not due to differences in uptake of the two compounds. The stimulation of elongation by both compounds was prevented by 3.6 × 10^-2mol.m^-3 cycloheximide (CH), and acid invertase activites were greatly reduced compared with samples treated with growth substances alone. A saturating concentration of the specific auxin efflux carrier inhibitor N-1-naphthylphthalamic acid (NPA) slightly promoted the growth of control segments, probably by reducing the loss of residual endogenous auxin to the incubation medium. The elongation induced by PAA at its optimum concentration was considerably greater than the elongation induced by NPA, indicating that PAA did not cause growth by preventing the loss of endogenous auxin from the segments. Elongation responses to combinations of IAA and PAA suggested that the compounds were acting additively and that they were affecting growth by the same mechanism.     

Aerobic Gram-Positive and Gram-Negative Bacteria Exhibit Differential Sensitivity to and Transformation of 2,4,6-Trinitrotoluene (TNT)

A systematic evaluation of the ability of different bacterial genera to transform 2,4,6-trinitrotoluene (TNT), and grow in its presence, was conducted. Aerobic Gram-negative organisms degraded TNT and evidenced net consumption of reduced metabolites when cultured in molasses medium. Some Gram-negative isolates transformed all the initial TNT to undetectable metabolites, with no adsorption of TNT or metabolites to cells. Growth and TNT transformation capacity of Gram-positive bacteria both exhibited 50% reductions in the presence of approximately 10 μg TNT ml⁻¹. Most non-sporeforming Gram-positive organisms incubated in molasses media amended with 80 μg TNT ml⁻¹ became unculturable, whereas all strains tested remained culturable when incubated in mineral media amended with 98 μg TNT ml⁻¹, indicating that TNT sensitivity is linked to metabolic activity. These results indicate that the microbial ecology of soil may be severely impacted by TNT contamination. Received: 2 December 1996 / Accepted: 3 February 1997     

Epidermal Growth Factor Interacts with Indole-3-Acetic Acid and Promotes Coleoptile Growth

We used coleoptile sections of Avena sativa, Sorghum bicolor,and Zea mays seedlings to examine interactions between epidermalgrowth factor (EGF) and indole-3-acetic acid (IAA) that mayaffect plant growth and development. Our 24-h bioassays employedthree controls ranging in dilution from 10^–4 to 10^–8g ml^–1: (1) 50 mM potassium-phosphate buffer solution(pH=6.0), (2) bovine serum albumin, a nonspecific protein; and(3) IAA; plus two treatments: (1) mouse epidermal growth factor(EGF) ranging from 10^–6 to 10^–10gml^–1, and(2) EGF + IAA. In all three species growth in IAA, EGF, andEGF + IAA treatments showed significant increases over controls;EGF+IAA showed significant increases in growth over IAA alone.As the concentrations of IAA decreased, the EGF and IAA interactionbecame more pronounced. At the highest IAA concentrations, EGF+ IAA increased growth rates ca. 2% to 39%, whereas at lowerIAA concentrations EGF + IAA promoted growth as much as 121%,thereby lowering the normal IAA physiological set point up tothree or four orders of magnitude. Our data suggest that aninteraction between EGF and IAA may allow plants to recognizeand respond to animal biochemical messengers, resulting in changesin plant cell elongation that ultimately may alter plant growthpatterns. (Received April 27, 1994; Accepted September 5, 1994)     

The effects of temperature and IAA concentration on the latent period for IAA-induced rapid growth of Avena coleoptile segments

Summary Indoleacetic acid buffered at pH 7.0 induces a high growth rate in Avena coleoptile segments after a latent period, the duration of which is dependent upon both IAA concentration and temperature. A minimum latent period of 7.3 min is observed at 25° C with 10^-3 M IAA in phosphate buffer at pH 7.0.In contrast, 5×10^-3 M IAA made up in 0.01 M KH₂PO₄ alone, promotes elongation almost immediately, regardless of whether the segments have been previously incubated in 0.01 M KH₂PO₄ at pH 4.7, or phosphate buffer at pH 7.0. This immediate response is unaffected by 10^-4 M KCN which abolishes the rapid growth induced by 5×10^-3 M IAA buffered at pH 7.0 but does not affect the immediate appearance of low-pH-induced growth. Since we consistently find solutions of 5×10^-3 M IAA in 0.01 M KH₂PO₄ to have a pH of 3.5, our results indicate that the immediate growth response elicited by this solution is attributable to its low pH rather than to the presence of IAA as previously reported in the literature.     

High regenerative nature ofMentha arvensis internodes

Media and incubation conditions have been defined for highly efficient regeneration of shoots from internode explants of slow and fast growing cultivars ofMentha arvensis. Internodal segments excised from thein vitro raised shoots were inoculated on the MS medium supplemented with combinations of 5 concentrations of l-napthalene acetic acid (NAA) and 3 concentrations of 6-benzyl amino purine (BAP). The media containing 2 μg ml⁻¹ NAA, 10 Μg ml⁻¹ BAP and 1 μg ml⁻¹ NAA, 5 μg ml⁻¹ BAP proved best for shoot regeneration and growth responses on cv Himalaya and cv Kalka explants, respectively. In 12 weeks time, on average one explant of cv Himalaya produced about 200 shoots and that of cv Kalka produced about 180 shoots. The Himalaya explants required higher concentrations of NAA and BAP for high efficiency proliferation as compared to the Kalka explants. The experiments demonstrated that internodal tissue inMentha arvensis can be induced to obtain direct shoot regenerants with high efficiency. The analysis of the RAPD profiles of 100 regenerated plantlets each of cv Himalaya and Kalka showed more than 99.9% homogeneity in bands with respect to the parents.     

Plant-growth-promoting compounds produced by two agronomically important strains of <Emphasis Type="Italic">Azospirillum brasilense</Emphasis>, and implications for inoculant formulation

We evaluated phytohormone and polyamine biosynthesis, siderophore production, and phosphate solubilization in two strains (Cd and Az39) of Azospirillum brasilense used for inoculant formulation in Argentina during the last 20 years. Siderophore production and phosphate solubilization were evaluated in a chemically defined medium, with negative results. Indole 3-acetic acid (IAA), gibberellic acid (GA₃), and abscisic acid (ABA) production were analyzed by gas chromatography-mass spectrometry. Ethylene, polyamine, and zeatin (Z) biosynthesis were determined by gas chromatography-flame ionization detector and high performance liquid chromatography (HPLC-fluorescence and -UV), respectively. Phytohormones IAA, Z, GA₃, ABA, ethylene, and growth regulators putrescine, spermine, spermidine, and cadaverine (CAD) were found in culture supernatant of both strains. IAA, Z, and GA₃ were found in all two strains; however, their levels were significantly higher (p < 0.01) in Cd (10.8, 2.32, 0.66 μg ml⁻¹). ABA biosynthesis was significantly higher (p < 0.01) in Az39 (0.077 μg ml⁻¹). Ethylene and polyamine CAD were found in all two strains, with highest production in Cd cultured in NFb plus l-methionine (3.94 ng ml⁻¹ h⁻¹) and Az39 cultured in NFb plus l-lysine (36.55 ng ml⁻¹ h⁻¹). This is the first report on the evaluation of important bioactive molecules in strains of A. brasilense as potentially capable of direct plant growth promotion or agronomic yield increase. Az39 and Cd showed differential capability to produce the five major phytohormones and CAD in chemically defined medium. This fact has important technological implications for inoculant formulation as different concentrations of growth regulators are produced by different strains or culture conditions.     

Comparison of the effect of some phenolic compounds on wheat coleoptile section growth with their effect on iaa-oxidase activity

P-coumaric acid (HCA), 2,4-dichlorophenol (DCP) and resorcionol acted as cofactors for IAA-oxidase isolated from young wheat plants. Ferulic acid (FA) and 3,4-dihydroxybenzoic acid (DHBA) induced a lag phase prior to IAA oxidation. HCA, FA (0.2-1 mg ml^-1) and DCP (0.03-1 mg ml^-1) strongly inhibited wheat coleoptile section growth. DHBA (0.01-1 mg ml^-1) slightly stimulated it and resorcinol was without effect. HCA inhibited IAA-induced growth of coleoptile sections and FA stimulated it at low IAA levels and inhibited it at higher ones. DHBA, DCP and resorcinol did not affect IAA-induced growth of coleoptile sections.     

Stimulatory effects of potassium iodide on auxin action in the coleoptile segments of maize (Zea mays)

Potassium iodide (KI) was found to stimulate IAA-induced elongation of coleoptile segments in maize (Zea mays L.). The promoting effects of KI on coleoptile elongation, which were optimal at 1 mM in the presence of IAA, did not occur as a result of better conservation of IAA in the incubation medium. In addition, KI did not affect fusicoccin- or epibrassinolide-induced elongation. Additionally, sodium iodide (NaI) induced similar stimulatory effects on IAA-induced elongation, however, potassium chloride (KCl) showed no effect, suggesting that iodide is the active component. KI also enhanced IAA-induced ethylene biosynthesis in maize coleoptile segments. Taken together, these results suggest the involvement of KI-sensitive step(s) in auxin action before effectors of the signal transduction pathway split to elongation growth and ethylene biosynthesis. In-yong Hwang and Soo Chul Chang contributed equally to this work.     

Red light causes a reduction in IAA levels at the apical tip by inhibiting de novo biosynthesis from tryptophan in maize coleoptiles

When maize coleoptiles were unilaterally exposed to red light (7.9 μmol m⁻²s⁻¹ for 5 min), 3 h after treatment IAA levels in coleoptiles decreased in all regions, from top to basal, with levels about 60% of dark controls. Localized irradiation in the 5 mm top zone was sufficient to cause the same extent of IAA reduction in the tips to that in the tips of whole irradiated shoots. When coleoptiles were treated with N-1-naphthylphthalamic acid (NPA), an accumulation of IAA in the tip and a decrease of diffusible IAA from tips were simultaneously detected. IAA accumulation in red-light treated coleoptiles by NPA was much lower than that of dark controls. NPA treatment did not affect the content of conjugated IAA in either dark or light treated coleoptile tips. When ¹³C₁₁ ¹⁵N₂-tryptophan (Trp) was applied to the top of coleoptiles, substantial amounts of stable isotope were incorporated into free IAA in dark and red-light treated coleoptile tips. The ratio of incorporation was slightly lower in red-light treated coleoptile tips than that in dark controls. The label could not be detected in conjugated IAA. The rate of basipetal transport of IAA was about 10 mm h⁻¹ and the velocity was not affected by red light. These results strongly suggest that red light does not affect the rates of conversion of free IAA to the conjugate form or of the basipetal transport, but just reduces the IAA level in the tips, probably inhibited by IAA biosynthesis from Trp in this region.Electronic Supplementary Material Supplementary material is available to authorised users in the online version of this article at .