Further Evidence in Support of an Interactive Model in Stomatal Control

The interaction between CO₂ IAA, ABA, and temperature in thecontrol of stomatal behaviour, was investigated in the chill-resistantPisum sativum and chill-hardened Phaseolus vulgaris. It wasfound that the ability of kBA to induce stomatai closure wasdependent upon the presence of CO₂ in both species, at bothtemperatures (22 ?C, 5?C) Similarly, the ability of IAA to decreasestomatal resistance, was dependent upon the presence of CO₂in both species, at both temperatures. Chilling at 5?C in thelight did not influence the response characteristics of stomatato CO₂ ABA or IAA, in either species. These results are discussedin relation to a model of the interactions of these regulatorsof stomatal aperture. Key words: Stomata, modelling, chilling     

A Model for the Interaction of Low Temperature, ABA, IAA, and CO2 in the Control of Stomatal Behaviour

In the chilling sensitive (C.S.) species Phaseolus vulgarisit was found that at 22 ?C ABA induced stomatal closure butthis effect was dependent on the presence of CO₂. In the absenceof CO₂ the effect of ABA was completely lost. In contrast toABA, the effect of IAA at 22 ?C was to increase stomatal openingas the IAA concentration increased from 10^–2 to 10 molm^–3, and this effect was dependent upon the presence ofCO₂. However, at 5 ?C the action of ABA was reversed and itwas found to induce stomatal opening when fed via the transpirationstream in excised leaves. Similarly, the CO₂ response characteristicswere reversed at low temperatures as removal of CO₂ from theatmosphere caused stomatal closure. However, the effect of IAAat 5 ?C in the presence of CO₂ and with or without ABA was toincrease stomatal aperture with increasing IAA concentration.Significantly, ABA was found to have no effect upon aperturein the presence of CO₂ when IAA was added. The interactive effectsof ABA, IAA, CO₂ and low temperature are discussed in relationto a model proposed by the authors. Key words: IAA, ABA, CO₂, Stomata     

Cell Wall Acidification and its Role in Auxin-Stimulated Growth

The role of cell wall acidification in auxin-stimulated growthwas examined in abraded hypocotyl segments of etiolated Cucumis.sativus seedlings. Acidification of the medium by these segmentswas strongly inhibited by a pretreatment and the continued presenceof 1?0 mol m^–3 vanadate, widely used as an inhibitor ofplasma membrane ATPase activity. Elongation of segments in pH6?5 buffer was almost completely inhibited by such a treatmentwith vanadate, and the promotion of growth by indole-3-aceticacid (IAA) seen in the absence of vanadate was completely abolished.However, both inhibited and uninhibited segments showed a pronouncedelongation in response to pH 4?0) buffer. In pH 4?0 buffer,in contrast to the results obtained at pH 6?5, IAA significantlypromoted growth in both the presence and absence of vanadate.The results indicate that IAA can promote growth in the absenceof endogenous acidification, but that an acid wall is necessaryfor wall loosening to occur. Key words: Acidification, auxin-stimulated growth, Cucumis sativus, vanadate     

Optimization of indole acetic acid production by isolated bacteria from Stevia rebaudiana rhizosphere and its effects on plant growth

The ability to synthesize Indole-3-acetic acid (IAA) is widely associated with the plant growth promoting rhizobacteria (PGPR). The present work deals with isolation and characterization of such bacteria from the rhizosphere of medicinal plant Stevia rebaudiana and optimization of IAA production from its isolates. The optimization of IAA production was carried out at different pH and temperature with varied carbon and nitrogen sources of culture media. Out of different isolates obtained, three of them were screened as efficient PGPRs on the basis of different plant growth promoting attributes. Isolates CA1001 and CA2004 showed better production of IAA at pH 9 (91.7?µg?ml^?1) and at temperature 37?°C (81.7?µg?ml^?1). Dextrose (1%) was found to be the best carbon source for isolate CA1001 with 104?µg?ml^?1 IAA production. Isolate CA 2004 showed best production of IAA 36?µg?ml^?1 and 34?µg?ml^?1 at 1.5% and 1% Beef extract as nitrogen source respectively. Isolate CA 1001 showed 32?µg?ml^?1 IAA production at 0.5% nicotinic acid concentration. From the current study, CA1001 and CA2004 emerged as noble alternatives for IAA production further which also resulted in root and shoot biomass generation in crop plants, hence can be further used as bio-inoculants for plant growth promotion.     

A hormonal misunderstanding in Acca sellowiana embryogenesis: levels of zygotic embryogenesis do not match those of somatic embryogenesis

Endogenous levels of IAA, ABA and four types of CKs were analyzed in zygotic and indirect (ISE) and direct somatic embryogenesis of Acca sellowiana. Zygotic and somatic embryos at different developmental stages were sampled for morphological and hormonal analysis. Both embryo types showed substantial asymmetry in hormone levels. Zygotic embryos displayed a conspicuous peak of IAA in early developmental stages. The results outlined the hormonal variations occurring during zygotic and somatic embryogenesis regarding the timing, nature and hormonal status involved in both processes. The short transient pulse of IAA observed on the 3rd day in culture was suggested to be involved with the signaling for the induction of somatic embryogenesis. Fertilized ovule development was associated with increased IAA levels 21?C24?days after pollination, followed by a sharp decrease in the cotyledonary stage, both in zygotic and somatic embryos. There was a prominent increase in ABA levels in cultures which generated ISE 24?C30?days after pollination, a period that corresponds to the heart and torpedo stages. The levels of total CKs (Z, [9R]Z, iP and [9R]iP) were also always higher in zygotic than in somatic embryogenesis. While zygotic embryogenesis was dominated by the presence of zeatin, the somatic process, contrarily, was characterized by a large variation of the other cytokinin forms and amounts studied. The above results, when taken together, could be related to the previously observed high frequency formation of anomalous somatic embryos formed in A. sellowiana, as well as to their low germination ability.     

Construction of IAA-Deficient Mutants of Pseudomonas moraviensis and Their Comparative Effects with Wild Type Strains as Bio-inoculant on Wheat in Saline Sodic Soil

Tryptophan role in microbial biosynthesis of Indole Acetic Acid (IAA) is very distinct. In present study IAA producing bacteria Pseudomonas moraviensis was applied on wheat for improving growth and physiology; in the presence or absence of L-tryptophan in saline sodic field. Aqueous solution of tryptophan was added to the rhizosphere soil at 10?mg L^?1 with irrigated water. The survival efficiency of P. moraviensis measured in the presence of NaCl and mixture of salts. P. moraviensis increased P, NO₃–N and K contents in soil by 18–35% and further 12–15% increase was recorded in the presence of tryptophan. There were 40–80% increases in indole acetic acid (IAA), abscisic acid (ABA) and gibberellic acid (GA) contents of rhizosphere soil, and 40–45% increase in leaves when tryptophan was added with P. moraviensis. In the second phase, IAA deficient mutants of P. moraviensis were constructed and tested for the conversion of tryptophan to IAA. In transposon mutagenesis, 1800 trans-conjugants were generated and tested for tryptophan conversion. Among these, 11 mutants were selected and inoculated into wheat to compare their growth responses to the wild type. P. moraviensis wild type served as PGPR under salinity, but IAA- deficient mutants of P. moraviensis were unable to produce IAA and halted plant growth.     

棉花花芽分化时期茎尖内源激素的变化

实验结果表明,从子叶展平后到肉眼可花芽（现蕾）,所测几种激素（ABA、IAA、GA3、iPA、ZR）的含量均表现出明显的动态变化,而且在花芽分化临界期表现出最显著的变化（出现高峰或出现低峰）。推测所测几种激素均与花芽分化有密切关系。其中ABA、GA3和CTK（iPA、ZR）在花芽分化临界期时,其含量变化均呈现出一个高峰;而IAA则在花芽分化临界期时出现一个低峰。经比较分析得知,随着花芽分化的进行,ABA/IAA、GA3／IAA、CTK／IAA均表现一个较明显的变化规律。即从子叶展平时起,其比值开始上升,到花芽开始分化时达到一个峰值,之后逐渐下降,并维持在一个较稳定的水平。显然,ABA／IAA、GA3／IAA、CTK／IAA在棉花的花芽分化过程中起着重要的调控作用。由此推测,增加植物体内的ABA、GA3、CTK的含量或降低IAA的含量,都可以促进棉花的花芽分化;反之则抑制棉花的花芽分化。     

Indole-3-acetic acid and indole-3-butyric acid in tissues of carrot inoculated withAgrobacterium rhizogenes

The role of auxins in induction of roots byAgrobacterium rhizogenes was studied in carrot root disks. Transformed roots were produced on root disks by inoculation withA. rhizogenes, A4. Measurement of indole-3-acetic acid (IAA) by gas chromatography-mass spectrometry (GC-MS) indicated that there was a significant increase in the concentration of IAA in transformed callus and induced roots compared with initial IAA concentrations in carrot disks. Indole-3-butyric acid (IBA) was found to occur naturally in carrot roots. The presence of IBA, a potent root inducer, must be taken into account when assessing the role of auxin during transformation and induction of roots byA. rhizogenes.     

Indole acetic acid distribution coincides with vascular differentiation pattern during Arabidopsis leaf ontogeny

We used an anti-indole acetic acid (IAA or auxin) monoclonal antibody-based immunocytochemical procedure to monitor IAA level in Arabidopsis tissues. Using immunocytochemistry and the IAA-driven beta-glucuronidase (GUS) activity of Aux/IAA promoter::GUS constructs to detect IAA distribution, we investigated the role of polar auxin transport in vascular differentiation during leaf development in Arabidopsis. We found that shoot apical cells contain high levels of IAA and that IAA decreases as leaf primordia expand. However, seedlings grown in the presence of IAA transport inhibitors showed very low IAA signal in the shoot apical meristem (SAM) and the youngest pair of leaf primordia. Older leaf primordia accumulate IAA in the leaf tip in the presence or absence of IAA transport inhibition. We propose that the IAA in the SAM and the youngest pair of leaf primordia is transported from outside sources, perhaps the cotyledons, which accumulate more IAA in the presence than in the absence of transport inhibition. The temporal and spatial pattern of IAA localization in the shoot apex indicates a change in IAA source during leaf ontogeny that would influence flow direction and, consequently, the direction of vascular differentiation. The IAA production and transport pattern suggested by our results could explain the venation pattern, and the vascular hypertrophy caused by IAA transport inhibition. An outside IAA source for the SAM supports the notion that IAA transport and procambium differentiation dictate phyllotaxy and organogenesis.     

The effect of salt concentration on auxin stability in culture media

The concentrations of indole-3-acetic acid (IAA), naphthaleneacetic acid (NAA) and 2,4-dichlorophenoxyacetic acid (2,4-D) were followed for 35 days in cell-free liquid medium containing 100, 50, or 0% Murashige-Skoog (MS) salt base. Although the concentrations of NAA or 2,4-D remained constant the level of IAA decreased to only 11% of the original concentration after 35 days in the presence of 100% MS salt base. The observed rate of IAA degradation was accelerated by the presence of MS salts.     

Characterization of iodoacetate-mediated neurotoxicity in vitro using primary cultures of rat cerebellar granule cells

The neuroprotective efficacy of antioxidant molecules against iodoacetate (IAA) neurotoxicity in rat cerebellar granule cell (CGC) cultures was investigated. Transient exposure to IAA caused a concentration-dependent decrease in cell viability (ED50 = 9.8 microM). Dizocilpine maleate (MK-801), and 1,2,3,4-tetrahydro-6-nitro-2,3-dioxobenzo[f]quinoxaline-7-sulfonamide (NBQX), failed to prevent IAA toxicity. Certain antioxidant molecules were shown to be neuroprotective against IAA when combined with MK-801 but were ineffective when administered alone. (S)-(-)-Trolox, butylated hydroxytoluene (BHT), and U-83836E exhibited EC50 values of 78, 5.9, and 0.25 microM, respectively, in the presence of 10 microM MK-801. IAA also induced an increase in intracellular oxidative stress, which was quenched by the antioxidants (in the presence of MK-801) in cultures loaded with the oxidant sensitive dye 2'7'-dichlorodihydrofluorescein diacetate (DCFH-DA).     

Endogenous auxin level is a critical determinant for in vitro adventitious shoot regeneration in potato (Solanum tuberosum L.)

Endogenous levels of indole-3-acetic acid (IAA) were determined in the internodal explants of Indian tetraploid potato cultivars (cvs) viz., Kufri Sutlej (K.Sutlej) and Kufri Giriraj (K.Giriraj). Seven fold higher level of endogenous IAA was recorded for cv K.Sutlej over cv K.Giriraj. As a result, perhaps there was a callusing response from the cut end of the internodal explants of both the cvs in the MS basal medium. The extent of callusing was relatively higher in cv K.Sutlej when compared to that in K.Giriraj. The callusing response was inhibitory to shoot morphogenesis. Inclusion of an established anti-auxin, 2,3,5-tri-iodobenzoic acid (TIBA) in the regeneration medium facilitated a high frequency adventitious shoot regeneration response with lower cytokinin levels. Murashige and Skoog (MS) medium containing TIBA at 2.5?mg?l^?1 and 0.25?mg?l^?1 zeatin evoked a 100% regeneration response (4.5 shoot buds per explant) in cv K.Sutlej within 20?C25?days. However, in cv K.Giriraj, which had lower levels of endogenous IAA, 80% regeneration response (1.4 shoot buds per explant) was recorded in an extended period of 40?C45?days on a medium containing 0.5?mg?l^?1 TIBA and 0.1?mg?l^?1 zeatin. Although, TIBA and zeatin induced shoot bud formation, it failed to support sustained growth of the regenerated shoots in cv K.Giriraj. Hence, 0.01?mg?l^?1 ??-naphthaleneacetic acid (NAA) with a relatively higher concentration of zeatin (1.0?mg?l^?1) were used for sustained shoot regeneration (3.3 shoot buds per explant) within 25?days. From our results, it is evident that there was a difference in the requirement of exogenous zeatin levels required to induce a regeneration response in two cultivars of potato and this is attributed to the variable levels of endogenous IAA.     

Protease activity, organisation of vegetative primordia and effect of putrescine in tobacco thin layers

Since in tobacco thin layers exogenous putrescine alters the physiological and mor-phogenic responses induced by IAA (indole-3-acetic acid) and/or BA (benzylade-nine), the effect of this polyamine on protease activity and on the formation of meristemoids and vegetative primordia was studied during morphogenesis. Superficial thin layer explants, excised from the stem of tobacco (Nicotiana tabacum L. cv. Samsun) plants in the vegetative stage, were cultured under various hormonal conditions (IAA, IAA+BA, BA) and in a hormone-free medium, in the presence or absence of 100 μM putrescine. Histological analysis showed that no meristemoids were formed on the control medium or with putrescine alone and only a few were formed on IAA-treated explants with or without putrescine. An increasing number of meristemoids was observed in IAA+BA and BA treatments during culture; in both cases this number was enhanced by the presence of exogenous putrescine. Protease activity was evaluated spectrophotometrically using two synthetic substrates, azocasein and N-benzoyl-DL-arginine-p-nitroanilide (BAPNA). In the former, maximum protease activity was observed in IAA+BA- and BA-treated explants on days 10 and 15, respectively, while with IAA activity was lowest, the maximum occurring on days 5–10. In this case exogenous putrescine enhanced protease activity in the presence of IAA alone or with BA, while it decreased it in the presence of BA. BAPNA-mediated proteolytic activity (serine-proteases) was highest in IAA+BA-treated explants, intermediate in BA- and not different from controls in IAA-treated explants. Putrescine only affected proteolytic activity in IAA+BA treatments. The use of specific inhibitors of protease activities indicated that these enzymes belong to two main classes of proteases, that is serine- and thiol-proteases. The pattern of proteolytic activities during culture appeared to be related to the differentiation of meristemoids into vegetative primordia. The effect of exogenous putrescine on protease activity was different depending on different synthetic substrates, developmental patterns, pH and ionic strength.     

Inhibitory activity of IAA and IBA against lipoxygenase: in silico and in vitro validation

Inhibition of leukotriene biosynthesis is considered to be one of the potential treatment strategies for controlling inflammation, respiratory diseases and many neurodegenerative disorders. Designing of specific functional inhibitors against Lipoxygenases (LOX) has got considerable attention due to its ability to block leukotriene biosynthesis. Molecular docking analysis of two indole derivatives such as indoleacetic acid (IAA) and indolebutyric acid (IBA) are reported here. Both compounds give glide scores better than that of protocatechuic acid and nitro catechol, the two known LOX inhibitors. From the enzyme kinetic analysis, it was revealed that IAA and IBA inhibit competitively. The IC₅₀ values determined for both IAA and IBA were 42.98 μM and 17.82 μM, respectively. The binding free energy of these compounds was determined using isothermal titration calorimetric assay and was found to be ? 6.12 kcal/mol for IAA and ? 7.84 kcal/mol for IBA. From the analysis, it can be concluded that both IAA and IBA might be useful as anti-inflammatory agents.     

Morphogenesis of potato plants in vitro. II. Endogenous levels,distribution, and metabolism of IAA and cytokinins

The levels of endogenous IAA and cytokinins (zeatin, zeatin riboside, isopentenyladenine, and isopentenyladenosine) were determined in potato plants cultured in vitro under red light (R) and blue light (B) on medium with or without hormones. On medium without hormones in B, plants contained much higher cytokinin levels, particularly in leaves and roots, and also slightly elevated IAA levels. Kinetin in the medium in B changed the distribution of cytokinins and significantly increased IAA level in roots. In R, the presence of kinetin led to an increased cytokinin level in the whole plant, while the IAA level was slightly lower. IAA in the medium in B decreased cytokinin level in all plant parts, while the IAA level did not change significantly. In R, the presence of IAA in the medium led to a moderate increase of CK level and to a significant increase in IAA level, especially in roots. Uptake of 1-¹⁴C-IAA and of ³H-zeatin was generally higher in B than in R. Higher percentage of IAA taken up in B was converted to conjugates in the roots. Metabolism of ³H-zeatin was similar in R and B with only slight differences in metabolite amounts.Thus, in all experimental situations in which tuber formation was stimulated, IAA level in roots and stolons rose significantly, stressing the importance of an IAA gradient for tuber formation.     

Rhamnose Bound Indole-3-Acetic Acid in the Floral Parts of Peltophorum ferrugineum

The presence of rhamnose bound indole-3-acetic acid (IAA) was reported from acetone extract of anthers and carpels of the flowers of Peltophorum ferrugineum. Hydrolysis of the sugar ester gave IAA and rhamnose. Identification of IAA was based on physical measurements supported by bioassay. Bound and free IAA were not detected in petals, seeds and seed coats.     

The Brain's Response to an Essential Amino Acid-Deficient Diet and the Circuitous Route to a Better Meal

The essential (indispensable) amino acids (IAA) are neither synthesized nor stored in metazoans, yet they are the building blocks of protein. Survival depends on availability of these protein precursors, which must be obtained in the diet; it follows that food selection is critical for IAA homeostasis. If even one of the IAA is depleted, its tRNA becomes quickly deacylated and the levels of charged tRNA fall, leading to disruption of global protein synthesis. As they have priority in the diet, second only to energy, the missing IAA must be restored promptly or protein catabolism ensues. Animals detect and reject an IAA-deficient meal in 20?min, but how? Here, we review the molecular basis for sensing IAA depletion and repletion in the brain's IAA chemosensor, the anterior piriform cortex (APC). As animals stop eating an IAA-deficient meal, they display foraging and altered choice behaviors, to improve their chances of encountering a better food. Within 2?h, sensory cues are associated with IAA depletion or repletion, leading to learned aversions and preferences that support better food selection. We show neural projections from the APC to appetitive and consummatory motor control centers, and to hedonic, motivational brain areas that reinforce these adaptive behaviors.     

Effect of Auxin and Gibberellin on Conidial Germination in Neurospora crassa II. "Conidial Density Effect" and Auxin

Conidial germination in liquid shake culture of Neurospora crassawas affected by the number of conidia in the medium (conidialdensity effect) with the optimum density being around 2?10⁶conidia/ml. The conidial density effect at 2?10⁴ and 2?10⁵ conidia/mlwas eliminated by the addition of auxin, IAA or 2,4-D with theoptimum concentrations of IAA and 2,4-D being around 10^–6M. IAA and 2,4-D had no effect on the effect at 2?10⁷ conidia/ml.An active substance(s) for conidial germination which was relatedto the conidial density effect was detected in the cell-freefiltrate of the germination medium, and was found to be non-dialyzableand thermolabile. At the early stage of germination, the concentrationof active substance(s) in the medium increased in proportionto the conidial density and reached a supraoptimum amount forgermination at 2?10⁷ conidia/ml. IAA (10^–6M) enhancedthe concentration. Endogenous auxin concentrations in filtratesof the germination media containing 2?10⁵, 2?10⁶ and 2?10⁷ conidia/mlwere 5.8?10^–12, 4.6?10^–11 and 1.7?10^–10M IAAequivalent, respectively. The conclusion reached was that auxinmay control conidial germination with mediation by the activesubstance(s). (Received June 8, 1982; Accepted September 27, 1982)     

Iodoacetic acid-induced rigor in ileal longitudinal smooth muscle of guinea-pig

1. Ileal tensions to iodoacetic acid (IAA) develop when tissue ATP concentration falls below approximately 60-55% of the control. 2. As the IAA concentration is increased (0.1-10 mM), the ATP concentrations decrease rapidly, and both the time of the onset and the duration of the contraction shorten. 3. In the presence of lactate, IAA failed to decrease the tissue ATP concentration and did not develop tension. 4. The contraction to IAA developed in the presence of Ca2+ antagonist, D-600 or in Ca2(+)-free solution, however, onset time was prolonged. 5. These results suggest that the contraction to IAA is referred to as 'rigor' because it increases with decreasing tissue ATP concentration in ileum.