Distribution and transport of IAA in tomato plants

We determined as to indole-3-acetic acid (IAA), endogenous levels byliquid chromatography-mass spectrometry using ¹³C₆-IAA, diffusible levels byfluorometric detection using indole-propionic acid, and polar transportactivityby radioactive IAA in 3-month-old tomato plants (stems, leaves or roots). TheIAA concentration in the apoplast (AP) solution was higher than those in thesymplast (SP) solution in both the upper and lower parts of stems, showing thatIAA analysis of AP solution is important. Younger leaves exported much morediffusible IAA than older leaves. The IAA concentration in the main roots wasalmost at the same level as in the stems. The results suggested that thetransport capacity of IAA is probably the limiting factor for the amount of IAAtransported in stems and the amount of polar IAA transport might be only 19% ofthe endogenous IAA amount in stems.     

喷施吲哚-3-乙酸 (IAA) 对番茄及其上B型烟粉虱的影响

【目的】不同植物生长调节物质对植食性昆虫产卵、发育、取食等常有促进或抑制作用,进而影响植物与昆虫的互作关系。本研究旨在阐明常用的植物生长调节剂吲哚-3-乙酸对B型烟粉虱Bemisia tabaci (Gennadius)的影响,进而探索防治烟粉虱环境友好的方法,同时期望获得更加优质的烟粉虱用作替代寄主饲养寄生蜂。【方法】对番茄 Solanum lycopersicum L.植株外源喷施吲哚-3-乙酸(IAA),检测其生理生化的响应;记录B型烟粉虱存活率、产卵量并测量解毒酶等指标。【结果】喷施IAA后番茄叶片含水量略有上升,叶面积增大,叶绿素含量增加,过氧化物酶(POD)活性降低,多酚氧化酶(PPO)活性升高,超氧化物歧化酶(SOD)活性变化不显著(P＞0.05)。喷施IAA后番茄上B型烟粉虱成虫存活率高于对照组,其中50 mg/L IAA番茄上B型烟粉虱成虫存活率和总产卵量最高,250 mg/L IAA存活率最低;喷施IAA 120 h后烟粉虱总产卵量升高;碱性磷酸酶(AKP)、超氧化物歧化酶(SOD)活性较对照升高。【结论】喷施不同浓度的IAA溶液后,番茄植株的生理生化水平发生不同程度的改变,烟粉虱成虫的存活状况、产卵量以及体内解毒活性也会产生不同程度的改变。适宜剂量的IAA处理能够使烟粉虱的生存表现更加优异,从而为饲养寄生蜂提供优质的替代寄主。     

The effect of assimilate supply on fruit growth and hormone levels in tomato plants

Rates of dry matter accumulation and contents of starch, sugars and abscisic acid (ABA) of tomato fruits differed significantly during development at three positions (proximal, middle and distal) on a truss. Proximal fruits, which accumulated dry matter most rapidly during early development, generally had least ABA (per g DW).Partial defoliation reduced carbon accumulation by all fruits but increased ABA, especially in distal fruit, and indoleacetic acid (IAA), particularly in proximal fruits. The ABA content of leaves in partially defoliated plants was similar to that of leaves on non-defoliated plants.Removal of distal fruits on a truss enhanced carbon movement to the remaining proximal fruits and also increased their ABA content early in development but did not affect their IAA content. On the other hand, when proximal fruit were removed there was no large or lasting increased accumulation of carbon by the remaining distal fruits and they contained less ABA and IAA than fruits on plants without fruit thinning. Leaf carbon and ABA levels showed no marked trend in response to fruit thinning.The amount of carbon in the stems was increased by fruit thinning but decreased by partial defoliation.The possible roles of ABA and IAA in regulating fruit growth are discussed.Part of this work has been presented to a Symposium on Phloem loading and related processes at Bad Grund/Oberhar, W. Germany, July 1979.     

Diffusible IAA and dominance phenomena in fruits of apple and tomato

The relationships between indole-3-acetic acid (IAA) diffusing out of the fruit and competition among fruits, and between fruits and shoot tips were investigated using apple ( Malus domestica Borkh. cv. Jonagold) and tomato ( Lycopersicon esculentum Mill.) plants. Dominant fruits always had more diffusible IAA than subordinated, inhibited fruits. Alterations in dominance – by fruit- or shoot tip removal – led to significant changes in diffusible IAA by the remaining fruits. This change could be detected one day after dominance modification.
It is suggested that diffusible IAA is involved in the correlative signal regulating dominance relationship between fruits, and between fruits and shoots in apple and tomato.     

Glyphosate-increased levels of indole-3-acetic acid in yellow nutsedge leaves correlate with gentisic acid levels

The effects of glyphosate [N-(phosphonomethyl)glycine] on endogenous in-dole-3-acetic acid (IAA) level, IAA oxidase activity, and possible interactions with alterations in phenolic metabolism have been examined in yellow nutsedge ( Cyperus esculentus L.) plants. IAA was quantified by flame ionization detector gas-chroma-tography, phenols were quantified by high-performance liquid chromatography and the auxin protection and the IAA oxidase activities were determined spectrophoto-metrically and/or polarographically. A significant increase in IAA content was recorded after glyphosate treatment. No IAA oxidase activity was detected in control and treated tissues. Auxin protection activity and gentisic acid were present in all extracts assayed, and their concentrations increased as the rate of glyphosate application increased. Addition of gentisic acid to an extract of control plants increased the auxin protection detected. These findings indicate that the high levels of free IAA in yellow nutsedge leaves after glyphosate application are due to the inhibition of the IAA oxidase activity by increased levels of the IAA-protecting phenol gentisic acid.     

水分胁迫对棉花叶片中IAA从含量、IAA氧化酶和过氧化物酶活性的影响

整株干旱降低盐棉46号叶片中的IAA总量,叶龄愈小下降愈多。幼叶中IAA总量的下降主要是结合态IAA减少的结果。气干和-1.7MPa PEG溶液渗透胁迫处理也降低离体成熟叶片的IAA总量,其变化与叶片含水量呈直线相关(r=0.905)。整株干旱处理提高各叶片的过氧化物酶活性,叶龄愈小提高愈多,但IAA氧化酶活性无显著变化。离体和整株干旱时IAA总量的下降,可能是过氧化物酶活性增加所致。     

Effect of Cyclanilide on Auxin Activity

Cyclanilide is a plant growth regulator that is registered for use in cotton at different stages of growth, to either suppress vegetative growth (in combination with mepiquat chloride) or accelerate senescence (enhance defoliation and boll opening, used in combination with ethephon). This research was conducted to study the mechanism of action of cyclanilide: its potential interaction with auxin (IAA) transport and signaling in plants. The activity of cyclanilide was compared with the activity of the auxin transport inhibitors NPA and TIBA. Movement of [³H]IAA was inhibited in etiolated corn coleoptiles by 10 μM cyclanilide, NPA, and TIBA, which demonstrated that cyclanilide affected polar auxin transport. Although NPA inhibited [³H]IAA efflux from cells in etiolated zucchini hypocotyls, cyclanilide had no effect. NPA did not inhibit the influx of IAA into cells in etiolated zucchini hypocotyls, whereas cyclanilide inhibited uptake 25 and 31% at 10 and 100 μM, respectively. Also, NPA inhibited the gravitropic response in tomato roots (85% at 1 μM) more than cyclanilide (30% at 1 μM). Although NPA inhibited tomato root growth (30% at 1 μM), cyclanilide stimulated root growth (165% of control at 5 μM). To further characterize cyclanilide action, plasma membrane fractions from etiolated zucchini hypocotyls were obtained and the binding of NPA, IAA, and cyclanilide studied. Cyclanilide inhibited the binding of [³H]NPA and [³H]IAA with an IC₅₀ of 50 μM for both. NPA did not affect the binding of IAA, nor did IAA affect the binding of NPA. Kinetic analysis indicated that cyclanilide is a noncompetitive inhibitor of both NPA and IAA binding, with inhibition constants (K _i) of 40 and 2.3 μM, respectively. These data demonstrated that cyclanilide interacts with auxin-regulated processes via a mechanism that is distinct from other auxin transport inhibitors. This research identifies a possible mechanism of action for cyclanilide when used as a plant growth regulator.     

Shoots from MM. 106 apple rootstocks grown in a polythene tunnel do not contain a higher IAA concentration than shoots from field-grown plants

MM. 106 apple rootstock plants grown in a polythene tunnel show greater apical dominance and a higher propensity to root as cuttings than plants grown in the field. Experiments were conducted to test the hypothesis that the growth habit and rooting behaviour of polythene tunnel plants were caused by increased concentrations of idole-3yl-acetic acid. Cuttings taken from field-grown plants which had been sprayed with IAA showed increased rooting. In shoots of both field-grown and polythene tunnel-grown plants endogenous IAA levels were highest in the upper shoot region and declined progressively with distance from the apex. Plants grown in the polythene tunnel, however, did not contain significantly higher IAA levels than field plants. The analytical data do not support the hypothesis that the growth and rooting behaviour of plants grown in a polythene tunnel were caused by increased concentrations of IAA.Abbreviations IAA indol-3yl-acetic acid     

LED光质对番茄幼苗生长及内源性GA和IAA含量的影响

采用发光二极管调制光谱能量分布,以荧光灯为对照,研究不同光质(红光、蓝光、黄光、绿光)下番茄幼苗生理特性及内源性GA和IAA水平与其生长的关系。结果表明:(1)红光和蓝光有利于番茄幼苗茎的伸长和叶面积的增加。(2)除蓝光处理下可溶性糖含量和SOD活性与对照无显著性差异外,各单色光质处理下番茄幼苗根系活力、色素含量、可溶性蛋白和可溶性糖含量、SOD活性较对照均显著降低。(3)与对照相比,各单色光质处理下番茄幼苗叶片中GA含量显著降低,IAA含量在红光下显著升高,在黄光和绿光下显著降低,且叶面积与IAA含量呈显著正相关关系。(4)番茄幼苗茎中GA和IAA含量在红光和蓝光处理下显著高于对照和黄、绿光处理,且株高与茎中GA和IAA含量呈正相关关系。     

Ameliorative Effect of Chlormequat Chloride and IAA on Drought Stressed Plants of <Emphasis Type="Italic">Cymbopogon Martinii</Emphasis> and <Emphasis Type="Italic">C. winterianus</Emphasis>

Responses of Cymbopogon martinii and C. winterianus to drought stress and chlormequat chloride and IAA application are compared. These two species are important source of essential oil production in drought regions. For both species and their cultivars relative water content (RWC), herbage yield and oil amount decreased under drought, while oil biosynthesis increased. Oil concentration increased significantly under drought in C. winterianus while peroxidase activity increased in C. martinii. Amount of geraniol increased under drought stress in C. martinii while citronellal and geraniol accumulation decreased in C. winterianus. Ameliorative effects of chlormequat chloride and IAA were observed in drought stressed plants of both species. Herbage yield increased significantly in chlormequat chloride and IAA treated stressed plants of C. winterianus, while oil concentration increased in C. martinii. Ameliorative effect of IAA in increasing oil yield was significant in drought stressed plants of both the species. Changes in various morpho-physiological traits indicated that chlormequat chloride and IAA can partially alleviate the detrimental effect of drought in these aromatic grasses.     

Growth rate of potato tubers and endogenous contents of indolylacetic acid and abscisic acid

Potato plants ( Solanum tuberosum L. ev. Ostara) were grown in water culture and the growth rate of individual tubers was measured daily or at two day intervals. Tubers of different growth rate and/or different age (days after tuberization) were harvested and analysed for indolylacetic acid (IAA) and abscisic acid (ABA). Within individual tubers the IAA content decreases from the apical to the basal part of the tuber. Tuber age and corresponding fresh weight are negatively correlated with the endogenous IAA content. If, however, individual tubers of comparable age but different growth rates are compared, a significant positive correlation between growth rate and IAA content is revealed, while ABA showed a significant negative correlation with growth rate. Removal of all fast-growing tubers from individual plants causes an increase in the growth rate of the remaining tubers within 3–4 days. This coincides with a particularly steep increase in IAA content. The data support the idea that endogenous IAA content may be one factor responsible for controlling the growth rate ("sink-activity ") of individual tubers.     

IBA和NAA对山杜英组培苗生根过程中内源IAA、ABA含量变化的影响

本文研究山杜英组培苗生根过程中内源IAA、ABA含量变化规律。结果表明,培养基添加IBA和NAA后,在生根过程中内源IAA、ABA含量变化类似,根点出现前内源IAA、ABA含量一直上升,根点出现后含量开始下降,产生愈伤组织时两种处理的IAA/ABA分别是2.526和3.226。在不添加外源生长素情况下,内源IAA含量一直维持在较低水平,而内源ABA含量一直呈现上升趋势,IAA/ABA始终都在1.211以下。     

Low-fluence red light increases the transport and biosynthesis of auxin

In plants, light is an important environmental signal that induces photomorphogenesis and interacts with endogenous signals, including hormones. We found that light increased polar auxin transport in dark-grown Arabidopsis (Arabidopsis thaliana) and tomato (Solanum lycopersicum) hypocotyls. In tomato, this increase was induced by low-fluence red or blue light followed by 1 d of darkness. It was reduced in phyA, phyB1, and phyB2 tomato mutants and was reversed by far-red light applied immediately after the red or blue light exposure, suggesting that phytochrome is involved in this response. We further found that the free indole-3-acetic acid (IAA) level in hypocotyl regions below the hook was increased by red light, while the level of conjugated IAA was unchanged. Analysis of IAA synthesized from [13C]indole or [13C]tryptophan (Trp) revealed that both Trp-dependent and Trp-independent IAA biosynthesis were increased by low-fluence red light in the top section (meristem, cotyledons, and hook), and the Trp-independent pathway appears to become the primary route for IAA biosynthesis after red light exposure. IAA biosynthesis in tissues below the top section was not affected by red light, suggesting that the increase of free IAA in this region was due to increased transport of IAA from above. Our study provides a comprehensive view of light effects on the transport and biosynthesis of IAA, showing that red light increases both IAA biosynthesis in the top section and polar auxin transport in hypocotyls, leading to unchanged free IAA levels in the top section and increased free IAA levels in the lower hypocotyl regions.     

Production and characterization of auxin-insensitive rice by overexpression of a mutagenized rice IAA protein

Since auxin was first isolated and characterized as a plant hormone, the underlying molecular mechanism of auxin signaling has been elucidated primarily in dicot plants represented by Arabidopsis. In monocot plants, the molecular mechanism of auxin signaling has remained unclear, despite various physiological experiments. To understand the function and mechanism of auxin signaling in rice ( Oryza sativa ), we focused on the IAA gene, a well-studied gene in Arabidopsis that serves as a negative regulator of auxin signaling. We found 24 IAA gene family members in the rice genome. OsIAA3 is one of these family members whose expression is rapidly increased in response to auxin. We produced transgenic rice harboring m OsIAA3 - GR , which can overproduce mutant OsIAA3 protein containing an amino acid change in domain II to cause a gain-of-function phenotype, by treatment with dexamethasone. The transgenic rice was insensitive to auxin and gravitropic stimuli, and exhibited short leaf blades, reduced crown root formation, and abnormal leaf formation. These results suggest that , in rice, auxin is important for development and its signaling is mediated by IAA genes.     

Stimulatory effect of cytokinins and interaction with IAA on the release of lateral buds of pea plants from apical dominance

Lateral buds of pea plants can be released from apical dominance and even be transformed into dominant shoots when repeatedly treated with synthetic exogenous cytokinins (CKs). The mechanism of the effect of CKs, however, is not clear. The results in this work showed that the stimulatory effects of CKs on the growth of lateral buds and the increase in their fresh weights in pea plants depended on the structure and concentration of the CKs used. The effect of N-(2-chloro-4-pyridyl)-N'-phenylurea (CPPU) was stronger than that of 6-benzylaminopurine (6-BA). Indoleacetic acid (IAA) concentration in shoot, IAA export out of the treated apex and basipetal transport in stems were markedly increased after the application of CPPU or 6-BA to the apex or the second node of pea plant. This increase was positively correlated with the increased concentration of the applied CKs. These results suggest that the increased IAA synthesis and export induced by CKs application might be responsible for the growth of lateral shoots in intact pea plants.     

活性氧对外源IAA诱导的ACC合酶活性的影响

本文试图从活性氧的角度阐明外源IAA诱导ACC合酶活性的机制.绿豆(Phaseolus radiatus L.)幼苗的乙烯产生及ACC合酶活性从萌发的第5天开始上升,到第10天达到高峰,接着下降.10 μmol/L的外源IAA能明显促进绿豆幼苗乙烯的产生及ACC合酶的活性,同时也促进了超氧阴离子自由基(O(-)/(*)2)、过氧化氢(H2O2)的产生.显示外源IAA诱导的ACC合酶的活性与其诱导的活性氧的产生具有某种相关性.外源O(-)/(*)2处理能明显提高绿豆幼苗的乙烯产生速率及ACC合酶的活性,而外源H2O2无论对乙烯产生或ACC合酶的活性均没有明显的作用.外加O(-)/(*)2的清除剂SOD对绿豆幼苗乙烯的产生及ACC合酶活性的提高有一定的抑制作用,而外源过氧化氢酶却没有明显的作用.为此我们可以得出结论:外源IAA诱导的绿豆幼苗ACC合酶活性的提高可能是由于其诱导的O(-)/(*)2产生的升高引起的,这可能也是高等植物中调控乙烯生物合成的机制之一;而IAA诱导的H2O2产率的升高并不是其诱导ACC合酶活性升高的原因.     

IAA对孔石莼生长及叶绿素和蛋白质含量的影响

在22℃、40μE·s^-1·m^-2连续光照培养条件下,研究了植物生长调节物质(IAA)对孔石莼(Ulvapertusa)的生长及叶绿素和蛋白质含量的影响。研究表明,与对照组相比,0.01～10.00mg·L^-1IAA对孔石莼的生长及叶绿素和蛋白质含量都有不同程度的影响。随着IAA的质量浓度的增大,实验组藻体的直径以及叶绿素和蛋白质含量都相应增大。并且发现,当IAA的浓度达到1.00mg·L^-1时,对孔石莼的促生长作用最佳,且叶绿素和蛋白质的含量达最高值;而当IAA的浓度大于3.00mg·L^-1时,对孔石莼的生长却相对抑制,叶绿素和蛋白质的含量也开始降低。     

Auxin-induced leaf blade expansion in Arabidopsis requires both wounding and detachment

Elevation of leaf auxin (indole-3-acetic acid; IAA) levels in intact plants has been consistently found to inhibit leaf expansion whereas excised leaf strips grow faster when treated with IAA. Here we test two hypothetical explanations for this difference in growth sensitivity to IAA by expanding leaf tissues in vivo versus in vitro. We asked if, in Arabidopsis, IAA-induced growth of excised leaf strips results from the wounding required to excise tissue and/or results from detachment from the plant and thus loss of some shoot or root derived growth controlling factors. We tested the effect of a range of exogenous IAA concentrations on the growth of intact attached, wounded attached, detached intact, detached wounded as well as excised leaf strips. After 24 h, the growth of intact attached, wounded attached, and detached intact leaves was inhibited by IAA concentrations as little as 1 µM in some experiments. Growth of detached wounded leaves and leaf strips was induced by IAA concentrations as low as 10 µM. Stress, in the form of high light, increased the growth response to IAA by leaf strips and reduced growth inhibition response by intact detached leaves. Endogenous free IAA content of intact attached leaves and excised leaf strips was found not to change over the course of 24 h. Together these results indicate growth induction of Arabidopsis leaf blade tissue by IAA requires both substantial wounding as well as detachment from the plant and suggests in vivo that IAA induces parallel pathways leading to growth inhibition.     

Indole-3-butyric acid in plants: occurrence, synthesis, metabolism and transport

Indole-3-butyric acid (IBA) was recently identified by GC/MS analysis as an endogenous constituent of various plants. Plant tissues contained 9 ng g^?1 fresh weight of free IBA and 37 ng g^?1 fresh weight of total IBA, compared to 26 ng g^?1 and 52 ng g^?1 fresh weight of free and total indole-3-acetic acid (IAA), respectively. IBA level was found to increase during plant development, but never reached the level of IAA. It is generally assumed that the greater ability of IBA as compared with IAA to promote rooting is due to its relatively higher stability. Indeed, the concentrations of IAA and IBA in autoclaved medium were reduced by 40% and 20%, respectively, compared with filter sterilized controls. In liquid medium, IAA was more sensitive than IBA to non-biological degradation. However, in all plant tissues tested, both auxins were found to be metabolized rapidly and conjugated at the same rate with amino acids or sugar. Studies of auxin transport showed that IAA was transported faster than IBA. The velocities of some of the auxins tested were 7. 5 mm h^?1 for IAA, 6. 7 mm h^?1 for naphthaleneacetic acid (NAA) and only 3. 2 mm h^?1 for IBA. Like IAA, IBA was transported predominantly in a basipetal direction (polar transport). After application of ³H-IBA to cuttings of various plants, most of the label remained in the bases of the cuttings. Easy-to-root cultivars were found to absorb more of the auxin and transport more of it to the leaves. It has been postulated that easy-to-root, as opposed to the difficult-to-root cultivars, have the ability to hydrolyze auxin conjugates at the appropriate time to release free auxin which may promote root initiation. This theory is supported by reports on increased levels of free auxin in the bases of cuttings prior to rooting. The auxin conjugate probably acts as a ‘slow-release’ hormone in the tissues. Easy-to-root cultivars were also able to convert IBA to IAA which accumulated in the cutting bases prior to rooting. IAA conjugates, but not IBA conjugates, were subject to oxidation, and thus deactivation. The efficiency of the two auxins in root induction therefore seems to depend on the stability of their conjugates. The higher rooting promotion of IBA was also ascribed to the fact that its level remained elevated longer than that of IAA, even though IBA was metabolized in the tissue. IAA was converted to IBA by seedlings of corn and Arabidopsis. The K_m value for IBA formation was low (approximately 20 μM), indicating high affinity for the substrate. That means that small amounts of IAA (only a fraction of the total IAA in the plant tissues) can be converted to IBA. It was suggested that IBA is formed by the acetylation of IAA with acetyl-CoA in the carboxyl position via a biosynthetic pathway analogous to the primary steps of fatty acid biosynthesis, where acetyl moieties are transferred to an acceptor molecule. Incubation of the soluble enzyme fraction from Arabidopsis with ³H-IBA, IBA and UDP-glucose resulted in a product that was identified tentatively as IBA glucose (IBGIc). IBGIc was detected only during the first 30 min of incubation, showing that it might be converted rapidly to another conjugate.