Influence of IAA upon the longitudinal and tangential movement of labelled sugars in the phloem of Willow

Summary Using a bark abrasion technique, the influence of IAA upon patterns of sugar translocation in isolated stem segments of Willow (Salix viminalis L.) has been studied. IAA was found to exert a considerable influence over translocation in both a longidutinal and tangential direction. Studies on longitudinal movement have led to the postulation of two possible effects of IAA on this system. Firstly a stimulation of sugar loading from the storage parenchyma into the sieve elements as described by Lepp and Peel (1970), and secondly a direct effect upon, the longitudinal transport process. The situation with regard to the tangential transport system is not as clear in all its aspects, though once again it is postulated that IAA may have a direct effect upon the movement of sugars in the tangential transport system.     

On the genetic components of the responsiveness of Kniphofia to growth regulators and sugars★

As part of an ongoing study about the genetic determinants of shoot regeneration we tested the hypothesis that the process of shoot formation and rooting in tissue culture involves groups of genetic determinants that can be discerned from each other. We used Kniphofia lines that were part of a breeding program and were crossed to produce a F1 hybrid. We used the Kniphofia propagation protocol to study the response of the parental lines to the propagation protocol and to see if we can discern some genetic insight from the F1 cross. It was found that the response to glucose was a receive type genetic response while the response to cytokinin to auxin ratio varied and dependent on the type of auxin. But in general, the response to cytokinin to auxin ratio was dominant and additive in most cases. The response to IBA in the rooting medium was semi dominant. This is publication number 05/05 from Horticulture Institute Aro.     

Modelling of auxin transport affected by gravity and differential radial growth

When a tree stem deviates from verticality, as a result of different environmental factors, patterns of differential radial growth appear. Higher rates of wood production have been observed on the lower side of the tree and lower rates in the opposite side. Biological studies on plant hormones have shown that the concentration of auxin induces radial growth. They also have demonstrated the redistribution of auxin transport in response to gravity. Auxin is then designated as a mediator for differential growth. This paper presents a model for three-dimensional (3-D) auxin transport in conifer trees, which includes gravity dependence. We obtain realistic heterogeneous patterns of auxin distribution over the tree. Then, we propose a law of growth based on auxin concentration to simulate successive differential radial growths. The predicted growths are compared with experimental results of reconstruction of 3-D annual growth of Radiata pine.     

Long-term effects of growth regulators on growth and turnover of symplastic and apoplastic sugars in the suspension subculture of kidney bean

Suspension cells of kidney bean were grown for 42 d in MS medium supplemented with growth regulators (2.0 mgL^-1 2,4-D and 0.5 mgL^-1 kinetin) or without At the stationary growth phase (42 d), the sugars were fractionated into the symplastic (ethanol and starch) and apoplastic [low-molecular pectin (lm-pectin), high-molecular pectin (hm-pectin), hemicellulose, and cellulose] sugars. The neutral sugars (NS) of hm-pectin and hemicellulose fractions were analyzed by GLC. The growth of the suspension cells in the liquid MS media, in terms of settled cell volume (SCV), remained similar, to the end of the experiment, irrespective of the presence or absence of growth regulators, indicating the nonnecessity of the exogenous growth regulators for the subculture. Total sugar (TS) of the ethanol fraction and NS of the Im-pectin of the suspension cells grown in the medium with growth regulators were higher than in the medium without growth regulators. However, starch content in the starch fraction and uronic acid (UA) content of the Im-pectin fraction did not exhibit any differences. From these results, it was suggested that the growth regulators modulated the structure of the cell wall polysaccharide. Analysis of the NS composition of the hm-pectin fractions revealed that the Rha, Arb, and Gal contents in the presence of growth regulators were higher than in the absence, while the Xyl, Man, and Glc contents in the presence of growth regulators were higher than in the absence, indicating the turnovers of rhamnogalacturonan and/or arabinogalactan. On the other hand, analysis of NS composition of hemicellulose fractions revealed that the Ara and Glc contents in the presence of growth regulators was higher than in the absence, whereas Xyl and Glc contents were nearly consistent, indicating the turnovers of arabinaogalactan I or II. The cellulose contents remained similar, irrespective of the presence (19.1%) or absence (18.7%) of growth regulators.     

The influence of plant growth regulators on explant performance, bud break, and shoot growth from large stem segments of Acer saccharinum L

Benzyladenine (BA) and/or gibberellic acid (GA₃) were applied in 20% white exterior latex paint separately at 0, 0.3, 1, 3, 10, or 30 mM; and at 1, 10, or 30 mM of each plant growth regulator (PGR) in a 3 × 3 factorial to 40 cm long stem segments of Acer saccharinum L. Softwood shoots were forced from these stem segments at various times of the year in a greenhouse and in a laboratory, these resulting shoots were surface disinfested and used as explants in vitro on Driver and Kuniyuki Walnut medium with 0 or 0.01 μM thidiazuron (TDZ). There was some response to the plant growth regulators applied in paint for shoot production from the stem segments and in vitro. Explants from softwood shoots forced from stems painted with 3 mM BA and cultured on medium with 0.01 μM TDZ produced more shoots than explants taken from softwood shoots forced with other BA concentrations or controls. Callus also grew significantly more on explants from stems treated with 3 mM BA cultured on 0.01 μM TDZ than explants harvested from stems painted with other concentrations of BA excluding 10 mM BA. When stem segments treated with BA plus GA₃ were compared as a group to controls, more and longer softwood shoots grew on the stems painted with PGRs when all four runs were pooled (Sept. 2005 through Feb. 2006). Application of PGRs in paint extends the season of production of softwood shoots that may be used as explant materials and their subsequent performance in vitro.     

Regulation of stem elongation in chinese cabbage by inflorescence removal and application of growth regulators

The effect of inflorescence removal on stem elongation in Chinese cabbage cv. Spring A was studied. Removal of the inflorescence before its visibility, or upon its appearance but before the beginning of bolting (stages 1–3), markedly reduced the stem length. Removal after the beginning of bolting (stage 5) had no effect on stem length. Application of GA₃ to the treated plants partially or fully restored the elongation of the flowering stem, whereas paclobutrazol inhibited the elongation of the treated, as well as the control stems. Indole-3-acetic acid (IAA) or kinetin was ineffective in restoring stem elongation of the plants from which the inflorescence had been removed. Inflorescences at stages 1–2 were found to secrete about 10 times more gibberellic acid (GA)-like activity compared with control apices or inflorescences at stage 5. It is suggested that the developing inflorescence is the major source of GAs which control stem elongation. However, shortly after the appearance of the inflorescence at the onset of bolting, stem elongation is no longer dependent on GAs derived from the apical inflorescence but require GAs from other sources.     

Regulation of stem elongation in chinese cabbage by inflorescence removal and application of growth regulators

The effect of inflorescence removal on stem elongation in Chinese cabbage cv. Spring A was studied. Removal of the inflorescence before its visibility, or upon its appearance but before the beginning of bolting (stages 1–3), markedly reduced the stem length. Removal after the beginning of bolting (stage 5) had no effect on stem length.Application of GA₃ to the treated plants partially or fully restored the elongation of the flowering stem, whereas paclobutrazol inhibited the elongation of the treated, as well as the control stems. Indole-3-acetic acid (IAA) or kinetin was ineffective in restoring stem elongation of the plants from which the inflorescence had been removed. Inflorescences at stages 1–2 were found to secrete about 10 times more gibberellic acid (GA)-like activity compared with control apices or inflorescences at stage 5.It is suggested that the developing inflorescence is the major source of GAs which control stem elongation. However, shortly after the appearance of the inflorescence at the onset of bolting, stem elongation is no longer dependent on GAs derived from the apical inflorescence but require GAs from other sources.Contribution from the Agricultural Research Organization, The Volcani Center Bet Dagan, Israel No. 2218-E, 1987 series.     

Inhibition of auxin-stimulated growth of pea stem segments by a specific nonasaccharide of xyloglucan

Hemicellulose extracted from cell walls of suspension-cultured rose (Rosa Paul's Scarlet) cells was digested with cellulase from Trichoderma viride. The quantitatively major oligosaccharide products, a nonasaccharide and a heptasaccharide derived from xyloglucan, were purified by gel permeation chromatography. The nonasaccharide was found to inhibit the 2,4-dichlorophenoxy-acetic-acid-induced elongation of etiolated pea (Pisum sativum) stem segments. This confirms an earlier report (York et al., 1984, Plant Physiol. 75, 295–297). The inhibition of elongation by the nonasaccharide showed a maximum at around 10^-9M with higher and lower concentrations being less effective. The heptasaccharide did not significantly inhibit elongation at 10^-7–10^-10M and also did not affect the inhibition caused by the nonasaccharide when co-incubated with the latter.Abbreviations 2,4-D 2,4-dichlorophenoxyacetic acid - XG xyloglucan - XG7 xyloglucan heptasaccharide (Glc₄·Xyl₃) - XG9 xyloglucan nonasaccharide (Glc₄·Xyl₃·Gal·Fuc)     

超氧物歧化酶（SOD）与柳树分布相关性的研究

在研究红松苗越冬伤害原因时,发现超氧物歧化酶(SOD),在防止针叶越冬伤害中起着重要作用。75%术条遮荫,可安全越冬的红松苗针叶,早春仍保持较强的活性,脂质过氧化产物积累较少。而暴露于全光下,则终于发生不可逆伤害,红松苗针叶SOD活性低而脂质过氧化产物(丙二醛)积累较多。并且暴露在全光下不出现伤害的红松大树针叶,酶活性也高于幼苗。此外,关于SOD对植物在低温、干旱、日灼、臭氧、大气污染(SO_2)等逆境中的抗性作用,也已有不少报道。日本学者曾     

Components of auxin transport in stem segments of Pisum sativum L.

1. The uptake of indol-3-yl acetic acid ([1-¹⁴C]IAA, 0–2.0 M) into light-grown pea stem segments was measured under various conditions to investigate the extent to which mechanisms of auxin transport in crown gall suspension culture cells (Rubery and Sheldrake, Planta 118, 101–121, 1974) are also found in a tissue capable of polar auxin transport. — 2. IAA uptake increased as the external pH was lowered. IAA uptake was less than that of benzoic acid (BA), naphthylacetic acid (NAA) or 2,4 dichlorophenoxyacetic acid (2,4D) under equivalent conditions. TIBA enhanced net IAA uptake through inhibition of efflux, and to a lesser extent, also increased uptake of NAA and 2,4D while it had no effect on BA uptake. — 3. Both DNP and, at higher concentrations, BA, reduced IAA uptake probably because of a reduction of cytoplasmic pH. However, low concentrations of both BA and DNP caused a slight enhancement of IAA net uptake, possibly through a reduction of carrier-mediated IAA efflux. In the presence of TIBA, the inhibitory effects of DNP and BA were more severe and there was no enhancement of uptake at low concentrations. — 4. Non-radioactive IAA (10 M) reduced uptake of labelled IAA but further increases in concentration up to 1.0 mM produced first an inhibition (0–10 min) of labelled IAA uptake, followed by a stimulation at later times. Non-radioactive 2,4 D decreased, but was not observed to stimulate, uptake of labelled IAA. In the presence of TIBA labelled IAA uptake was inhibited by non-radioactive IAA regardless of its concentration. — 5. Sulphydryl reagents PCMB and PCMBS promoted or inhibited IAA uptake depending, respectively, on whether they penetrated or were excluded from the cells. The penetrant PCMB also reduced the promotion of labelled IAA uptake by TIBA or by high concentrations of added non-labelled IAA. — 6. Our findings are interpreted as being consistent with the diffusive entry of unionised IAA into cells together with some carrier-mediated uptake. Auxin efflux from the cells also appears to have a carrier-mediated contribution, at least part of which is inhibited by TIBA, and which has a capacity at least as great as that of the uptake carrier. The data indicate that pea stem segments contain cells whose mechanisms of trans-membrane auxin transport fit the model of polar auxin transport proposed from experiments with crown gall suspension cells, although differences, particularly of carrier specificity, are apparent between the two systems.Abbreviations IAA indol-3-yl acetic acid - BA benzoic acid - NAA 1-naphthylacetic acid - 2,4-D 2,4-dichlorophenoxyacetic acid - TIBA 2,3,5-triiodobenzoic acid - DNP 2,4-dinitrophenol - PCMB p-chloromercuribenzoic acid - PCMBS p-chloromercuribenzene sulphonic acid This work was performed in Cambridge during the tenure of a sabbatical leave by P.J.D. Supported by a grant for supplies from the American Philosophical Society to P.J.D.     

Bud emergence and shoot growth from mature citrus nodal stem segments

Bud emergence and shoot growth from adult phase citrus nodal cultures were studied using Citrus mitis (calamondin), Citrus paradisi (grapefruit), and Citrus sinensis (sweet orange). The effects of 6-benzyladenine (BA), indole 3-acetic acid (IAA), and citrus type on shoot quality and growth of mature bud explants from greenhouse grown trees were determined using a 2-component mixture-amount × citrus type experiment. BA increased shoot number and IAA improved shoot growth. The best shoot quality (fewer shoots but large shoots) was obtained with 1 μM IAA for calamondin, 15.5 μM IAA for sweet orange, and 30 μM IAA for grapefruit. Grapefruit exhibited substantial leaf abscission compared to calamondin and sweet orange. Four factors (AgNO₃, silver thiosulphate (STS), CaNO₃, or gelling) were screened individually for their efficacy in reducing leaf abscission. Five factors (AgNO₃, gelling, MS ion concentration, plant growth regulator and venting) were investigated to identify potential combinations for reducing leaf abscission and maximizing shoot growth and bud emergence. The factor combination identified as most effective in minimizing leaf drop, promoting shoot growth, and maximizing bud emergence for grapefruit was 2 mg l^?1 AgNO_3, Gelrite, 1 × MS ion concentration, 30 μM IAA, and vented.     

Effect of galactoglucomannan-derived oligosaccharides on elongation growth of pea and spruce stem segments stimulated by auxin

Galactoglucomannan-derived oligosaccharides (GGMOs) (degree of polymerization 4–8) isolated from the wood of poplar (Populus monilifera Ait.) were shown to be inhibitors of the 2,4-dichlorophenoxyacetic acid-stimulated elongation growth of pea (Pisum sativum L. cv. Tyrkys) and spruce [Picea abies (L.) Karst] stem segments. A dependence on the concentration of GGMOs (between 10^-5-10^-10M) as well as plant species was ascertained. Pea stem segments were much more sensitive (10^-10M) than spruce (10^-8M). The GGMOs did not exhibit toxicity even at high concentrations and during long-term bioassays. The timing of the action of GGMOs and auxin in the growth process was also studied.Abbreviations 2,4-D 2,4-dichlorophenoxyacetic acid - d.p degree of polymerization - GGMOs galactoglucomannan-derived oligosaccharides This research was supported by the Slovak Grant Agency for Science.     

Nitrate reductase dephosphorylation is induced by sugars and sugar-phosphates in corn leaf segments

The in situ and in vitro regulation of nitrate reductase (NR; EC 1.6.6.1) activity by glucose (Glc) and glucose‐6‐phosphate (Glc‐6P) was studied in leaf segments of 7‐day‐old corn plants. In situ, Glc and Glc‐6P not only prevented NR inactivation, but also slightly activated the enzyme relative to that in fresh attached leaves in the light. Glc and Glc‐6P also reactivated NR that had previously been inactivated by incubating the segments for 30 min in the dark. Sugars were effective, even in the presence of cycloheximide, but not of cantharidin, an inhibitor of type 2A phosphoprotein phosphatase (PP2A). In segments kept in the dark, the inhibition of protein dephosphorylation by cantharidin showed that the phosphorylation of NR was not inhibited by either Glc or Glc‐6P, as the enzyme was inactivated to the same extent whether or not sugars (P) were present in the incubation medium. In vitro, as in situ, neither Glc nor Glc‐6P could prevent NR phosphorylation. In spite of some reports showing that sugar‐phosphates can act on kinases and prevent NR phosphorylation, the results presented here suggest that, in corn leaves, sugars and their phosphorylated derivatives probably activate NR in situ mainly by inducing protein dephosphorylation. The incubation of crude extract in a water bath at 27°C for 45 min resulted in the activation of NR that was blocked by cantharidin, but was not increased by either Glc or Glc‐6P. This result suggests that the presence of another metabolite(s) and the maintenance of cell functionality may be necessary for the sugar‐induced activation of NR. A sugar‐triggered signalling pathway independent of protein synthesis may be involved in the process. l ‐Glc and 6‐deoxyglucose were ineffective in reactivating NR in darkened segments, whilst 2‐deoxyglucose was as effective as Glc itself. The effect of sugar analogues shows that, although Glc has to enter the cell and be phosphorylated to activate NR, further metabolism is not necessary. As sugar‐phosphates, such as Glc‐6P and fructose‐6‐phosphate (Fru‐6P), also activate NR, it seems that hexokinases are not involved in the pathway that leads to the in situ dephosphorylation of NR. In vitro, Glc‐6P mildly but rapidly activated NR by a mechanism insensitive to cantharidin. The addition of an increasing concentration of Mg²⁺ to crude extract containing Glc‐6P increased the Mg²⁺ inhibition of NR. This result suggests that the hexose‐phosphate does not prevent Mg²⁺ association with NR. It is possible that Glc‐6P activates NR in vitro by inducing the dissociation of 14‐3‐3 from the phospho‐NR (pNR)/Mg/14‐3‐3 complex.     

The kinetics of inhibition of auxin-induced growth in green pea stem segments by actinomycin D and other substances

Inhibitors of nucleic acid and protein synthesis were applied to excised green pea stem sections in the absence and presence of IAA and the effects on growth noted as a function of time. Actinomycin D, which inhibits de novo RNA synthesis, ribonuclease, which degrades RNA, and puromycin, which prevents transfer of aminoacyl residues into the growing polypeptide chain, inhibit section growth only after lengthy lag periods of, respectively, 2, 8 and 5 hr. For actinomycin D and ribonuclease, preincubation in the inhibitor alone, prior to IAA application, does not reduce the lag period, indicating that the lag is not caused by slow penetration of the inhibitor. By contrast, chloramphenicol, which prevents binding of messenger RNA to ribosomes, and p-fluorophenylalanine, a competitive antagonist of phenylalanine, produce significant inhibitions in the first hour. The implications of these results for the mechanism of auxin action are considered.     

Retardation of tree growth by injection of plant growth regulators

Previously topped American sycamore (Platanus occidentalis L.), cottonwood (Populus deltoides Bartr. ex Marsh), water oak (Quercus nigra L.), and bigleaf maple (Acer macrophyllum Pursh) trees were injected with aqueous solutions of maleic hydrazide or dikegulac-sodium in April-June, 1979 at various locations around the United States. Measurements made later in the autumn showed that dikegulac-sodium reduced sprout regrowth in all four species, whereas maleic hydrazide was only effective in controlling regrowth of American sycamore and cottonwood. The effects of dikegulac persisted through the second growing season. Significant variability was observed among treated trees and must be reduced in order to achieve consistent growth responses from an application of growth retardants.This paper reports the results of research only. Mention of a growth regulator does not consitute a recommendation for use by the U.S. Department of Agriculture nor does it imply registration under FIFRA as amended. Mention of a trademark or propriety product does not constitute a guarantee or warranty of the product by the U.S. Department of Agriculture and does not imply its approval to the exclusion of other products that may also be suitable.     

Developmental changes in the gibberellin-induced growth response in stem segments of light-grown pea genotypes

The effects of GA on stem elongation were studied using segments from one tall and three dwarf light-grown pea genotypes varying in endogenous hormone content. Stem segments were cut at two distinct ages: when the fourth internode was at about 6–13% of full expansion (early-expansion) or at 18–25% of full expansion (mid-expansion). Light microscopy and flow cytometry were used to demonstrate that GA does not induce cell division in excised pea stem segments. The growth studied here was strictly elongation. Measurement of final segment length after 48 hours and high resolution measurement of growth kinetics over 20 hours using an angular position transducer were done on segments treated with hormone solutions. Our data indicate that the action of GA on stem elongation can be classified into two distinct modes. The first, apparent in early-expansion stem segments, shows distinct growth kinetics and is independent of the endogenous IAA concentration of the segments. Quantitation of IAA by GC/MS in early-expansion segments of wild type pea incubated with gibberellin shows that an increase in IAA concentration is part of the GA response in such segments. The second mode of GA action is evinced in mid-expansion segments. Whereas there is no short term (<20 h) response to GA alone (as determined by growth kinetics), there is a long term (48 h) response whose magnitude decreases across the genotypes with decreasing endogenous hormone content. Growth responses indicate that in mid-expansion segments exogenous GA acts by enhancing IAA action but appears to be unable to augment endogenous IAA content. Contradictory reports of the response of excised stem segments to GA can be reconciled when tissue genotype and developmental stage are considered.     

Interaction of indoleacetic Acid and gibberellic Acid in the short-term growth kinetics of oat stem segments

Gibberellins and auxins are the only hormones known that promote growth in oat (Avena sativa) stem segments, but when applied together, indoleacetic acid inhibits gibberellic acid-induced growth appreciably. This study shows that in addition to this inhibitory role, indoleacetic acid shortens the response time of the tissue to gibberellic acid.     

Effects of gibberellic Acid and sucrose on the growth of oat (Avena) stem segments

Gibberellic acid induced growth in Avena (oat) stem segments within 35 minutes after hormone application. The total elongation elicited by gibberellic acid was greater than 15 times the control growth. The sensitivity of the segments to low concentrations of gibberellic acid (1 pmole) and the specificity of the segments to the gibberellin class of hormones suggest that oat stem segments would be a valuable tool for gibberellin bioassays. Both gibberellic acid-induced growth and control growth are temperature-dependent and showed a Q₁₀ of two or greater. Although the most apparent effect of gibberellic acid was to promote the uptake of water into the internode, the hormone also promoted transport of endogenous substrate and the uptake of exogenous substrate into the growing region. The growth promotion was accomplished without an apparent increase in osmotic pressure.     

Effect of sugars on amino acid transport by symbiotic Chlorella

Symbiotic Chlorella F36-ZK isolated from Paramecium bursaria F36 has constitutive amino acid transport systems, whereas free-living Chlorella does not. We found that in symbiotic algae, the rate of serine (Ser) uptake increased in the presence of glucose (Glc) and non-metabolisable analogues, whilst incorporation of Ser into protein was not affected. The activation did not involve new protein synthesis and was enhanced under alkaline conditions. An increase in the rate of Ser transport resulted from Glc treatment even when pulsed for only 1min at low concentrations (EC(50)=3muM). No uptake of Glc itself was observed in F36-ZK. Thus, the transport signal appears to be transmitted via a glucose sensing and signalling pathway. Many Glc-related compounds also increased the rate of Ser uptake without an additive effect, suggesting recognition of these sugars by the same receptor and providing some insight into features of the structure-activity relationship. Ser uptake by F36-ZK is inhibited by Ca(2+), which is typically considered to be a positive modulator of amino acid uptake. Given that Glc restored Ser uptake from inhibition by Ca(2+), we propose that this compound is possibly involved in regulation of amino acid transport in this symbiotic relationship.