Inhibition Of Stem Elongation Research Articles

2-Phenyl-5H-pyrazolo[5,1-a]isoquinolin-5-ones: Development of new auxin transport inhibitors and their plant growth regulating properties

2-Phenylisoxazolylphenylacetic acids (isoxazoles) and 2-phenyl-5H-pyrazolo[5,1-alpha]isoquinolin-5-ones (isoquinolines) inhibited auxin polar transport (ATP) and inhibited hypocotyl elongation in the same concentration as benzoic acid APT inhibitors, known as phytotropins. At early growth stages of rice, tomato, cucumber, and soybean, isoquinolines inhibited stem elongation in a lower concentration than isoxazoles triiodobenzoic acid and 2-phenylisoxazolylbenzoic acid (phytotropin). p-OMe, F, Br, or CF3 substituent on isoquinoline increased the growth inhibiting activity in rice stem, whereas m-Cl, F, or m,p-DiOMe substituents increased the activity in soybean. In fields, p-F isoquinoline had more favorable properties than the other isoquinolines and structurally related compounds such as m-Cl isoxazole and DPX-1840 (phytotropin) in that it (25 g.ha-1) sometimes increased seed yields of rice and wheat. The early morphological changes due to apical dominance inhibition, increase of tiller or branch number, and reduction of plant height were observed on various rice cultivars of Japonica and Indica, whereas they seem not to be concerned with seed yield.

The differential effects of C-16,17-dihydro gibberellins and related compounds on stem elongation and flowering in Lolium temulentum

Plants of Lolium temulentum L. cv. Ceres grown under short days (SDs) can be induced to initiate inflorescences either by exposure to one long day (LD) or by single applications of some gibberellins (GAs), which also enhance the flowering response to one LD. Single doses of up to 25 μg per plant of C-16, 17-dihydro-GA5 were about as effective as GA5 for promoting flowering after one LD but inhibited stem elongation by up to 40% over three weeks. The promotion of flowering but not the inhibition of elongation by 16, 17-dihydro-GA5 was reduced in SDs or in LDs low in far-red (FR) radiation. With shoot apices cultured in vitro, 16, 17-dihydro-GA5 was more florigenic than GA3 for apices excised after one LD of 14 h or more, but less florigenic for apices excised from plants in shorter days. 16, 17-Dihydro-GA5 was ineffective compared with GA1, GA3 and GA5 for α-amylase production by half-seeds of Lolium, a response concordant with its effect on stem elongation. As with GA5, 16, 17-dihydro derivatives of GA1, GA3, GA20 and several other GAs were more effective for flowering and less effective for stem elongation than the GAs from which they were derived. Hydroxylation at C-17 and/or C-16 generally reduced the effectiveness of 16, 17-dihydro-GA5 for flowering. These results extend the known features of GA structure which favour flowering relative to stem elongation in L. temulentum. Moreover, C-16, 17-dihydro-GA5 mimics, in its daylength- and wavelength-dependence and lack of stem elongation, characteristics of the LD stimulus in L. temulentum.

Juvenility, Flowering, and the Effects of a Limited Inductive Photoperiod in Coreopsis grandiflora and C. lanceolata

Juvenility and flowering requirements of Coreopsis grandiflora Hogg ex Sweet. `Sunray' and C. lanceolata L. `Early Sunrise' were examined by growing plants under short days (SD) and transferring them to long days (LD) upon reaching the designated true leaf stages. Neither cultivar flowered in continuous SD, and `Sunray' remained vegetative in LD. However, LD induced flowering in `Early Sunrise' plants in each leaf count treatment and the loss of juvenility was gradual, with most rapid flowering occurring when plants were transferred to LD at the 16 leaf stage. The limited inductive photoperiod (LIP) inhibited stem elongation of `Early Sunrise' plants in all LD treatments and selectively inhibited axillary flower bud development compared to plants grown in continuous LD. LIP did not affect scape length at first flower even though plant height was significantly diminished if given relatively few LD before transfer to SD. Height reduction was attributed to LIP inhibition of stem elongation with no significant loss of axillary flower bud potential.

Interaction of growth retardants, daylength, and gibberellins A19, A20, and A1 on shoot elongation in birch and alder

Gibberellins A19, A20, and A1 were applied to seedlings of birch (Betula pubescens Ehrh.) and alder (Alnus glutinosa (L.) Gaertn.) in order to test their ability to counteract growth inhibition induced by growth retardants (ancymidol and BX-112) or short day (SD, 12 h) photoperiod. Ancymidol inhibits early and BX-112 inhibits late steps in gibberellin biosynthesis. BX-112 inhibited stem elongation in both species while ancymidol, applied as a soil drench, was effective in alder only. Growth retardants affected stem elongation mainly by inhibiting elongation of internodes. All three gibberellins were equally active when applied to seedlings treated with ancymidol; however, only GA1 was able to counteract the growth inhibition induced by BX-112. SD-induced cessation of elongation growth in birch was counteracted by GA1, and to some degree, by GA20, while GA19 was inactive. SD treatment did not induce cessation of apical growth in alder. These results are consistent with the hypothesis that of gibberellins belonging to the early C-13 hydroxylation pathway, GA1 is the only active gibberellin for stem elongation.

Gibberellins and Stem Growth as Related to Photoperiod in Silene armeria L.

Stem growth and flowering in the long-day plant Silene armeria L. are induced by exposure to a minimum of 3 to 6 long days (LD). Stem growth continues in subsequent short days (SD), albeit at a reduced rate. The growth retardant tetcyclacis inhibited stem elongation induced by LD, but had no effect on flowering. This indicates that photoperiodic control of stem growth in Silene is mediated by gibberellins (GA). The objective of this study was to analyze the effects of photoperiod on the levels and distribution of endogenous GAs in Silene and to determine the nature of the photoperiodic after-effect on stem growth in this plant. The GAs identified in extracts from Silene by full-scan combined gas chromatography-mass spectrometry (GC-MS), GA(12), GA(53), GA(44), GA(17), GA(19), GA(20), GA(1), GA(29), and GA(8), are members of the early 13-hydroxylation pathway. All of these GAs were present in plants under SD as well as under LD conditions. The GA(53) level was highest in plants in SD, and decreased in plants transferred to LD conditions. By contrast, GA(19), GA(20), and GA(1) initially increased in plants transferred to LD, and then declined. Likewise, when Silene plants were returned from LD to SD, there was an increase in GA(53), and a decrease in GA(19), GA(20), and GA(1) which ultimately reached levels similar to those found in plants kept in SD. Thus, measurements of GA levels in whole shoots of Silene as well as in individual parts of the plant suggest that the photoperiod modulates GA metabolism mainly through the rate of conversion of GA(53). As a result of LD induction, GA(1) accumulates at its highest level in shoot tips which, in turn, results in stem elongation. In addition, LD also appear to increase the sensitivity of the tissue to GA, and this effect is presumably responsible for the photoperiodic after-effect on stem elongation in Silene.

Effect of Light Quality on Growth, Contents of Carbohydrates, Protein and Pigments, and Nitrate Reductase Activity in Soybean Plants

Summary Soybean ( Glycine max L. cv. Williams) plants were grown from germination with nitrate as the nitrogen source under a 16-h photoperiod supplied by white, blue or red fluorescent lamps at a photon fluence rate of 46 µmol m -2 s -1 . As compared with white-light-grown plants, blue light inhibited stem elongation whereas red light had a stimulatory effect. By contrast, leaf growth was increased by blue light and reduced by red light. The high initial concentrations of carbohydrates and protein in the cotyledons gradually declined during seedling growth, irrespective of the light quality. Both in primary and first trifoliate leaves, the levels of carbohydrates and protein progressively increased up to leaf maturation. The accumulation of protein was higher in the plants grown under blue light, especially in the first trifoliate leaves. On the contrary, red light stimulated carbohydrate accumulation. The levels of nitrate reductase (EC 1.6.6.1) activity in leaves were found to be higher under red than under blue light. Accordingly, the greater protein concentration occurring in the soybean plants illuminated with blue light cannot be ascribed to a blue light activation of nitrate reductase leading to a higher availability of ammonia for the synthesis of amino acids and proteins, as has been previously suggested. Red light was more effective than blue light in stimulating the synthesis of chlorophyll and carotenoids in leaves.

Inhibition of Stem Elongation in Cucumis Seedlings by Blue Light Requires Calcium

The effects of blue light and calcium on elongation of hypocotyl segments of Cucumber (Cucumis sativa L. cv Burpee's Pickler) were studied. Cucumber seedlings grown in dim red light showed a rapid decline in the rate of hypocotyl elongation when irradiated with high intensity (100 micromoles per square meter per second) blue light. In intact, 4-day-old seedlings the inhibition began within 2 minutes after the onset of blue-light irradiation and reached a maximum of approximately 55% within 4 minutes. Hypocotyl segments cut from 4-day-old seedlings also showed an inhibition of elongation in response to blue light when segments were floated on aqueous buffer and exposed to blue light for 3 hours. In the presence of 2 micromolar indole-3-acetic acid, blue light caused a 50% inhibition of elongation. Buffering free calcium in the incubation medium with 0.1 millimolar ethylene glycol bis(-aminoethyl ether)- N,N,N',N'-tetraacetic acid eliminated the blue-light inhibition of segment elongation. Several experiments confirmed a specific requirement for calcium for the blue-light-induced inhibition of segment elongation. Treating segments with 0.2 micromolar fusicoccin abolished the inhibition of elongation by blue light as did buffering the medium at pH 4. Adding 1 millimolar ascorbate to incubation medium also eliminated the inhibition of segment elongation caused by blue light. Several compounds implicated in cell-wall redox reactions alter the magnitude of the blue-light-induced inhibition. The activity of peroxidase isolated from the cell-wall free space of cucumber hypocotyls was inhibited by ascorbate and low pH. The results are consistent with the hypothesis that blue light inhibits elongation by inducing an increase in cell-wall peroxidase activity and implicate calcium ions in the response to blue light.

Gravitropism in higher plant shoots. IV. Further studies on participation of ethylene.

Ethylene at 1.0 and 10.0 cubic centimeters per cubic meter decreased the rate of gravitropic bending in stems of cocklebur (Xanthium strumarium L.) and tomato (Lycopersicon esculentum Mill), but 0.1 cubic centimeter per cubic meter ethylene had little effect. Treating cocklebur plants with 1.0 millimolar aminoethoxyvinylglycine (AVG) (ethylene synthesis inhibitor) delayed stem bending compared with controls, but adding 0.1 cubic centimeter per cubic meter ethylene in the surrounding atmosphere (or applying 0.1% ethephon solution) partially restored the rate of bending of AVG-treated plants. Ethylene increases in bending stems, and AVG inhibits this. Virtually all newly synthesized ethylene appeared in bottom halves of horizontal stems, where ethylene concentrations were as much as 100 times those in upright stems or in top halves of horizontal stems. This was especially true when horizontal stems were physically restrained from bending. Ethylene might promote cell elongation in bottom tissues of a horizontal stem or indicate other factors there (e.g. a large amount of 'functioning' auxin). Or top and bottom tissues may become differentially sensitive to ethylene. Auxin applied to one side of a vertical stem caused extreme bending away from that side; gibberellic acid, kinetin, and abscisic acid were without effect. Acidic ethephon solutions applied to one side of young seedlings of cocklebur, tomato, sunflower (Helianthus annuus L.), and soybean (Glycine max [L.] Merr.) caused bending away from that side, but neutral ethephon solutions did not cause bending. Buffered or unbuffered acid (HCl) caused similar bending. Neutral ethephon solutions produced typical ethylene symptoms (i.e. epinasty, inhibition of stem elongation). HCl or acidic ethephon applied to the top of horizontal stems caused downward bending, but these substances applied to the bottom of such stems inhibited growth and upward bending--an unexpected result.

Growth and Photosynthesis of Easter Lily in Response to Flower Bud Removal

Abstract Buds or open flowers are often removed in the production of Easter lily (Lilium longiflorum Thunb.) bulbs. To determine if time of flower removal affects bulb size or plant growth, flower buds of container-grown ‘Nellie White’ plants were removed when the length of the largest flower bud was 1.0 cm (early) or 3.5 cm (late). Net photosynthesis of the 5th (upper) and 25th (mid-shoot) leaves was monitored and plants were harvested 2 months after full bloom of intact controls. Early disbudding stopped pedicel growth, inhibited stem elongation, and reduced total leaf area 12%, but did not affect bulb weight. Stem elongation was inhibited less by late disbudding; leaf area and plant weight were unaffected. Both fresh and dry bulb weights of late disbudded plants increased by 15%. Early disbudding reduced the rate of net photosynthesis of leaf 5 (particularly during the 3 weeks following full bloom), whereas late disbudding had less effect. Treatments did not affect photosynthesis of leaf 25. Reduced stem growth under late disbudding, without a severe reduction in photosynthesis, may have increased the availability of assimilate for bulb growth. Early disbudding caused 81% of the daughter bulbs to sprout prematurely, compared to 27% for late disbudding and 9% for controls. In a field study, removing flower buds at 1.5 cm or 4.0 cm in length increased bulb fresh weight over intact controls by 12% and 30%, respectively. Disbudding did not increase sprouting of field-grown plants. Delaying removal until the first flower bud is 3.5–4.0 cm long reduces deleterious effects on shoot growth while significantly improving bulb size.

Thigmomorphogenesis: anatomical, morphological and mechanical analysis of genetically different sibs of Pinus taeda in response to mechanical perturbation.

Twenty-three open pollinated families (half-sibs) and four controlled pollinated families (full-sibs) of Pinus taeda L. (loblolly pine) were grown in a greenhouse and analyzed for changes induced by mechanical perturbation (MP). These changes included inhibition of stem and needle elongation, bracing of branch nodes, and increased radial growth in the direction of the MP. Inhibition of stem elongation was the least variable feature measured. Leaf extension and stem diameter were highly variable between half-sibs. MP induced increased drag in greenhouse grown P. taeda in wind-tunnel tests. In P. taeda, MP induced decreased flexibility and increased elasticity and plasticity of the stem. The increased radial growth of the stems overrode the increase in elasticity, resulting in an overall decrease in flexibility. MP trees had a higher rupture point than non-MP controls. Increased radial growth is a result of more rapid cell divisions of the vascular cambium, resulting in increased numbers of tracheids. The decreased leader growth is partly due to a decreased tracheid length in response to MP.

Effects of Morphactin and Other Auxin Transport Inhibitors on Soybean Senescence and Pod Development

Because triiodobenzoic acid increases pod number, albeit variably, in soybean (Glycine max), we tested other auxin-transport inhibitors. Morphactins, especially methylchlorflurenol (MCF), were found to be very active (optimal concentration 10 micromolar) when sprayed onto the foliage. Applications at 1 week after the start of flowering were most effective, producing a 40% increase in pod number with little inhibition (12%) of stem elongation. MCF increased the number of pods initiated (reaching 1 cm length) at least partially by prolonging the initiation period, while pod abortion (failure of pods > 1 cm long) remained low. Generally, MCF did not increase seed yield (dry weight/plant); more, but smaller seeds, were formed by the treated plants. The promotive effect of MCF on pod initiation seems to be independent of its inhibition of stem elongation, which is insignificant at 10 micromolar. MCF delayed pod maturation by 3 to 4 days, while foliar yellowing, blade abscission, and petiole abscission were retarded by 2, 4, and 2 days, respectively. MCF has only a small effect on senescence and that could be indirect, due to a delay in pod development. Other auxin-transport inhibitors tested, including N-1-naphthylphthalamic acid, produced little or no increase in pod number; however, 0.1 millimolar 5-[2'-carboxyphenyl]-3-phenylpyrazole caused a 27% increase. These results implicate auxin as a potential regulator of pod development, and they show that soybean seed yield is not simply sink limited.

Thigmomorphogenesis: the relationship of mechanical perturbation to elicitor-like activity and ethylene production.

An extracellular solution obtained from bean (Phaseolus vulgaris L. cv. Resistant Cherokee Wax) stems induced phytoalexin-like substance and ethylene production in a soybean [Glycine max (L.) Merr. cv. Wayne] cotyledon bioassay. The elicitor-like activity for phytoalexin formation and ethylene production was increased by mechanical perturbation of bean stems. Moreover, the application of extracted or known elicitors to bean plants mimicked the effect of mechanical perturbation (i.e., inhibition of stem elongation and enhancement of radial growth). The effects of extract when applied exogenously, on elicitor-like activity in the bioassay as well as stem thickening were decreased by aminoethoxyvinylglycine, an inhibitor of ethylene biosynthesis. These results suggest that elicitor-like substances which are formed in response to mechanical perturbation contribute to the thigmomorphogenesis.

Effects of an Oxathiin on Morphological Development, Histological Changes, and Auxin Activity within the Shoot Apex of Chrysanthemum

Abstract UBI-P293 (2-3-dihydro-5,6-diphenyl-l,4 oxathiin) applied to stem tips of Chrysanthemum X morifolium ‘Paragon’ inhibited stem elongation and promoted formation of lateral branches without apex removal. Treated shoot apexes were inhibited temporarily in their development and in endogenous auxin activity as indicated by bioassay. There was a negative growth response of bean sections treated with extracts from tips for 4 days after treatment with UBI-P293 at 0.02 m, and this concentration led to a disruption of normal organization within the apex.

Influence of Foliarly Applied Growth Regulators on Sex Expression in Watermelon1

Abstract The growth regulators abscisic acid (ABA), 6-benzylamino purine (BA), (2-chloroethyl)phosphonic acid (ethephon), aminoethoxyvinylglycine (AVG), and silver nitrate were applied in weekly or biweekly foliar sprays to watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] plants grown in a greenhouse. Both 10−3 mBA and 10−4 m ABA inhibited stem elongation, but had no effect on flowering patterns. Ethephon at 60 ppm and above prevented flower development, and at 15 and 30 ppm inhibited pistillate flowering and increased staminate/pistillate (S/P) flower ratios fivefold to sevenfold. Grafting watermelon scions to rootstocks of gynomonoecious and andromonoecious muskmelon did not affect sex expression or the response of watermelon to ethephon. AVG at 100 and 200 ppm and 500 ppm AgNO3 reduced the number of staminate flowers and promoted hermaphroditic flowering. In watermelon, contrary to other cucurbits, applied ethylene appears to suppress rather than promote ovary development during flower bud differentiation.

Rapid Suppression of Growth by Blue Light

The inhibition of stem elongation in dark-grown seedlings by blue light was studied with marking techniques and with a high-resolution, growth-measuring apparatus. Blue light rapidly suppresses growth in a variety of cultivated species. In some species, the inhibition persists only during the period of irradiation, after which time growth quickly returns to the high dark rate, whereas, in other species, the light response has an additional long-term component which lasts for at least several hours in the dark. The long-term inhibition may be mediated by phytochrome, whereas the rapid, short-term component is specific to a blue-light receptor.The rapid inhibition of growth in cucumber (Cucumis sativus L.) requires high-energy blue irradiation, which is perceived directly by the growing region of the hypocotyl and inhibits all regions below the hook to the same extent. Detailed investigation of the kinetics of the inhibition in cucumber and in sunflower (Helianthus annuus L.) shows that, after a short lag period (20 to 30 seconds in cucumber, 60 to 70 seconds in sunflower), the growth rate declines in an exponential fashion to a lower rate, with a half-time of 15 to 25 seconds in cucumber and 90 to 150 seconds in sunflower. Excision of the hypocotyl greatly reduces the sensitivity of the growth rate to blue-light inhibition. Because of the rapid kinetics, the blue-light photoreceptor cannot affect cell enlargement by altering the supply of growth hormone or the sensitivity to hormones but probably operates more directly either on the biochemical process which loosens cell walls or on cell turgor.

Gibberellins and the photoperiodic control of stem elongation in the long-day plant Agrostemma githago L.

Agrostemma githago is a long-day rosette plant in which transfer from short days (SD) to long days (LD) results in rapid stem elongation, following a lag phase of 7-8 d. Application of gibberellin A20 (GA20) stimulated stem elongation in plants under SD, while 2-isopropyl-4-dimethylamino-5-methylphenyl-1-piperidine-carboxylate methyl chloride (AMO-1618, an inhibitor of GA biosynthesis) inhibited stem elongation in plants exposed to LD. This inhibition of stem elongation by AMO-1618 was overcome by simultaneous application of GA20, indicating that GAs play a role in the photoperiodic control of stem elongation in this species. Endogenous GA-like substances were analyzed using reverse-phase high-performance liquid chromatography and the d-5 corn (Zea mays L.) assay. Three zones with GA-like activity were detected and designated, in order of decreasing polarity, as A, B, and C. A transient, 10-fold increase in the activity of zone B occurred after 8-10 LD, coincident with the transition from lag phase to the phase of rapid stem elongation. After 16 LD the activity in this zone had returned to a level similar to that under SD, even though the plants were elongating rapidly by this time. However, when AMO-1618 was applied to plants after 11 LD, there was a rapid reduction in the rate of stem elongation, indicating that continued GA biosynthesis was necessary following the transient increase in activity of zone B, if stem elongation was to continue under LD. It was concluded that control of stem elongation in A. githago involves more than a simple qualitative or quantitative change in the levels of endogenous GAs, and that photoperiodic induction alters both the sensitivity to GAs and the rate of turnover of endogenous GAs.

Effects of ethylN-phenylcarbamate on wall microtubules and on gibberellin- and kinetin-controlled cell expansion

In azuki bean epicotyl segments, ethylN-phenylcarbamate, at the concentration where it brought about almost complete disappearance of wall microtubules, reversed the gibberellin promotion and the kinetin inhibition of stem elongation.

Phytochrome Involvement in Stimulation and Alleviation of Inhibition of Plant Growth by Malformin

Stimulation of stem elongation on green cuttings of Phaseolus aureus by malformin occurred only in red light and was specifically reversible by subsequent treatment with far red radiation. Inhibition of stem elongation of etiolated cuttings by malformin in the dark was alleviated by red light and was repeatedly reversible with far red irradiation. A direct or indirect effect of malformin on phytochrome action was suggested.

Pressurized injection of aqueous solutions into tree trunks

A more precise analysis of the factors limiting pressurized trunk injection using dye solutions, a growth retardant (daminozide, succinic acid 2,2dimethyl hydrazide) and a my cobacteriostatic agent (tetracycline) has been completed. This included methods of drilling injection ports, influence of port diameter, depth, and pressure system. Results of these investigations suggest that trunk injection of aqueous solutions is feasible in many angiospermous species. Injected solutions moved up and down the 1- and 2-year old xylem into major scaffold and secondary branches, into terminal bud tissues of elongating shoots and secondary and tertiary lateral roots. Depending upon species, injection rates varied from 200 to 1800 ml/min at 14.08 kg cm −2 through injection ports 0.63 cm in diameter and 5 cm deep. Inhibition of stem elongation in Prunus persica var. nectarina (Ait.) Maxim and Prunus persica L. ‘Johnson’ and ‘Loadel’ trees was obtained with 5 to 50 g daminozide/tree, using 0.5 to 5% solutions. Tetracycline-induced remission of “pear decline” was achieved with 100–800 mg dosages depending on tree size. Dormant-season injections were effective for controlling growth and/or pear decline.

Site of in vivo Regulation of Tree Stem Elongation by Bark‐Banded Morphactins

AbstractMorphactin ester applied as a bark band to stems of Monterey pine seedlings (Pinus radiata D. Don) at first stimulated and then inhibited the rate of stem elongation over a 20‐day period. The inhibition was caused by a direct action of morphactin on the shoot rather than by indirect action on the root system. 14C labelled morphactin applied to the bark accumulated in the shoot apices and the amount accumulated could be related to the inhibition of growth. More than 70% of labelled material isolated from roots and shoot apices was in the form of a metabolite similar to the carboxylic acid derivative of the morphactin ester. A preparation of 14C labelled acid derivative applied to the bark was translocated to the shoot apex and to the roots and inhibited stem elongation.