Elongation Of Segments Research Articles

(Aminooxy)acetic acid inhibits petunia growth and gibberellin- and cytokinin-stimulated growth in bioassays

(Aminooxy)acetic acid (AOA) was applied to greenhouse-grown petunias and was used in bioassays for three plant growth hormones so that its growth regulator properties could be studied. In greenhouse studies foliar sprays of 4.8–12 mm AOA inhibited vegetative growth of petunia seedlings (Petunia xhybrida Vilm. ‘White Flash’). When gibberellin A 3 (GA3) was applied to shoot tips previously treated with AOA, plant growth was stimulated, but there was no AOA x GA3 interaction. Some changes in petunia leaf morphology induced by AOA were reversed by GA3. AOA inhibited elongation of corn coleoptile segments (Zea mays L. B73 x Mol7) whether or not 10 μm indole-3-acetic acid (IAA) was present, but there was no AOA x IAA interaction. AOA reduced lettuce hypocotyl (Lactuca sativa L. ‘Grand Rapids’) elongation induced by GA3 and radish cotyledon (Raphanus sativus L. ‘Champion’) expansion induced by benzyladenine (BA). We propose that AOA interferes with postsynthetic metabolism of plant hormones during cell elongation induced by GA3 and cell expansion induced by BA.

Gibberellic acid promotes growth and cell wall synthesis in Avena internodes regardless of the orientation of cell expansion

Segments cut from the next‐to‐last (peduncular‐1) internode of Avena sativa L. cv. Victory (oat) shoots elongate as much as 10‐fold in response to gibberellic acid (GA3). The objective of the present investigation was to differentiate the effects of GA3 on growth from its effects on wall synthesis (measured gravimetrically and through the incorporation of [14C]‐glucose) by using several cell wall synthesis inhibitors with widely varying mechanisms of action. Four compounds, viz. monensin, cycloheximide, lanthanum, and galactose. caused (1) relatively little inhibition of either cell wall synthesis or elongation in segments without GA3, (2) roughly proportionate, dose‐dependent inhibition of elongation and wall synthesis in GA3‐treated segments and (3) generally greater inhibition of GA3‐promoted uptake of radioactivity than of wall incorporation or elongation. Two other compounds, colchicine and 2,6‐dichlorobenzonitrile (DCB). (1) inhibited GA3‐induced elongation considerably more than cell wall synthesis and (2) caused swelling (radial expansion). especially of GA3‐treated segments. DCB‐treated internodal cells apparently compensated for inhibited cellulose synthesis by greater synthesis of matrix polysaccharide (beginning between 3 and 6 h). While normal cellulose synthesis was not required for short‐term (up to 6 h) GA3‐induced elongation or for long‐term hormone‐promoted radial expansion, it was required for sustained GA3‐induced elongation. These results indicate that GA3‐promoted cell wall loosening (manifested as radial expansion) and cell wall synthesis in Avena internodes occur at least partially independently of any hormonal effect on the orientation of microtubules and microfibrils.

Inhibition of the synthesis of cell wall polysaccharides in oat coleoptile segments by jasmonic acid: Relevance to its growth inhibition

The inhibitory mode of action of jasmonic acid (JA) on the growth of etiolated oat (Avena sativa L. cv. Victory) coleoptile segments was studied in relation to the synthesis of cell wall polysaccharides using [14C]glucose. Exogenously applied JA significantly inhibited indoleacetic acid (IAA)-induced elongation of oat coleoptile segments and prevented the increase of the total amounts of cell wall polysaccharides in both the noncellulosic and cellulosic fractions during coleoptile growth. JA had no effect on neutral sugar compositions of hemicellulosic polysaccharides but substantially inhibited the IAA-stimulated incorporation of [14C]glucose into noncellulosic and cellulosic polysaccharides. JA-induced inhibition of growth was completely prevented by pretreating segments with 30 mm sucrose for 4 h before the addition of IAA. The endogenous levels of UDP-sugars, which are key intermediates for the synthesis of cell wall polysaccharides, were not reduced significantly by JA. Although these observations suggest that the inhibitory mode of action of JA associated with the growth of oat coleoptile segments is relevant to sugar metabolism during cell wall polysaccharide synthesis, the precise site of inhibition remains to be investigated.

Autoradiographic and biochemical assessment of rod outer segment renewal in the vitiligo (C57BL/6-mi vit/mi vit) mouse model of retinal degeneration

Rod outer segment renewal was assessed in vitiligo (C57BL/6-mivit/mivit) mice using autoradiographic and biochemical methods. This process was examined because the number of phagosomes is reduced in this mouse. Rod outer segment renewal was detectable in the mivit/mivit retina. Within 24 hr of intraperitoneal injection of 3H leucine, there was a distinct band of radioactivity present at the junction of the ROS and RIS in mutant mice that was similar to controls. The displacement of the radioactive band progressed normally in the peripheral regions of the vitiligo retina, but did not in the posterior retina. Morphometric analysis of the posterior region of mutant retinas, indicated that the band of radioactivity became less distinct between 1 and 3 days post-injection. In vitiligo retinas it remained at 2.23 microns, whereas in controls, the band migrated 6.16 microns from the ROS base. When posterior regions of retinas were evaluated 8 days post-injection, there was no band discernible in the vitiligo retinas, but a very dense band at the ROS apex in controls. Assessment of incorporation of radioactivity into rhodopsin using SDS-PAGE indicated a progressive displacement of radio-labeled rhodopsin through the RER, but not as complete a progression through the outer segments. The elongation of the outer segments in the posterior regions of the mutant retina suggests impaired shedding. This, plus the lack of attachment in the posterior retina of photoreceptor cells to RPE in this mouse, seem to be likely causes for the decreased number of phagosomes.

Elongation of the Grass Leaf and its Relationship to the Phyllochron

The phyllochron (interval between appearance of successive leaves) in grasses is determined by timing of leaf initiation at the stem apex and duration of leaf tip elongation through the whorl of mature sheaths. Primordia in tall fescue (Festuca arundinacea Schreber) are initiated and enlarge to ⊄ 1.5 nun in length by production of cells that remain ⊄ 20 um long. As a young leaf continues to grow, epidermal cells beyond 1.5 nun from the base elongate to form a cell elongation zone of 7 to 40 mm, depending on genotype and environment, which pushes older tissue through the whorl. Leaf elongation rate is a function of length of the elongation zone and segmental elongation rate of positions within the zone. This zone constitutes a major sink for carbohydrate, N, and water deposition in the leaf. Ligule formation occurs in the cell division zone when the blade is ⊄20% of its final length. Blade and sheath elongation take place simultaneously thereafter with their relative proportion depending on position of the ligule in the elongation zone. Initiation of leaf elongation from a resting primordium at a given node is coordinated with ligule initiation in the next‐older leaf one node below and with cessation of cell division in the sheath and commencement of tiller elongation at the axillary bud two nodes below. Duration of leaf tip elongation through the whorl depends on elongation rate and sheath length. The importance of these factors in determining the phyllochron is often overlooked due to calculation procedures that assume a constant phyllochron when in fact the phyllochron often changes for each leaf.

Architectural alterations in rat cerebral microvessels after hypobaric hypoxia

We performed 3-dimensional studies of vascular casts of the microvasculature of the cerebral cortex of rats that were exposed to three weeks of hypobaric hypoxia and of control rats. Scanning electron microscopy of the casts gave the qualitative impression of increased vascularity of the cerebral cortex, particularly the deeper layers, in hypoxic rats. Quantitative analysis of capillary segment lengths revealed a significant shift in the frequency distribution to longer lengths (from 77 ± 8 to 90 ± 14 μm) in the deep, but not in the superficial, layers of the cerebral cortex of hypoxic rats. These findings agree with previous results reporting increased capillary density in the brain after exposure to prolonged hypobaric hypoxia and suggest that capillary segment elongation plays a role in the increased capillary density in the deeper layers of the cerebral cortex.

Postnatal maturation of the layer III pyramidal neurons in the human prefrontal cortex: a quantitative Golgi analysis

In this study we examined the morphological maturation of the basal dendritic field of layer III pyramidal neurons located in the human dorsolateral prefrontal cortex in subjects ranging from 7.5 months after birth up to 27 years. The sections were stained with the Golgi-Cox method and the three-dimensional branching pattern was measured with a semi-automatic dendrite measuring system. Results show a rapid growth phase of the dendritic field from 7.5 months after birth up to one year. A marked increase in total dendritic length is observed, for which elongation of the terminal segments, longer intermediate segments and an increase in number of segments is an explanation. The dendritic length appears to have stabilized after one year, leading us to conclude that the postnatal morphological maturation of the layer III pyramidals does not continue well into childhood, but is completed at a much younger age. Additionally we analyzed the effect of varying section thickness on dendritic parameters and found no tendency for higher dendritic values with increasing section thickness for the range of thickness values of the histological sections used.

The current status of the acid‐growth hypothesis

SUMMARYExcised coleoptile segments that were depleted of endogenous auxin after pre‐incubation in water respond to the phytotoxin fusicoccin (FC) and the plant hormone auxin (indole‐3‐acetic acid, IAA) with an enhancement of growth. This promotion of organ elongation is caused by an increase in the extensibility of the thick, growth‐limiting outer epidermal wall. The acid‐growth hypothesis postulates that both FC and IAA cause wall‐loosening and the concomitant induction of growth by rapid acidification of the extension‐limiting cell wall. At saturating concentrations FC and IAA cause very similar growth responses. However, the equilibrium‐pH in the incubation medium (∼ pH of the peripheral cell wall) of abraded FC‐treated segments is 3.5–4.0, whereas in the presence of IAA a pH of 4.8–5.0 is established. The FC‐ and IAA‐mediated induction of growth can be stimulated by an external buffer of pH 3.5–4.0. Acid buffers of pH 5, however, cause almost no enhancement of growth compared WJth the water‐control. FC‐mediated growth can be inhibited by neutral buffers infiltrated into the outer epidermal wall, but a substantial growth response occurs after addition of IAA under identical conditions. A sub‐optimal concentration of FC was used to mimic the effect of IAA on acid secretion. When a pH of 4.8–5.0 was established by FC in the peripheral wall no promotion of growth occurred. Hence, IAA‐induced proton excretion is insufficient to cause cell‐wall loosening in the coleoptile. Abraded segments that rapidly elongate in acid buffers (pH 3.5–4.0) respond to IAA with an additional enhancement of growth, but under identical conditions FC is without effect. The growth‐promoting effects of acid and IAA are additive, i.e. IAA and acid act via separate mechanisms. These results are consistent with the acid‐growth hypothesis of FC action. However, they indicate that IAA induces growth by a mechanism independent of cell‐wall acidification. Alternative hypotheses of IAA‐mediated cell‐wall loosening are discussed. Contents Summary 549 I. Introduction 550 II. Segment elongation and the organismal concept of multicellularity 550 III. FC‐ and IAA‐mediated acid secretion 552 IV. The acid‐growth hypothesis of FC action 555 V. The acid‐growth hypothesis of IAA action 560 VI. Conclusions 567 Acknowledgements 568

Elevated Levels of Tubulin Transcripts Accompany the GA<sub>3</sub>-Induced Elongation of Oat Internode Segments

Elevated Levels of Tubulin Transcripts Accompany the GA<sub>3</sub>-Induced Elongation of Oat Internode Segments

Role of xyloglucan breakdown in epidermal cell walls for auxininduced elongation of azuki bean epicotyl segments

Auxin‐induced elongation of epicotyl segments of azuki bean (Vigna angularis Ohwi et Ohashi cv. Takara) was suppressed by a fucose‐binding lectin from Tetragonolobus purpureas Moench and by polyclonal antibodies raised against xyloglucan heptasaccharide (Xyl3Glc4) when the cuticle present in the outer surface of epicotyls was abraded. In contrast, elongation of non‐abraded segments was not influenced by the lectin or the antibodies. Epicotyl segments, from which the epidermal and the outer cortical cells had been removed, elongated rapidly for 2 h and than only slowly. Auxin slightly stimulated elongation of the inner tissue segments in the phase of slow growth. Neither in the presence nor in the absence of auxin did the lectin or the antibodies affect elongation of the inner tissue segments. The split portions of outer surface‐abraded epicotyl segments incubated in buffer extended outward, and auxininhibited this outward bending. The lectin and the antibodies reversed the effect of auxin on bending. The fucose‐binding lectin pretreated with fucose or the immunoglobulin fraction obtained from preimmune serum exhibited little or no inhibitory effect on auxin‐induced elongation of abraded or split segments. These results support the view that a breakdown of xyloglucans in the epidermal cell walls plays an essential role in auxin‐induced elongation in dicotyledons.

Calcium Antagonists Inhibit Sustained Gibberellic Acid-Induced Growth of Avena (Oat) Stem Segments.

The elongation response of Avena sativa (oat) stem segments to gibberellic acid (GA3) is of large magnitude, with high hormonal sensitivity and specificity, but without cell division activity. This system is therefore an excellent model for mechanistic studies on higher plant cell elongation and the action of gibberellin. At millimolar concentrations, the calcium antagonists verapamil, D-600, nicardipine, diltiazem, bepridil, 8-(N,N,-diethylamino)-octyl-3,4,5-trimethoxybenzoate HCl, and lanthanum substantially inhibited the growth of GA3-treated segments but had no effect on the elongation of nonhormone-treated segments. Although verapamil reduced the maximum growth rate and caused premature cessation of growth, even preincubation of the segments with the drug prior to treatment with GA3 failed to inhibit the earliest measured stimulation of growth by the hormone. Inhibition by verapamil was not reversed by increased concentrations of GA3 or calcium. Neither the calcium ionophore A23187 nor agonist BAY K 8644 had any effect on growth. Light microscopic examination of epidermal peels from antagonist-treated internodal tissue revealed no obvious differences from the control except that the cells were not as elongated. Although these results may support a role for calcium ion movement in maintaining the GA3-induced growth of Avena stem segments, they do not support the involvement of calcium ion movement in the hormone-mediated initiation of growth.

Role of xyloglucan breakdown in epidermal cell walls for auxin-induced elongation of azuki bean epicotyl segments

Role of xyloglucan breakdown in epidermal cell walls for auxin-induced elongation of azuki bean epicotyl segments

Distal Roux-en-Y Gastric Bypass Conversion Operation for Failed Vertical Banded Gastroplasty.

Forty-five cases of failed vertical banded gastroplasty were converted to gastric bypass with distal Roux-en-Y constructed with a 250 cm alimentary limb and a 150 cm common channel. The gastroenterostomy is side-to-side, unrestricted and is at least 3 cm wide. We believe that this wide anastomosis is responsible for the zero incidence of stomal ulcers in this group. A nasogastric tube is not used and the patient is placed on ranitidine 150 mg one b.i.d. for the first 4 weeks. The weight loss is excellent and sustained, and the resulting life-style is very close to that of a normal person. All varieties of foods are tolerated in adequate amounts, and diarrhea occurs only if the patient indulges in fatty foods. Hypoproteinemia is generally mild and transient except in five early cases where TPN was needed, and four of these required elongation of the intestinal segments. Wound infection was 4.5%, and there was no mortality.

Evolution of protein complexity: the blue copper-containing oxidases and related proteins.

The blue copper proteins and their relatives have been compared by sequence alignments, by comparison of three-dimensional structures, and by construction of phylogenetic trees. The group contains proteins varying in size from 100 residues to over 2,300 residues in a single chain, containing from zero to nine copper atoms, and with a broad variation in function ranging from electron carrier proteins and oxidases to the blood coagulation factors V and VIII. Difference matrices show the sequence difference to be over 90% for many pairs in the group, yet alignment scores and other evidence suggest that they all evolved from a common ancestor. We have attempted to delineate how this evolution took place and in particular to define the mechanisms by which these proteins acquired an ever-increasing complexity in structure and function. We find evidence for six such mechanisms in this group of proteins: domain enlargement, in which a single domain increases in size from about 100 residues up to 210; domain duplication, which allows for a size increase from about 170 to about 1,000 residues; segment elongation, in which a small segment undergoes multiple successive duplications that can increase the chain size 50-fold; domain recruitment, in which a domain coded elsewhere in the genome is added on to the peptide chain; subunit formation, to form multisubunit proteins; and glycosylation, which in some cases doubles the size of the protein molecule. Size increase allows for the evolution of new catalytic properties, in particular the oxidase function, and for the formation of coagulation factors with multiple interaction sites and regulatory properties. The blood coagulation system is examined as an example in which a system of interacting proteins evolved by successive duplications of larger parts of the genome. The evolution of size, functionality, and diversity is compared with the general question of increase in size and complexity in biology.

Effects of Deuterium Oxide on Growth, Proton Extrusion, Potassium Influx, and in Vitro Plasma Membrane Activities in Maize Root Segments

Elongation of subapical segments of maize (Zea mays) roots was greatly inhibited by (2)H(2)O in the incubation medium. Short-term exposure (30 min) to (2)H(2)O slightly reduced O(2) uptake and significantly increased ATP levels. (2)H(2)O inhibited H(+) extrusion in the presence of both low (0.05 mm) and high (5 mm) external concentrations of K(+) (about 30 and 53%, respectively at 50% [v/v] (2)H(2)O). Experiments on plasma membrane vesicles showed that H(+)-pumping and ATPase activities were greatly inhibited by (2)H(2)O (about 35% at 50% [v/v] (2)H(2)O); NADH-ferricyanide reductase and 1,3-beta-glucan synthase activities were inhibited to a lesser extent (less than 15%). ATPase activities present in both the tonoplast-enriched and submitochondrial particle preparations were not affected by (2)H(2)O. Therefore, the effect of short incubation time and low concentration of (2)H(2)O is not due to a general action on overall cell metabolism but involves a specific inhibition of the plasma membrane H(+) -ATPase. K(+) uptake was inhibited by (2)H(2)O only when K(+) was present at a low (0.05 mm) external concentration where absorption is against its electrochemical potential. The transmembrane electric potential difference (E(m)) was slightly hyperpolarized by (2)H(2)O at low K(+), but was not affected at the higher K(+) concentrations. These results suggest a relationship between H(+) extrusion and K(+) uptake at low K(+) external concentration.

Immunoaffinity purification using monoclonal antibodies for the isolation of indole auxins from elongation zones of epicotyls of red-light-grown Alaska peas

The endogenous indole auxins of red-light grown pea (Pisum sativum L.) epicotyls were investigated. Immunoaffinity purification of indole-3-acetic acid (IAA) and its methylester was achieved using two monoclonal antibodies. Antibodies against free IAA were raised against IAA-C5-BSA, a hapten-carrier-conjugate giving rise to highly specific antibodies for indole auxins with a free acetic-acid group at position 3. Immunoaffinity adsorbents prepared with these antibodies were used for single-step purification of extracts of Alaska pea epicotylar tissue prior to quantification by high-performance liquid chromatography (HPLC) with on-line fluorescence detection. Monoclonal antibodies against a hapten-carrier-conjugate with IAA linked to bovine serum albumin through the carboxyl group (IAA-C1'-BSA) were used for the isolation of IAA esters. Indol-3-acetic acid was identified in the elongation zone of the third internode of red-light-grown Alaska pea. 4-Chloro-indole-3-acetic acid, a constituent of immature pea seeds which is considered to be a very active auxin, was absent from the elongation zone. Several compounds were retained by the column based on antibodies against IAA-C1'-BSA. Of these the methylester of IAA was identified by HPLC with on-line fluorescence detection, by co-migration in thin-layer chromatography and by gas chromatography-mass spectrometry. The methyl ester of IAA was very active in promoting elongation of pea third-internode segments. When fed to the epicotylar segments the IAA methylester was rapidly metabolized with IAA being the major metabolite. The methylester of IAA should therefore be classified as a labile auxin conjugate.

Neurite branching pattern formation: Modeling and computer simulation

A model for nerve cell pattern formation is proposed in this paper. The model is based on some experimental results and an assumption that there is a kind of inhibitive interaction between growing neurites on the same nerve cell. In this paper, this interaction is termed lateral inhibition. A group of ordinary differential equations are used to describe the elongation of the terminal neurite segments of individual nerve cells. Computer simulation and comparison of it with in vitro studies are also made in this paper.

Further Studies of the Ability of Xyloglucan Oligosaccharides to Inhibit Auxin-Stimulated Growth

The structural features required for xyloglucan oligosaccharides to inhibit 2,4-dichlorophenoxyacetic acid-stimulated elongation of pea stem segments have been investigated. A nonasaccharide (XG9) containing one fucosyl-galactosyl side chain and an undecasaccharide (XG11) containing two fucosyl-galactosyl side chains were purified from endo-beta-1,4-glucanase-treated xyloglucan, which had been isolated from soluble extracellular polysaccharides of suspension-cultured sycamore (Acerpseudoplatanus) cells and tested in the pea stem bioassay. A novel octasaccharide (XG8') was prepared by treatment of XG9 with a xyloglucan oligosaccharide-specific alpha-xylosidase from pea seedlings. XG8' was characterized and tested for its ability to inhibit auxin-induced growth. All three oligosaccharides, at a concentration of 0.1 microgram per milliliter, inhibited 2,4-dichlorophenoxyacetic acid-stimulated growth of pea stem segments. XG11 inhibited the growth to a greater extent than did XG9. Chemically synthesized nona- and pentasaccharides (XG9, XG5) inhibited 2,4-dichlorophenoxyacetic acid-stimulated elongation of pea stems to the same extent as the same oligosaccharides isolated from xyloglucan. A chemically synthesized structurally related heptasaccharide that lacked a fucosyl-galactosyl side chain did not, unlike the identical heptasaccharide isolated from xyloglucan, significantly inhibit 2,4-dichlorophenoxyacetic acid-stimulated growth.

Comparison of the Outer and Inner Epidermis

Polyclonal antibodies, raised against beta-d-glucans prepared from oat (Avena sativa L.) caryopses, cross-reacted specifically with (1-->3),(1-->4)-beta-d-glucans when challenged in a dot blot analysis of related polymers bound to a cellulose thin layer chromatography plate. The antibodies suppressed indoleacetic acid (IAA)-induced elongation of segments from maize (Zea mays L.) coleoptiles when the outer surface was abraded. However, IAA-induced elongation of nonabraded segments or segments with abrasion restricted to the interior of the cylinder was not influenced by the antibodies. Fab fragments prepared from the antibodies gave similar results. The capacity for IAA to overcome outward curvature of split coleoptile segments was partially reversed by treatment of the segments with the antibodies. Fluorescence microscopy revealed that antibody penetration was largely restricted to the epidermal cell wall region. These results support the view that the degradation of (1-->3),(1-->4)-beta-d-glucans in the outer epidermal cell wall serves an essential role in auxin-induced elongation of Poaceae coleoptiles.

Auxin and Growth Regulation of Rice Coleoptile Segments

Auxin-stimulated elongation of apical segments of rice (Oryza sativa L. cv Arborio) coleoptiles occurring in the first 4 hours of treatment has been studied. Cell extension promoted in the first 2 hours by 10 micromolar indole-3-acetic acid (IAA) is specifically auxin-dependent, whereas after 4 hours, elongation also depends on endogenous production of ethylene. Similar to other systems, rice coleoptile cell elongation stimulated by auxin requires continuous synthesis of RNA and protein. Two-dimensional gel analysis of the in vitro translation products obtained from polyadenylated RNAs extracted from treated and untreated segments after 1 or 4 hours from the initial addition of IAA shows few transcriptional differences. At 60 minutes of treatment, the level of three mRNAs coding for proteins of 22.5, 25, and 33 kilodaltons was moderately enhanced while the disappearance of a 38 kilodalton translation product was observed. Additional repression of another mRNA coding for a 28 kilodalton product begins to show by this time, but becomes more evident after 4 hours treatment. At 4 hours, four IAA-specific mRNA enhancements coding for proteins with molecular masses ranging between 35 to 40 kilodaltons were also observed. We discuss these data in relation to the possible involvement of IAA-mediated transcriptional regulation in growth promotion of rice coleoptiles and, more widely, in control of cell elongation.