Cell Elongation In Response Research Articles

The RCN1-encoded A subunit of protein phosphatase 2A increases phosphatase activity in vivo.

Protein phosphatase 2A (PP2A), a heterotrimeric serine/threonine-specific protein phosphatase, comprises a catalytic C subunit and two distinct regulatory subunits, A and B. The RCN1 gene encodes one of three A regulatory subunits in Arabidopsis thaliana. A T-DNA insertion mutation at this locus impairs root curling, seedling organ elongation and apical hypocotyl hook formation. We have used in vivo and in vitro assays to gauge the impact of the rcn1 mutation on PP2A activity in seedlings. PP2A activity is decreased in extracts from rcn1 mutant seedlings, and this decrease is not due to a reduction in catalytic subunit expression. Roots of mutant seedlings exhibit increased sensitivity to the phosphatase inhibitors okadaic acid and cantharidin in organ elongation assays. Shoots of dark-grown, but not light-grown seedlings also show increased inhibitor sensitivity. Furthermore, cantharidin treatment of wild-type seedlings mimics the rcn1 defect in root curling, root waving and hypocotyl hook formation assays. In roots of wild-type seedlings, RCN1 mRNA is expressed at high levels in root tips, and accumulates to lower levels in the pericycle and lateral root primordia. In shoots, RCN1 is expressed in the apical hook and the basal, rapidly elongating cells in etiolated hypocotyls, and in the shoot meristem and leaf primordia of light-grown seedlings. Our results show that the wild-type RCN1-encoded A subunit functions as a positive regulator of the PP2A holoenzyme, increasing activity towards substrates involved in organ elongation and differential cell elongation responses such as root curling.

Genetic analysis of a seedling stress response to ethylene in Arabidopsis

A genetic framework has been devised for the action of genes within the ethylene-response pathway. This working model is based on the epistatic interactions among a variety of ethylene response mutations. Most of the mutations that have been described act in a linear pathway. Genes controlling cell elongation in response to ethylene must, at some level, act to affect the architecture of the cytoskeleton. Genes that act late in the pathway, in mutant form, may lead to highly specific phenotypes such as the increased sensitivity to taxol in the ein6 mutant. Analysis of these downstream components may provide critical insights into the nature of ethylene's effect on the cell elongation machinery.

Distribution and virulence ofVibrio choleraebelonging to serogroups other than O1 and O139: A nationwide survey

The distribution and virulence of Vibrio cholerae serogroups other than O1 and O139 in India before, during and after the advent of O139 serogroup was investigated. A total of 68 strains belonging to 31 different 'O' serogroups were identified during the study period. With the exception of O53, there was no spatial or temporal clustering of any particular non-O1 non-O139 serogroup at any given place. Two of the 68 strains examined produced cholera toxin (CT) which could only be partially absorbed with anti-CT immunoglobulin G. Tissue culture assay revealed that some of the non-O1 non-O139 strains produced factors which evoked either a cell rounding or cell elongation response depending upon the medium used. This study indicates that serogroups other than O1 and O139 should also be continuously monitored.

Plasma membrane protein composition and synthesis in soybean hypocotyl segments undergoing auxin-induced elongation

The types and amount of plasma membrane proteins synthesized during cell elongation in response to auxin (2,4-dichlorophenoxyacetic acid) treatment were investigated. Auxin-treated and control soybean (Glycine max L.) hypocotyl segments were incubated with [35S]methionine for various times, ranging from 0.5 to 18 h, prior to isolation of plasma membrane by aqueous two-phase partitioning. Protein accumulated in the plasma membrane after auxin treatment. Despite this accumulation, the protein incorporation rate, estimated by the amount of label in the plasma membrane following a 0.5 h [35S]methionine pulse, was unaffected by auxin treatment at both 0.5 and 18 h of treatment. Protein apparently accumulated by a mechanism distinct from enhanced incorporation. The plasma membrane proteins synthesized by elongating segments differed from controls at 18 h, as evidenced by the pattern of fluorographs following a 0.5 h radiolabelling. However, auxin treatment did not alter the 2-D gel pattern of the polypeptides detectable by silver stain.

Studies on the mechanism of cell elongation in Blepharisma japonicum: 4. Three dimensional construction of the kinetosomal complex and its functional role on cell elongation

The kinetosomal complex of a heterotrich ciliate Blepharisma japonicum was investigated at ultrastructural level, with special reference to its cell elongation in response to light stimulation. In serial sections, vacuole-associated microtubules were found to be originated from both anterior fiber sheet and left surface of the anterior kinetosome. These microtubules form a bundle and extend toward the anterior end of the organism. The postciliary microtubular sheet is attached to the proximal half of the posterior kinetosome. Two types of transverse microtubules are present: the anterior 8-9 microtubules arising at the base of the anterior kinetosome and the posterior 2-3 microtubules arising between the paired kinetosomes. Based on these results, a three dimensional model of the kinetosomal complex was proposed and the mechanism of cell elongation in Blepharisma was discussed.

Three-dimensional construction of the kinetosomal complex in a ciliate Blepharisma, revealed by isolation technique and serial sectioning

In a heterotrichous ciliate, Blepharisma japonicum, pairs of basal bodies (kinetosomes) and their fibrous associates containing microtubular sheets and bundles are closely related to cell elongation in response to light stimulation. Up to date, however, three dimensional construction of them has not been clarified because of their own complexity and difficulty of establishment of their isolation technique. By applying the newly devised isolation medium, however, they were found to be isolated fruitfully from the cell bodies. The present isolation medium was composed of 10 mM MgSO4, 10 mM EGTA, 1 mM dithiothreitol, 32 mM sucrose, AH Triton X-100, 20% glycerol, 100 mM HEPES and 20 mM PIPES adjusted to pH 7.2 with KOH. The isolated complexes were mounted onto Formvar-coated grid, fixed briefly with 2% glutai-aldehyde (GA) buffered with 0.1 mM sodium cacodylate at pH 7.2, rinsed with deionized distilled water and finally stained with 1% aqueous uranyl acetate (UA). For thin sectioning, on the other hand, the organisms were fixed for 10 min with a mixture of 2.5% GA and 1% OsO4 in cacodylate buffer (pH 7.2) at room temperature.

20-Hydroxyecdysone-induced changes in the cell volume of lepidopteran cells associated with population dynamics

SUMMARY The insect cell line MRRL-CH derived from embryos of the lepidopteran Manduca sexta responded rapidly, within 15 min, to 20-hydroxyecdysone (20-OH-Ec) (1 x 10-s M) by increasing in cell volume. The induction time for this response contrasts with that for the cell elongation response that appears only after 24 to 48 h. The increase in cell volume represents the most rapid 20-OH-Ec-induced change in cell morphology reported to date. It also has some steroid specificity because no volume change was induced by ecdysone (4 x 10-6 M) under the experimental conditions. The magnitude of the cell volume response to 20-OH-Ec varied with the population dynamics of the cell line and was associated with cell size at the time of treatment.

Petiole growth in the celery-leaved crowfoot ( Ranunculus sceleratus L.): Effects of auxin-transport inhibitors

Leaves of the semi-aquatic celery-leaved crowfoot ( Ranunculus sceleratus L.) exhibited petiole growth through cell elongation in response to submergence or when treated with ethylene or auxin. The auxin-transport inhibitors, naptalam (1- N-naphthylphthalamic acid) and the morphactins IT 3456 (2-chlorofluorenol methyl ester) and IT 3233 (9-hydroxyfluorenolcarboxylic acid-9-n-butyl ester) had no effect on the response to 10 −4 M indole acetic acid (IAA), but inhibited the growth response to 1 μl 1 −1 ethylene. Isolated petiole segments were more sensitive to auxin than to ethylene.

Osmotic Stress in Coleoptiles and Primary Leaves of Wheat: I. EFFECTS ON SIZE, WEIGHT, TOTAL PROTEIN, DNA, AND PHOSPHORUS

Osmotic Stress in Coleoptiles and Primary Leaves of Wheat: I. EFFECTS ON SIZE, WEIGHT, TOTAL PROTEIN, DNA, AND PHOSPHORUS

Specificity of Auxin-binding Sites on Maize Coleoptile Membranes as Possible Receptor Sites for Auxin Action

Dissociation coefficients of auxin-binding sites on maize (Zea mays L.) coleoptile membranes were measured, for 48 auxins and related ring compounds, by competitive displacement of (14)C-naphthaleneacetic acid from the binding sites. The sites bind with high affinity several ring compounds with acidic side chains 2 to 4 carbons long, and much more weakly bind neutral ring compounds and phenols related to these active acids, most phenoxyalkylcarboxylic acids, and arylcarboxylic acids except benzoic acid, which scarcely binds, and triiodobenzoic acids, which bind strongly. Specificity of the binding is narrowed in the presence of a low molecular weight "supernatant factor" that occurs in maize and other tissues. Activity of many of the analogs as auxin agonists or antagonists in the cell elongation response was determined with maize coleoptiles. These activities on the whole roughly parallel the affinities of the binding sites for the same compounds, especially affinities measured in the presence of supernatant factor, but there are some quantitative discrepancies, especially among phenoxyalkylcarboxylic acids. In view of several factors that can cause receptor affinity and biological activity values to diverge quantitatively among analogs, the findings appear to support the presumption that the auxin-binding sites may be receptors for auxin action.

Germination Behavior of Salsola as Influenced by Temperature, Moisture, Depth of Planting, and Gamma Irradiation1

AbstractSalsola kali, L. seeds contain fully differentiated seedlings and these uncoil in minutes with favorable temperature and moisture. If germinated on the soil surface, the uncoiled seedling will dehydrate and the if it cannot push its roots into the soil. Germination is most favorable for seeds covered with soil. For this reason the species generally appears only on disturbed soils. Seeds germinate satisfactorily at 17 C and at 9.1% soil moisture in Yolo loam stabilized with krilium and seedlings emerged from a planting depth of 7.5 cm. Evidence obtained with gamma irradiation from a Co60 source indicates that germination consists of rapid cell elongation in response to moisture and that new cell division is not necessary to the process. Irradiation of seed at levels above about 50,000 R impaired cell division but levels of over 400,000 R were necessary to cause additional germination injury.

STUDIES ON PLANT GROWTH‐REGULATING SUBSTANCES

Fifteen series of aryloxyacetic, α‐aryloxy‐propionic, ‐butyric and ‐isobutyric acids and the corresponding arylthio‐analogues have been synthesized and their growth‐regulating activity has been assessed in the tomato‐leaf epinasty, wheat cylinder and the pea curvature tests. It is shown that in general arylthio‐derivatives are less active than their aryloxy‐analogues. Although for a cell elongation response the presence in the molecule of an a‐hydrogen atom is usually necessary, three exceptions to this generalization have now been found. A lower activity in the 3:5‐dichloro‐ compared with the 2:6‐dichloro‐compounds has been demonstrated. Evidence is presented to show that an ortho hydrogen atom in the nucleus is not an essential requirement for cell elongating activity as is postulated by other workers.