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At least 415 records · Page 23Linked to original sources
PubMed2006

Molecular characterization of PgAGO, a novel conifer gene of the Argonaute family expressed in apical cells and required for somatic embryo development in spruce.

A new member of the Argonaute (AGO) family of proteins was isolated from conifers and designated as PgAGO (Gene Bank Accession No. DQ068741; protein ID AAY67884). The complete coding sequence of PgAGO was obtained through screening cDNA libraries generated from white spruce (Picea glauca (Moench) Voss) somatic embryos. The PgAGO gene has an open reading frame of 2880 bp and encodes a protein of 960 amino acids. The predicted protein has an isolectric point of 9.17, a molecular mass of 107 kD and lacks prominent hydrophobic domains, which makes its cellular location inconclusive. The PgAGO protein contains the two conserved regions (the PAZ and PIWI domains) typically found in all members of the AGO family. The PAZ domain of PgAGO comprises 117 amino acid residues and shares a low degree of homology with similar domains in other species. The C-terminal PIWI domain contains 86 amino acids and is more conserved. Localization and transformation studies suggest that PgAGO is required for embryo development, specifically for proper shoot and root apical meristem differentiation. Based on RNA-in situ hybridization, the PgAGO transcripts are preferentially localized in cells of the shoot and root apical meristems from the early phases of embryo development. The RNA-mediated suppression of PgAGO results in severe abnormalities during embryo development, including the formation of poorly organized apical meristems. The root meristems lack the group of large central cells that separate the procambial region from the root cap, whereas the shoot meristem fails to differentiate apical initials. These abnormalities result in poor post-embryonic performance, leading to meristem abortion and growth cessation.

Amino Acid Sequence↗
PubMed2005

GFP-FABD2 fusion construct allows in vivo visualization of the dynamic actin cytoskeleton in all cells of Arabidopsis seedlings.

In vivo visualization of filamentous actin in all cells of Arabidopsis thaliana seedlings is essential for understanding the numerous roles of the actin cytoskeleton in diverse processes of cell differentiation. A previously introduced reporter construct based on the actin-binding domain of mouse talin proved to be useful for unravelling some of these aspects in cell layers close to the organ surface. However, cells more deeply embedded, especially stelar cells active in polar transport of auxin, show either diffuse or no fluorescence at all due to the lack of expression of the fusion protein. The same problem is encountered in the root meristem. Recently introduced actin reporters based on fusions between A. thaliana fimbrin 1 and GFP gave brilliant results in organs from the root differentiation zone upwards to the leaves, however failed to depict the filamentous actin cytoskeleton in the transition zone of the root, in the apical meristem and the root cap. To overcome these problems, we have prepared new transgenic lines for the visualization of F-actin in vivo. We report here that a construct consisting of GFP fused to the C-terminal half of A. thaliana fimbrin 1 reveals dynamic arrays of F-actin in all cells of stably transformed A. thaliana seedlings.

Actins↗
PubMed1984

Ultrastructural detection of fucosyl residues at the surface of axenically grown maize roots/sequential use of UeA lectin and fucosyl ferritin as the specific glycosylated marker.

This study reports the ultrastructural detection of fucosyl residues at the surface of axenically grown roots of Zea mays. The method used involved sequential binding of UeA lectin to the root and coupling of the bound UeA with fucosyl ferritin. Superficial dense ferritin labelling was found in the slime droplet ensheathing the root cap and in the external layer of the three-layered epidermal root surface. This pattern of binding of the fucose-specific lectin UeA suggests an overall distribution of the fucosyl residues on the root surface. Their localization within slime components of the root cap and the root epidermis is also assessed by the use of PATAg controls. Treatment of whole roots with alpha-L-fucosidase was ineffective in removing the fucosyl residues present at the root surface. The biological role of the fucosyl residues at the root-soil interface is discussed.

Cell Membrane↗
PubMed2003

Arabidopsis mutants affected in the transcriptional control of allene oxide synthase, the enzyme catalyzing the entrance step in octadecanoid biosynthesis.

Allene oxide synthase (AOS) catalyzes the entrance reaction in the biosynthesis of the octadecanoids 12-oxophytodienoic acid (OPDA) and jasmonic acid (JA). The enzyme is feedback-regulated by JA and thus a target of the JA-signalling pathway. A fusion genetic approach was used to isolate mutants in this signalling pathway. Seeds from transgenic Arabidopsis thaliana plants expressing the Escherichia coli uidA gene encoding beta-glucuronidase (GUS) under the control of the AOS promoter were mutagenized with ethylmethane sulfonate and the progeny was screened for individuals exhibiting constitutive expression of uidA in the absence of an added octadecanoid. From 21,000 mutagenized plants, 8 lines showing constitutive AOS expression were obtained. The mutant lines were characterized further and fell into four classes, I to IV. All showed signs of growth inhibition encompassing both shoot and root systems, and accumulated higher than normal levels of OPDA. Mutants belonging to classes I and IV failed to set seeds due to defects in flower development which prevented self-pollination. One mutant, designated cas1, was characterized in more detail and showed, in addition to elevated levels of AOS mRNA, AOS polypeptide, OPDA, and JA, constitutive expression of JA-responsive genes ( VSP2, PDF1.2). The cas1 mutation is recessive and affects a single locus. Using cleaved amplified polymorphic sequences (CAPS) and simple sequence length polymorphisms (SSLP), the mutated gene was mapped to chromosome IV next to the SSLP marker CIW7.

Arabidopsis↗
PubMed1999

Expression of a polygalacturonase associated with tomato seed germination.

Radicle protrusion from tomato (Lycopersicon esculentum Mill.) seeds to complete germination requires weakening of the endosperm tissue opposite the radicle tip. In common with other cell wall disassembly processes in plants, polygalacturonases (PGs) may be involved. Only calcium-dependent exo-PG activity was detected in tomato seed protein extracts. Chromatographic profiles of a partially acid-hydrolyzed fraction of polygalacturonic acid further digested with seed extract were consistent with the presence of only calcium-dependent exo-PG activity. In addition, a transcript encoding a previously unknown PG was detected prior to the completion of germination. The mRNA, produced from a gene (LeXPG1) estimated by Southern analysis to be represented once in the genome, was also present in flowers (anthers) and in lower amounts in roots and stems. LeXPG1 mRNA abundance was low during seed development, increased during imbibition, and was even greater in seeds that had completed germination. Expression of LeXPG1 during germination predominates in the endosperm cap and radicle tip, and in the radicle appears as a distinct band possibly associated with vascular tissue differentiation. We suggest that PG is involved in cell wall loosening of the endosperm necessary for radicle protrusion from tomato seeds and in subsequent embryo and seedling growth.

Gene Expression Regulation, Enzymologic↗
PubMed2006

Germin-like genes are expressed during somatic embryogenesis and early development of conifers.

Germins and germin-like proteins (GLPs) are members of a superfamily of proteins widely distributed in plants. Their localization within the extracellular matrix and in some cases their hydrogen peroxide-producing activity suggests that these proteins are involved in cell wall metabolism during stress responses and developmental processes. Several very highly conserved conifer GLPs have been identified in somatic embryo tissues. In order to gain more knowledge on their potential involvement in the development of this particular tissue, we have characterized a new GLP gene, LmGER1 in hybrid larch. Anti-GLP immunserum and in-gel activity analyses suggested the presence of superoxide dismutase activity in apoplastic proteins from larch somatic embryos. These results could indicate a possible role for LmGER1 in this physiological process. The expression of LmGER1 has been followed during the maturation of somatic embryos and in different organs of young plantlets by homologous transformation with a promoter-gus construct. This promoter was activated in the root cap of young embryos and, later on, in the cotyledons and in the vascular procambium and xylem. Furthermore, the importance of this gene in embryo development was evaluated by transforming embryonal masses with a gene construct encoding a hairpin RNA leading to gene silencing. The potential role of LmGER1 in cross-linking of cell wall components is discussed.

Amino Acid Sequence↗
PubMed2004

Immunolocalization and histochemical evidence for the association of two different Arabidopsis annexins with secretion during early seedling growth and development.

Annexins are a multigene, multifunctional family of calcium-dependent, membrane-binding proteins found in animal and plant cells. In plants, annexins have been localized in the cytoplasm and at the cell periphery of highly secretory cell types, and in the tip region of polarly growing cells. Consequently, one proposed function for annexins in plant cells is participation in the Golgi-mediated secretion of new wall materials. In Arabidopsis, there are eight different annexin cDNAs, which share between 30% and 81% deduced amino acid sequence identity. We have used two monospecific Arabidopsis anti-annexin antibodies, raised against divergent 31-mer peptides from AnnAt1 and AnnAt2 and a previously characterized pea anti-annexin p35 antibody, for Western blot and immunolocalization studies in Arabidopsis. Western blot analyses of various Arabidopsis protein fractions showed that the two Arabidopsis antibodies are able to specifically recognize annexins in both soluble and membrane fractions. Immunofluorescence results with the three annexin antibodies show staining of secretory cells, especially at the cell periphery in developing sieve tubes, outer root cap cells, and in root hairs, consistent with previous results. In developmentally different stages some staining was also seen near the apical meristem, in some leaf cells, and in phloem-associated cells. Autoradiography following 3H-galactose incorporation was used to more clearly correlate active secretion of wall materials with the localization patterns of a specific individual annexin protein in the same cells at the same developmental stage. The results obtained in this study provide further support for the hypothesis that these two Arabidopsis annexins function in Golgi-mediated secretion during early seedling growth and development.

Amino Acid Sequence↗
PubMed2000

Root hair formation: F-actin-dependent tip growth is initiated by local assembly of profilin-supported F-actin meshworks accumulated within expansin-enriched bulges.

Plant root hair formation is initiated when specialized elongating root epidermis cells (trichoblasts) assemble distinct domains at the plasma membrane/cell wall cell periphery complexes facing the root surface. These localities show accumulation of expansin and progressively transform into tip-growing root hair apices. Experimentation showed that trichoblasts made devoid of microtubules (MTs) were unaffected in root hair formation, whereas those depleted of F-actin by the G-actin sequestering agent latrunculin B had their root hair formation blocked after the bulge formation stage. In accordance with this, MTs are naturally depleted from early outgrowing bulges in which dense F-actin meshworks accumulate. These F-actin caps remain associated with tips of emerging and growing root hairs. Constitutive expression of the GFP-mouse talin fusion protein in transgenic Arabidopsis, which visualizes all classes of F-actin in a noninvasive mode, allowed in vivo confirmation of the presence of distinct F-actin meshworks within outgrowing bulges and at tips of young root hairs. Profilin accumulates, at both the protein and the mRNA levels, within F-actin-enriched bulges and at tips of emerging hairs. ER-based calreticulin and HDEL proteins also accumulate within outgrowing bulges and remain enriched at tips of emerging hairs. All this suggests that installation of the actin-based tip growth machinery takes place only after expansin-associated bulge formation and requires assembly of profilin-supported dynamic F-actin meshworks.

Actins↗
PubMed1967

Cytochemical demonstration of a sodium-activated and a potassium-activated adenosine triphosphatase in loblolly pine seedling root tips.

Sodium stimulated ATPase activity in the nuclei of the meristematic cells, while potassium stimulated it in the mycorrhizae between root cap cells. The detection of these 2 mutually exclusive cation-stimulated ATPases, which both require magnesium-ATP in equivalents, which have a similar optimum pH of about 5.5, and which are located in entirely different parts of the root tip, suggests that particular enzyme systems can only be activated by a specific cation and that one cation cannot substitute for the other. Such a feature may explain the capacity of plants to differentiate between ions as closely similar as sodium and potassium. The similarities between the enzyme system described for salt transport in animal tissues and that depicted here cytochemically in pine roots at the most active site of salt uptake in roots indicate this may be a carrier mechanism for salt entry into plant roots. The presence of the potassium-activated enzyme only in the mycorrhizae may relate to the dependence of pine trees on mycorrhizae for growth.

Journal Article↗
PubMed1986

Distribution of calmodulin in pea seedlings: immunocytochemical localization in plumules and root apices.

Immunofluorescence techniques have been used to study the distribution of calmodulin in several tissues in young etiolated pea (Pisum sativum L.) seedlings. A fairly uniform staining was seen in the nucleoplasm and background cytoplasm of most cell types. Cell walls and nucleoli were not stained. In addition, patterned staining reactions were seen in many cells. In cells of the plumule, punctate staining of the cytoplasm was common, and in part this stain appeared to be associated with the plastids. A very distinctive staining of amyloplasts was seen in the columella of the root cap. Staining associated with cytoskeletal elements could be shown in division stages. By metaphase, staining of the spindle region was quite evident. In epidermal cells of the stem and along the underside of the leaf there was an intense staining of the vacuolar contents. Guard cells lacked this vacuolar stain. Vacuolar staining was sometimes seen in cells of the stele, but the most distinctive pattern in the stele was associated with young conducting cells of the xylem. These staining patterns are consistent with the idea that the interactions of plastids and the cytoskeletal may be one of the Ca(2+)-mediated steps in the response of plants to environmental stimuli. Nuclear functions may also be controlled, at least in part, by Ca2+.

Calcium↗
PubMed1989

Effects of vegetation, a clay cap and environmental variables on 222Rn fluence rate from reclaimed U mill tailings.

We measured 222Rn fluence rate and several environmental variables on two plots with U mill tailings buried beneath 30 cm of overburden and 20 cm of topsoil. An additional 30 cm of clay covered the tailings on one plot and each plot was subdivided into bare soil and vegetated subplots. We used linear correlation, two-way ANOVA and stepwise multiple regression to analyze the effects of the plot characteristics and the environmental variables on 222Rn fluence rate. The most important effect on 222Rn fluence rates from these plots was the combination of a clay cap and a vegetated surface. The mean annual fluence rate from the plot having both of these characteristics (520 +/- 370 mBq m-2 s-1) was over three times that of the vegetated plot without a clay cap (170 +/- 130 mBq m-2 s-1) and 18 times that of the bare plot with a clay cap (29 +/- 13 mBq m-2 s-1). The interaction effect may have been due to the growth of roots in the moist clay and active transport of dissolved 222Rn to the surface in water. This speculation is supported by the observation that on vegetated plots with a clay cap, moisture in the clay enhanced the fluence rate.

Air Pollutants↗
PubMed2005

Gibberellin biosynthesis in developing pumpkin seedlings.

A gibberellin (GA) biosynthetic pathway was discovered operating in root tips of 7-d-old pumpkin (Cucurbita maxima) seedlings. Stepwise analysis of GA metabolism in cell-free systems revealed the conversion of GA(12)-aldehyde to bioactive GA(4) and inactive GA(34). Highest levels of endogenous GA(4) and GA(34) were found in hypocotyls and root tips of 3-d-old seedlings. cDNA molecules encoding two GA oxidases, CmGA20ox3 and CmGA3ox3, were isolated from root tips of 7-d-old LAB150978-treated seedlings. Recombinant CmGA20ox3 fusion protein converted GA(12) to GA(9), GA(24) to GA(9), GA(14) to GA(4), and, less efficiently, GA(53) to GA(20), and recombinant CmGA3ox3 protein oxidized GA(9) to GA(4). Transcript profiles were determined for four GA oxidase genes from pumpkin revealing relatively high transcript levels for CmGA7ox in shoot tips and cotyledons, for CmGA20ox3 in shoot tips and hypocotyls, and for CmGA3ox3 in hypocotyls and roots of 3-d-old seedlings. Transcripts of CmGA2ox1 were mainly found in roots of 7-d-old seedlings. In roots of 7-d-old seedlings, transcripts of CmGA7ox, CmGA20ox3, and CmGA3ox3 were localized in the cap and the rhizodermis by in situ hybridization. We conclude that hypocotyls and root tips are important sites of GA biosynthesis in the developing pumpkin seedling.

Cell-Free System↗
PubMed2005

Gravitropic bending and plant hormones.

Gravitropism is a complex multistep process that redirects the growth of roots and various above-ground organs in response to changes in the direction of the gravity vector. The anatomy and morphology of these graviresponding organs indicates a certain spatial separation between the sensing region and the responding one, a situation that strongly suggests the requirement of phytohormones as mediators to coordinate the process. The Cholodny-Went hypothesis suggested auxin as the main mediator of gravitropism. So far, ample evidence has been gathered with regard to auxin asymmetrical detection, polar and lateral transport involving influx and efflux carriers, response signaling pathway, and possible modes of action in differential cell elongation, supports its major role in gravitropism at least in roots. However, it is becoming clear that the participation of other hormones, acting in concert with auxin, is necessary as well. Of particular importance is the role of ethylene in shoot gravitropism, possibly associated with the modulation of auxin transport or sensitivity, and the key role implicated for cytokinin as the putative root cap inhibitor that controls early root gravitropism. Therefore, the major advances in the understanding of transport and signaling of auxin, ethylene, and cytokinin may shed light on the possibly tight and complicated interactions between them in gravitropism. Not much convincing evidence has been accumulated regarding the participation of other phytohormones, such as gibberellins, abscisic acid, brassinosteroids, jasmonates, and salicylic acid, in gravitropism. However, the emerging concept of cooperative hormone action opens new possibilities for a better understanding of the complex interactions of all phytohormones and their possible synergistic effects and involvement in the gravitropic bending process.

Gravitropism↗
PubMed2001

Nonsymbiotic hemoglobins in rice are synthesized during germination and in differentiating cell types.

Nonsymbiotic hemoglobins (ns-Hbs) previously have been found in monocots and dicots; however, very little is known about the tissue and cell type localization as well as the physiological function(s) of these oxygen-binding proteins. We report the immunodetection and immunolocalization of ns-Hbs in rice (Oryza sativa L.) by Western blotting and in situ confocal laser scanning techniques. Ns-Hbs were detected in soluble extracts of different tissues from the developing rice seedling by immunoblotting. Levels of ns-Hbs increased in the germinating seed for the first six days following imbibition and remained relatively constant thereafter. In contrast, ns-Hb levels decreased during leaf maturation. Roots and mesocotyls contained detectable, but low levels of ns-Hbs. Split-seed experiments revealed that ns-Hbs are synthesized de novo during seed germination and are expressed in the absence of any signal originating from the embryo. Immunolocalization of ns-Hbs by confocal microscopy indicated the presence of ns-Hbs primarily in differentiated and differentiating cell types of the developing seedling, such as the aleurone, scutellum, root cap cells, sclerenchyma, and tracheary elements. To our knowledge, this is the first report of the specific cellular localization of these proteins during seedling development.

Blotting, Western↗
PubMed2006

Intracellular calcium regulation among subpopulations of rat dorsal root ganglion neurons.

Primary afferent neurons are functionally heterogeneous. To determine whether this functional heterogeneity reflects, in part, heterogeneity in the regulation of the concentration of intracellular Ca(2+) ([Ca(2+)](i)), the magnitude and decay of evoked Ca(2+) transients were assessed in subpopulations of dorsal root ganglion (DRG) neurons with voltage clamp and fura-2 ratiometric imaging. To determine whether differences in evoked Ca(2+) transients among subpopulations of DRG neurons reflected differences in the contribution of Ca(2+) regulatory mechanisms, pharmacological techniques were employed to assess the contribution of influx, efflux, release and uptake pathways. Subpopulations of DRG neurons were defined by cell body size, binding of the plant lectin IB(4) and responsiveness to the algogenic compound capsaicin (CAP). Ca(2+) transients were evoked with 30 mm K(+) or voltage steps to 0 mV. There were marked differences between subpopulations of neurons with respect to both the magnitude and decay of the Ca(2+) transient, with the largest and most slowly decaying Ca(2+) transients in small-diameter, IB(4)-positive, CAP-responsive neurons. The smallest and most rapidly decaying transients were in large-diameter, IB(4)-negative and CAP-unresponsive DRG neurons. These differences were not due to a differential distribution of voltage-gated Ca(2+) currents. However, these differences did appear to reflect a differential contribution of other influx, efflux, release and uptake mechanisms between subpopulations of neurons. These results suggest that electrical activity in subpopulations of DRG neurons will have a differential influence on Ca(2+)-regulated phenomena such as spike adaptation, transmitter release and gene transcription. Significantly more activity should be required in large-diameter non-nociceptive afferents than in small-diameter nociceptive afferents to have a comparable influence on these processes.

Animals↗
PubMed1992

The role of calcium in the regulation of hormone transport in gravistimulated roots.

Prior research has shown that gravistimulation induces preferential movement of calcium toward the lower side of the tips of maize roots and that roots depleted of calcium show impaired gravitropism. To further investigate the role of calcium in root gravitropism, we examined the effects of calcium on auxin movement in both vertical and gravistimulated roots of maize. Longitudinal movement of auxin was basipetally polar in intact roots but acropetally polar in decapped roots. Treatment of the root tip with calcium increased basipetal auxin movement in both intact and decapped roots. Gravistimulation induced asymmetric auxin movement toward the lower side of the root tip. Both asymmetric auxin movement and gravicurvature were inhibited by treatment of the root tip with auxin transport inhibitors or with EGTA. The results indicate that there is a close correlation between curvature and gravity-induced asymmetric auxin movement across the root cap. Since gravistimulation causes calcium movement toward the lower side of the root tip, our observation that calcium promotes basipetal auxin movement supports the idea that gravity-induced calcium asymmetry is a key step linking gravistimulation to the establishment of auxin asymmetry during root gravitropism.

Biological Transport↗
PubMed1997

Light-regulated root gravitropism: a role for, and characterization of, a calcium/calmodulin-dependent protein kinase homolog.

Roots of many species grow downward (orthogravitropism) only when illuminated. Previous work suggests that this is a calcium-regulated response and that both calmodulin and calcium/calmodulin-dependent kinases participate in transducing gravity and light stimuli. A genomic sequence has been obtained for a calcium/calmodulin-dependent kinase homolog (MCK1) expressed in root caps, the site of perception for both light and gravity. This homolog consists of 7265 base pairs and contains 11 exons and 10 introns. Since MCK1 is expressed constitutively in both light and dark, it is unlikely that the light directly affects MCK1 expression, though the activity of the protein may be affected by light. In cultivars showing light-regulated gravitropism, we hypothesize that MCK1, or a homolog, functions in establishing the auxin asymmetry necessary for orthogravitropism.

Base Sequence↗
PubMed1986

Correlation between extracellular fibrils and attachment of Rhizobium leguminosarum to pea root hair tips.

As part of a project meant to characterize molecules involved in nodulation, a semiquantitative microscopic assay was developed for measuring attachment of Rhizobium leguminosarum cells to pea root hair tips, i.e., the site at which R. leguminosarum initiates nodulation. This form of attachment, designated as cap formation, was dependent on the incubation pH and growth phase, with optimal attachment at pH 7.5 and with bacteria in the early stationary phase of growth. Addition of glucose to the growth medium delayed the initiation of the stationary phase and cap formation, suggesting a correlation between cap formation and carbon limitation. Attachment of R. leguminosarum was not inhibited by pea lectin haptens which makes it unlikely that lectins are involved under the tested conditions. Moreover, heterologous fast-growing rhizobia adhered equally well to pea root hair tips. Since the attachment characteristics of a Sym plasmid-cured derivative were indistinguishable from those of the wild-type strain, the Sym plasmidborne nodulation genes are not necessary for attachment. Sodium chloride and various other salts abolished attachment when present during the attachment assay in final concentrations of 100 mM. R. leguminosarum produced extracellular fibrils. A positive correlation between the percentage of fibrillated cells and the ability of the bacteria to form caps and to adhere to glass and erythrocytes was observed under various conditions, suggesting that these fibrils play a role in attachment of the bacteria to pea root hair tips, to glass, and to erythrocytes.

Agglutination↗