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At least 451 records · Page 25Linked to original sources
PubMed1997

Calcium phosphate formation induced on silica in bamboo.

The effect of in vitro induction of calcium phosphate on bamboo surfaces is reported for the first time. Bamboo is studied for biomaterial application due to its elasticity modulus being closer to human bone than other biomaterials. Following an earlier study of cytotoxicity and precipitation of apatite on ground tissue and vascular bundles of bamboo, the composition and function of the minerals in bamboo, especially silica, are considered in the present work. It is found that in both outer and inner surfaces of bamboo culm, there exists some silica. Bamboo elicits an inert response when soaked directly in calcification solution. After the rind of bamboo is treated with sodium hydroxide solution, the silica underneath can induce precipitation of calcium phosphate in an ambient environment. Furthermore, by subsequent grafting with polyethylene glycol (PEG 1000), calcium phosphate induction of bamboo rind can be improved, depending on the concentration of NaOH solution and treatment time. Heat treatment of bamboo can remove the organic materials around the minerals in bamboo, allowing the calcification behaviour of the silica-containing inorganic phase of bamboo in aqueous solution to be studied.

Journal Article↗
PubMed2002

Knock-out of Arabidopsis metal transporter gene IRT1 results in iron deficiency accompanied by cell differentiation defects.

IRT1 and IRT2 are members of the Arabidopsis ZIP metal transporter family that are specifically induced by iron deprivation in roots and act as heterologous suppressors of yeast mutations inhibiting iron and zinc uptake. Although IRT1 and IRT2 are thought to perform redundant functions as root-specific metal transporters, insertional inactivation of the IRT1 gene alone results in typical symptoms of iron deficiency causing severe leaf chlorosis and lethality in soil. The irt1 mutation is characterized by specific developmental defects, including a drastic reduction of chloroplast thylakoid stacking into grana and lack of palisade parenchyma differentiation in leaves, reduced number of vascular bundles in stems, and irregular patterns of enlarged endodermal and cortex cells in roots. Pulse labeling with 59Fe through the root system shows that the irt1 mutation reduces iron accumulation in the shoots. Short-term labeling with 65Zn reveals no alteration in spatial distribution of zinc, but indicates a lower level of zinc accumulation. In comparison to wild-type, the irt1 mutant responds to iron and zinc deprivation by altered expression of certain zinc and iron transporter genes, which results in the activation of ZIP1 in shoots, reduction of ZIP2 transcript levels in roots, and enhanced expression of IRT2 in roots. These data support the conclusion that IRT1 is an essential metal transporter required for proper development and regulation of iron and zinc homeostasis in Arabidopsis.

Arabidopsis↗
PubMed2002

Tissue-specific regulation of BiP genes: a cis-acting regulatory domain is required for BiP promoter activity in plant meristems.

The binding protein BiP is an endoplasmic reticulum (ER)-resident member of the HSP70 stress-related protein family, which is essential for the constitutive function of the ER. In addition to responding to a variety of environmental stimuli, plant BiP exhibits a tissue-specific regulation. We have isolated two soybean BiP genomic clones, designated gsBiP6 and gsBiP9, and different extensions of their 5' flanking sequences were fused to beta-glucuronidase (GUS) reporter gene and introduced into Nicotiana tabacum by Agrobacterium tumefaciens-mediated transformation. Transgenic plants displayed prominent GUS activity in the vascular bundles of roots and shoots as well as in regions of intense cell division, such as procambial region and apical meristems. Promoter deletion analyses identified two cis-regulatory functional domains that are important for the spatially-regulated activation of BiP expression under normal plant development. While an AT-rich enhancer-like sequence, designated cis-acting regulatory domain 1, CRD1 (-358 to -211, on gsBiP6), activated expression of the BiP minimal promoter in all organs analyzed, BiP promoter activity in meristematic tissues and phloem cells required the presence of a second activating domain, CRD2 (-211 to -80). Apparently, the CRD2 sequence also harbors negative cis-acting elements, because removal of this region caused activation of gsBiP6 promoter in parenchymatic xylem rays. These results suggest that the tissue-specific control of BiP gene expression requires a complex integration of multiple cis-acting regulatory elements on the promoter.

Arabidopsis Proteins↗
PubMed2003

Quantification of photosynthetic gene expression in maize C(3) and C(4) tissues by real-time PCR.

Carbon assimilation in maize follows the C(4) mechanism. This requires the tissue-specific and light-induced expression of a set of different genes involved in CO(2) fixation as well as adaptations in the leaf anatomy including a reduced distance between vascular bundles compared to C(3) plants. However, several maize tissues exist with larger bundle distances and there is significant evidence that CO(2) fixation follows the C(3) mechanism in these tissues. We isolated maize C(3) and C(4) tissues and quantified the accumulation of mRNAs encoding PEPC, ME, the small subunit of Rubisco, and PPDK. For this, primer systems for the specific and sensitive detection by real-time PCR were established. The observed patterns show the expected distribution for foliar leaf tissues. Also in total husk leaves, all transcripts under investigation were detected, albeit at a lower level. When mesophyll cells which are located distant from bundles were isolated from husk leaves, only accumulation of RbcS was observed. Comparing the expression of two genes encoding for isoenzymes of the small subunit of RbcS in the different tissues differential patterns of relative transcript abundance were observed. Transcripts for the DOF1 transcription factor involved in the activation of photosynthetic genes in maize were found in leaf tissues performing both C(4) and C(3) photosynthesis with highest accumulation levels in C(4) mesophyll cells, whereas the homologous DOF2 gene was not expressed in any of the investigated samples. The results provide novel insights into the regulation of C(3) and C(4) carbon fixation pathways in maize.

Journal Article↗
PubMed2003

A novel brassinolide-enhanced gene identified by cDNA microarray is involved in the growth of rice.

Brassinosteroids (BRs) are growth-promoting natural substances required for normal plant growth and development. To understand the molecular mechanism of BR action, a cDNA microarray containing 1265 rice genes was analyzed for expression differences in rice lamina joint treated with brassinolide (BL). A novel BL-enhanced gene, designated OsBLE2, was identified and cloned. The full-length cDNA is 3243 bp long, encoding a predicted polypeptide of 761 amino acid residues and nine possible transmembrane regions. OsBLE2 expression was most responsive to BL in the lamina joint and leaf sheath in rice seedlings. Besides, auxin and gibberellins also increased its expression. OsBLE2 expressed more, as revealed by in situ hybridization, in vascular bundles and root primordia, where the cells are actively undergoing division, elongation, and differentiation. Transgenic rice expressing antisense OsBLE2 exhibits various degrees of repressed growth. BL could not enhance its expression in transgenic rice expressing antisense BRI1, a BR receptor, indicating that BR signaling to the enhanced expression of OsBLE2 is through BRI1 . BL effect in the d1 mutant rice was much weaker than that in its wild-type control, indicating that heterotrimeric G protein may be a component of BRs signaling. These results suggest that OsBLE2 is involved in BL-regulated growth and development processes in rice.

Amino Acid Sequence↗
PubMed2003

Characterization of two phosphate transporters from barley; evidence for diverse function and kinetic properties among members of the Pht1 family.

Putative phosphate transporters have been identified in a barley (Hordeum vulgare L.) genomic library by their homology to known phosphate transporters from dicot species. The genes designated HORvu;Pht1;1 and HORvu;Pht1;6 encode proteins of 521 and 535 amino acids respectively with 12 predicted membrane-spanning domains and other motifs common to the Phtl family of phosphate transporters. HORvu;Pht1;1 is expressed exclusively in roots and is strongly induced by phosphate deprivation. HORvu;Pht1;6 is expressed in the aerial parts of the plant with strongest expression in old leaves and flag leaves. In situ hybridization showed that HORvu;Pht1;6 is expressed in the phloem of vascular bundles in leaves and ears. In order to study the biochemical properties of HORvu;Pht1;1 and HORvu;Pht1;6, the genes were expressed in transgenic rice (Oryza sativa L.) plants under the control of the rice actin promoter and suspension cell cultures were generated. Cells derived from transgenic plants were able to take up phosphate at a much higher rate than control cells, demonstrating that both genes encode functional phosphate transporters. The estimated Km for phosphate for cells expressing HORvu;Pht1;1 was 9.06 +/- 0.82 microM, which is characteristic of a high-affinity transporter. The rate of phosphate uptake decreased with increasing pH, suggesting that HORvu;Pht1;1 operates as a H+/H2PO4(-) symporter. In contrast, the estimated Km for phosphate for cells expressing HORvu;Pht1;6 was 385 +/- 61 microM, which is characteristic of a low-affinity transporter. Taken together, the results suggest that HORvu;Pht1;1 functions in uptake of phosphate at the root surface, while HORvu;Pht1;6 probably functions in remobilization of stored phosphate from leaves.

Cloning, Molecular↗
PubMed2002

Aphid (Sitobion yakini) investigation suggests thin-walled sieve tubes in barley (Hordeum vulgare) to be more functional than thick-walled sieve tubes.

Barley, like most other grasses that have been studied, contains two kinds of sieve tube. The first formed are called thin-walled sieve tubes because of their thin wall compared to the late-formed, and are associated with companion cells. The late-formed are thick-walled sieve tubes, which differentiate next to the metaxylem vessels and lack companion cells. Aphid (Sitobion yakini (Eastop) feeding was studied using light microscopy to determine if they preferentially feed from thin- or thick-walled sieve tubes in the barley leaf. Penetration of the stylets through the leaf epidermis and mesophyll was largely intercellular, becoming partly intercellular and, partly, intracellular inside the vascular bundle. Sixteen of 19 pairs of stylets (84%), and 293 of 317 (92%) stylet tracks terminated at the thin-walled sieve tubes, suggesting that Sitobion yakini feeds preferentially on the thin-walled sieve tubes which seem to be more attractive to the aphid. These thin-walled sieve tubes are thus probably the most functional in terms of phloem loading and transport.

Journal Article↗
PubMed2002

A gene encoding stellacyanin is induced in Capsicum annuum by pathogens, methyl jasmonate, abscisic acid, wounding, drought and salt stress.

A stellacyanin cDNA clone (CASLP1) was isolated from a pepper cDNA library from hypersensitive response (HR) lesions of leaves infected with an avirulent strain of Xanthomonas campestris pv. vesicatoria. The deduced amino acid sequences of CASLP1 are homologous to those of stellacyanins from cucumber, maize, pea and Arabidopsis. The CASLP1 mRNA was not constitutively expressed in all organs of pepper, but strongly induced and accumulated in pepper tissues infected with X. campestris pv. vesicatoria, Colletotrichum coccodes, Phytophthora capsici or C. gloeosporioides. In situ hybridization results revealed that CASLP1 transcripts were strongly localized in the phloem areas of vascular bundles in infected tissues of pepper stems and fruits. CASLP1 mRNA accumulation was found in lower pepper leaves infected by either virulent or avirulent strains of X. campestris pv. vesicatoria and non-pathogenic Pseudomonas fluorescens, but not in uninoculated upper leaves. Induction of this CASLP1 gene occurred in pepper leaves applied with methyl jasmonate (MeJA), but not with ethylene, salicylic acid, dl-beta-amino-n-butyric acid and benzothiadiazole. Accumulation of CASLP1 transcripts was locally or systemically induced in pepper leaves upon mechanical wounding and was activated in a MeJA-dependent manner. The CASLP1 transcript was also strongly induced in leaf and stem tissues after exposure of pepper plants to abscisic acid, salt and drought.

Journal Article↗
PubMed2003

Expression of subtilisin-like serine proteases in Arabidopsis thaliana is cell-specific and responds to jasmonic acid and heavy metals with developmental differences.

The expression of two novel subtilisin-like serine proteases At-SLP2 and At-SLP3 from Arabidopsis thaliana and the recently identified Arabidopsis subtilase ARA12 was analysed with respect to plant development, stress response and cell specificity. In juvenile plants the mRNAs of the subtilisin-like proteases At-SLP2, At-SLP3 and ARA12 were detected with varying transcript levels in leaves but not in roots. In mature Arabidopsis plants transcripts were abundant in leaves, roots and flowers revealing developmental regulation of synthesis of subtilases. By in situ hybridization it was shown that the subtilisin-like proteases were predominantly present in epidermal cells and in the vascular bundles, in the phloem and in developing xylem elements. In flowers additional signals were localized, for example, in pistils, ovules and anthers. In flowers and juvenile developing leaves, expression of the subtilisin-like proteases increased following treatment with jasmonate and cadmium, respectively, suggesting that these proteases are responsive to stress and pathogen stimuli. The physiological relevance of these data in relation to plant morphogenesis and development is discussed.

Journal Article↗
PubMed2002

Prenatal morphogenesis of the human mental foramen.

The mental foramen, at first glance, merely looks like a hole where the mental nerve and the vascular bundle runs through. From a morphogenetic point of view, however, the mental foramen is a suitable model to study the development of a structure where different components are involved. To understand this developmental process, a three-dimensional description at different developmental stages first has to be given. From histological serial sections of human embryos and fetuses, ranging in size from 19 to 117 mm crown rump length (CRL), three-dimensional reconstructions of the foraminar regions were made. Outline and form of the developing foramen, size, course of the mental nerve and the adjacent blood vessels could be shown in detail. In this way, the formation of these structures became concrete in three dimensions. In the future, to understand the mechanisms regulating this complex system, where a nerve and blood vessels became successively surrounded by bone, molecular biological data have to be correlated with morphological findings.

Chin↗
PubMed2002

Characteristics of C4 photosynthesis in stems and petioles of C3 flowering plants.

Most plants are known as C3 plants because the first product of photosynthetic CO2 fixation is a three-carbon compound. C4 plants, which use an alternative pathway in which the first product is a four-carbon compound, have evolved independently many times and are found in at least 18 families. In addition to differences in their biochemistry, photosynthetic organs of C4 plants show alterations in their anatomy and ultrastructure. Little is known about whether the biochemical or anatomical characteristics of C4 photosynthesis evolved first. Here we report that tobacco, a typical C3 plant, shows characteristics of C4 photosynthesis in cells of stems and petioles that surround the xylem and phloem, and that these cells are supplied with carbon for photosynthesis from the vascular system and not from stomata. These photosynthetic cells possess high activities of enzymes characteristic of C4 photosynthesis, which allow the decarboxylation of four-carbon organic acids from the xylem and phloem, thus releasing CO2 for photosynthesis. These biochemical characteristics of C4 photosynthesis in cells around the vascular bundles of stems of C3 plants might explain why C4 photosynthesis has evolved independently many times.

Carbon↗
PubMed1987

Cycles and separations: the histotopography of the urinary concentrating process.

We have analyzed the histotopography of the renal medulla of the rat in terms of cycles and separations. Cycles are pathways by which solute leaving the medulla in an ascending structure (AVR, AHL) is returned to a deeper medullary level. Separations are based on spatial incontiguity and special characteristics of the interstitium and blood supply. The two concepts are complementary: the compartmentalization resulting from separations imparts specificity to the cycles. Structural lateral heterogeneity, consisting in distinct domains organized around vascular bundles, is present in one form or another in all three medullary zones. Such compartmentalization probably leads to heterogeneity in interstitial solute concentrations, a state of affairs inconsistent with the requirements of a "central core". In all such considerations of exchanges between compartments, the lack of a unitary interstitium must be borne in mind. Instead, three general types of interstitium may be distinguished: corresponding roughly to those of the OS and VB, the interbundle region of the IS, and the IM. Among the histotopographic features of the renal medulla not usually included in models of the urinary concentrating mechanism but likely to have functional significance are the association of CD with completely distinct populations of AVR and AHL in the OM and IM; a clear-cut separation throughout the medulla between cycles involving long loops and those involving short loops; the lack of an effective countercurrent association between ascending and descending limbs of short loops in the IS; and a pronounced separation of the venous drainage of the IM from that of the OM.

Animals↗
PubMed1987

The medullary microcirculation.

Like other regional circulations, the medullary circulation supplies oxygen and other primary substrates to the medulla and removes carbon dioxide and other waste metabolites. It also acts as a countercurrent exchanger and simultaneously removes water reabsorbed from the renal tubule to preserve mass balance. Our present understanding of how the medulla serves both these functions at the same time is illustrated in Figure 3. Blood leaves the efferent arteriole with an elevated plasma protein concentration as a consequence of glomerular filtration, and flows down descending vasa recta within a vascular bundle. The increased interstitial osmotic-concentration coupled with a finite capillary reflection coefficient for small solutes causes additional water to be extracted so that at the termination of descending vasa recta, the plasma protein concentration exceeds that in the systemic circulation by approximately twofold. Solute, urea more than sodium chloride, also enters descending vasa recta. As blood flows through the interconnecting capillary plexus and up ascending vasa recta, transcapillary oncotic and osmotic pressure differences combine to cause capillary uptake of fluid. There is also simultaneous loss of urea such that the medullary trapping of urea is very effective. Countercurrent exchange of sodium chloride, however, appears to be less efficient and as a consequence, not only water but sodium chloride is removed from the medulla. Antidiuretic hormone reduces medullary blood flow, both directly by its vasoconstrictor (V1-receptor mediated) effect and indirectly by its antidiuretic (V2-receptor mediated) effects. Prostaglandins are able to enhance medullary blood flow by counteracting vasoconstrictive influences.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Localization of connexin43 in rat kidney.

The localization of connexin43 (Cx 43) in rat kidney was investigated by the indirect immunofluorescence technique with polyclonal antisera raised against Cx 43. Cx 43 is a gap junction protein expressed in a variety of tissues. The typically punctuated gap junction immunofluorescence (GJI) was observed in the renal arterial and arteriolar system. In the renal artery the GJI was concentrated in the media. In the juxtamedullary nephrons, the GJI is particularly abundant in the vascular bundles. There is abundant GJI in the extraglomerular mesangium while in the afferent arteriole GJI appears decreased. Abundant GJI was observed in the inner medullary collecting ducts and pelvic epithelium. The localization of Cx 43 immunofluorescence observed in this study is only in partial agreement with the results of ultrastructural investigations on the distribution of gap junctions in the kidney. An extensive tight junctional system has been demonstrated in the collecting duct system. However, gap junctions have been reported to be absent. Further studies to resolve this discrepancy are required.

Animals↗
PubMed1985

alpha 2-Adrenoceptors in dog kidney: autoradiographic localization and putative functions.

The location of alpha 2-adrenoceptors has been examined in slide-mounted sections of dog kidney by using labelling in vitro with [3H]rauwolscine and autoradiography. [3H]Rauwolscine binding in dog kidney was of high affinity, saturable, and to a single population of sites. Stereoselectivity was observed for (-)-noradrenaline and the relative affinity of a series of competing antagonists indicated binding to alpha 2-adrenoceptors. Autoradiography of [3H]rauwolscine binding revealed localization to three areas: glomeruli, the intimal and adventitial surfaces of arcuate blood vessels and the medullary vascular bundles.

Animals↗
PubMed1993

Myb genes from Hordeum vulgare: tissue-specific expression of chimeric Myb promoter/Gus genes in transgenic tobacco.

The structures of the three Myb-related genes Hv1, Hv5 and Hv33 from barley were determined. They contain a single intron located in the second repeat unit of the Myb-related domain. By analogy to the animal MYB oncoproteins this conserved region of the gene product was shown by filter-binding experiments to exhibit nucleic acid-binding activity. Tobacco plants transgenic for chimeric Myb promoter/Gus genes express the enzyme in a developmentally controlled and tissue-specific manner. During germination and early stages of plant growth, GUS activity is seen in the root cap and adjacent meristematic tissue. At later stages of plant development, GUS activity is predominantly observed in the shoot apical meristem, the roots and the nodal regions of the stem. Within the stem at stages of secondary growth, Myb promoters are active in defined cell types. In the internode low GUS activity is displayed by the innermost cell layer of the cortex, the starch sheath, that surrounds the vascular cylinder of secondary xylem and phloem tissue, as well as in pith rays originating from vascular cambium initials. In the nodal region Myb promoter-controlled Gus expression is mainly confined to the abaxial starch sheath of the leaf trace, to the branch traces and to internal strands of primary phloem. It is suggested that in addition to their activity in meristematically active plant tissues Myb genes are expressed in conductive tissues that are closely associated with vascular bundles.

Amino Acid Sequence↗
PubMed1993

Molecular cloning and expression patterns of three alleles of the Deficiens-homologous gene St-Deficiens from Solanum tuberosum.

Three alleles of the Deficiens-homologous potato gene St-Deficiens (St-Def) present in the genome of a tetraploid Solanum tuberosum variety were isolated and characterized. For one allele (St-Def pD13) the complete molecular structure was determined by sequence analysis and comparison with its cDNA, while for the other two alleles (pD10, pD12) only partial sequences of regulatory and coding regions were obtained. All three alleles showed (except for one amino acid exchange in pD10) identical sequences in the coding region. While sequence variation was observed within the respective promoters starting some 300 nt upstream of the putative transcriptional start site, the 3' terminal promoter sequences were highly conserved. Within this region, a sequence of 81 nt was identified which showed 73% sequence identity to a corresponding sequence in the Deficiens promoter. This region which contains a putative serum response element was previously shown to regulate the expression of the Deficiens gene in Antirrhinum majus. Expression patterns for the three alleles in transgenic potato lines expressing St-Def promoter/Gus constructs were identical. GUS activity was predominantly located in petals and stamens as expected for the activity of a Def-homologous gene, but a significant level of expression was also detected in the ovary wall and in the vascular bundles supporting anthers and petals. The promoters were also active in abscission structures at the junction of flower stem and pedicel, as well as in anther stomium.

Alleles↗
PubMed1993

Structure and regulation of tobacco extensin.

A tobacco cDNA clone (pCNT1) was characterized that encodes an extensin apoprotein almost entirely composed of the repeats Ser-Pro4(-Lys2), Pro-Tyr2-Pro2-His and Thr-Pro-Val-Tyr-Lys. In healthy plants extensin transcripts are abundant in the roots, less prevalent in the stem and rare in the leaves. In leaves extensin mRNA is induced by wounding, ethylene or virus infection. Tobacco was transformed with pCNT1 cDNA coupled in sense or antisense orientation to the CaMV 35S promoter. Analysis of transgenic plants that over- or underexpressed pCNT1 mRNA demonstrated that the encoded protein constituted the majority of hydroxyproline-rich glycoproteins in roots, stems and leaves. The pCNT1-encoded protein contained at least 50% of total hydroxyproline present in these organs and was abundant in the soluble protein fraction of stems and roots as well as in the cell wall of stem vascular bundles. Analysis of transgenic plants expressing sense or antisense extensin gene constructs showed no correlation between total hydroxyproline concentration or soluble HRGP content and plant development.

Amino Acid Sequence↗