60 research outputs found
Double crystal topographic investigations of PbTe grown by the travelling heater method (THM)
No full textTHM-grown PbTe and PbTe: Tl were examined near the (n, - n)-position by means of X-ray double crystal arrangement. The half-width of the rocking curves of Tl doped PbTe is larger than that of undoped PbTe by factor two. Long range and local lattice plane distortions, as well as disturbances induced during preparation, in the from of dislocation slip lines and greatly disoriented areas were observed
Crystal growth of PbTe and (Pb, Sn)Te by the bridgman method and by THM
No full textSynthesis and growth of PbTe and (Pb, Sn)Te single crystals by the Bridgman method and by the Travelling Heater Method (THM) from Te-rich solutions are described. It is to be seen from comparative investigations that seeded THM growth reproducibly provides oriented single-crystalline ingots free of low-angle grain boundaries and with etch pit densities of 8-12 × 104 cm-2. All the materials were p-type with carrier concentrations from 1 to 2 × 1018 cm-3
Similarity between class A and class B G-protein-coupled receptors exemplified through calcitonin gene-related peptide receptor modelling and mutagenesis studies
No full text
Modelling class B G-protein-coupled receptors (GPCRs) using class A GPCR structural templates is difficult due to lack of homology. The plant GPCR, GCR1, has homology to both class A and class B GPCRs. We have used this to generate a class A–class B alignment, and by incorporating maximum lagged correlation of entropy and hydrophobicity into a consensus score, we have been able to align receptor transmembrane regions. We have applied this analysis to generate active and inactive homology models of the class B calcitonin gene-related peptide (CGRP) receptor, and have supported it with site-directed mutagenesis data using 122 CGRP receptor residues and 144 published mutagenesis results on other class B GPCRs. The variation of sequence variability with structure, the analysis of polarity violations, the alignment of group-conserved residues and the mutagenesis results at 27 key positions were particularly informative in distinguishing between the proposed and plausible alternative alignments. Furthermore, we have been able to associate the key molecular features of the class B GPCR signalling machinery with their class A counterparts for the first time. These include the [K/R]KLH motif in intracellular loop 1, [I/L]xxxL and KxxK at the intracellular end of TM5 and TM6, the NPXXY/VAVLY motif on TM7 and small group-conserved residues in TM1, TM2, TM3 and TM7. The equivalent of the class A DRY motif is proposed to involve Arg
2.39
, His
2.43
and Glu
3.46
, which makes a polar lock with T
6.37
. These alignments and models provide useful tools for understanding class B GPCR function.
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<scp>R. A. COX</scp> and <scp>A. A. HADJIOLOV</scp> (Editors). Functional Units in Protein Biosynthesis (FEBS Meetings Vol. 23). 422 S., zahlr. Abb. London-New York 1972: Academic Press. L 7.00.
No full textAmino acid conjugates of jasmonic acid induce jasmonate-responsive gene expression in barley (Hordeum vulgare L.) leaves
No full textAbstractLeaves of barley (Hordeum vulgare L. cv. Salome) treated with jasmonic acid (JA), its methyl ester (JM), or its amino acid conjugates exhibit up-regulation of specific genes and down-regulation of house-keeping genes. This transcriptional regulation exhibits several specificities. (i) The (−)-enantiomers are more active, and conjugates are mainly active if they carry an l-amino acid moiety. (ii) The various JA-responsive genes respond differentially to enantiomeric and chiralic forms. (iii) Both JA and its amino acid conjugates exhibiting no or negligible interconversion induce/repress genes
Plastogenesis and Cytokinin Action. Cytokinin and Light Interactions in Plastid Enzyme Formation of Detached Cucurbita Cotyledons
No full textThe role of octadecanoids and functional mimics in soybean defense responses
No full textOxylipins of the jasmonate pathway and synthetic functional analogs have been analyzed for their elicitor like activities in an assay based on the induced accumulation of glyceollins, the phytoalexins of soybean (Glycine max L.), in cell suspension cultures of this plant. Jasmonic acid (JA) and its methyl ester showed weak phytoalexininducing activity when compared to an early jasmonate biosynthetic precursor, 12-oxophytodienoic acid (OPDA), as well as to the bacterial phytotoxin coronatine and certain 6-substituted indanoylLisoleucine methyl esters, which all were highly active. Interestingly, different octadecanoids and indanoyl conjugates induced the accumulation of transcripts of various defenserelated genes to different degrees, indicating distinct induction competencies. Therefore, these signaling compounds and mimics were further analyzed for their effects on signal transduction elements, such as the transient enhancement of the cytosolic Ca2+ concentration and MAP kinase activation, which are known to be initiated by a soybean pathogenderived {[}beta]glucan elicitor. In contrast to the {[}beta]glucan elicitor, none of the other compounds tested triggered these early signaling elements. Moreover, endogenous levels of OPDA and JA in soybean cells were shown to be unaffected after treatment with {[}beta]glucans. Thus, OPDA and JA, which are functionally mimicked by coronatine and a variety of 6-substituted derivatives of indanoylLisoleucine methyl ester, represent highly efficient signaling compounds of a lipidbased pathway not deployed in the {[}beta]glucan elicitorinitiated signal transduction
Temporal pattern of jasmonate-induced alterations in gene expression of barley leaves
No full textLeaf tissues of barley (Hordeum vulgare L. cv. Salome) respond to methyl jasmonate (JaMe) treatment with a characteristic pattern of gene expression. Jasmonate-induced proteins (JIPs), such as leaf thionins (jip15 gene product) and ribosome-inactivating proteins (jip60 gene product), rapidly accumulate. Their genes are transiently transcriptionally activated, as shown here by the determination of in-vitro transcription rates in run-off assays. In contrast to jip genes, expression of photosynthetic genes encoding the small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (rbcS gene product) and a type III light-harvesting chlorophyll-a/b-binding protein (LHCP; lhbC1 gene product), for example, was rapidly down-regulated in JaMe-treated barley leaves. Despite decreasing rates of rbcS and lhbC1 gene transcription, their transcripts were maintained in JaMe-treated leaf tissues for at least 36 h. Only at a later stage, was there a decline in the levels of rbcS and lhbC1, but not jip, transcripts, suggesting a selective destabilization of photosynthetic mRNAs in JaMe-treated leaf tissue
Cloning and characterisation of heat shock and wound-induced genes in pea (pisum sativum L.)
No full textPlant productivity in many regions of the world is limited primarily as a result of environmental stresses. High temperature and wounding caused by pest and pathogen infection are among the main factors accounting for unpredictable and often severe yield losses worldwide. These stresses, force the plants to alter then gene expression in order to adapt to the changed environment. Attempts were made in the study to isolate and characterise the differentially expressed heat shocked and wound-induced genes to understand the underlying molecular mechanism of heat shock and wounding response. The isolation of the promoters and their use to derive the tissue-specific and high expression of the linked coding sequences will be proved practically more significant. A cDNA clone designated LP 19 was isolated from a differential screening of a cDNA library prepared from lignifying pods of pea line L59. Sequence homology analysis showed that LP19 belongs to the hsp70 gene family. Northern analysis of RNA from pods from pea lines of different genotypes, showing the presence or absence of pod lignification, showed that LP 19 expression was specifically associated with lignification. Several cDNA species derived from transcripts of the LP 19 gene were subsequently isolated, which showed varying positions of poly (A) addition to the 3' untranslated region. Southern blotting of genomic DNA indicated the presence of single gene corresponding to LP 19.The pea hsp70 gene corresponding to LP 19 was isolated from a pea genomic library using LP 19 as a probe. The pea hsp70(LP19) gene predicts an open reading frame encoding a polypeptide of 648 amino acid residues. This sequence is similar to other plant hsp70 proteins. However, unlike most other plant hsp70 genes, the pea hsp70(LP19) gene lacks an intron. 1.8 kb of 5' flanking sequence of hsp70(LP19) gene was also sequenced. The promoter region contains 6 putative consensus heat shock elements (HSEs) as well as 4 A-T rich sites upstream from TATA box. Induction of gene expression of the pea hsp70(LP19) was observed in all organs of the plant after heat shock; the highest level of expression was observed in root, followed by stem and least in leaves. A similar expression pattern for a corresponding gene was observed in chickpea (Cicer arietinum L.). Other stress conditions such as salt stress and wounding failed to induce the expression of hsp70LP(19) gene both in pea and chickpea. The pea hsp70(LP19) promoter region, including 1.8 kb 5'-flanking sequence, and the first 18 amino acids of the coding region, was fused with coding sequence for P- glucuronidase (GUS). Tobacco plants were transformed with this chimaeric gene in order to study tissue specific and developmental expression of the hsp70(LP19) promoter. Histological staining of GUS activity in transgenic tobacco plants showed that protein was present predominantly in the phloem tissue in stem, root and petioles In addition, developmental expression of the hsp70(LP19) gene promoter, without heat shock, was observed in petals, pollen grains, developing seeds as well as in germinating seeds and seedlings at different stages of growth. Quantitative assay of GUS activity by fluorometric assay was used to follow the time course of protein accumulation. Activity was detected within few minutes of the start of heat shock and increased to a maximum after 6 hrs. A high level of GUS activity was observed only in the heat shocked parts of the plant; no endogenous signal that spread systemically from the heat shocked areas to the rest of the plant was observed.Pea and chickpea plants showed a transient increase of polyphenol oxidase (PPO) with maximum level at 48 hrs after wounding. No systemic induction of PPO was observed in unwounded parts in response to both wounding and MeJA treatment. In order to isolate transcripts expressed differentially in response to wounding, a pea subtractive cDNA library was made. 21 subtracted cDNA clones were partially sequenced. Most of the subtracted cDNA clones showed homology with wound or pathogen induced sequences. Northern analysis of the genes corresponding to the subtracted cDNA clones (SC3, SC7, SC12, SC33, SC57 and SC58), indicated differential expression in response to wounding. Full length or nearly full length cDNAs corresponding to 4 subtracted cDNA clones, designated SC10, SC15, SC57 and SC58, were isolated and sequenced. These cDNA clones will be further studied and efforts will be made to isolate their promoters. The tissue-specific expression will be carried out by using promoter-reporter system. These isolated cDNA clones were partially characterised and will be available for further studies to isolate their respective promoters. The tissue specific expression will be carried out by using promoter-reporter system
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