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D Bartels

Publications and source records attributed to D Bartels.

At least 37 records · Page 2Linked to original sources
PubMed1997

Analysis of cDNA clones encoding sucrose-phosphate synthase in relation to sugar interconversions associated with dehydration in the resurrection plant Craterostigma plantagineum Hochst.

Sucrose-phosphate synthase (SPS) is a key enzyme in the regulation of sucrose metabolism, being responsible for the synthesis of sucrose 6-phosphate from fructose 6-phosphate and uridine 5'-diphosphate-glucose. We report on the isolation and characterization of cDNA clones encoding SPS from Craterostigma plantagineum Hochst., a resurrection plant in which the accumulation of sucrose is considered to play an important role in tolerance to severe protoplastic dehydration. Two distinct classes of cDNAs encoding SPS were isolated from C. plantagineum, and are represented by the clones Cpsps1 and Cpsps2. The transcripts corresponding to both cDNAs decrease to very low levels in dehydrating leaves of C. plantagineum. Only the Cpsps1 transcript occurs in the roots, where it is present at a higher level than in leaves and increases upon dehydration of the plant. Higher enzymatic activities have been determined in protein extracts of dehydrated tissues compared with untreated tissues, which correlates with an increase in protein levels. It is suggested that the overall regulation of SPS is strongly influenced by the changing composition of the cytoplasm in C. plantagineum leaves during the dehydration-rehydration cycle.

Amino Acid Sequence↗
PubMed1996

Notification of a family history of breast cancer: issues of privacy and confidentiality.

Little information is available about notifying individuals with a family history of cancer about their risk of cancer. With the recent identification of BRCA1, an important predisposition gene for breast and ovarian cancer, genetic testing is becoming available to high-risk women and their families. Some of these individuals, may not be aware of their family history and may be notified of their family history by medical personnel or biomedical investigators. This disclosure could be detrimental to the individual by changing their perception of risk, sense of privacy, or psychosocial well-being. Members of 544 breast cancer families are currently being contacted as part of an epidemiologic follow-up study at the University of Minnesota. Some family members were unaware of their relative's diagnosis and therefore, notification occurred when they were contacted by study personnel. To determine the impact of risk notification in this context, 376 male and female relatives of 160 breast cancer probands were surveyed to assess their prior knowledge of their family history of cancer, issues relating to study participation, and their concerns regarding the possibility of developing cancer. Following a telephone interview about family history, family members were administered a short, open-ended questionnaire. The majority of individuals (82%) were blood relatives of the proband and 71% were either first- or second-degree relatives. A proportion of blood relatives (24%) were not aware of their family history of breast cancer. More blood relatives (76%) than nonblood relatives (62%, P < 0.01) were aware of their family history. 43 respondents (12%) expressed specific concerns about participating in the large genetic follow-up study and 16 comments concerned privacy issues. Neither the reasons for participation nor an individual's concern about developing cancer was associated with gender of the respondent, relationship to the proband, or awareness of breast cancer in the family. Interestingly, individuals who were notified about their family history through the large follow-up study were no more likely than other family members to be more concerned about developing cancer. Understanding the privacy and psychosocial issues of family members who are informed about a family history of breast cancer may aid in developing appropriate guidelines for notification. Risk notification in this setting does not appear to have a significant impact on these family members.

Breast Neoplasms↗
PubMed1996

Differential regulation of two ABA-inducible genes from Craterostigma plantagineum in transgenic Arabidopsis plants.

In Craterostigma plantagineum the CDeT-6-19 and CDeT-27-45 genes are expressed following desiccation and/or ABA treatment. Their promoters were fused to the beta-glucuronidase reporter gene (GUS) and tested in transgenic Arabidopsis. GUS activity was measured in mature Arabidopsis seeds, and the responsiveness to ABA in vegetative tissue was found to be limited to the early developmental stages. When transgenic plants were crossed with plants over-expressing the ABI3 gene, it was observed that ABI3 is not required for ABA induction of the CDeT-6-19 promoter, whereas it is crucial for expression of the CDeT-27-45 promoter.

Abscisic Acid↗
PubMed1996

A family of novel myb-related genes from the resurrection plant Craterostigma plantagineum are specifically expressed in callus and roots in response to ABA or desiccation.

A cDNA and two genomic clones comprising highly similar genes that encode a protein with a Myb-related DNA-binding domain were isolated from the resurrection plant Craterostigma plantagineum. The structure of cpm5 and cpm10 (Craterostigma plantagineum myb) genes consists of three putative exons encoding a protein of 36.6 kDa. The cDNA of cpm7 encodes a closely related protein of 36.8 kDa. The canonical Myb domain present in transcriptional activators of yeast, animals and plants was localized in the amino terminus of deduced Cpm5, Cpm7 and Cpm10 proteins and corresponds to the two Myb repeats found in plants. The Myb domain of Cpm deduced proteins and a short stretch of amino acids adjacent to this region are closely related to a myb gene from Arabidopsis thaliana which is expressed in response to osmotic stress and ABA. The rest of the deduced protein has no similarity to other reported sequences. The myb-related genes in the Craterostigma genome comprise a small gene family of 6-8 members as estimated by hybridization with a bona fide Myb domain probe. Northern blot experiments showed specific expression of cpm10 in undifferentiated callus tissue up-modulated by ABA and expression of cpm7 mRNA in roots up-regulated by dehydration.

Abscisic Acid↗
PubMed1996

The recombinant dehydrin-like desiccation stress protein from the resurrection plant Craterostigma plantagineum displays no defined three-dimensional structure in its native state.

Dehydration stress in the drought-tolerant resurrection plant Craterostigma plantagineum is accompanied by the accumulation of a large number of desiccation stress proteins (Dsp). One abundant class of these is represented by the dehydrin-related Dsp16 protein which contains 15 amino acid conserved lysine-rich repeats and a stretch of eight serine residues providing extremely hydrophilic characteristics. Recombinant Dsp16 from Craterostigma plantagineum has been cloned and expressed in Escherichia coli. The protein was purified and characterized regarding its physicochemical properties. Irrespective of successful crystallization experiments, dilute aqueous buffer solutions do not display a well-defined three-dimensional structure in terms of the canonical secondary structural elements. 1H-NMR (nuclear magnetic resonance) spectra in aqueous solution are characterized by a small chemical shift dispersion typical for an unfolded protein; however, the observed line-widths are not typical for a highly mobile random coil structure. Instead they indicate an equilibrium between conformational states with preferentially extended substructures. As a consequence of its loose structure, Dsp16 is extremely sensitive towards proteolysis unless its structure is stabilized by structure-making additives such as trifluoroethanol. Denaturants such as guanidinium chloride do not induce cooperative structural transitions. pH-dependent fluorescence changes reflect protonation/deprotonation rather than conformational changes. Sedimentation/diffusion experiments confirm the predicted molecular mass of 16 kDa. Due to the high serine/threonine content and its loose structure, Dsp16 is accessible to phosphorylation, supporting the idea that in situ the structurally relatively undefined protein may be involved in both water binding and phosphorylation.

Cloning, Molecular↗
PubMed1995

The transketolase gene family of the resurrection plant Craterostigma plantagineum: differential expression during the rehydration phase.

Transketolases, key enzymes of the reductive and oxidative pentose phosphate pathways, are responsible for the synthesis of sugar phosphate intermediates. Here we report the first molecular analysis of transketolase genes from plants. Three distinct classes of transketolase-encoding cDNA clones were isolated from the desiccation-tolerant resurrection plant Craterostigma plantagineum. One class represented by the transcript tkt3 is constitutively expressed in leaves and roots under all physiological conditions tested. By biochemical analysis and protein sequencing of purified transketolase, it was shown that tkt3 is expressed in three enzymatically active isoforms. An intriguing discovery was that accumulation of the two other transketolase transcripts, tkt7 and tkt10, is preferentially associated with the rehydration process of the desiccated plant; whereas tkt10 is only expressed in leaves, tkt7 was detected in leaves and roots. This observation suggests a possible role for these transketolases in the conversion of sugars, which are a major phenomenon in the rehydration process. Despite an abundant level of tkt7 and tkt10 transcripts in rehydrating leaves, proteins could not be isolated. This is due in part to a translational control mechanism acting on the loading of mRNAs to polysomes.

Adaptation, Biological↗
PubMed1995

Constitutive expression of small heat shock proteins in vegetative tissues of the resurrection plant Craterostigma plantagineum.

Using antibodies raised against two sunflower small heat shock proteins (sHSPs), we have detected immunologically related proteins in unstressed vegetative tissues from the resurrection plant Craterostigma plantagineum. In whole plants, further accumulation of these polypeptides was induced by heat-shock or water-stress. In desiccation-intolerant Craterostigma callus tissue, we failed to detect sHSP-related polypeptides, but their expression, and the concurrent acquisition of desiccation tolerance was induced by exogenous abscisic acid (ABA) treatment. In untressed plants, the cross-reacting polypeptides were abundant in the roots and lower part of the shoots, where they showed homogeneous tissue-distributions. This constitutive expression is novel for vegetative tissues of higher plants, and resembles the expression patterns of sHSPs in desiccation-tolerant zygotic embryos and germinating seeds.

Abscisic Acid↗
PubMed1995

ABA-regulated promoter activity in stomatal guard cells.

CDeT6-19 is an ABA-regulated gene which has been isolated from Craterostigma plantagineum. The CDeT6-19 gene promoter has been fused to the beta-glucuronidase reporter gene (GUS) and used to stably transform Arabidopsis thaliana and Nicotiana tabacum. This construct has been shown to be expressed in stomatal guard cells and often in the adjacent epidermal cells of both species in response to both exogenous ABA and drought stress. These results indicate that the stomatal guard cell is competent to relay an ABA signal to the nucleus. In contrast GUS expression directed by the promoter from a predominantly seed-specific, ABA-regulated gene, Em, or the promoter from the ABA-regulated CDeT27-45 gene is not detectable in the epidermal or guard cells of tobacco or Arabidopsis in response to ABA. The fact that not all ABA-regulated gene promoters are active in stomatal guard cells suggests that effective transduction of the signal is dependent upon particular regions within the gene promoter or that guard cells lack all or part of the specific transduction apparatus required to couple the ABA signal to these promoters. This suggests that there are multiple ABA stimulus response coupling pathways. The identification of a regulatory sequence from an ABA-induced gene which is expressed in stomatal guard cells creates the possibility of examining the role of Ca2+ and other second messengers in ABA-induced gene expression.

Abscisic Acid↗
PubMed1995

An aldose reductase homologous gene from barley: regulation and function.

The expression of a barley gene homologous to aldose reductase and aldehyde reductase is restricted to the embryo and temporally correlated with its acquisition of desiccation tolerance. In the work presented, two aspects of this barley gene were investigated: its transcriptional regulation and the initial characterization of the enzymatic function. The transcriptional regulation of the gene was studied in transgenic tobacco by analysing the expression of chimeric genes containing 5' sequences of the barley gene transcriptionally fused to the GUS reporter gene. This functional analysis of the promoter revealed that a 1364 bp 5' fragment confers the appropriate pattern of expression to the reporter gene in tobacco and that a short promoter fragment (-114 to +75) containing the sequence TACGTGGC, homologous to plant G-box elements, is sufficient for developmental expression during embryogenesis. To investigate the enzymatic properties of the gene product the wild-type protein and a mutant carrying a lysine 259 to methionine substitution were overexpressed in a procaryotic system and purified to homogeneity. The wild-type protein exhibits aldose reductase activity in the reduction of DL-glyceraldehyde and D-erythrose specifically using NADPH as co-factor whereas the mutant shows markedly reduced activity. However, the barley protein possesses some properties different to those of animal aldose and aldehyde reductases and its biological target still needs to be identified.

Aldehyde Reductase↗
PubMed1994

Structure and regulation of an ABA- and desiccation-responsive gene from the resurrection plant Craterostigma plantagineum.

A gene from the resurrection plant Craterostigma plantagineum (CDeT6-19) encoding a protein with sequence similarity to a major group of late embryogenesis-abundant proteins (termed rab17, dehydrin or Lea D11) is regulated by abscisic acid (ABA) and desiccation. The corresponding transcript and protein is highly inducible in vegetative and callus tissue. To analyse the mechanism of CDeT6-19 regulation its promoter was fused to the beta-glucuronidase reporter gene (GUS) and introduced by PEG (polyethylene glycol) into protoplasts of Craterostigma or tobacco. With 889 bp of promoter sequence the GUS expression was significantly stimulated by ABA treatment in transient expression assays. ABA responsiveness was still observed with shorter promoter fragments, although they gave rise to lower GUS activities. Sequence comparisons with promoters from related genes of other species identified the conservation of potential ABA-responsive elements. In tobacco and Craterostigma plants stably transformed with CDeT6-19 promoter constructs a basal GUS activity is observed. However, GUS expression is enhanced by ABA or drying treatment of leaf tissues. In tobacco high promoter activity was observed in mature seeds (embryos) and in pollen.

Abscisic Acid↗
PubMed1994

Dehydration and ABA increase mRNA levels and enzyme activity of cytosolic GAPDH in the resurrection plant Craterostigma plantagineum.

We report the identification of a full-length cDNA clone encoding cytosolic glyceraldehyde-3-phosphate dehydrogenase (GAPDH, EC 1.2.1.12) in the desiccation-tolerant plant Craterostigma plantagineum. The DNA sequence of the cDNA clone is homologous to cytosolic GAPDH cDNAs from other higher plants. The GAPDH transcript increases rapidly in abundance during dehydration or abscisic acid (ABA) treatment. The increase in mRNA levels is directly correlated with higher protein and enzyme levels. These results imply that enhanced rates of glycolysis are one of the immediate cellular responses to water deficit. This may be a mechanism by which the plant cell prepares for a demand of ATP and NADH2 during recovery.

Abscisic Acid↗
PubMed1994

A novel embryo-specific barley cDNA clone encodes a protein with homologies to bacterial glucose and ribitol dehydrogenase.

In order to analyze the genetic programme expressed during the early stages of embryogenesis a cDNA clone bank was constructed from desiccation-tolerant excised barley embryos 18 d after pollination (D. Bartels et al., 1988, Planta 175, 485-492). One of the selected cDNA clones pG31 encodes a transcript of 1300 nucleotides and a protein of 31 kDa, both are specifically expressed in developing embryos and are not detected in other tissues. The expression of the pG31 mRNA is not modulated by the plant hormone cis-abscisic acid but it ceases to be expressed in germinating embryos. The protein sequence deduced from the pG31 transcript shows substantial sequence homologies to bacterial glucose dehydrogenase and ribitol dehydrogenase. Biochemical analysis indicates that glucose dehydrogenase activity is present in protein extracts from embryos 18 d after pollination. This glucose dehydrogenase activity is inhibited by antiserum raised against the recombinant pG31 protein. These findings provide evidence for the discovery of a novel pathway in carbohydrate metabolism acting specifically during embryogenesis.

Amino Acid Sequence↗
PubMed1994

Abscisic acid promotes novel DNA-binding activity to a desiccation-related promoter of Craterostigma plantagineum.

Abscisic acid-treated callus of the resurrection plant Craterostigma plantagineum tolerates extreme desiccation. Nuclear proteins from tolerant callus bind specific sequence elements in the promoter region of the ABA and desiccation-inducible CDeT27-45 gene. One specific region of the promoter, which is protected from DNAase I treatment by DNA-binding activities, is different from previously reported ABA response elements. Four complexes of nuclear proteins and this DNA region are detected by electrophoretic mobility shift assay: two of these complexes (I and II) are readily detectable in untreated samples and are increased by ABA treatment while two other complexes (III and IV) accumulate only following ABA treatment and are prevented from accumulating by protein synthesis inhibitors. When a fragment containing the novel binding site is deleted from the wild-type promoter the ABA responsiveness of the promoter is removed; however, gain of function experiments using synthetic promoters in a protoplast transient assay suggest that besides the binding site other promoter elements are required. A second region of the promoter, containing the sequence element ACGT which is found in abscisic acid response elements, is also bound by nuclear proteins. The level of this second binding activity is similar in both untreated and ABA- treated cells and promoter/reporter gene constructs which contain only the four ACGT elements of the CDeT27-45 promoter are not ABA responsive in a C. plantagineum transient assay system.

Abscisic Acid↗
PubMed1993

Analysis of a desiccation and ABA-responsive promoter isolated from the resurrection plant Craterostigma plantagineum.

The resurrection plant Craterostigma plantagineum can recover from severe desiccation within 24 h of contact with water, and it is used as a model system to analyse desiccation tolerance in higher plants. During drying or ABA treatment a specific set of transcripts accumulates rapidly in leaves and other tissues. In order to study transcriptional mechanisms of stress-induced gene expression one gene (CDeT27-45) was selected for promoter analysis. Chimeric gene fusions were constructed of the CDeT27-45 promoter and beta-glucuronidase or luciferase. These constructs were tested in a homologous transient expression system which allowed the identification of promoter elements conferring ABA inducibility. By introducing the chimeric gene fusions into tobacco via Agrobacterium-mediated transformation we found that the promoter activity is under strict tissue-specific and developmental control. In tobacco the promoter was only active in developing embryos and in mature pollen grains-two tissues which are naturally desiccation tolerant in tobacco. The specific temporal expression pattern was attributed to particular 5' upstream sequences. The promoter analysis presented here should allow the separation of important regulatory components as a first step in dissecting events in the signal transduction chain.

Abscisic Acid↗
PubMed1992

A desiccation-related Elip-like gene from the resurrection plant Craterostigma plantagineum is regulated by light and ABA.

The resurrection plant Craterostigma plantagineum tolerates an extreme loss of cellular water. Therefore this plant is being studied as model system to analyse desiccation tolerance at the molecular level. Upon dehydration, new transcripts are abundantly expressed in different tissues of the plant. One such desiccation-related nuclear gene (dsp-22 for desiccation stress protein) encodes a mature 21 kDa protein which accumulates in the chloroplasts. Sequence analysis indicates that dsp-22 is closely related to early light inducible genes (Elip) of higher plants and to a carotene biosynthesis related gene (cbr) isolated from the green alga Dunaliella bardawil. In contrast to other desiccation-related genes, light is an essential positive factor regulating the expression of dsp-22: ABA-mediated gene activation leads to the accumulation of the transcript only in the presence of light. During the desiccation process, light acts at the transcriptional and post-transcriptional levels. The implications of these different controls and the possible role of the dsp-22 protein in the desiccation/rehydration process are discussed.

Abscisic Acid↗
PubMed1992

Expression of desiccation-related proteins from the resurrection plant Craterostigma plantagineum in transgenic tobacco.

Three cDNAs encoding desiccation-induced proteins from the resurrection plant Craterostigma plantagineum were each ligated to a triplicated CaMV 35S promoter and a nopaline synthase 3'-flanking region in an Agrobacterium vector and introduced into tobacco. Transgenic plants expressed the encoded Craterostigma proteins at high levels. This did not lead to changes in the phenotype, in the growth habit or in basic photosynthetic parameters. In tobacco, one protein was targeted to the chloroplast stroma which is its normal location in Craterostigma. These desiccation-related proteins are not sufficient per se to increase drought tolerance as measured by ion-leakage tests.

Biological Transport↗
PubMed1991

An ABA and GA modulated gene expressed in the barley embryo encodes an aldose reductase related protein.

In most higher plants a period of desiccation is the terminal event in embryogenesis. Excised barley embryos acquire desiccation tolerance at a precise developmental stage and cDNA clones have been isolated which are temporally linked with desiccation tolerance. One such clone (pG22-69) with a putative gene product of 34 kd displays high structural homology to mammalian genes encoding an NADPH dependent aldose reductase involved in the synthesis of sorbitol. This first aldose reductase gene of plants is expressed constitutively during embryo maturation and is modulated by the plant hormones abscisic acid (ABA) and gibberellic acid (GA). Immunohistochemistry showed that the protein is preferentially expressed in tissues formed at early stages in embryogenesis. Measurements of enzymatic activity indicate that pG22-69 encodes an active aldose reductase. The finding of this reductase activity and the cloning of the corresponding gene supports the existence of a metabolic pathway in plants playing a role in the synthesis of osmolytes like sorbitol. The significance of this work is that genes of related structure and functions are being used in diverse organisms to fulfil stress related biological requirements.

Abscisic Acid↗