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D G Lynn

Publications and source records attributed to D G Lynn.

35 records · Page 2Linked to original sources
PubMed1994

Cell-autonomous cytokinin-independent growth of tobacco cells transformed by Agrobacterium tumefaciens strains lacking the cytokinin biosynthesis gene.

Mutations at the cytokinin biosynthesis locus (tmr) of Agrobacterium tumefaciens usually result in strains that induce tumors exhibiting the rooty phenotype associated with high auxin-to-cytokinin ratios. However, tobacco (Nicotiana tabacum cv Havana 425) leaf disc explants responded to tmr- mutant strain A356 by producing rapidly growing, unorganized tumors, indicating that these lines can grow in a cytokinin-independent fashion despite the absence of a functional tmr gene. Several methods have been used to characterize the physiological and cellular basis of this phenotype. The results indicate that tmr- tumors have a physiologically distinct mechanism for cytokinin-independent growth in comparison to tumors induced by wild-type bacteria. The cytokinin-independent phenotype of the tmr- transformants appears to be cell autonomous in nature: only the transformed cells and their progeny were capable of cytokinin-independent growth. Specifically, the tmr- tumors did not accumulate cytokinin, and clonal analysis indicated the tmr- transformed cells were not capable of stimulating the growth of neighboring nontransformed cells. Finally, the cytokinin-independent phenotype of the tmr- transformants was shown to be cold sensitive, whereas the wild-type tumors exhibited a cold-resistant cytokinin-independent phenotype. Potential mechanisms for this novel form of cytokinin-independent growth, including the role of the dehydrodiconiferyl alcohol glucosides found in both tumor types, are discussed.

Agrobacterium tumefaciens↗
PubMed1993

Strategies in pathogenesis: mechanistic specificity in the detection of generic signals.

The virulence genes of the plant pathogen Agrobacterium tumefaciens are induced by more than 40 low-molecular-weight phenolic compounds. The prevailing opinion is that (i) wound-derived phenols produced on breach of the integrity of the cell wall act as the initiating signal in a series of events which results in host cell transformation, and (ii) a classical membrane receptor, putatively VirA, is responsible for the recognition of all such phenolic inducers. Here, we argue that the discovery of the subset of inducers that are relatives of the dehydrodiconiferyl alcohol glucoside (DCG) growth factors redirects our attention to work on the plant wound as a site of cell division, and suggests that we further explore the implications of early work on the relationship between transformation efficiency and the status of the cell cycle of the host. In addition, we argue that the significant structural diversity allowed in the para position of the phenol ring of inducers suggests that a receptor-ligand interaction based solely on structural recognition is insufficient, but that recognition followed by a specific proton transfer event may be sufficient to explain vir induction activity. Hence, the specificity of the response of A. tumefaciens may be a consequence of the features required for a chemical reaction to occur on the receptor surface. Finally, we review affinity labelling studies which exploit this phenol detection mechanism and which provide evidence that the phenol receptor may be other than VirA, the sensory kinase of the two component regulatory system implicated in Agrobacterium virulence.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetophenones↗
PubMed1992

Mechanism of activation of Agrobacterium virulence genes: identification of phenol-binding proteins.

Agrobacterium tumefaciens initiates the expression of pathogenic genes (vir genes) in response to host-derived phenolic signals through a two-component regulatory system consisting of VirA and VirG. alpha-Bromoacetosyringone (ASBr) was developed as an inhibitor of this induction process and found to be a specific and irreversible inhibitor of vir gene induction in this pathogen. Formal replacement of one of the methoxy groups of ASBr with iodine gave an equally effective inhibitor that could carry an 125I label. We report here that the resulting radiolabeled inhibitor does not react with the sensory component of this system, VirA, either in vivo or in vitro. Rather, two small proteins, p10 and p21, bind labeled inhibitor in vivo in a time period that is consistent with the exposure time required for the inhibition of vir gene expression. Labeling to these proteins was protected by preexposure to ASBr but not by alpha-bromo-3,5-dimethoxyacetophenone, a compound of comparable chemical reactivity but previously shown not to inhibit vir gene expression. Our findings suggest that proteins that are not tumor-inducing plasmid-encoded mediate vir gene activation in a step prior to the VirA/VirG two-component regulatory system.

Affinity Labels↗
PubMed1992

Metabolic thermotolerance: magnetic resonance detected protection of glutamate synthase.

Metabolism in maize meristem cultures exposed to different heat treatments has been analyzed by 13C-NMR spectroscopy of tissue extracts. The effects of a 40 degrees C permissive stress were compared with a 45 degrees C lethal stress, and the metabolism of glutamate and glutamine were markedly altered by both temperatures. Changes in the incorporation of labeled precursors, alterations due to the in vivo application of enzyme inhibitors, and differences in the activity of enzymes in cell free extracts have confirmed that glutamate synthase (GluS) is partially inactivated by the lethal thermal exposure. This enzyme is quantitatively protected by the induction of thermotolerance. The time dependence for the protection correlates with the appearance of a set of late-arising heat shock proteins (hsps). The function of these late-arising proteins is not yet known, but only one of them, a 67-kDa protein, is spatially correlated with GluS protection. Therefore, the quantitative protection of a key metabolic enzyme has been correlated with the in vivo function of a specific hsp.

Autoradiography↗
PubMed1992

Biosynthesis of dehydrodiconiferyl alcohol glucosides: implications for the control of tobacco cell growth.

The dehydrodiconiferyl alcohol glucosides A and B are factors isolated from transformed Vinca rosea tumor cells that can replace the cytokinin requirement for growth of tobacco (Nicotiana tabacum) pith and callus cells in culture. These factors, present in tobacco pith cells, have their concentrations elevated approximately 2 orders of magnitude after cytokinin exposure. Biosynthesis experiments showed that these compounds are not cell wall fragments, as previously suggested, but are produced directly from coniferyl alcohol. Their synthesis is probably associated with the existing pathway for cell wall biosynthesis in both Vinca tumors and tobacco pith explants. The pathway requires only two steps, the dimerization of coniferyl alcohol by a soluble intracellular peroxidase and subsequent glycosylation. Biosynthetic experiments suggested that dehydrodiconiferyl alcohol glucoside breakdown was very slow and control of its concentration was exerted through restricted availability of coniferyl alcohol.

Journal Article↗
PubMed1991

Mechanism of phenolic activation of Agrobacterium virulence genes: development of a specific inhibitor of bacterial sensor/response systems.

The aglycone of the dihydrodiconiferyl alcohol glycosides, a series of phenolic growth factors able to substitute for some of the hormone requirements of tobacco cell division, are also potent inducers of virulence gene expression in Agrobacterium tumefaciens. However, these factors do not conform to the previously established structural requirements necessary for vir expression. Systematic evaluation of the structural requirements of these inducers has led to a model detailing the role of the phenolics in induction. With this model, a specific inhibitor of vir induction has been developed. This inhibitor does not affect the induction of other genes on the Ti plasmid but irreversibly blocks vir expression. The inhibitor has been used to show that the inducing phenolics must be constantly present to maintain expression of the vir regulon.

Gene Expression Regulation, Viral↗
PubMed1991

Activity and accumulation of cell division-promoting phenolics in tobacco tissue cultures.

Dehydrodiconiferyl alcohol glucosides (DCGs) are derivatives of the phenylpropanoid pathway that have been isolated from Catharansus roseus L. (Vinca rosea) crown gall tumors. Fractions containing purified DCGs have been shown previously to promote the growth of cytokinin-requiring tissues of tobacco in the absence of exogenous cytokinins. In this study, we utilized synthetic DCG isomers to confirm the cell division-promoting activity of DCG isomers A and B and show that they neither promote shoot meristem initiation on Nicotiana tabacum L., cv Havana 425, leaf explants nor induce betacyanin synthesis in amaranth seedlings. Analysis of cultured tobacco pith tissue demonstrated that DCG accumulation was stimulated by cytokinin treatment and correlated with cytokinin-induced cell division. Thus, the accumulation of metabolites that could replace cytokinin in cell division bioassays is stimulated by cytokinins. These data support the model that DCGs are a component of a cytokinin-mediated regulatory circuit controlling cell division.

Journal Article↗
PubMed1990

Control of Germination in Striga asiatica: Chemistry of Spatial Definition.

Striga asiatica (Scrophulariaceae), a member of a heterogeneous group known as the parasitic plants, is totally dependent on host root attachment for survival. In agar, Striga seeds germinated in high percentages within 5 millimeters of a sorghum (Sorghum bicolor (L.) Moench) host root surface, and no germination was observed at distances greater than 1 centimeter. This spatially restricted germination may be explained by the chemistry of a single compound, 2-hydroxy-5-methoxy-3-[8'Z, 11'Z)-8', 11', 14' -pentadecatriene]-p-hydroquinone, structure 1, which is exuded by sorghum roots. The presence of the compound was chemically imaged with pigments such as methylene blue. The use of methylene blue suggested that structure 1 was exuded along the entire surface of the root for long periods. This exudation and the inherent instability of structure 1 together establish an apparent steady state concentration gradient of the germination stimulant around the sorghum root. The Striga seed must be exposed to micromolar concentrations of 1 for >/=5 hours before high germination percentages were observed. Such a requirement for a long term exposure to a steady state concentration of an inherently labile, exuded compound would provide an extra degree of resolution to signal detection and host commitment in Striga parasitism.

Journal Article↗
PubMed1990

Vegetative/Parasitic transition: control and plasticity in striga development.

Striga asiatica (Scrophulariaceae), an obligate parasite of grasses including many of the world's major grain crops, switches from vegetative to parasitic development by the differentiation of the root meristem into the host attachment organ, the haustorium. This change was induced in culture by the exposure to a single, low molecular weight signal molecule, 2,6-dimethoxy-p-benzo-quinone. A concentration of 10(-6) molar quinone and an exposure time of >/=6 hours were required before the developmental process could be completed. With shorter exposure times, haustorial development was prematurely aborted and meristematic elongation was reestablished. The new meristem was capable of developing a second haustorium if reexposed to the signal molecule. These results are discussed in terms of the transition to the parasitic phase and the general control of plant cellular development.

Journal Article↗
PubMed1990

Involvement of gamma-glutamyl peptides in osmoadaptation of Escherichia coli.

Accumulation of K+ ions and glutamate plays a primary role in maintaining osmotic balance in Escherichia coli, as illustrated by the high concentrations of these ions present in cells growing in medium of high osmolality. We found that two gamma-glutamyl peptides and glutamine also accumulated during growth at high osmolarity. In a mutant unable to make trehalose growing in 1.3 osM medium, glutathione, gamma-glutamylglutamine, and glutamine accumulated to levels of 73, 33, and 140 mumol/g of protein, respectively. In such cells, K+ was present at 1,450 mumol/g of protein, indicating that glutathione and gamma-glutamylglutamine accounted for less than 10% of the low-molecular-weight anions accumulated with K+. However, glutathione is needed for wild-type osmotolerance in this species. A mutant deficient in glutathione because of an insertion in the gshA gene was unable to grow above 1.4 osM, grew more slowly at intermediate osmolarities, and took longer to adapt to growth following osmotic upshock. The involvement of glutathione in osmoregulation was independent of the effect of glutathione on K+ retention.

Chromatography, High Pressure Liquid↗
PubMed1987

The structural characterization of endogenous factors from Vinca rosea crown gall tumors that promote cell division of tobacco cells.

The ability of two compounds, a cytokinin and an auxin, to stimulate tobacco cell growth and differentiation has been known for greater than 30 years, but the molecular mechanism of this activation is still unknown. Previous reports of factors endogenous in crown gall tumors of Vinca rosea that could replace the cytokinin requirement in tobacco cell culture has motivated an investigation of these tissues. The optimization of a reverse-phase isolation scheme has led to the purification of sufficient material to allow for the identification of six different related compounds. The structures of two of these compounds have been assigned as a set of epimeric dehydrodiconiferyl alcohol beta-D-glycosides. The structure of these compounds suggests that they would most likely be derived from the plant cell wall.

Cell Division↗
PubMed1987

Cell division promoting activity of naturally occurring dehydrodiconiferyl glucosides: do cell wall components control cell division?

Naturally occurring isomers of the dehydrodiconiferyl glucosides have been isolated from Vinca rosea crown gall tumors and have been tested for cell division promoting activities in the tobacco pith and leaf assay systems. The enantiomeric isomers A and B are active, although they are required at concentrations up to 2 orders of magnitude higher than zeatin riboside to promote comparable growth. We estimate that the active dehydrodiconiferyl glucosides are present in rapidly growing tissues (tumor tissue, habituated tissue, cultured nontransformed tissue) in micromolar concentrations. In quiescent tobacco pith tissue, the levels of these compounds are reduced by a factor of 100. These results suggest that cytokinin may exert control of cell division through the accumulation of molecules (the dehydrodiconiferyl glucosides) that are apparent cell wall components.

Cell Division↗
PubMed1985

Modulation of oocyte maturation by cyclic adenosine 3', 5'-pyrophosphate.

The germinal vesicle (GV) of follicle-enclosed oocytes in mammals remains arrested at the dictyate state of meiosis. Upon releasing the oocytes from the follicles, the meiotic process resumes, leading to dissolution of the GV (GVBD), suggesting that factors in the follicular fluid sustain the meiotic arrest of oocytes. In the present study the spontaneous resumption of meiosis was blocked by the addition of cyclic adenosine 3', 5'-pyrophosphate (cAPP) plus dibutyryl cyclic adenosine 3',5'-monophosphate (dbcAMP), at final concentrations of 25 and 50 microM, respectively. These compounds were ineffective when added separately at these concentrations. None of the other related compounds tested with dbcAMP blocked GVBD. Bovine follicular fluid (BFF) was analyzed for inhibitors of GVBD. BFF was extracted with 70% ethanol and the ethanolic extract chromatographed on Dowex 1-X8 column. The fraction eluted with 0.1 N HCl markedly inhibited GVBD of isolated mouse oocytes in combination with dbcAMP. The active BFF substance and cAPP block spontaneous GVBD of mouse oocytes and may be related substances. The present study supports the thesis that meiotic arrest at the dictyate stage in oocytes is sustained by factors present in follicular fluid and may act in association with cAMP.

Animals↗
PubMedDate not supplied

Faeriefungin: a new broad-spectrum antibiotic from Streptomyces griseus var. autotrophicus.

Faeriefungin, a polyol polyene macrolide lactone antibiotic, was isolated from the mycelium of Streptomyces griseus var. autotrophicus, MSU-32058/ATCC 53668, collected from the soil sample of a fairy ring in an old lawn in Lansing, Michigan. Faeriefungin has some properties similar to the previously reported polyene macrolides, mycoticin and flavofungin, but possesses different physiochemical and biological properties. Aspergillus, Fusarium, Microsporum, Trichophyton, and Alternaria spp. were completely inhibited by faeriefungin at 3.2 micrograms/ml, Candida spp. at 5.5 micrograms/ml, and Pythium, Phialophora, Leptosphaeria spp., and some selected Gram-negative penicillin-resistant strains of Neisseria gonorrhoeae at 16.0 micrograms/ml. At a concentration of 100 ppm, it caused 100% mortality of mosquito larvae (Aedes aegypti, Rockefeller strain) and free-living nematodes (Panagrellus redivivus). Unlike the related polyene macrolides, faeriefungin is crystalline and stable with broad-spectrum antimicrobial and insecticidal activity. Preliminary cytotoxicity studies with human erythrocytes and rat liver epithelial cells indicated that faeriefungin and amphotericin B have comparable toxicity. Solution nmr study has indicated that faeriefungin is a mixture of two compounds, faerifungins A [1] and B [2], and that they differ in the attachment of a H or an Me at C-33.

Acetylation↗
PubMedDate not supplied

Source and function of keto elaidic acids from lungs of cotton workers.

A series of cytotoxic oxygenated derivatives of oleic acid, 8-oxo-9, 9-oxo-10, 10-oxo-8-, and 11-oxo-9 trans octadecenoic acid, uniquely found at post-mortem in airway cells of cotton workers, were synthesized and shown to be cytotoxic, i.e., inhibitory of growth for several cell lines, including HL-60 and U-937 promyelocytes and Eagle's KB carcinoma cells. At microM concentrations, the 8- and 11- keto acids: are chemokinetic for human neutrophils; activate production of O2-. and H2O2; stimulate promyelocytes in culture to differentiate into neutrophils; and increase diglyceride metabolism in inflammatory cells. These results indicate that these four monooxygenated fatty acids, which are found in airways of cotton workers and initiate both inflammation and differentiation in vitro, may be etiologic in the abnormal differentiation and inflammation seen in small airways of cotton workers. This abnormal differentiation in bronchi may result from altered diglyceride metabolism with resultant activation of phosphoprotein kinase C initiated by the keto fatty acids.

Cells, Cultured↗