Biomedical subjects

J P Métraux

Publications and source records attributed to J P Métraux.

18 recordsLinked to original sources

PubMed2001

beta-Aminobutyric acid-induced protection of Arabidopsis against the necrotrophic fungus Botrytis cinerea.

The non-protein amino acid beta-aminobutyric acid (BABA) protects numerous plants against various pathogens. Protection of Arabidopsis plants against virulent pathogens involves the potentiation of pathogen-specific defense responses. To extend the analysis of the mode of action of BABA to necrotrophs we evaluated the effect of this chemical on Arabidopsis plants infected with the gray mold fungus Botrytis cinerea. BABA-treated Arabidopsis were found to be less sensitive to two different strains of this pathogen. BABA protected mutants defective in the jasmonate and ethylene pathways, but was inactive in plants impaired in the systemic acquired resistance transduction pathway. Treatments with benzo-(1,2,3)-thiadiazole-7-carbothioic acid S-methyl ester, a functional analog of salicylic acid (SA), also markedly reduced the level of infection. Moreover, BABA potentiated mRNA accumulation of the SA-associated PR-1, but not the jasmonate/ethylene-dependent PDF1.2 gene. Thus, besides jasmonate/ethylene-dependent defense responses, SA-dependent signaling also contributes to restrict B. cinerea infection in Arabidopsis. Our results also suggest that SA-dependent signaling is down-regulated after infection by B. cinerea. The observed up-regulation of the PDF1.2 gene in mutants defective in the SA-dependent signaling pathway points to a cross-talk between SA- and jasmonate/ethylene-dependent signaling pathways during pathogen ingress.

Aminobutyrates↗

PubMed2001

Numeric simulation of plant signaling networks.

Plants have evolved an intricate signaling apparatus that integrates relevant information and allows an optimal response to environmental conditions. For instance, the coordination of defense responses against pathogens involves sophisticated molecular detection and communication systems. Multiple protection strategies may be deployed differentially by the plant according to the nature of the invading organism. These responses are also influenced by the environment, metabolism, and developmental stage of the plant. Though the cellular signaling processes traditionally have been described as linear sequences of events, it is now evident that they may be represented more accurately as network-like structures. The emerging paradigm can be represented readily with the use of Boolean language. This digital (numeric) formalism allows an accurate qualitative description of the signal transduction processes, and a dynamic representation through computer simulation. Moreover, it provides the required power to process the increasing amount of information emerging from the fields of genomics and proteomics, and from the use of new technologies such as microarray analysis. In this review, we have used the Boolean language to represent and analyze part of the signaling network of disease resistance in Arabidopsis.

Algorithms↗

PubMed2000

Transgenic Arabidopsis plants expressing a fungal cutinase show alterations in the structure and properties of the cuticle and postgenital organ fusions.

A major structural component of the cuticle of plants is cutin. Analysis of the function of cutin in vivo has been limited because no mutants with specific defects in cutin have been characterized. Therefore, transgenic Arabidopsis plants were generated that express and secrete a cutinase from Fusarium solani f sp pisi. Arabidopsis plants expressing the cutinase in the extracellular space showed an altered ultrastructure of the cuticle and an enhanced permeability of the cuticle to solutes. In addition, pollen could germinate on fully differentiated leaves of cutinase-expressing plants but not on control leaves. These differences coincided with strong postgenital organ fusions. The junctions of the fusions contained pectic polysaccharides. As fused organs grew apart from each other, organ deformations and protrusions of epidermal cells developed at positions with high mechanical stress. These results demonstrate that an intact cutin layer not only is important for plant-environment interactions but also prevents fusions between different plant organs and is therefore necessary for normal epidermal differentiation and organ formation.

Arabidopsis↗

PubMed1999

Nanogram amounts of salicylic acid produced by the rhizobacterium Pseudomonas aeruginosa 7NSK2 activate the systemic acquired resistance pathway in bean.

Root colonization by specific nonpathogenic bacteria can induce a systemic resistance in plants to pathogen infections. In bean, this kind of systemic resistance can be induced by the rhizobacterium Pseudomonas aeruginosa 7NSK2 and depends on the production of salicylic acid by this strain. In a model with plants grown in perlite we demonstrated that Pseudomonas aeruginosa 7NSK2-induced resistance is equivalent to the inclusion of 1 nM salicylic acid in the nutrient solution and used the latter treatment to analyze the molecular basis of this phenomenon. Hydroponic feeding of 1 nM salicylic acid solutions induced phenylalanine ammonia-lyase activity in roots and increased free salicylic acid levels in leaves. Because pathogen-induced systemic acquired resistance involves similar changes it was concluded that 7NSK2-induced resistance is mediated by the systemic acquired resistance pathway. This conclusion was validated by analysis of phenylalanine ammonia-lyase activity in roots and of salicylic acid levels in leaves of soil-grown plants treated with Pseudomonas aeruginosa. The induction of systemic acquired resistance by nanogram amounts of salicylic acid is discussed with respect to long-distance signaling in systemic acquired resistance.

Fabaceae↗

PubMed1999

Salicylic acid induction-deficient mutants of Arabidopsis express PR-2 and PR-5 and accumulate high levels of camalexin after pathogen inoculation.

In Arabidopsis, systemic acquired resistance against pathogens has been associated with the accumulation of salicylic acid (SA) and the expression of the pathogenesis-related proteins PR-1, PR-2, and PR-5. We report here the isolation of two nonallelic mutants impaired in the pathway leading to SA biosynthesis. These SA induction-deficient (sid) mutants do not accumulate SA after pathogen inoculation and are more susceptible to both virulent and avirulent forms of Pseudomonas syringae and Peronospora parasitica. However, sid mutants are not as susceptible to these pathogens as are transgenic plants expressing the nahG gene encoding an SA hydroxylase that degrades SA to catechol. In contrast to NahG plants, only the expression of PR-1 is strongly reduced in sid mutants, whereas PR-2 and PR-5 are still expressed after pathogen attack. Furthermore, the accumulation of the phytoalexin camalexin is normal. These results indicate that SA-independent compensation pathways that do not operate in NahG plants are active in sid mutants. One of the mutants is allelic to eds5 (for enhanced disease susceptibility), whereas the other mutant has not been described previously.

Alleles↗

PubMed1998

Structure, expression and localization of a germin-like protein in barley (Hordeum vulgare L.) that is insolubilized in stressed leaves.

The primary leaves of young barley seedlings contain two major, extracellular, acid-soluble proteins of ca. 22 and 23 kDa apparent molecular mass. These proteins disappeared from the intercellular washing fluid upon stress treatments that enhanced H2O2 levels and that induced resistance to subsequent challenge by the powdery mildew fungus Erysiphe graminis f. sp. hordei. A partial peptide sequence of the 22 kDa protein was determined, and a cDNA clone was isolated. The 22 kDa protein belongs the the group of germin-like proteins (GLPs) and was designated HvGLP1. Despite its similarity to germin, i.e. oxalate oxidase, no oxalate oxidase activity of HvGLP1 could be detected. The RNA and soluble protein of HvGLP1 was highly abundant in young leaves, less abundant in older leaves and absent in roots. HvGLP1 RNA oscillated with a circadian rhythm, the minimum and maximum of RNA abundance being at the end of the dark and light periods, respectively. Heat and H2O2 treatment as well as pathogen infection caused disappearance of HvGLP1 protein from the fraction of soluble proteins of the intercellular space. HvGLP1 protein could be re-solubilized from cell walls of heat- or H2O2-treated leaves by boiling in SDS suggesting non-covalent cross linking. Although a physiological role of HvGLP1 insolubilization is still open, the protein may serve as marker for oxidative stress in cereals.

Amino Acid Sequence↗

PubMed1998

Concomitant activation of jasmonate and ethylene response pathways is required for induction of a plant defensin gene in Arabidopsis.

Activation of the plant defensin gene PDF1.2 in Arabidopsis by pathogens has been shown previously to be blocked in the ethylene response mutant ein2-1 and the jasmonate response mutant coi1-1. In this work, we have further investigated the interactions between the ethylene and jasmonate signal pathways for the induction of this defense response. Inoculation of wild-type Arabidopsis plants with the fungus Alternaria brassicicola led to a marked increase in production of jasmonic acid, and this response was not blocked in the ein2-1 mutant. Likewise, A. brassicicola infection caused stimulated emission of ethylene both in wild-type plants and in coi1-1 mutants. However, treatment of either ein2-1 or coi1-1 mutants with methyl jasmonate or ethylene did not induce PDF1.2, as it did in wild-type plants. We conclude from these experiments that both the ethylene and jasmonate signaling pathways need to be triggered concomitantly, and not sequentially, to activate PDF1.2 upon pathogen infection. In support of this idea, we observed a marked synergy between ethylene and methyl jasmonate for the induction of PDF1.2 in plants grown under sterile conditions. In contrast to the clear interdependence of the ethylene and jasmonate pathways for pathogen-induced activation of PDF1.2, functional ethylene and jasmonate signaling pathways are not required for growth responses induced by jasmonate and ethylene, respectively.

Acetates↗

PubMed1997

Systemic acquired resistance.

This paper examines induced resistance (SAR) in plants against various insect and pathogenic invaders. SAR confers quantitative protection against a broad spectrum of microorganisms in a manner comparable to immunization in mammals, although the underlying mechanisms differ. Discussed here are the molecular events underlying SAR: the mechanisms involved in SAR, including lignification and other structural barriers, pathogenesis-related proteins and their expression, and the signals for SAR including salicylic acid. Recent findings on the biological role of systemin, ethylene, jasmonates, and electrical signals are reviewed. Chemical activators of SAR comprise inorganic compounds, natural compounds, and synthetic compounds. Plants known to exhibit SAR and induced systemic resistance are listed.

Journal Article↗

PubMed1996

Salicylic acid-independent induction of pathogenesis-related protein transcripts by sugars is dependent on leaf developmental stage.

Soluble sugars have been found to regulate a number of genes involved in functions associated with sink metabolism, defense reactions and photosynthesis. As viruses and pathogens induce the expression of pathogenesis-related (PR) protein genes and have also been reported to lead to localized sugar accumulation in leaves, it was investigated whether a salicylic acid-independent but sugar-dependent pathway for PR-protein gene induction may exist in plant cells. Leaf discs of tobacco plants were floated on different sugar solutions, transcript accumulation and salicylic acid (SA) levels were subsequently determined. PR-Q and PAR-1 transcripts were found to be inducible by glucose, fructose and sucrose. No significant change in SA content could be detected, following incubation. On the other hand, SAR8.2 transcripts were repressed by elevated levels of soluble sugars and sorbitol, respectively, suggesting sensitivity to turgor pressure. Since leaves undergo sink to source transition during growth, sugar responsiveness was investigated in leaves of different developmental stages. Interestingly, induction of PR-Q and PAR-1 by soluble sugars was essentially restricted to fully expanded leaves and was independent of plant age. Induction by salicylate was not confined to the source capacity of a leaf but was dependent on the age of the respective leaf. Repression of transcripts encoding photosynthetic genes (ribulose-1,5-bisphosphate carboxylase/oxygenase (rbcS) and chlorophyll a/b binding protein (cab) by soluble sugars were largely independent from the leaf developmental state. These findings hint to the possibility of salicylic acid-independent defense reactions of plants against pathogens by induction of a set of PR proteins in source leaves. Furthermore, the data suggest different mechanisms for the induction of PR-protein genes and the repression of photosynthetic genes by soluble sugars.

Carbohydrate Metabolism↗

PubMed1996

Pathogen-induced systemic activation of a plant defensin gene in Arabidopsis follows a salicylic acid-independent pathway.

A 5-kD plant defensin was purified from Arabidopsis leaves challenged with the fungus Alternaria brassicicola and shown to possess antifungal properties in vitro. The corresponding plant defensin gene was induced after treatment of leaves with methyl jasmonate or ethylene but not with salicylic acid or 2,6-dichloroisonicotinic acid. When challenged with A. brassicicola, the levels of the plant defensin protein and mRNA rose both in inoculated leaves and in nontreated leaves of inoculated plants (systemic leaves). These events coincided with an increase in the endogenous jasmonic acid content of both types of leaves. Systemic pathogen-induced expression of the plant defensin gene was unaffected in Arabidopsis transformants (nahG) or mutants (npr1 and cpr1) affected in the salicylic acid response but was strongly reduced in the Arabidopsis mutants eln2 and col1 that are blocked in their response to ethylene and methyl jasmonate, respectively. Our results indicate that systemic pathogen-induced expression of the plant defensin gene in Arabidopsis is independent of salicylic acid but requires components of the ethylene and jasmonic acid response.

Alternaria↗

PubMed1995

Cholera toxin elevates pathogen resistance and induces pathogenesis-related gene expression in tobacco.

In animals, plants and fungi, cholera toxin (CTX) can activate signalling pathways dependent on heterotrimeric GTP binding proteins (G-proteins). We transformed tobacco plants with a chimeric gene encoding the A1 subunit of CTX regulated by a light-inducible wheat Cab-1 promoter. Tissues of transgenic plants expressing CTX showed greatly reduced susceptibility to the bacterial pathogen Pseudomonas tabaci, accumulated high levels of salicylic acid (SA) and constitutively expressed pathogenesis-related (PR) protein genes encoding PR-1 and the class II isoforms of PR-2 and PR-3. In contrast, the class I isoforms of PR-2 and PR-3 known to be induced in tobacco by stress, by ethylene treatment and as part of the hypersensitive response to infection, were not induced and displayed normal regulation. In good agreement with these results, microinjection experiments demonstrated that CTX or GTP-gamma-S induced the expression of a PR1-GUS reporter gene but not that of a GLB-GUS reporter gene containing the promoter region of a gene encoding the class I isoform of PR-2. Microinjection and grafting experiments strongly suggest that CTX-sensitive G-proteins are important in inducing the expression of a subset of PR genes and that these G-proteins act locally rather than systemically upstream of SA induction.

Cholera Toxin↗

PubMed1993

Ortho-anisic acid as internal standard for the simultaneous quantitation of salicylic acid and its putative biosynthetic precursors in cucumber leaves.

Salicylic acid (SA) acts as an endogenous signal for the induction of systemic acquired resistance (SAR) in plants infected by pathogens. In order to study SA biosynthesis in plants, a quantitative method using an internal standard was developed for the simultaneous measurement of SA and three of its putative bioprecursors, namely trans-cinnamic acid (CA), trans-ortho-hydroxycinnamic acid (oHCA), and benzoic acid (BA). ortho-Anisic acid (oANI) was found to be a suitable internal standard for all four compounds. It was not present as endogenous compound in cucumber leaves, no substance interfered with its detection, and it followed identical losses as SA, CA, oHCA, and BA during the extraction procedure. Baseline separation of these four compounds and of eight other plant phenolics was achieved in 35 min using deactivated reversed-phase HPLC. On-line detection was performed fluorimetrically for SA, oANI, and oHCA (with the excitation and emission wavelengths optimized for each compound) and with uv detection for CA and BA. Correlation equations for SA, CA, oHCA, and BA using oANI as internal standard were linear for a broad range of concentrations. The limits of detection (in ng/g fresh weight, FW) obtained during routine analyses were as follows: SA, 4; oHCA, 100; CA, 150; and BA, 500. The method was used to quantify levels of free and acid-hydrolyzed bound SA in cucumber plants either 5 days postinoculation with Pseudomonas lachrymans or after mock-inoculation with water on their first leaf.(ABSTRACT TRUNCATED AT 250 WORDS)

Benzoates↗

PubMed1983

The role of ethylene in the growth response of submerged deep water rice.

We investigated the effect of partial submergence on internode elongation in a Bangladesh variety of floating or deep water rice (Oryza sativa L., cv. Habiganj Aman II). In plants which were at least 21 days old, 7 days of submergence led to a 3- to 5-fold increase in internodal length. During submergence, the ethylene concentration in the internodes increased from about 0.02 to 1 microliters per liter. Treatment of nonsubmerged plants with ethylene also stimulated internode elongation. When ethylene synthesis in partially submerged plants was blocked with aminooxyacetic acid and aminoethoxyvinylglycine, internode elongation was inhibited. This growth inhibition was reversed when ethylene biosynthesis was restored with 1-aminocyclopropane-1-carboxylic acid (ACC). Radio-labeling studies showed that ethylene in floating rice was synthesized from methionine via ACC. Internodal tissue from submerged plants had a much higher capacity to form ethylene than did internodal tissue from nonsubmerged plants. This increase in ethylene synthesis appeared to be due to enhanced ACC formation rather than to increased conversion of ACC to ethylene. Our results indicate that ethylene produced during submergence is required for the stimulation of growth in submerged floating rice plants.

Journal Article↗

PubMed1980

Control of Cell Elongation in Nitella by Endogenous Cell Wall pH Gradients: MULTIAXIAL EXTENSIBILITY AND GROWTH STUDIES.

The multiaxial stress of turgor pressure was stimulated in vitro by inflating isolated Nitella cell walls with mercury. The initial in vitro extension at pH 6.5, 5 atmospheres pressure, returned the wall approximately to the in vivo stressed length, and did not induce any additional extension during a 15-minute period. Upon release of pressure, a plastic deformation was observed which did not correlate with cell growth rates until the final stages of cell maturation. Since wall plasticity does not correlate with growth rate, a metabolic factor(s) is implicated. Walls at all stages of development exhibited a primary yield stress between 0 and 2 atmospheres, while rapidly growing cells (1-3% per hour) exhibited a secondary yield stress of 4 to 5 atmospheres. The creep rate and plastic deformation of young walls were markedly enhanced by acid buffers (10 millimolar, pH </= 5.3).Nitella cells produce acid and base "bands" along their length due to localized excretion of protons and hydroxyl ions. Marking experiments showed that growth is largely restricted to the acid regions. Growth in the acid bands was inhibited by alkaline buffers, and growth in the base bands was stimulated by acidic buffers. The two zones have similar mechanical properties. When the proton-binding capacity of the wall was taken into account, the pH of the solution in contact with inner wall surface in the acid band was estimated to be about 4.3, well within the threshold of acid-enhanced creep. Since the inner 25% of the wall controls extensibility, we conclude that growth in the acid band is caused by the action of protons on the wall.

Journal Article↗

PubMed1980

Cell expansion patterns and directionality of wall mechanical properties in nitella.

As a means of assessing the extent to which deformation of isolated walls relates to in vivo cell expansion, the directionality of wall mechanical properties was examined in Nitella. Measurements were made of plastic and elastic deformation and creep under both uniaxial and multiaxial stress conditions. Walls of different structural characteristics were obtained from control, isopropyl N-phenylcarbamate (IPC)-treated and IPC recovery cells. Although microfibrils in the inner portion of the wall were transverse for control and recovery cells but random for IPC cells, all walls had similar over-all microfibrillar orientations. Consequently, differences in wall mechanical properties should reflect structural differences in the inner wall. It is the action of the prevailing stress pattern on the inner, not overall, wall microfibrillar organization which dictates the directionality of growth in Nitella. The results indicate that the directional character of expansion is preserved to a large extent in the mechanical properties of isolated walls, and that most, but not all, of the deformation is determined by the inner wall. In addition, directional differences in the threshold for acid-induced extension varied in accord with the pattern of inner wall microfibrils.

Journal Article↗

PubMed1979

Transverse Viscoelastic Extension in Nitella: II. Effects of Acid and Ions.

The transverse viscoelastic extension of isolated Nitella cell walls is stimulated by acid pH and by Mg(2+) and K(+) ions. In the presence of 1 millimolar citrate-phosphate buffer the threshold pH in the transverse direction is 3.5, compared to 4.5 in the longitudinal direction. The relative amounts of extension stimulated by acid are comparable in the two directions at their respective thresholds. Longitudinal and transverse Mg(2+) ion-induced extensibility begins at 10 millimolar and reaches a plateau between 10 and 100 millimolar. The threshold for K(+) ion enhancement is near 10 millimolar in the longitudinal direction and 50 millimolar in the transverse direction. Maximum stimulation by K(+) is obtained at 250 millimolar. At their respective maxima, Mg(2+) and K(+) induce equal amounts of extension. However, the relative amount of extension induced by ions is significantly less in the transverse than in the longitudinal direction. Ions and acids appear to affect different sites in the wall, inasmuch as neither treatment abolishes the effect of the other. Walls from rapidly growing cells are more sensitive to stimulation than nongrowing cells in the longitudinal direction but not in the transverse direction.

Journal Article↗

PubMed1978

Transverse viscoelastic extension in nitella: I. Relationship to growth rate.

Transverse viscoelastic extensibility was measured directly in isolated walls of Nitella internode cells. Cell walls extended transversely exhibit a yield point which is approximately twice the yield point in the longitudinal direction. Walls from young, growing cells are four to seven times more extensible longitudinally than transversely, while walls from mature, nongrowing cells are only two times more extensible longitudinally. Although longitudinal extensibility decreases drastically with the decrease in the growth rate, lateral extensibility is constant through development. There is a discrepancy between the lateral growth rate and transverse creep, since the lateral growth rate is not constant. However, the degree of wall anisotropy observed is consistent with the view that the transversely oriented cellulose microfibrils act as a "reinforcing filler" in Nitella cell walls.

Journal Article↗

PubMed1977

Cell wall extension in Nitella as influenced by acids and ions.

The giant internode cells of Nitella axillaris exhibit acid-induced growth similar to that found in higher plants. The threshold pH is 4.5, with a maximum at 3.5. The acid growth effect is transient, lasting no more than 32 min. Extensibility measurements of isolated cell walls showed a similar pattern of acid enhancement. Prolonged boiling in water (12 hr) only partially inhibited the acid-induced wall extensibility and actually increased the extensibility at pH 6. It was concluded that physical, rather than enzymatic, processes were responsible for acid-enhanced continuous extension ("creep") in Nitella walls. A complex cation-sensitive mechanism that affects extensibility was also characterized. Among the stimulatory (wall-softening) cations, divalents were generally more effective than monovalents, with magnesium being the most stimulatory. The inhibitory (wall-hardening) cations included divalents and trivalents, aluminum being the most inhibitory. Ionic effects on extensibility were even less sensitive to prolonged boiling in water than acid effects.

Cations, Divalent↗