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F Schaller

Publications and source records attributed to F Schaller.

At least 19 recordsLinked to original sources
PubMed2001

Enzymes of the biosynthesis of octadecanoid-derived signalling molecules.

It is known that octadecanoids, i.e. jasmonic acid and related compounds are involved in plant defence reactions against (1) microbial pathogens, (2) herbivores and (3) damage by UV-B or UV-C light as well as (4) senescence and (5) mechanotransduction. Jasmonic acid is likely to occur ubiquitously in the plant kingdom, and it has also been found in some fungi. The pathway of octadecanoid biosynthesis was elucidated in the early 80s by Vick and Zimmerman. This review summarizes recent progress in the identification and characterization of octadecanoid biosynthetic enzymes and in the understanding of the regulation of octadecanoid biosynthesis.

Cyclopentanes↗
PubMed2000

Transgenic Nicotiana tabacum and Arabidopsis thaliana plants overexpressing allene oxide synthase.

Allene oxide synthase (AOS), encoded by a single gene in Arabidopsis thaliana (L.) Heynh., catalyzes the first step specific to the octadecanoid pathway. Enzyme activity is very low in control plants, but is upregulated by wounding, octadecanoids, ethylene, salicylate and coronatine (D. Laudert and E.W. Weiler, 1998, Plant J 15: 675-684). In order to study the consequences of constitutive expression of AOS on the level of jasmonates, a complete cDNA encoding the enzyme from A. thaliana was constitutively expressed in both A. thaliana and tobacco (Nicotiana tabacum L.). Overexpression of AOS did not alter the basal level of jasmonic acid; thus, output of the jasmonate pathway in the unchallenged plant appears to be strictly limited by substrate availability. In wounded plants overexpressing AOS, peak jasmonate levels were 2- to 3-fold higher compared to untransformed plants. More importantly, the transgenic plants reached the maximum jasmonate levels significantly earlier than wounded untransformed control plants. These findings suggest that overexpression of AOS might be a way of controlling defense dynamics in higher plants.

Arabidopsis↗
PubMed2000

12-Oxophytodienoate reductase 3 (OPR3) is the isoenzyme involved in jasmonate biosynthesis.

In addition to OPR1 and OPR2, two isoenzymes of 12-oxophytodienoate reductase, a third isoform (OPR3) has recently been identified in Arabidopsis thaliana (L.) Heynh. The expression of the OPR3 gene is induced not only by a variety of stimuli, such as touch, wind, wounding, UV-light and application of detergent, but also by brassinosteroids. The three enzymes were expressed in a functional form in Escherichia coli, and OPR2 was additionally expressed in insect cell cultures and overexpressed in A. thaliana. Substrate conversion was analyzed using a stereospecific assay. The results show that OPR3 effectively converts the natural (9S,13S)-12-oxophytodienoic acid [Km = 35 microM, Vmax 53.7 nkat (mg protein)-1] to the corresponding 3-2(2'(Z)-pentenyl) cyclopentane-1-octanoic acid (OPC-8:0) stereoisomer while OPR1 and OPR2 convert (9S,13S)-12-oxophytodienoic acid with greatly reduced efficiency compared to OPR3. Thus, OPR3 is the isoenzyme relevant for jasmonate biosynthesis.

Arabidopsis↗
PubMed1998

12-Oxophytodienoate-10,11-reductase: occurrence of two isoenzymes of different specificity against stereoisomers of 12-oxophytodienoic acid

The reduction of 12-oxophytodienoic acid (OPDA) to 3-oxo-2(2'[Z]-pentenyl)-cyclopentane-1-octanoic acid is catalyzed by 12-oxophytodienoate-10,11-reductase (OPR). Analysis of the isomer preference of OPR has indicated that the activity is composed of two isoenzymes exhibiting different stereoselectivities. The two isoforms of OPR have been separated, using protein extracts of Rock Harlequin (Corydalis sempervirens) as the starting material. OPRI, the enzyme reported earlier from the same species and corresponding to the cloned OPR from Arabidopsis, utilized 9R,13R-OPDA >> 9S, 13R-OPDA but not the 13S-configured isomers, whereas the new activity, OPRII, effectively reduced all four OPDA isomers, including the natural 9S,13S-OPDA (cis-[+]-OPDA). OPRII activity is characterized in detail. The enzyme's enzymatic, biochemical, and immunological properties prove that it is a close relative of OPRI. The roles of OPRI and OPRII in octadecanoid biology are discussed.

Journal Article↗
PubMed1998

Left ventricular wall thickening does occur in elite power athletes with or without anabolic steroid Use.

Reports on the occurrence of left ventricular wall thickening in resistance-trained athletes have rejected the possibility for this physiological adaptation to occur without concomitant anabolic steroid abuse. Others have concluded short bursts of arterial hypertension that occur with maximal weight lifting are not sufficient to induce left ventricular wall thickening, and left ventricular wall thickness >/=13 mm should not be found in pure resistance-trained athletes. Therefore, we examined 4 elite resistance-trained athletes by two-dimensional echocardiography. In addition, we retrospectively examined the individual left ventricular dimensions of 13 bodybuilders from our previous echocardiographic studies. All 4 elite resistance-trained athletes had left ventricular wall thicknesses beyond 13 mm. One of the elite bodybuilders has the largest left ventricular wall thickness (16 mm) ever reported in a power athlete. Retrospectively, 43% of the drug-free bodybuilders and 100% of the steroid users had left ventricular wall thickness beyond the normal range of 11 mm. In addition, 1 drug-free subject and 3 steroid users were beyond the critical mark of 13 mm. No subjects demonstrated diastolic dysfunction. In contrast to previous reports, we have demonstrated that left ventricular wall thicknesses >/=13 mm can be found routinely in elite resistance-trained athletes. The use of anabolic steroids concomitant with intensive resistance exercise does appear to augment left ventricular size without dysfunction. Anabolic steroids may accelerate left ventricular wall thickening indirectly by increasing strength, thus augmenting the pressor response.

Adult↗
PubMed1997

Molecular cloning and characterization of 12-oxophytodienoate reductase, an enzyme of the octadecanoid signaling pathway from Arabidopsis thaliana. Structural and functional relationship to yeast old yellow enzyme.

Using partial amino acid sequence information for 12-oxophytodienoate-10,11-reductase obtained from Corydalis sempervirens we have cloned the homologous enzyme from Arabidopsis thaliana. The open reading frame of the cDNA encodes a polypeptide of 372 amino acids (Mr = 41,165) with significant similarity to the sequence of Old Yellow Enzyme from Saccharomyces carlsbergensis (Saito, K., Thiele, D. J., Davio, M., Lockridge, O., and Massey, V. (1991) J. Biol. Chem. 266, 20720-20724), a flavin (FMN)-protein catalyzing the NADPH-dependent reduction of the olefinic bond of alpha,beta-unsaturated carbonyls. Specifically, all residues required for binding of FMN in Old Yellow Enzyme are conserved in the A. thaliana sequence, as are all residues associated with catalytic activity. The enzyme was functionally expressed from its cDNA in Escherichia coli and thus proven to encode OPDA reductase. Further similarities of OPDA reductase and yeast Old Yellow Enzyme include their binding to and elution by reductant from N-(4-hydroxybenzoyl)aminohexyl-Sepharose, the immunoreactivity of yeast Old Yellow Enzyme with an antiserum raised against plant OPDA reductase and the demonstration that Old Yellow Enzyme is an active OPDA reductase. It is thus conceivable that the physiological role of Old Yellow Enzymes now known from bacteria, yeasts, and higher plants, is in oxylipin metabolism.

Amino Acid Sequence↗
PubMed1997

Enzymes of octadecanoid biosynthesis in plants--12-oxo-phytodienoate 10,11-reductase.

Octadecanoids, potent cyclic plant signaling molecules derived from alpha-linolenic acid, are involved in the regulation of a multitude of physiological processes such as senescence, herbivore and pathogen defense, mechanoperception and morphogenesis. The first cyclic intermediate in the Vick-Zimmerman pathway of octadecanoid biosynthesis is 12-oxo-phytodienoic acid. Its conversion to the end product of the pathway, jasmonic acid, a C12 compound, first proceeds through reduction to 3-oxo-2-(pent-2'-enyl)-cyclopentane-1-octanoic acid, which is then converted to jasmonic acid by three cycles of beta-oxidation. The first of these conversions is a decisive point in the biosynthetic sequence, in that it channels the octadecanoid into the pathway of beta-oxidation. 12-Oxo-phytodienoate reductase was purified to apparent homogeneity from a cell suspension culture of Corydalis sempervirens. The enzyme is soluble and a monomer of apparent molecular mass 41 kDa which prefers NADPH over NADH to reduce the 10,11-double bond of 12-oxo-phytodienoic acid. The structure of the reaction product was proved by derivatization, GC/MS and NMR analysis. The enzyme accepts both the cis and the trans isomer of 12-oxo-phydodienoic acid, with a preference for the cis-isomer (6:1). 12-Oxo-phytodienoate reductase will also convert the synthetic substrate 2-cyclohexenone to cyclohexanone, but the enzyme did not reduce some other cyclic alpha,beta-unsaturated ketones tested (the plant hormone abscisic acid or the steroids testosterone and progesterone). Characteristic parameters of 12-oxo-phytodienoate reductase were determined.

Cells, Cultured↗
PubMed1997

Left ventricular size and function in elite bodybuilders using anabolic steroids.

OBJECTIVE: To investigate the relationship between resistance training, anabolic steroid use, and left ventricular function. DESIGN: Sixteen competitive bodybuilders were recruited for an echocardiography study. SETTING: University of North Texas Health Science Center (Fort Worth, TX, U.S.A.); the cardiologist and technician were blinded as to subjects' drug status. SUBJECTS: Eight competitive heavyweight drug-free (DF) bodybuilders and eight competitive heavyweight body-builders on self-directed regimens of anabolic steroids. RESULTS: Average body mass indexes (BMI; kg/m2) for the drug-user (DU) and DF groups were not significantly different (34.1 +/- 2.8 and 32.0 +/- 4.3, respectively). Increases in left ventricular posterior wall and ventricular septal thickness were apparent in the DU group (p < 0.05). The ratio of echocardiographic findings to BMI revealed a significantly smaller left ventricular end-diastolic dimension (LVDEd/BMI; p < 0.05) in the DU group. The smaller LVDEd in DUs is coupled with a significantly disproportionate septal and posterior wall thickness in DUs when indexed to body mass compared to DFs. There was no direct evidence of diastolic dysfunction detected by mitral inflow velocity patterns. CONCLUSION: Anabolic steroids may potentiate concentric left ventricular hypertrophy with decreasing ventricular compliance without affecting cardiac function.

Adult↗
PubMed1995

Sudden cardiac death in a 20-year-old bodybuilder using anabolic steroids.

Anabolic steroid use is widespread and has been associated with a variety of pathological conditions. The subject of this case is a 20-year-old amateur bodybuilder who died of sudden cardiopulmonary arrest. He had no previous medical complaints but had a history of anabolic steroid abuse and a hypertrophic heart (515 g) at autopsy. This case presentation will discuss the cardiovascular effects of these drugs and the possible impact of long-term abuse.

Adult↗
PubMed1975

[Effect of the destruction of the pars intercerebralis on molting in Aeshne cyanes Müll. larva (Insecta, Odonata)].

The cauterization of the pars intercerebralis blocks the moulting process in Aeshna. The critical period for this experiment has been determined in the 2 last instars. After this period brain cautery only delays moulting without preventing this process. Cauterization of the pars intercerebralis after the critical period of the prothoracic gland activity does not affect moulting in any way.

Age Factors↗