RESUMEN
The biosynthesis of camalexin, the main phytoalexin of the model plant Arabidopsis thaliana, involves at least two CYP (cytochrome P450) steps. It is synthesized from tryptophan via indole-3-acetaldoxime in a reaction catalysed by CYP79B2 and CYP79B3. Based on the pad3 mutant phenotype, CYP71B15 (PAD3) had also been suggested as a camalexin biosynthetic gene. CYP71B15 catalyses the final step in camalexin biosynthesis, as recombinant CYP71B15 and microsomes from Arabidopsis leaves expressing functional PAD3 converted dihydrocamalexic acid into camalexin. The biosynthetic pathway is co-ordinately induced, strictly localized to the site of pathogen infection. This provides a model system to study the regulation of CYP enzymes involved in phytoalexin biosynthesis.
Asunto(s)
Sistema Enzimático del Citocromo P-450/metabolismo , Indoles/metabolismo , Tiazoles/metabolismo , Arabidopsis/metabolismo , Cinética , Sesquiterpenos , Terpenos/metabolismo , Triptófano/metabolismo , FitoalexinasRESUMEN
For the biosynthesis of the phytohormone indole-3-acetic acid (IAA), a number of tryptophan-dependent and -independent pathways have been discussed. Maize is an appropriate model system to analyze IAA biosynthesis particularly because high quantities of IAA conjugates are stored in the endosperm. This allowed precursor feeding experiments in a kernel culture system followed by retrobiosynthetic NMR analysis, which strongly suggested that tryptophan-dependent IAA synthesis is the predominant route for auxin biosynthesis in the maize kernel. Two nitrilases ZmNIT1 and ZmNIT2 are expressed in seeds. ZmNIT2 efficiently hydrolyzes indole-3-acetonitrile (IAN) to IAA and thus could be involved in auxin biosynthesis. Redundant pathways, e.g., via indole-3-acetaldehyde could imply that multiple mutants will be necessary to obtain IAA-deficient plants and to conclusively identify relevant genes for IAA biosynthesis.
Asunto(s)
Ácidos Indolacéticos/metabolismo , Reguladores del Crecimiento de las Plantas/metabolismo , Zea mays/metabolismo , Acetonitrilos/metabolismo , Aminohidrolasas/fisiología , Triptófano/metabolismo , Triptófano/fisiología , Zea mays/enzimologíaRESUMEN
The ring expansion of 3-hydroxyindolin-2-one to 2-hydroxy-1,4-benzoxazin-3-one (HBOA) was investigated by labelling experiments. Action of the cytochrome P450 enzyme BX4 from maize on 3-hydroxyindolin-2-one under an 18O2 atmosphere induced production of 2-hydroxy-1,4-benzoxazin-3-one in which the ring oxygen--but not the 2-hydroxy group of HBOA--is labelled. A mechanism for this transformation is proposed.
Asunto(s)
Sistema Enzimático del Citocromo P-450/metabolismo , Indoles/metabolismo , Oxazinas/metabolismo , Zea mays/metabolismo , Benzoxazinas , Biotransformación , Espectrometría de Masas , Conformación Molecular , Estructura Molecular , Isótopos de OxígenoRESUMEN
Information on metabolic networks could provide the basis for the design of targets for metabolic engineering. To study metabolic flux in cereals, developing maize (Zea mays) kernels were grown in sterile culture on medium containing [U-(13)C(6)]glucose or [1,2-(13)C(2)]acetate. After growth, amino acids, lipids, and sitosterol were isolated from kernels as well as from the cobs, and their (13)C isotopomer compositions were determined by quantitative nuclear magnetic resonance spectroscopy. The highly specific labeling patterns were used to analyze the metabolic pathways leading to amino acids and the triterpene on a quantitative basis. The data show that serine is generated from phosphoglycerate, as well as from glycine. Lysine is formed entirely via the diaminopimelate pathway and sitosterol is synthesized entirely via the mevalonate route. The labeling data of amino acids and sitosterol were used to reconstruct the labeling patterns of key metabolic intermediates (e.g. acetyl-coenzyme A, pyruvate, phosphoenolpyruvate, erythrose 4-phosphate, and Rib 5-phosphate) that revealed quantitative information about carbon flux in the intermediary metabolism of developing maize kernels. Exogenous acetate served as an efficient precursor of sitosterol, as well as of amino acids of the aspartate and glutamate family; in comparison, metabolites formed in the plastidic compartments showed low acetate incorporation.
Asunto(s)
Aminoácidos/biosíntesis , Zea mays/metabolismo , Aminoácidos/metabolismo , Isótopos de Carbono , Resonancia Magnética Nuclear Biomolecular , Fitosteroles/biosíntesis , Zea mays/enzimología , Zea mays/crecimiento & desarrolloRESUMEN
Auxin biosynthesis was analyzed in a maize (Zea mays) kernel culture system in which the seeds develop under physiological conditions similar to the in vivo situation. This system was modified for precursor feeding experiments. Tryptophan (Trp) is efficiently incorporated into indole-3-acetic acid (IAA) with retention of the 3, 3' bond. Conversion of Trp to IAA is not competed by indole. Labeling with the general precursors [U-(13)C(6)]glucose and [1, 2-(13)C(2)]acetate followed by retrobiosynthetic analysis strongly suggest that Trp-dependent IAA synthesis is the predominant route for auxin biosynthesis in the maize kernel. The synthesis of IAA from indole glycerol phosphate and IAA formation via condensation of indole with an acetyl-coenzyme A or phosphoenolpyruvate derived metabolite can be excluded.
Asunto(s)
Ácidos Indolacéticos/biosíntesis , Ácidos Indolacéticos/metabolismo , Reguladores del Crecimiento de las Plantas/metabolismo , Semillas/metabolismo , Zea mays/metabolismo , Aminoácidos/análisis , Cromatografía de Gases y Espectrometría de Masas , Espectroscopía de Resonancia Magnética , Reguladores del Crecimiento de las Plantas/biosíntesis , Triptófano/metabolismoRESUMEN
DIBOA and DIMBOA are secondary metabolites of grasses which function as natural pesticides. The four maize genes BX2 through BX5 encode cytochrome P450-dependent monooxygenases that catalyse four consecutive reactions in the biosynthesis of these secondary products. Although BX2-BX5 share significant sequence homology, the four enzymes have evolved into specific enzymes each catalysing predominantly only one reaction in the pathway. In addition to these natural reactions, BX3 hydroxylates 1,4-benzoxazin-3-one and BX2 shows pCMA demethylase activity. With respect to DIBOA biosynthesis, identical enzymatic reactions have been found in rye as compared to maize, indicating early evolution of the P450 enzymes in the grasses.
Asunto(s)
Sistema Enzimático del Citocromo P-450/metabolismo , Grano Comestible/metabolismo , Oxazinas/metabolismo , Benzoxazinas , Sistema Enzimático del Citocromo P-450/genética , ADN Complementario/genética , Grano Comestible/enzimología , Grano Comestible/genética , Hordeum/enzimología , Hordeum/genética , Hordeum/metabolismo , Isoenzimas/genética , Isoenzimas/metabolismo , Cinética , Saccharomyces cerevisiae/enzimología , Saccharomyces cerevisiae/genética , Secale , Especificidad por Sustrato , Zea mays/enzimología , Zea mays/genética , Zea mays/metabolismoRESUMEN
In the Gramineae, the cyclic hydroxamic acids 2,4-dihydroxy-1, 4-benzoxazin-3-one (DIBOA) and 2,4-dihydroxy-7-methoxy-1, 4-benzoxazin-3-one (DIMBOA) form part of the defense against insects and microbial pathogens. Five genes, Bx1 through Bx5, are required for DIBOA biosynthesis in maize. The functions of these five genes, clustered on chromosome 4, were demonstrated in vitro. Bx1 encodes a tryptophan synthase alpha homolog that catalyzes the formation of indole for the production of secondary metabolites rather than tryptophan, thereby defining the branch point from primary to secondary metabolism. Bx2 through Bx5 encode cytochrome P450-dependent monooxygenases that catalyze four consecutive hydroxylations and one ring expansion to form the highly oxidized DIBOA.
Asunto(s)
Genes de Plantas , Oxazinas/metabolismo , Zea mays/genética , Benzoxazinas , Clonación Molecular , Cruzamientos Genéticos , Sistema Enzimático del Citocromo P-450/genética , Sistema Enzimático del Citocromo P-450/metabolismo , Elementos Transponibles de ADN , Hidroxilación , Indoles/metabolismo , Datos de Secuencia Molecular , Brotes de la Planta/metabolismo , Especificidad por Sustrato , Triptófano Sintasa/genética , Triptófano Sintasa/metabolismo , Zea mays/metabolismoRESUMEN
In a problem herd the losses by E. coli-infection of weaning piglets could not be reduced neither applicating an oral vaccine before 4-2 weeks to weaning nor via feed of antibiotics or sulfonamides. Therefore many feeding trials were carried out by 1247 weaning piglets which are feeded with high raw fibre rations (wheatbran coarse grained, strawmeal) beginning 2 weeks before weaning till 3 weeks afterwards. The most effective feeding additive was 25-30% wheatbran. In fact of this results the diarrhea, a problem in many herds infected with a lot of EEC (08, 045, 0138, 0139, 0141, 0147 and 0149) could be reduced effectively. Light cases of diarrhea during the trials could be stopped by two applications of TMQ (20 mg Terramycin/kg BW). Based on these results the use of the supplementing wheatbran to the normal feed during the weaning period can be recommended for such problem herds.
Asunto(s)
Alimentación Animal , Diarrea/veterinaria , Infecciones por Escherichia coli/veterinaria , Enfermedades de los Porcinos/prevención & control , Destete , Animales , Diarrea/prevención & control , Fibras de la Dieta/administración & dosificación , Infecciones por Escherichia coli/prevención & control , PorcinosRESUMEN
A cow, trisomic for chromosome 22, became pregnant and gave birth to a karyotypically normal and healthy calf. Thus, a second example of reproductive capability in autosomal trisomies in mammals, in addition to trisomy 21 in man, is provided.
Asunto(s)
Bovinos/genética , Preñez , Trisomía , Animales , Femenino , Cariotipificación , EmbarazoAsunto(s)
Bovinos/sangre , Gentamicinas/sangre , Porcinos/sangre , Animales , Inyecciones Intramusculares , CinéticaRESUMEN
Karyotyping of eight malformed calves resulted in the detection of trisomy 22 in one calf. This calf had a hernia umbilicalis, a urachus fistula, and slight brachygnathia inferior. This trisomy was not associated with lethality.