Unser 10. Leibniz Plant Biochemistry Symposium am 7. und 8. Mai war ein großer Erfolg. Thematisch ging es in diesem Jahr um neue Methoden und Forschungsansätze der Naturstoffchemie. Die exzellenten Vorträge über Wirkstoffe…
Omanische Heilpflanze im Fokus der Phytochemie IPB-Wissenschaftler und Partner aus Dhofar haben jüngst die omanische Heilpflanze Terminalia dhofarica unter die phytochemische Lupe genommen. Die Pflanze ist reich an…
Geschmack ist vorhersagbar: Mit FlavorMiner. FlavorMiner heißt das Tool, das IPB-Chemiker und Partner aus Kolumbien jüngst entwickelt haben. Das Programm kann, basierend auf maschinellem Lernen (KI), anhand der…
Xu, H.; Wang, Z.-X.; Schmidt, J.; Heide, L.; Li, S.-M.;Genetic analysis of the biosynthesis of the pyrrole and carbamoyl moieties of coumermycin A1 and novobiocinMol. Gen. Genomics268387-396(2002)DOI: 10.1007/s00438-002-0759-1
The aminocoumarin antibiotic coumermycin A1 contains a central and two terminal pyrrole moieties. The coumermycin gene cluster in Streptomyces rishiriensis contains three genes (couN3, couN4 and couN5) that show sequence similarity to genes involved in the biosynthesis of the pyrrole moieties of pyoluteorin in Pseudomonas fluorescens and of undecylprodiginine in S. coelicolor. The gene couN3, which codes for a putative L-prolyl-S-PCP dehydrogenase, and the gene couN4, which encodes a putative L-prolyl-AMP ligase, were disrupted using in-frame deletion and insertional inactivation, respectively. HPLC analysis of culture extracts showed that formation of the two terminal pyrrole moieties was abolished in the couN3 - und couN4 - mutants. The mutants accumulated coumermycin D, which contains only the central pyrrole moiety. This result not only confirmed the involvement of couN3 and couN4 in the biosynthesis of the terminal pyrrole-2-carboxylic acid moieties of coumermycin A1, but also indicated, for the first time, that the central 3-methylpyrrole-2,4-dicarboxylic acid unit of the coumermycins is formed by a biosynthetic pathway that differs from that used to assemble the terminal pyrrole moieties. novN, a putative carbamoyl transferase gene from the gene cluster for novobiocin biosynthesis in S. spheroides was expressed in the couN3 - mutant. This led to the formation of bis-carbamoylated coumermycin D, a novel compound of the coumermycin series.
Publikation
Weichert, H.; Kolbe, A.; Kraus, A.; Wasternack, C.; Feussner, I.;Metabolic profiling of oxylipins in germinating cucumber seedlings - lipoxygenase-dependent degradation of triacylglycerols and biosynthesis of volatile aldehydesPlanta215612-619(2002)DOI: 10.1007/s00425-002-0779-4
A particular isoform of lipoxygenase (LOX) localized on lipid bodies was shown by earlier investigations to play a role in initiating the mobilization of triacylglycerols during seed germination. Here, further physiological functions of LOXs within whole cotyledons of cucumber (Cucumis sativus L.) were analyzed by measuring the endogenous amounts of LOX-derived products. The lipid-body LOX-derived esterified (13S)-hydroperoxy linoleic acid was the dominant metabolite of the LOX pathway in this tissue. It accumulated to about 14 µmol/g fresh weight, which represented about 6% of the total amount of linoleic acid in cotyledons. This LOX product was not only reduced to its hydroxy derivative, leading to degradation by β-oxidation, but alternatively it was metabolized by fatty acid hydroperoxide lyase leading to formation of hexanal as well. Furthermore, the activities of LOX forms metabolizing linolenic acid were detected by measuring the accumulation of volatile aldehydes and the allene oxide synthase-derived metabolite jasmonic acid. The first evidence is presented for an involvement of a lipid-body LOX form in the production of volatile aldehydes.
Publikation
Wang, Q.; Grubb, C. D.; Abel, S.;Direct analysis of single leaf disks for chemopreventive glucosinolatesPhytochem. Anal.13152-157(2002)DOI: 10.1002/pca.636
Natural isothiocyanates, produced during plant tissue damage from methionine‐derived glucosinolates, are potent inducers of mammalian phase 2 detoxification enzymes such as quinone reductase (QR). A greatly simplified bioassay for glucosinolates based on induction and colorimetric detection of QR activity in murine hepatoma cells is described. It is demonstrated that excised leaf disks of Arabidopsis thaliana (ecotype Columbia) can directly and reproducibly substitute for cell‐free leaf extracts as inducers of murine QR, which reduces sample preparation to a minimum and maximizes throughput. A comparison of 1 and 3 mm diameter leaf disks indicated that QR inducer potency was proportional to disk circumference (extent of tissue damage) rather than to area. When compared to the QR inducer potency of the corresponding amount of extract, 1 mm leaf disks were equally effective, whereas 3 mm disks were 70% as potent. The QR inducer potency of leaf disks correlated positively with the content of methionine‐derived glucosinolates, as shown by the analysis of wild‐type plants and mutant lines with lower or higher glucosinolate content. Thus, the microtitre plate‐based assay of single leaf disks provides a robust and inexpensive visual method for rapidly screening large numbers of plants in mapping populations or mutant collections and may be applicable to other glucosinolate‐producing species.
Publikation
Walter, M. H.; Hans, J.; Strack, D.;Two distantly related genes encoding 1-deoxy-D-xylulose 5-phosphate synthases: differential regulation in shoots and apocarotenoid-accumulating mycorrhizal rootsPlant J.31243-254(2002)DOI: 10.1046/j.1365-313X.2002.01352.x
Isopentenyl diphosphate, the universal precursor of isoprenoids, is synthesized by two separate routes, one in the cytosol and the other in plastids. The initial step of the plastidial pathway is catalysed by 1‐deoxy‐d ‐xylulose 5‐phosphate synthase (DXS), which was previously thought to be encoded by a single‐copy gene. We have identified two distinct classes of DXS‐like cDNAs from the model legume Medicago truncatula . The deduced mature MtDXS1 and MtDXS2 proteins, excluding the predicted plastid‐targeting peptides, are similar in size (72.7 and 71.2 kDa) yet share only 70% identity in their amino acid sequences, and both encode functional DXS proteins as shown by heterologous expression in Escherichia coli. Available DXS sequences from other plants can easily be assigned to either class 1 or class 2. Partial sequences of multiple DXS genes in a single genome may be found in the databases of several monocot and dicot plants. Blot analyses of RNA from M. truncatula , maize, tomato and tobacco demonstrate preferential expression of DXS1 genes in many developing plant tissues except roots. By contrast, DXS2 transcript levels are low in most tissues but are strongly stimulated in roots upon colonization by mycorrhizal fungi, correlated with accumulation of carotenoids and apocarotenoids. Monoterpene‐synthesizing gland cells of leaf trichomes appear to be another site of DXS2 gene activity. The potential importance of DXS1 in many housekeeping functions and a still hypothetical role of DXS2 in the biosynthesis of secondary isoprenoids is discussed.