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Displaying results 1 to 10 of 73.

Publications

Ibdah, M.; Krins, A.; Seidlitz, H.K.; Heller, W.; Strack, D.; Vogt, T. Spectral dependence and dose response of flavonol and betacyanin accumulation in <em>Mesembryanthemum crystallinum</em> under enhanced UV radiation Plant Cell Environm. 25, 1145-1154, (2002)

Mesembryanthemum crystallinum L. (Aizoaceae) is a drought and salt tolerant halophyte, able to endure harsh environmental conditions. Upon irradiation with high light irradiance (1200 - 1500 µmol·m-2·s-1) it displays a rapid cellspecific accumulation of plant secondary metabolites in the upper leaf epidermis, a phenomenon not detectable with salt or drought treatment. The accumulation of these compounds the betacyanins and acylated flavonol glycosides increases if the plants are exposed to polychromatic radiation with a progressively decreasing short wave cut-off in the UV range. The response is localized in epidermal bladder cells on the tips of young leaves and epidermal layers of fully expanded leaves. We demonstrate that the accumulation of flavonols and betacyanins can be described by a weakly sigmoid dose function in combination with an exponential de-crease of the plant's response function with increasing wavelength.
Publications

Vogt, T. Substrate specificity and sequence analysis define a polyphyletic origin of betanidin 5- and 6-O-glucosyltransferase from <em>Dorotheanthus bellidiformis</em> Planta 214, , 492-495, (2002)

Betanidin 6-O-glucosyltransferase (6-GT) is involved in the gly-cosylation of betacyanins, which replace the chromogenic anthocyanins as flower colorants in the Caryophyllales. The 6-GT cDNA was cloned from a cDNA library of Dorotheanthus bellidiformis and the amino acid and nucleotide sequences were shown to be distinctly different from the corresponding betanidin 5-O-glucosyltransferase (5-GT) from the same plant species. Although both enzymes share very similar substrates, the proteins show only 19 % amino acid sequence identity. In contrast, the protein sequence of the 6-GT showed signifi-cant identity to GTs from other species and may identify a new cluster of putative anthocyanidin GTs. Therefore, 6-GT and 5-GT apparently have evolved independently from ancestral glucosyltransferases involved in flavonoid biosynthesis.
Publications

Fester, T.; Hause, B.; Schmidt, D.; Halfmann, K.; Schmidt, J.; Wray, V.; Hause, G.; Strack, D. Occurrence and localization of apocarotenoids in arbuscular mycorrhizal plant roots Plant Cell Physiol 43, 256-265, (2002) DOI: 10.1093/pcp/pcf029

The core structure of the yellow pigment from arbuscular mycorrhizal (AM) maize roots contains the apocarotenoids mycorradicin (an acyclic C14 polyene) and blumenol C cellobioside (a C13 cyclohexenone diglucoside). The pigment seems to be a mixture of different esterification products of these apocarotenoids. It is insoluble in water and accumulates as hydrophobic droplets in the vacuoles of root cortical cells. Screening 58 species from 36 different plant families, we detected mycorradicin in mycorrhizal roots of all Liliopsida analyzed and of a considerable number of Rosopsida, but also species were found in which mycorradicin was undetectable in mycorrhizal roots. Kinetic experiments and microscopic analyses indicate that accumulation of the yellow pigment is correlated with the concomitant degradation of arbuscules and the extensive plastid network covering these haustorium-like fungal structures. The role of the apocarotenoids in mycorrhizal roots is still unknown. The potential C40 carotenoid precursors, however, are more likely to be of functional importance in the development and functioning of arbuscules.
Publications

Hause, B.; Maier, W.; Miersch, O.; Kramell, R.; Strack, D. Induction of jasmonate biosynthesis in arbuscular mycorrhizal barley roots Plant Physiol. 130, 1213-1220, (2002) DOI: 10.1104/pp.006007

Colonization of barley (Hordeum vulgare cv Salome) roots by an arbuscular mycorrhizal fungus, Glomus intraradices Schenck & Smith, leads to elevated levels of endogenous jasmonic acid (JA) and its amino acid conjugate JA-isoleucine, whereas the level of the JA precursor, oxophytodienoic acid, remains constant. The rise in jasmonates is accompanied by the expression of genes coding for an enzyme of JA biosynthesis (allene oxide synthase) and of a jasmonate-induced protein (JIP23). In situ hybridization and immunocytochemical analysis revealed that expression of these genes occurred cell specifically within arbuscule-containing root cortex cells. The concomitant gene expression indicates that jasmonates are generated and act within arbuscule-containing cells. By use of a near-synchronous mycorrhization, analysis of temporal expression patterns showed the occurrence of transcript accumulation 4 to 6 d after the appearance of the first arbuscules. This suggests that the endogenous rise in jasmonates might be related to the fully established symbiosis rather than to the recognition of interacting partners or to the onset of interaction. Because the plant supplies the fungus with carbohydrates, a model is proposed in which the induction of JA biosynthesis in colonized roots is linked to the stronger sink function of mycorrhizal roots compared with nonmycorrhizal roots.
Publications

Berlich, M.; Menge, S.; Bruns, I.; Schmidt, J.; Schneider, B.; Krauss, G.-J. Coumarins give misleading absorbance with Ellmans reagent suggestive of thiol conjugates investigations with two moss species Analyst 127, 333-336, (2002) DOI: 10.1039/B110988J

In the course of a screening for phytochelatins in cadmium-exposed bryophytes in the terrestrial mosses Polytrichum formosum and Atrichum undulatum we detected compounds with absorption properties and retention times similar to phytochelatins when applying the commonly used standard method RP-HPLC and post-column derivatization with thiol-specific DTNB (Ellman) reagent. Moreover, as with phytochelatins known in other plants, the concentrations of these compounds increased slightly after Cd stress. The concentration of the precursor glutathione (γ-ECG), however, increased in the presence of Cd. In order to verify the identity of these putative phytochelatins we performed LC-ESI-MS analyses as well as 1H NMR on extracts from P. formosum and A. undulatum. Spectroscopic investigations indicated that the detected compounds were neither phytochelatins nor other thiol compounds. From the results of HPLC-1H NMR and mass spectrometry we concluded that at least one of these substances was a coumarin, probably a 5,8-dihydroxy-7-methoxycoumarin-5-β-glucopyranoside, which has already been described for A. undulatum and P. formosum. The results of our investigations prove that under the basic pH conditions essential for the Ellman test for thiol compounds, coumarins show comparable UV/VIS absorption properties. Therefore, a positive post-column Ellman reaction cannot unambiguously prove the presence of thiol-containing compounds in plants.
Publications

Shu-Ming, Li; Westrich, L.; Schmidt, J.; Kuhnt, C.; Heide, L. Methyltransferase genes in <span>Streptomyces rishiriensis</span>: new coumermycin derivatives from gene inactivation experiments Microbiology 148, 3317-3326, (2002) DOI: 10.1099/00221287-148-10-3317

The coumarin antibiotic coumermycin A1 contains at least eight methyl groups, presumably derived from S-adenosylmethionine. Two putative methyltransferase genes, couO and couP, of the coumermycin A1 biosynthetic gene cluster were inactivated by in-frame deletion. In the resulting mutants, coumermycin A1 production was abolished. New coumermycin derivatives were accumulated instead, and were identified by HPLC-MS using selected reaction monitoring via electrospray ionization. couO mutants accumulated a coumermycin derivative lacking the methyl groups at C-8 of the characteristic aminocoumarin rings, whereas in the couP mutant a coumermycin derivative lacking the methyl groups at the 4-hydroxyl groups of the two deoxysugar moieties was identified. These results provided evidence that couO encodes a C-methyltransferase responsible for the transfer of a methyl group to C-8 of the aminocoumarin ring, and couP an O-methyltransferase for methylation of 4-OH of the sugar in the biosynthesis of coumermycin A1, respectively. C-methylation of the aminocoumarin ring is considered as an early step of coumermycin biosynthesis. Nevertheless, the intermediates with the non-methylated aminocoumarin ring were accepted by the enzymes catalysing the subsequent steps of the pathway. The new, demethylated secondary metabolites were produced in an amount at least as high as that of coumermycin A1 in the wild-type.
Books and chapters

Wasternack, C.; Hause, B. Jasmonates and octadecanoids: Signals in plant stress responses and development (Moldave, K.). 72, 165-221, (2002) DOI: 10.1016/S0079-6603(02)72070-9

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Publications

Hause, B.; Meyer, K.; Viitanen, P.V.; Chapple, C.; Strack, D. Immunolocalization of 1-O-sinapoylglucose:malate sinapoyltransferase in Arabidopsis thaliana Planta 215, 26-32, (2002) DOI: 10.1007/s00425-001-0716-y

The serine carboxypeptidase-like protein 1-O-sinapoylglucose:malate sinapoyltransferase (SMT) catalyzes the transfer of the sinapoyl moiety of 1-O-sinapoylglucose to malate in the formation of sinapoylmalate in some members of the Brassicaceae. Rabbit polyclonal monospecific antibodies were raised against the recombinant SMT produced in Escherichia coli from the corresponding Arabidopsis thaliana (L.) Heynh. cDNA. Immunoblot analysis of protein from different Arabidopsis tissues showed that the SMT is produced in all plant organs, except in the seeds and young seedlings. The enzyme was most abundant in older seedlings as well as in rosette leaves and the flowering stem of the plant. Minor amounts were found in the cauline leaves, flower buds and siliques. Traces were detected in the root and flowers. Arabidopsis and transgenic tobacco (Nicotiana tabacum L.) plants expressing the full-length Arabidopsis SMT containing an N-terminal signal peptide showed apparent molecular masses of the protein of 52-55 kDa. The difference of ca. 8 kDa compared to the recombinant protein produced in E. coli was shown to be due to post-translational N-glycosylation of SMT in plants. Immunofluorescent labeling of Arabidopsis leaf sections localized SMT to the central vacuoles of mesophyll and epidermal cells. Comparable leaf sections of an SMT deletion mutant showed no vacuolar immunofluorescent labeling. We conclude that Arabidopsis SMT is synthesized as a precursor protein that is targeted to the endoplasmic reticulum where the signal peptide is removed. The correct N-terminus of the recombinantly produced SMT protein lacking the signal peptide was confirmed by Edman degradation. The protein is probably glycosylated in the Golgi apparatus from where it is subsequently routed to the vacuole.
Books and chapters

Scheel, D.; Wasternack, C. Signal transduction in plants: Cross-talk with the environment (Scheel, D., Wasternack, C.). University Press, Oxford, UK 1-5, (2002)

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Publications

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 roots Plant J. 31, 243-254, (2002)

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.
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