Rescuing activity of galactoglycerolipids from cellular lesions induced by 5-aminolevulinic acid.
(25/1585)
An anti-oxygen radical reagent of a bacterial metabolite, M874 monogalactoglycerolipid (di-O-12-methyl-tetradecanoyl-3-O-beta-D-galactopyranosyl-sn-glycerol ), was tested for its ability to protect two organisms against cellular lesions induced by 5-aminolevulinic acid (ALA) and light. In Corynebacterium flavescens ATCC 10340, extracellular uroporphyrin and coproporphyrin were the main porphyrin products. Although less than 2 mM ALA increased porphyrin synthesis, ALA levels above 3 mM inhibited the synthesis. Depending on the light intensity, the amount of porphyrin decreased and ALA-induced cytotoxicity increased. The lesion was more severe in the case of coproporphyrin than uroporphyrin. The porphyrin lesion produced in low intensity light (300 lx) was considerably reduced by 100 microM M874 glycolipid, although the reduction in intense light (3,000 lx) was restricted to a lower level. Similar results were obtained with radish (Raphanus sativus). The ALA concentration that inhibited porphyrin synthesis and stem growth was similar to that seen with C. flavescens. Although the exogenous addition of M874 glycolipid to the radish did not prevent ALA-induced cellular injury, the co-culture of radish and a glycolipid producing bacterium (Microbacterium sp. M874) resulted in a significant prevention of cellular injury. This was true only under enforced adhesion conditions through the action of a polysaccharide flocculant H12. Some species of monogalactoglycerolipids were found in Corynebacterium and radish that showed prominent oxygen radical-protecting activities similar to that of M874 glycolipid. These monogalactoglycerolipids might function in vivo as agents to prevent ALA-induced cytological lesions, although the concentrations were low in Corynebacterium and radish. (+info)
Enhancement of plant stem growth by flocculation of the antibiotic-producing bacterium, Pseudomonas fluorescens S272, on the roots.
(26/1585)
The antibiotic-producing bacterium, Pseudomonas fluorescens, is assumed to be important in protecting plants from soilborne diseases. S. fluorescens S272, a hyper-producing strain of pyoluteorin (PT) and 2,4-diacetylphloroglucinol (DG), had previously been isolated from soil. The present paper reported that the growth of water-cultivated Kaiware radish was promoted to 120-140% of its normal level by the coaddition of an S272 culture broth (0.01-1% v/v) and a polysaccharide flocculant (1-100 ppm) from Klebsiella pneumoniae H12. Tight adhesion of S272 cells to the root tissue was microscopically observed. The growth promotion is assumed to have been caused by antibiotic effects for the following two reasons: 1) PT (4 mg/l) and DG (24 mg/l) addition to a radish culture enhanced stem growth to 130% of the normal level; 2) a culture solution containing the S272 culture broth (0.01-1% v/v) markedly inhibited the decomposition of hypersensitive chrysanthemum leaves. A soil-cultivation experiment with Gomphrena globosa under natural conditions also exhibited enhanced stem length (160%) by coaddition of the S272 culture broth and H12 polysaccharide. These results suggest that polysaccharide-enhanced adhesion of P. fluorescens S272 cells might be useful for promoting plant growth through the increased antibiotic effect. (+info)
A homologue of EGL1 encoding endo-1,4-beta-glucanase in elongating pea stems.
(27/1585)
A gene (EGL2) encoding an endo-1,4-beta-glucanase in peas has been cloned as a homologue of EGL1. EGL2 encodes a polypeptide of 506 amino acids, including a 24-mer putative signal polypeptide. The gene product contains a domain conserved in endo-1,4-beta-glucanase (family 9) showing 60% amino acid identity to EGL1. EGL2 mRNA was accumulated only in the elongating regions of pea stems, although EGL1 mRNA was abundant in both elongating and non-elongating tissues. However, the level of EGL2 mRNA was not increased by the treatment with sucrose and auxin in pea segments. These results suggest that the expression of EGL2 either requires the presence of other factors related to the auxin effect or occurs independent of auxin in the elongating pea stems. (+info)
Ectopic deposition of lignin in the pith of stems of two Arabidopsis mutants.
(28/1585)
The biosynthesis of lignin in vascular plants is regulated both developmentally and environmentally. In the inflorescence stems of Arabidopsis, lignin is mainly deposited in the walls of xylem cells and interfascicular fiber cells during normal plant growth and development. The mechanisms controlling the spatial deposition of lignin remain unknown. By screening ethyl methanesulfonate-mutagenized populations of Arabidopsis, we have isolated two allelic elp1 (ectopic deposition of lignin in pith) mutants with altered lignin deposition patterns. In elp1 stems, lignin was ectopically deposited in the walls of pith parenchyma cells in addition to its normal deposition in the walls of xylem and fiber cells. Lignin appeared to be deposited in patches of parenchyma cells in the pith of both young and mature elp1 stems. The ectopic deposition of lignin in the pith of elp1 stems was accompanied by an increase in the activities of enzymes in the lignin biosynthetic pathway and with the ectopic expression of caffeoyl coenzyme A O-methyltransferase in pith cells. These results indicate that the ELP1 locus is involved in the repression of the lignin biosynthetic pathway in the pith. Isolation of the elp1 mutants provides a novel means with which to study the molecular mechanisms underlying the spatial control of lignification. (+info)
Nodule-expressed Cyp15a cysteine protease genes map to syntenic genome regions in Pisum and Medicago spp.
(29/1585)
PsCyp15a is a gene that encodes a vacuolar cysteine protease expressed in wilt-induced shoots of Pisum sativum (pea) and in root nodules. To further the understanding of nodular PsCyp15a expression, a region 5' to the coding sequence of the gene was cloned. Varying lengths of 5' untranslated sequence were fused with the uidA coding region and introduced from Agrobacterium rhizogenes into "hairy roots" of Vicia hirsuta. In this transgenic root nodulation assay, a promoter sequence of 900 bp was sufficient to give an expression pattern indistinguishable from that obtained in pea nodules by in situ hybridization. An orthologue of PsCyp15a was cloned from nodule mRNA of Medicago sativa and a corresponding gene identified in M. truncatula was also shown to express strongly in nodules. With molecular mapping techniques, it was demonstrated that these genes map to a syntenic genome location in pea and Medicago spp., but the map positions of the Cyp15a genes cannot be correlated with existing nodulation mutants. (+info)
The BMP1 gene is essential for pathogenicity in the gray mold fungus Botrytis cinerea.
(30/1585)
In Magnaporthe grisea, a well-conserved mitogen-activated protein (MAP) kinase gene, PMK1, is essential for fungal pathogenesis. In this study, we tested whether the same MAP kinase is essential for plant infection in the gray mold fungus Botrytis cinerea, a necrotrophic pathogen that employs infection mechanisms different from those of M. grisea. We used a polymerase chain reaction-based approach to isolate MAP kinase homologues from B. cinerea. The Botrytis MAP kinase required for pathogenesis (BMP) MAP kinase gene is highly homologous to the M. grisea PMK1. BMP1 is a single-copy gene. bmp1 gene replacement mutants produced normal conidia and mycelia but were reduced in growth rate on nutrient-rich medium. bmp1 mutants were nonpathogenic on carnation flowers and tomato leaves. Re-introduction of the wild-type BMP1 allele into the bmp1 mutant restored both normal growth rate and pathogenicity. Further studies indicated that conidia from bmp1 mutants germinated on plant surfaces but failed to penetrate and macerate plant tissues. bmp1 mutants also appeared to be defective in infecting through wounds. These results indicated that BMP1 is essential for plant infection in B. cinerea, and this MAP kinase pathway may be widely conserved in pathogenic fungi for regulating infection processes. (+info)
Cell-specific and conditional expression of caffeoyl-coenzyme A-3-O-methyltransferase in poplar.
(31/1585)
Caffeoyl coenzyme A-3-O-methyltransferase (CCoAOMT) plays an important role in lignin biosynthesis and is encoded by two genes in poplar (Populus trichocarpa). Here, we describe the expression pattern conferred by the two CCoAOMT promoters when fused to the gus-coding sequence in transgenic poplar (Populus tremula x Populus alba). Both genes were expressed similarly in xylem and differentially in phloem. In xylem, expression was preferentially observed in vessels and contact rays, whereas expression was barely detectable in storage rays and fibers, suggesting different routes to monolignol biosynthesis in the different xylem types. Furthermore, after wounding, fungal infection, and bending, the expression of both genes was induced concomitantly with de novo lignin deposition. Importantly, upon bending and leaning of the stem, the cell-specific expression pattern was lost, and both genes were expressed in all cell types of the xylem. CCoAOMT promoter activity correlated well with the presence of the CCoAOMT protein, as shown by immunolocalization. These expression data may explain, at least in part, the heterogeneity in lignin composition that is observed between cell types and upon different environmental conditions. (+info)
Exploiting secondary growth in Arabidopsis. Construction of xylem and bark cDNA libraries and cloning of three xylem endopeptidases.
(32/1585)
The root-hypocotyl of Arabidopsis produces a relatively large amount of secondary vascular tissue when senescence is delayed by the removal of inflorescences, and plants are grown at low population density. Peptidase zymograms prepared from isolated xylem and phloem revealed the existence of distinct proteolytic enzyme profiles within these tissues. cDNA libraries were constructed from isolated xylem and bark of the root-hypocotyl and screened for cDNAs coding for cysteine, serine, and aspartic peptidases. Three cDNAs, two putative papain-type cysteine peptidases (XCP1 and XCP2) and one putative subtilisin-type serine peptidase (XSP1), were identified from the xylem library for further analysis. Using RNA gel blots it was determined that these peptidases were expressed in the xylem and not in the bark. Quantitative reverse transcriptase-polymerase chain reaction confirmed the RNA gel-blot results and revealed high levels of XCP1 and XCP2 mRNA in stems and flowers of the infloresence. A poly-histidine-tagged version of XCP1 was purified from Escherichia coli by denaturing metal-chelate chromatography. Following renaturation, the 40-kD recombinant XCP1 was not proteolytically active. Activation was achieved by incubation of recombinant XCP1 at pH 5.5 and was dependent on proteolytic processing of the 40-kD inactive polypeptide to a 26-kD active peptidase. (+info)