Acquired cycloheximide resistance inNeurospora crassa andSclerotium rolfsii

Acquired resistance to the antibiotic cycloheximide developed byNeurospora crassa andSclerotium rolfsii was studied. Both the fungi gained certain level of tolerance to the antibiotic just after a single exposure and by serial transfers could adapt to the several-fold initial inhibitory dosage. Cycloheximide-resistance in both the cases was not a stable characteristic and was lost gradually on serial transfers in fungicide-free media. The resistant strains of both the fungi showed poor growth and decreased sporulation or sclerotia formation in fungicide-free media.Sclerotium rolfsii developed cross-resistance to Difolatan but not to Polyoxin-D, Hinosan and Bayleton. The cycloheximide-resistance inSclerotium rolfsii was probably due to the conversion of cycloheximide into isocycloheximide which is a less toxic structural analog, as revealed by thin layer chromatographic studies of culture filtrates of resistant and sensitive strains. The resistant strain ofSclerotium rolfsii retained its pathogenicity to tomato, mustard and chilli seedlings. However, the loss of sclerotia forming capacity and the instability of the acquired resistance trait may prove to be of ecological disadvantage to the resistant strain

Expression of the legume symbiotic lectin genes psl and gs52 promotes rhizobial colonization of roots in rice

Transgenic rice (Oryza sativa L. cv. Murasaki) carrying genes encoding pea (Pisum sativum) lectin (PSL) or wild-soybean (Glycine soja) lectin-nucleotide phosphohydrolase (GS52) were inoculated with Rhizobium leguminosarum bv. viciae or Bradyrhizobium japonicum USDA110, respectively, as well as with Rhizobium sp. NGR234, and root colonization was assessed in comparison to comparably inoculated control plants. The data showed that expression of PSL and GS52 significantly promoted rhizobial colonization of root epidermal cells including root hairs in rice. In addition, in the case of R. leguminosarum bv. viciae and B. japonicum USDA110 colonization of the psl and gs52 transgenic rice plants, respectively, the bacterial cells were found to preferentially home towards and aggregate maximally at the root hair tip regions rather than on the root hair "stalks". The above data suggest that the lectins PSL and GS52, which participate in rhizobial recognition by root epidermal cells in pea and soybean, respectively, are also able to facilitate rhizobial attachment and colonization of the epidermal cells in rice roots. Moreover, aggregation of R. leguminosarum bv. viciae and B. japonicum USDA110 cells preferentially at root hair tip regions suggest that similar to legumes, the PSL and GS52 lectins are targeted to the root hair tips in transgenic rice, enabling higher bacterial attachment/colonization at the tip region. Rhizobial colonization at root hair tips in the psl and gs52 rice plants frequently led to the localized dissolution of the cell wall creating perforations at the tip region. It is likely that the presence of lectins, such as PSL and GS52 leads to structural modifications in cell wall organization of the root hair/epidermal cells, making them prone to localized dissolution by the hydrolytic activity of compatible rhizobia to permit invasion of the root cells. © 2005 Elsevier Ireland Ltd. All rights reserved

Acquired cycloheximide resistance in Neurospora crassa and Sclerotium rolfsii

Acquired resistance to the antibiotic cycloheximide developed by Neurospora crassa and Sclerotium rolfsii was studied. Both the fungi gained certain level of tolerance to the antibiotic just after a single exposure and by serial transfers could adapt to the several-fold initial inhibitory dosage. Cycloheximide-resistance in both the cases was not a stable characteristic and was lost gradually on serial transfers in fungicide-free media. The resistant strains of both the fungi showed poor growth and decreased sporulation or sclerotia formation in fungicide-free media. Sclerotium rolfsii developed cross-resistance to Difolatan but not to Polyoxin-D, Hinosan and Bayleton. The cycloheximide-resistance in Sclerotium rolfsii was probably due to the conversion of cycloheximide into isocycloheximide which is a less toxic structural analog, as revealed by thin layer chromatographic studies of culture filtrates of resistant and sensitive strains. The resistant strain of Sclerotium rolfsii retained its pathogenicity to tomato, mustard and chilli seedlings. However, the loss of sclerotia forming capacity and the instability of the acquired resistance trait may prove to be of ecological disadvantage to the resistant strain. © 1985 Indian Academy of Sciences

Adaptation of Sclerotium rolfsii to polyoxin-​D

Even a single exposure to polyoxin D [22976-​86-​9] (400 μg​/mL) resulted in tolerance of S. rolfsii. The adaptation was retained through successive generations. The resistance involved both growth and sclerotial germination

Effect of divalent metal ions in membrane permeability modified by polyene antibiotics

Disks of beet root and potato tuber exhibited increased efflux of betacyanin , carbohydrates, and amino acids on treatment with the polyene antibiotics aureofungin [8065-​41-​6] and hamycin [1403-​71-​0]​. The effect of aureofungin was reversed by calcium [7440-​70-​2] ions in the case of beet root; but calcium ions did not antagonize the effect of hamycin. The effect of calcium ions against aureofungin was not obsd. in potato tuber disks. A combination of aureofungin or hamycin with EDTA [60-​00-​4] caused greater permeability of the membranes than the antibiotics (aureofungin or hamycin) alone, and this effect of the chelating agent was reversed by both calcium and magnesium [7439-​95-​4] ions. Calcium ions apparently have a stabilizing effect on the beet root membrane against aureofungin, and in general, both metal ions contribute to membrane stability by involvment in the structure of the membrane

The antibiotic effect of culture filtrates of some soil fungi on rhizobial growth in cultures

Four strains of Rhizobium sp. from peanut (Arachis hypogaea L.) root nodules were tested for their sensitivity to metabolites (culture filtrates) of more than ten common soil inhabiting fungi, in yeast extract mannitol agar and broth cultures. Among the rhizobial strains tested strain CB-530, BU-1 and BU-2 were not sensitive to metabolites of Myrothecium roridum and Fusarium moniliforme whereas CB-1024 was sensitive. Culture filtrates of Gliocladium roseum, Thielavia basicola and Drechslera pedicellata inhibited the strains CB-530 and BU-2 but not CB-1024. Most of the soil inhabiting fungi tested were inhibitory to rhizobial growth in vitro and very few were stimulatory, their effect in either case being strain specific. © 1984 Martinus Nijhoff/Dr W. Junk Publishers

Influence of Glomus mosseae on seed-borne fungal diseases of leguminous vegetable crops

Though the control of seed-borne diseases is achieved mainly by chemical seed treatment, use of biocontrol agents like Trichoderma and other antagonists is gaining importance. Studies were conducted to find out the influence of Glomus mosseae on the germination rate and survival of plants, in leguminous vegetable seeds infected by different fungal pathogens. Against seed borne inoculum varied degree of protection was obtained in different crops in G. mosseae soil. In frenchbean very good protection was obtained against seed-borne diseases caused by Fusarium solani, Rhizoctonia solani and Sclerotium rolfsii. Similarly, pea and pigeon pea seeds infected by R. solani and S. rolfsii showed better crop stand in G. mosseae soil. Protection was obtained to some extent (10 to 15) in the case of cowpea seeds infected by Fusarium species and S. rolfsii. In clusterbean crop no protection was obtained against seed-borne diseases by mycorrhizal fungi excepting Fusarium. Glomus mosseae soil did not offer any protection to the seeds of any of the test crops infected by Macrophomina phaseolina

Biobleaching of composit textile-dye effluent using bacterial consortia

The mixed culture for biobleaching were isolated from the effluent of dyeing houses and sludge of the effluent treatment plants of dyeing houses. Among the several isolates representatives genera, Pseudomonas sp. and Bacillus sp. have found to be potential strains with synergetic mode of biobleaching the coloured effluents about 60-70 colour removal was observed associated with 2-3 fold decrease in BOD and COD using bacterial consortia. This study exemplified the treatment feasability or assessment of potent bacterial consortia as a biobleaching agents for treating composite textile dye effluent

Metabolic engineering of rice with soybean isoflavone synthase for promoting nodulation gene expression in rhizobia

Isoflavonoids are derived from a flavonone intermediate, naringenin, that is ubiquitously present in plants, and play a critical role in plant development and defence response. Isoflavonoids secreted by the legumes also play an important role in promoting the formation of nitrogen-fixing nodules by symbiotic rhizobia. In these plants, the key enzyme that redirects phenylpropanoid pathway intermediates from flavonoids to isoflavonoids is the cytochrome P450 mono-oxygenase, isoflavone synthase. In an effort to develop a rice variety possessing the ability to induce nodulation (nod) genes in rhizobia, the IFS gene from soybean was incorporated into rice (Oryza sativa L. cv. Murasaki R86) under the control of the 35S promoter. The presence of IFS in transgenic rice was confirmed by PCR and Southern blot analysis. Analyses of the 35S-IFS transgenic lines demonstrated that the expression of the IFS gene led to the production of the isoflavone genistein in rice tissues. These results showed that the soybean IFS gene-expressed enzyme is active in the R86 rice plant, and that the naringenin intermediate of the anthocyanin pathway is available as a substrate for the introduced foreign enzyme. The genistein produced in rice cells was present in a glycoside form, indicating that endogenous glycosyltransferases were capable of recognizing genistein as a substrate. Studies with rhizobia demonstrated that the expression of isoflavone synthase confers rice plants with the ability to produce flavonoids that are able to induce nod gene expression, albeit to varied degrees, in different rhizobia. © The Author 2006. Published by Oxford University Press on behalf of the Society for Experimental Biology. All rights reserved