J.A. van Pelt

Induction of systemic resistance byPseudomonas fluorescens in radish cultivars differing in susceptibility to fusarium wilt, using a novel bioassay

Pseudomonas fluorescens-mediated induction of systemic resistance in radish against fusarium wilt (Fusarium oxysporum f. sp.raphani) was studied in a newly developed bioassay using a rockwool system. In this bioassay the pathogen and bacterium were confirmed to be confined to spatially separate locations on the plant root, throughout the experiment. Pathogen inoculum obtained by mixing peat with microconidia and subsequent incubation for four days at 22 °C, yielded a better percentage of diseased plants than a microconidial suspension drench, an injection of a microconidial suspension into the hypocotyl, or a talcum inoculum.Pseudomonas fluorescens strain WCS374 applied in talcum or peat, but not as a suspension drench, induced systemic resistance. A minimal initial bacterial inoculum density of ≥105 CFU WCS374 root−1 was required to significantly reduce the percentage diseased plants. At least one day was necessary between bacterization of strain WCS374 in talcum on the root tips and inoculation of the pathogen in peat on the root base, for an optimal induction of systemic resistance. Strain WCS374 induced systemic resistance in six radish cultivars differing in their susceptibility toF. oxysporum f. sp.raphani. Significant suppression of disease by bacterial treatments was generally observed when disease incidence in the control treatment, depending on pathogen inoculum density, ranged between approximately 40 to 80%. Strains WCS374 and WCS417 ofPseudomonas fluorescens induced systemic resistance against fusarium wilt, whereasP. putida WCS358 did not. This suggests that the induction of systemic resistance byPseudomonas spp. is dependent on strain-specific traits.

Suppression of fusarium wilt of radish by co-inoculation of fluorescentPseudomonas spp. and root-colonizing fungi

In an earlier study, treatment of radish seed with the bacteriumPseudomonas fluorescens WCS374 suppressed fusarium wilt of radish (Fusarium oxysporum f. sp.raphani) in a commercial greenhouse [Leemanet al., 1991b, 1995a]. In this greenhouse, the areas with fusarium wilt were localized or expanded very slowly, possibly due to disease suppressiveness of the soil. To study this phenomenon, fungi were isolated from radish roots collected from the greenhouse soil. Roots grown from seed treated with WCS374 were more abundantly colonized by fungi than were roots from nonbacterized plants. Among these were several species known for their antagonistic potential. Three of these fungi,Acremonium rutilum, Fusarium oxysporum andVerticillium lecanii, were evaluated further and found to suppress fusarium wilt of radish in a pot bioassay. In an induced resistance bioassay on rockwool,F. oxysporum andV. lecanii suppressed the disease by the apparent induction of systemic disease resistance. In pot bioassays with thePseudomonas spp. strains, the pseudobactin-minus mutant 358PSB− did not suppress fusarium wilt, whereas its wild type strain (WCS358) suppressed disease presumably by siderophore-mediated competition for iron. The wild type strains of WCS374 and WCS417, as well as their pseudobactin-minus mutants 374PSB− and 417PSB− suppressed fusarium wilt. The latter is best explained by the fact that these strains are able to induce systemic resistance in radish, which operates as an additional mode of action. Co-inoculation in pot bioassays, ofA. rutilum, F. oxysporum orV. lecanii with thePseudomonas spp. WCS358, WCS374 or WCS417, or their pseudobactin-minus mutants, significantly suppressed disease (except forA. rutilum/417PSB− and all combinations with 358PSB−), compared with the control treatment, if the microorganisms were applied in inoculum densities which were ineffective in suppressing disease as separate inocula. If one or both of the microorganism(s) of each combination were applied as separate inocula in a density which suppressed disease, no additional suppression of disease was observed by the combination. The advantage of the co-inoculation is that combined populations significantly suppressed disease even when their individual population density was too low to do so. This may provide more consistent biological control. The co-inoculation effect obtained in the pot bioassays suggests that co-operation ofP. fluorescens WCS374 and indigenous antagonists could have been involved in the suppression of fusarium wilt of radish in the commercial greenhouse trials.

A fluorimetric enzyme assay for the diagnosis of Morquio disease type A (MPS IV A)

4-Methylumbelliferyl-beta-D-galactopyranoside-6-sulphate was synthesized and used for the determination of galactose-6-sulphate sulphatase activity. Fibroblasts and leucocytes from 12 different Morquio A patients, showed 0.0-2.7% of mean normal galactose-6-sulphate sulphatase activity. Heterozygotes showed intermediate activities. The enzymatic liberation of the fluorochrome from 4-methylumbelliferyl-beta-D-galactopyranoside-6-sulphate requires the sequential action of galactose-6-sulphate sulphatase and beta-galactosidase. Normal beta-galactosidase activity caused nearly complete hydrolysis of non-fluorescing 4-methylumbelliferyl-galactoside, formed during incubation. In cell extracts with a beta-galactosidase deficiency however, a second incubation in the presence of excess beta-galactosidase is needed to avoid underestimation of galactose-6-sulphate sulphatase activity.

Consumption of aphid honeydew, a wheat yield reduction factor, by phyllosphere yeasts under field conditions

Aphid honeydew on wheat leaves can affect host physiology directly and can stimulate infection by necrotrophic pathogens. The role of naturally occurring saprophytes on wheat flag leaves in removing aphid honeydew was examined in five field experiments at different locations in the Netherlands in 1987 and 1988. Aphid populations, saprophyte populations and aphid honeydew were measured weekly. Diseases were monitored at 1–4 week intervals.In the control treatment, sprayed with water, the naturally occurring saprophytes consumed the honeydew almost completely, except in one experiment in which the aphid population increased very rapidly. In the treatments in which the saprophytes were reduced by the broad-spectrum fungicide maneb in 1987 and with maneb alternated with anilazin in 1988, honeydew accumulated. The observed honeydew consumption by the naturally occurring saprophytic population is ascribed mainly to pink and white yeasts (Sporobolomyces spp. andCryptococcus spp., respectively).Additional treatments showed, that in the presence of the naturally occurring saprophytes the yield loss per aphid-infestation-day was lower than when the saprophytes were inhibited by fungicides, showing that yeasts can reduce the detrimental effect of aphid honeydew in wheat.

A comparative study of sialyloligosaccharides isolated from sialidosis and galactosialidosis urine

SummarySialic acid-containing carbohydrates were isolated from sialidosis urine by a combination of gel-filtration on Bio-Gel P-6 and medium-pressure anion-exchange chromatography on Mono Q. The Mono Q fractions were subjected to 500-MHz1H-NMR spectroscopy, sugar analysis and analytical HPLC on Lichrosorb-NH2. These methods indicated the presence of variousN-acetyllactosamine type sialyloligosaccharides differing from each other in branching pattern and sialic acid linkage types. Among the structures were fully and partially sialylated mono-, di-, tri- and tetra-antennary compounds. A comparison with the results from galactosialidosis urine indicated that essentially the same carbohydrates were present in both urines, but that the relative amounts of the various sialyloligosaccharides differ to some extent. Sialidosis urinary oligosaccharides contained relatively more α2–6 linked sialic acid than oligosaccharides from galactosialidosis urine. It could be concluded that the additionalβ-galactosidase deficiency in galactosialidosis did not influence the nature of the excreted material and that the sialidase deficiency determined completely the defective catabolism of glycoproteins in both sialidosis and galactosialidosis.

The role of ethylene in rhizobacteria-induced systemic resistance (ISR)

To protect themselves from disease, plants have evolved sophisticated defense mechanisms in which the signal molecules salicylic acid (SA), jasmonic acid (JA) and ethylene (ET) often play crucial role. Elucidation of signaling pathways controlling disease resistance is a major objective in research on plant-pathogen interactions. The capacity of a plant to develop a broad spectrum, systemic acquired resistance (SAR) after primary infection with a necrotizing pathogen is well known and its signal transduction pathway extensively studied. Plants of which the roots have been colonized by specific strains of nonpathogenic fluorescent Pseudomonas spp. develop a phenotypically similar form of protection that is called rhizobacteria-mediated induced systemic resistance( ISR). In contrast to pathogen induced SAR, which is regulated by SA, rhizobacteria mediated ISR is controlled by a signaling pathway in which ET and JA play key roles.In the past decade, the model plant species Arabidopsis thaliana was explored to study the molecular basis of rhizobacteria mediated ISR. Here we review the current knowledge of the signal transduction steps involved in the ISR pathway that leads from recognition of the rhizobacteria in the roots to systemic expression of broad-spectrum disease resistance in above-ground foliar tissues.

Carbohydrate-deficient transferrin values in neonatal and umbilical cord blood.

The carbohydrate-deficient glycoprotein syndrome (CDGS) is a newly defined inherited multisystemic disease with severe nervous system involvement. Since the initial report in 1980 by Jaeken et al more than 120 patients all over the world have been described. The clinical features can be very severe and several subtypes have been recognized. The biochemical hallmark is defective glycosylation of transferrin, although a variety of other glycoproteins is affected. The reduced glycosylation and sialylation can be made visible by isoelectric focusing (IEF) as a cathodal shift of the transferrin isoforms (Jaeken et al 1993). Evidence is increasing that the basic defect in CDGS type I results in a lack of one or more complete N-linked carbohydrate chains of glycoproteins, rather than in incomplete chains, which is the case in CDGS type II (Powell et al 1994). As CDGS occurs relatively frequently, a (semi-)automated biochemical test rather than IEF would be advantageous. We therefore investigated the possibility of using a commercially available test for the analysis of carbohydrate-deficient transferrin (CDT). This CDTect test has been developed for the detection of chronic alcohol abuse (Stibler 1991) and measures the amount of a-, mono- and disialotransferrin isoforms by an immunochemical, non-radioactive method. Analyses were carried out in umbilical cord blood and neonatal blood samples in order to collect reference values for use of CDTect in screening for CDGS.

Oligosaccharide excretion in adult Gaucher disease

Gaucher disease is a lysosomal storage disease characterized by storage of glucocerebroside due to lysosomal glucocerebrosidase deficiency. Increased urinary excretion of sialyloligosaccharides and mannosylglycoasparagines has been described for two patients with the infantile form of the disease, probably as a consequence of obstruction of lysosomal functioning due to the glycolipid accumulation in lysosomes. By thin-layer chromatography, we found increased urinary oligosaccharide excretion in a series of adult non-neuronopathic patients. Oligosaccharide patterns were comparable between patients and also with the pattern observed in infantile Gaucher disease. Composition was analysed by methanolysis and gas chromatography. Mannose and N-acetylglucosamine are the main carbohydrates in all oligosaccharide bands. A statistically significant correlation was found between oligosaccharide excretion and the severity of the disease expressed as severity score index. Patients treated with enzyme replacement therapy showed a reduction up to 65% of the original oligosaccharide excretion after 1 year of treatment, comparable with the reduction in spleen volume.