Biomedical subjects

R N Strange

Publications and source records attributed to R N Strange.

7 recordsLinked to original sources

PubMed1998

Plants under attack II.

In many diseases of plants there is a well defined genetic relationship between host and pathogen, the host possessing resistance genes and the pathogen possessing avirulence genes. Where these are cognate their products interact and trigger a variety of resistance responses, resulting in an incompatible interaction. Where they are not cognate the pathogen is not recognised and invades the host causing a compatible interaction. A few resistance genes and a larger number of avirulence genes have been cloned and this information has afforded us new perspectives of the recognition phenomenon itself and the means by which virulent pathogens avoid being recognised. Mechanisms of resistance range from preformed antimicrobial compounds to a series of components that are induced as a response to microbial challenge. Most of these induced reactions are preceded by and may be triggered by an oxidative burst which results in the cross-linking of cell wall proteins and also causes the death of one to several cells. This localized death of host cells, termed the hypersensitive response, provides an explanation for resistance to obligate parasites which require living host tissue but not for resistance to facultative parasites which colonise dying or dead tissue. However, the hypersensitive response appears to be intimately involved with several other defence responses such as the synthesis and accumulation of phytoalexins, lignification and the production of hydrolase enzymes that attack the invader. Salicylic acid has proved fundamental to the effecting of these defence responses and also to the phenomenon of systemic acquired resistance whereby a previous challenge from a pathogen induces the expression of enhanced resistance to a second challenge by the same or another organism. Despite these sophisticated defences plants still succumb to attack. Two of the weapons to which they are vulnerable and which are produced by many successful pathogens are toxins and enzymes. In some instances an understanding of these has pointed to novel methods of control supplementary to that obtained by conventional breeding for resistance.

Genes, Bacterial↗

PubMed1994

Production of a toxin stemphol by Stemphylium species.

Five of 11 isolates of Stemphylium botryosum Wallr. from oilseed rape produced the phytotoxin stemphol when cultured on rice, with yields varying from 15.0 to 98.4 mg/kg, and three of them also produced the toxin on Czapek Dox (CD) liquid medium supplemented with cations (0.12-0.31 mg/L) and potato-dextrose (PD) broth (0.37-1.47 mg/L). In liquid cultures about 95% of stemphol was found in the mycelium, and toxin production was slightly increased when cultures were exposed to near UV light rather than being grown in the dark. The LD50 concentrations for stemphol against isolated cells of oilseed rape and chickpea were 8.4 and 7.0 microM, respectively. One isolate of S. majusculum (strain no. 135459) produced much greater amounts of stemphol, i.e., 22.8 mg/L, 535.3 mg/L, and 548 mg/kg when grown on CD, PD, and rice, respectively. Leaves of oilseed rape, artificially infected with S. majusculum and bearing lesions that occupied an average of 70% of the lamina contained 0.9 microgram stemphol per gram dry weight of leaf tissue.

Biological Assay↗

PubMed1990

Chlamydosporol, a new metabolite from Fusarium chlamydosporum.

Extracts of rice on which an isolate of Fusarium chlamydosporum had been cultured were toxic to brine shrimps. The toxic fraction was purified by flash chromatography to give two compounds which were identified by UV, IR, NMR and mass spectroscopy at the 6 alpha and 6 beta isomers of 5-hydroxy-4-methoxy-6,8a-dimethyl-6,7-dihydro-2H, 8aH-pyrano[2,3-b]pyran-2-one. These lactones for which the name chlamydosporol is proposed have not been reported previously. When tested in brine shrimp and HeLa cell assays, the LC50 concentration for a mixture of the isomers was approximately 400 micrograms/ml in both systems.

Animals↗

PubMed1988

Toxigenicity of some fusaria associated with plant and human diseases in the Malaysian peninsula.

In the course of a plant disease survey of the Malaysian Peninsula (Malaysia comprises the Malaysian Peninsula, Sabah and Sarawak) during the period 1981-1986, more than 1000 isolates of Fusarium were obtained from diseased plants and seeds. Two further isolates were obtained from patients admitted to hospitals in the same area. The occurrences of F. proliferatum, F. nygamai and F. longipes are new records for the Malaysian Peninsula and the association of F. solani and F. oxysporum var. redolens with human diseases does not seem to have been reported previously. Ten representative species which could be classified into seven sections of the genus were selected for studies of their toxigenicity in liquid cultures and/or on rice. Crude toxin preparations from culture filtrates or extracts of the inoculated rice were tested for toxicity to brine shrimp larvae and tobacco mesophyll protoplasts. The protoplasts were more sensitive than the brine shrimp larvae to the toxin preparations, except those from the isolates of F. solani and F. oxysporum var. redolens obtained from either humans or tobacco. The toxicity of the preparations from rice cultures per g rice was always greater than the toxicity per ml of culture filtrates from cultures grown on Czapek-Dox broth, Czapek-Dox supplemented with 1% (w/v) peptone or Czapek-Dox supplemented with 5% (w/v) tobacco extract. The activity of all toxin preparations was stable to heat. It is concluded that the occurrence of toxigenic species of Fusarium in the Malaysian Peninsula is widespread and that they may pose a serious threat to the health of human, animal and plant populations.

Fusarium↗

PubMed1988

Evaluation of guar biscuits for use in the management of diabetes: tests of physiological effects and palatability in non-diabetic volunteers.

A guar-shortbread biscuit has been successfully developed and tested for possible use in the dietary management of diabetes. A dose-response study was undertaken to estimate the amount of guar gum needed in the biscuit recipe to reduce postprandial glycaemia and insulinaemia. A control biscuit and three types of guar biscuit corresponding to a low, medium and high dose of guar (2.9, 6.0 and 9.1 g of guar respectively) were given to 8 non-diabetic subjects, and blood glucose and plasma insulin levels were determined at fasting, and at the postprandial times 30, 60, 90 and 120 min. Integrated insulin increments were estimated by calculation of the area under the curve. Sensory analysis of the biscuits was carried out by 36 non-diabetic panellists using a standard smiley chart containing hedonic phrases. No significant differences in the blood glucose increments were found between the control biscuit and the guar biscuits. However, all three guar biscuits produced smaller insulin rises than the control at all the postprandial times; statistically significant falls were indicated at the 60-min peak and 120-min times and for the integrated values. A linear regression model describing the relationship between integrated insulin and the dose of guar ingested is proposed. We have estimated from this model that a reduction of 209 mU/min/l in the integrated insulin can be achieved for every 1 g of guar incorporated into the biscuit. Mean hedonic scores indicated that all the guar biscuits were palatable, particularly the low-dose variety which was given a score almost identical to that of the control. A significant insulin-sparing effect in non-diabetic subjects was achieved using a palatable guar biscuit containing less than 3 g of guar flour.

Administration, Oral↗

PubMed1987

Increased susceptibility and reduced phytoalexin accumulation in drought-stressed peanut kernels challenged with Aspergillus flavus.

Three genotypes of peanut (Arachis hypogaea L.), with ICG numbers 221, 1104, and 1326, were grown in three replicate plots and drought stressed during the last 58 days before harvest by withholding irrigation water. Within each plot there were eight levels of stress ranging from 1.1 to 25.9 cm of water. Kernels harvested from the plots were hydrated to 20% moisture and challenged with Aspergillus flavus. Fungal colonization, aflatoxin content, and phytoalexin accumulation were measured. Fungal colonization of non-drought-stressed kernels virtually ceased by 3 days after inoculation, when the phytoalexin concentration exceeded 50 micrograms/g (fresh weight) of kernels, but the aflatoxin concentration continued to rise exponentially for an additional day. When fungal colonization, aflatoxin production, and phytoalexin accumulation were measured 3 days after drought-stressed material was challenged, the following relationships were apparent. Fungal colonization was inversely related to water supply (r varied from -0.848 to -0.904, according to genotype), as was aflatoxin production (r varied from -0.876 to -0.912, according to genotype); the phytoalexin concentration was correlated with water supply when this exceeded 11 cm (r varied from 0.696 to 0.917, according to genotype). The results are discussed in terms of the critical role played by drought stress in predisposing peanuts to infection by A. flavus and the role of the impaired phytoalexin response in mediating this increased susceptibility.

Aflatoxins↗

PubMed1985

Circumstantial evidence for phytoalexin involvement in the resistance of peanuts to Aspergillus flavus.

Three stilbene phytoalexins, elicited by slicing and incubating imbibed peanut kernels under aerobic conditions, inhibited spore germination and hyphal extension of Aspergillus flavus with ED50 values in the range 4.9-12.8 micrograms ml-1. Phytoalexin yield was dependent on cultivar, conditions and duration of incubation after slicing, and crop history. The yield of phytoalexin from ten cultivars studied, after slicing and incubating at 25 degrees C for 24 h, ranged from 28 to 935 micrograms per g fresh weight and was negatively correlated with dry kernel colonization by A. flavus [r = -0.868 when plotted as 1n (phytoalexin concn) against 1n (percentage peanut colonization)]. When the incubation period was extended to 96 h there was no such correlation. Reduced phytoalexin yields were obtained when sliced kernels of one cultivar studied were incubated in water or at 37 degrees C, and no phytoalexin was obtained when the slices were incubated under nitrogen gas or frozen before aerobic incubation. Drought stress during pod development in four cultivars studied reduced phytoalexin yields of sliced kernels incubated at 25 degrees C for 24 h by 17-65% compared with non-stressed controls.

Arachis↗