Changes in apoplastic antioxidants induced by powdery mildew attack in oat genotypes with race non-specific resistance |
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Authors: | Hélène Vanacker Christine H Foyer Tim L W Carver |
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Institution: | (1) Department of Environmental Biology, Institute of Grassland and Environmental Research, Plas Gogerddan, Aberystwyth, Ceredigion SY23 3EB, UK, GB |
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Abstract: | Three oat (Avena sativa L.) lines which show differential responses to attack by the biotrophic fungal pathogen Blumeria graminis DC f. sp. avenae Marchal, which causes powdery mildew, were studied: Maldwyn shows the strongest resistance in adult plants; Selma shows greater
susceptibility; while a Selma × Maldwyn hybrid, OM1387, has a similar degree of resistance to Maldwyn. Host responses to pathogen
attack were complete 48 h after inoculation but largely accomplished within the first 24 h, the point when material was taken
for enzyme and metabolic assays. In Maldwyn and OM1387 about 80% of attacked cells showed localized autofluorescent host-cell
responses but this fell to less than 20% in Selma. A cytoplasmic marker enzyme, glucose 6-phosphate dehydrogenase, was used
to determine contamination of the apoplastic extracts by cellular components. After correction for cytoplasmic contamination,
up to 4% of the total foliar activities of superoxide dismutase, catalase, ascorbate peroxidase, glutathione reductase, dehydroascorbate
reductase and monodehydroascorbate reductase activities were detected in the apoplast. The apoplast contained about 2% of
the total foliar glutathione pool and dehydroascorbate, but not ascorbate, at values amounting to 10% of the total foliar
ascorbate plus dehydroascorbate pool. Twenty-four hours after inoculation the foliar or apoplastic ascorbate pools were similar
in inoculated and control leaves. Foliar catalase activity increased in both susceptible and resistant responses. Resistance
correlated with increased total foliar glutathione, an increase in the ratio of reduced to oxidized glutathione and with decreased
total activities of foliar ascorbate peroxidase, glutathione reductase, dehydroascorbate reductase and monodehydroascorbate
reductase.
Received: 17 April 1998 / Accepted: 28 August 1998 |
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Keywords: | : Antioxidant Avena (pathogen resistance) Blumeria Erysiphe Hydrogen peroxide Pathogen resistance (race non-specific) |
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