Role of ascorbate in detoxifying ozone in the apoplast of spinach (Spinacia oleracea L. ) leaves
- Univ. of Wuerzburg (Germany)
Both reduced and oxidized ascorbate (AA and DHA) are present in the aqueous phase of the extracellular space, the apoplast, of spinach (Spinacia oleracea L.) leaves. Fumigation with 0.3 [mu]L L[sup [minus]1] of ozone resulted in ozone uptake by the leaves close to 0.9 pmol cm[sup [minus]2] of leaf surface area s[sup [minus]1]. Apoplastic AA was slowly oxidized by ozone. The initial decrease of apoplastic AA was <0.1 pmol cm[sup [minus]2] s[sup [minus]1]. The apoplastic ratio of AA to (AA + DHA) decreased within 6 h of fumigation from 0.9 to 0.1. Initially, the concentration of (AA + DHA) did not change in the apoplast, but when fumigation was continued, DHA increased and AA remained at a very low constant level. After fumigation was discontinued, DHA decreased very slowly in the apoplast, reaching control level after 70 h. Insufficient AA reached the apoplast from the cytosol to detoxify ozone in the apoplast when the ozone flux into the leaves was 0.9 pmol cm[sup [minus]2] s[sup [minus]1]. The transport of DHA back into the cytosol was slower than AA transport into the apoplast. No dehydroascorbate reductase activity could be detected in the apoplast of spinach leaves. In contrast to its extracellular redox state, the intracellular redox state of AA did not change appreciably during a 24-h fumigation period. However, intracellular glutathione became slowly oxidized. At the beginning of fumigation, 90% of the total glutathione was reduced. Only 10% was reduced after 24-h exposure of the leaves to 0.3 [mu]L L[sup [minus]1] of ozone. Necrotic leaf damage started to become visible when fumigation was extended beyond a 24-h period. A close correlation between the extent of damage, on the one hand, and the AA content and the ascorbate redox state of whole leaves, on the other, was observed after 48 h of fumigation. Only the youngest leaves that contained high ascorbate concentrations did not exhibit necrotic leaf damage after 48 h. 30 refs., 6 figs., 1 tab.
- OSTI ID:
- 6331835
- Journal Information:
- Plant Physiology; (United States), Vol. 101:3; ISSN 0032-0889
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
OZONE
BIOLOGICAL EFFECTS
DETOXIFICATION
SPINACH
ASCORBIC ACID
DAMAGE
GLUTATHIONE
LEAVES
NECROSIS
PLANTS
SURFACE AREA
UPTAKE
DRUGS
FOOD
MAGNOLIOPHYTA
MAGNOLIOPSIDA
ORGANIC COMPOUNDS
PATHOLOGICAL CHANGES
PEPTIDES
POLYPEPTIDES
PROTEINS
RADIOPROTECTIVE SUBSTANCES
SURFACE PROPERTIES
VEGETABLES
VITAMINS
560400* - Other Environmental Pollutant Effects
560300 - Chemicals Metabolism & Toxicology