Dieter Grill

Complex interactive effects of drought and ozone stress on the antioxidant defence systems of two wheat cultivars

The response of antioxidative defence systems in flag leaf tissues of wheat to combinations of ozone and drought stress was investigated. Sensitive (Triticum aestivum Desf. cv. Nandu) and resistant (Triticum durum L. cv. Extradur) cultivars of wheat were grown in open-top chambers under two ozone (ambient; ambient plus 50 ppb) and two water regimes (well-watered and 40% of soil water capacity). Concentrations of antioxidants ascorbate, glutathione, and tocopherol as well as the contents of chloroplast pigments were determined to evaluate the capacity of radical scavenging systems. Additionally leaf water potential, stomatal conductance and chlorophyll fluorescence were measured. Leaf water potentials of the resistant cultivar were significantly lower than that of the sensitive cultivar grown under the same imposed drought exposure. Drought decreased total ascorbate and total chlorophyll concentrations, increased the protective carotenoids and the de-epoxidation state of the xanthophyll cycle as well as total glutathione and tocopherol concentrations. Drought stress combined with ozone exposure did not further affect the antioxidative system.

Content of low-molecular-weight thiols during the imbibition of pea seeds

The metabolism of low-molecular-weight thiols was investigated in seeds of Pisum sativum L. cv. Kleine Rheinländerin during imbibition in water for 14 h. The amount of oxidized glutathione (GSSG) decreased from 319 nmol (g dry weight)-1 in dry seeds to 38 nmol (g dry weight)-1 within the first 14 h of imbibition. The decrease may have been due to the reduction of GSSG to reduced glutathione (GSH), catalyzed by the enzyme glutathione reductase (GR; EC 1.6.4.2). The enzyme activity was high in dry seeds [25 nkat (g dry weight)-1 ] and decreased to 20 nkat (g dry weight)-1 within 14 h of imbibition. The activity of glucose-6-phosphate dehydrogenase (EC 1.1.1.49) decreased from 100 nkat (g dry weight)-1 in dry seeds to 67 nkat (g dry weight)-1 after 14 h of imbibition. Within 14 h the amount of γ-glutamyl-cysteine (γ-GC) decreased from 135 to 38 nmol (g dry weight)-1 , whereas the cysteine content rose from 81 nmol (g dry weight)-1 in dry seeds to a maximum of 170 nmol (g dry weight)-1 after 12 h of imbibition, which may be due to the degradation of γ-GC into cysteine.

Effect of sulphur dioxide on glutathione in leaves of plants

Abstract The content of total water extractable SH compounds was estimated in healthy and SO 2 -affected leaves of Picea, Pinus, Larix and Betula . SH concentrations of 0·24 to 0·35 μmole/g dry weight in control leaves were found to increase by a factor of 4 to 6 with increasing contamination of the air from SO 2 . In both control and SO 2 -affected leaves glutathione (GSH) is the most abundant SH compound, usually comprising more than 95% of the total SH content. It is assumed that the chronic increase in the level of GSH in SO 2 -affected leaves changes the natural balance of the SH/SS in the cell and thereby induces a general disruption of fundamental cellular processes.

Determination of Glutathione and Glutathione Disulphide in Lichens: a Comparison of Frequently Used Methods

The determination of glutathione (GSH) and glutathione disulphide (GSSG) is subject to substantial problems when analysing plants containing high amounts of phenolic compounds, since the phenolics may react with the GSH present during the extraction. Three frequently used methods for the analysis of GSH and GSSG in the lichen Pseudevernia furfuracea have been compared. Glutathione seemed to be underestimated by the enzymatic recycling assay. Determination by high-performance liquid chromatography after derivatization of glutathione with 2,4-dinitro-1-fluorobenzene (DNFB) or labelling with monobromobimane (mBBr), respectively, gave similar results. Derivatization with DNFB gave the lowest values for GSSG expressed as a percentage of total glutathione. Cyst(e)ine and γ-glutamyl-cyst(e)ine were only detected with the mBBr assay. In order to improve the yield of GSH, polyvinylpolypyrrolidone (PVP), which should serve to bind phenolics, was added during the extraction. The use of PVP improved the yield of glutathione dramatically in lichens harvested in June but not in October. However, addition of PVP led to oxidation of a portion of the GSH. This was demonstrated for each method and seemed to be independent of the thiol blocking agents used for the determination of GSSG, namely 2-vinylpyridine, iodoacetic acid or N-ethylmaleimide. For extensive studies on glutathione metabolism in Pseudevernia furfuracea we recommend that the use of PVP be avoided, by investigating thalli collected in autumn, that probably contain less phenolics than those harvested in summer.

Changes in antioxidant and pigment pool dimensions in UV-B irradiated maize seedlings

Abstract Ultraviolet-B (UV-B) radiation (280–320 nm) is an environmental challenge affecting a number of metabolic functions through the generation of reactive oxygen species (ROS). Plants protect themselves from this harmful radiation by synthesizing flavonoids, which act as a screen inside the epidermal cell layer, and by making adjustments to the antioxidant systems at both cell and whole organism level. This study describes the flavonoid content, the photosynthetic pigment composition and the proline, tocopherol and ascorbate content in UV-B exposed maize plants. Following exposure, the tocopherol content was slightly, but significantly lower, pointing to the membrane environment as a primary target for UV-B radiation. The water-soluble antioxidant content was largely unaffected, but an enhanced turnover in the ascorbate–glutathione cycle might be needed for tocopherol regeneration.

Effects of drought on needle anatomy of Pinus canariensis

Summary The needles of Pinus canariensis exhibit morphological drought adaptations, such as special stomata morphology or rigid sclerenchymatic hypodermis. In the present paper the hypothesis that drought exposure during needle elongation triggers formation of xeromorphic traits was tested. With onset of the elongation growth of the new flush, 5-year old P. canariensis seedlings were exposed to 53 days of reduced water supply under controlled climate chamber conditions. The treatment resulted in a decrease of needle water potentials from –1.5 MPa to −4 MPa in drought stressed plants, whereas no change was observed in water potentials of control needles. Needles of drought exposed trees remained shorter and thinner. Cross-sections of elongating needles taken at 1 cm distance from the needle base were taken repeatedly during the experiment. Cross-section areas of different needle tissues were measured in an image analysis system. In needles of drought stressed trees sclerenchymatic tissues in the hypodermis and adjacent to the vascular bundles increased due to large increases in the number – not the size – of sclerenchymatic cells. The ratio of assimilation parenchyma to the vascular bundle (supplied versus supplying tissue) decreased. We conclude that these changes, which adapt needles to drought conditions, are triggered by drought stress experienced while needles are growing.

Der jahreszeitliche Rhythmus des Ascorbinsäuresystems in Nadeln von Picea abies

Summary The ascorbic acid (AS) content of Picea abies follows a seasonal rhythm with a maximum of 1.9 mg/g fresh weight (f.w.) in April and a minimum of 0.6 mg/g f.w. in October. The dehydro-ascorbic acid (DAS) content is low (average 0.18 mg/g f.w.) and does not show significant seasonal variation. With increasing needle age AS decreases while DAS increases. DAS reductase shows an annual rhythm with minima of activity in April (0.22 units/g f.w.) and late August (0.55 units/g f.w.) and maxima of activity in July (0.75 units/g f.w.) and October (0.85 units/g f.w.). The curve of the annual rhythm of AS oxidase is in all details inverse to the curve for DAS reductase. The highest activity of AS oxidase is present in April (0.66 units/g f.w.), the lowest in October (0.27 units/g f.w.). It is assumed that increased levels of AS stimulate biosynthesis of AS-oxidase and inhibit biosynthesis of AS reductase, thus providing a control mechanism which prevents from extreme variations of the ascorbic acid level.

Short-term changes in free radical scavengers and chloroplast pigments in Pinus canariensis needles as affected by mild drought stress

Summary Potted Pinus canariensis seedlings were subjected to mild drought by withholding irrigation for one week. This treatment induced a reduction in maximum stomatal conductance (50 mmol m −2 s −1 ) compared to irrigated controls (130 mmol m −2 s −1 ). Needle water potentials of non-irrigated trees were maintained at control level (-0.44 MPa). Such a mild drought is a potential oxidative stressor due to the production of active oxygen species (AOS) in illuminated chloroplasts which lack CO 2 due to stomatal closure. Photoprotective pigments (e.g. the xanthophyll cycle) may avoid this situation through light energy dissipation, and antioxidants such as ascorbic acid, tocopherols, and glutathione, may detoxify AOS. Concentrations of ascorbate, glutathione, chlorophyll, and the xanthophyll cycle carotenoids were minimal in the evening (under low light) compared to light-saturated conditions. α-Carotene was highest in the evening. These short-term changes were not affected by drought. The xanthophyll cycle pool tended to be more de-epoxidized in strongly illuminated needles of non-irrigated trees at the beginning of the experiment, but this effect was transient. The glutathione pool was more oxidized in needles of non-irrigated trees (up to 20 percnt; of total vs. 10 percnt; at control) after the xanthophyll changes took place, whereas the redox state of ascorbate remained stable.

Physiology of young Norway spruce

In the Hohenheim experiment young spruce (Picea abies L. Karst.) were exposed to low levels of SO(2) and/or O(3) and acid precipitation. At the end of a five-year experimental period (1983-88) the following physiological parameters were examined: water soluble thiols, ascorbic acid, glutathionereductase activity and pigment content. Exposure to SO(2), leads to an increase in thiol content, to a slight decrease of ascorbic acid and to a pronounced decrease of pigments. O(3) exposure increases the content of ascorbic acid and decreases the thiols and the glutathione-reductase activity with no change in the pigment content. The combined exposure to SO(2), and O(3) results in the most distinct deviations compared to the control chamber response. These needles show the highest increase of ascorbic acid and thiols, the dry weight is decreased as is the glutathione-reductase activity and the pigment content is reduced. Consequences of these physiological alterations for the plants health are discussed.

Increased stress parameter synthesis in the yeast Saccharomyces cerevisiae after treatment with 4‐hydroxy‐2‐nonenal

© 1997 Federation of European Biochemical Societies.