Astrid Wonisch

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.

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.

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.

Photostress, photoprotection, and water soluble antioxidants in the canopies of five Canarian laurel forest tree species during a diurnal course in the field

Minimal relative water contents of more than 85% indicated that dehydration was not a stress factor. Stomatal conductances decreased from 150 to 200 mmol H 2 O m –2 s –1 in the morning to about 50 mmol H 2 O m –2 s –1 during the day in all species, but this did not limit CO 2 uptake. De-epoxidation of xanthophylls only occurred in sun leaves of I. canariensis (to more than 50%) and M. faya (more than 60%). Decreases in Fv/Fm were only found in sun leaves of P. indica (from ca. 0.80 in the morning to a minimum of 0.70) and, as a trend, also in L. azorica (from ca. 0.75 to ca. 0.65). I. perado showed neither of those responses. P. indica and L. azorica exhibited the highest photosynthesis rates of about 10 µmol CO2 m –2 s –1 compared to 8 in the other species. The photoprotection strategy of P. indica and L. azorica admitted slow recovery from photoinhibition, did not activate protective energy dissipation through xanthophylls, and allowed highest production under these typical conditions.

The significance of xanthophylls and tocopherols in photo-oxidative stress and photoprotection of three Canarian laurel forest tree species on a high radiation day

Summary Chloroplast pigments, chlorophyll fluorescence, and tocopherols in sun leaves of the Canarian laurel forest species Myrica faya, Laurus azorica, and Persea indica were characterized during the diurnal course of a high irradiation summer day. All species showed a de-epoxidation of the xanthophyll cycle and a decline of the photochemical efficiency of photosystem II measured as the Fv/Fm fluorescence ratio. Whereas in M. faya, decline and recovery of Fv/Fm was only correlated to zeaxanthin formation, these relations were divergent in L. azorica and P. indica .I nP. indica, Fv/Fm did not fully recover until the next morning. Apparently, the decrease of Fv/Fm during the day reflected only a zeaxanthin-dependent, quickly recovering component in M. faya, but an additional component, probably due to photodamage processes requiring repair activities, was observed in L. azorica and P. indica. In leaves of those two species, α -tocopherol concentrations varied during the diurnal course, probably indicating active oxygen scavenging action. In P. indica leaves, a degradation and restoration of chlorophyll contents were observed during the day. The conclusion is that M. faya is most resistent to high light stress and P. indica most sensitive, which coincides with known ecological traits of these species.

Uptake and distribution of 35S-sulfate in needles and roots of spruce seedlings as affected by exposure to SO2 and H2S

The interaction between pedospheric and atmospheric sulfur nutrition was studied in seedlings of Norway spruce. Spruce was grown on a 25% Hoagland nutrient solution containing S-35-sulfate and simultaneously exposed to 250 nl 1(-1) atmospheric SO2 or H2S. A 6-day exposure to SO2 and H2S resulted in a substantial increase in the total sulfur concentration of the needles. This increase could be ascribed to increased needle concentrations of sulfate, water-soluble non-protein thiols and organic sulfur. SO2 and H2S exposure resulted in slight but significant increases in the concentration of sulfur compounds in roots. In all sulfur fractions, except sulfate, there was a substantial decrease in the level of S-35 in needle and root sulfur fractions upon SO2 and H2S exposure, demonstrating that spruce was able to switch from pedospheric sulfate to atmospheric sulfur as a source for growth. In needles, the amount of S-35 decreased in total organic S and glutathione fraction, whereas it increased in sulfate. This supports continued import of S taken up by the roots into the needles in spite of a decreased channeling of S-35 into synthesis in needles. A greater part of total sulfate increase was due to unlabeled S, which points towards metabolic oxidation of H2S and SO2 to sulfate. Increased concentrations of S compounds (including sulfate) in roots were mainly due to unlabeled S, indicating an import of sulfur from the foliage. The significance of glutathione in the translocation of reduced sulfur from the needles to the roots is discussed

Stress-physiological investigations and chromosomal analyses on cloned Norway spruce trees exposed to various levels of ozone in open-top chambers

Abstract Antioxidants and pigments in needles as well as chromosomal aberrations in root tip meristems of young clonal Picea abies trees were investigated after exposure to different ozone concentrations (charcoal filtered, non-filtered, non-filtered +25ppb, non-filtered +50ppb) in open-top chambers for three months. The same analyses were conducted after keeping the trees under ambient conditions for one year. Ozone treatments induced a dose dependent increases in chromosomal aberrations (up to nearly 10%) which could be found even after one year. Antioxidants and pigments in needles varied between sample times but differences among ozone treatments were not observed.

Gas Exchange of Irrigated and Non-Irrigated Pinus canariensis Seedlings Growing Outdoors in La Laguna, Canary Islands, Spain

Chlorophyll fluorescence, gas exchange, water potential and relative water content were measured in the needles of five year old seedlings of Pinus canariensis in order to know their response to mild water stress. Two trial plots of ten plants per plot, of similar age and characteristics were irrigated daily until the experiment was undertaken, then one of the plots was left without watering while the other one was irrigated as before. After a week of treatment, the water potential at midday did not change in any of the irrigated or non-irrigated plants maintaining around -0 .4 MPa, and the relative water content changed from 93% in irrigated to 84% in non-irrigated seedlings. The stomatal conductance decreased 60% in non irrigated plants and as a result CO2 assimilation decreased by 50% and transpiration was reduced at a higher proportion (70% ), indicating a good control against water loss, before any change in water status in the needles could be observed suggesting an isohydric water economy in this plant

Seasonal variations of gas exchange, photosynthetic pigments, and antioxidants in Turkey oak (Quercus cerris L.) and Hungarian oak (Quercus frainetto Ten.) of different age

Seasonal changes in physiological and biochemical parameters were studied in 35-, 55- and 140-year-old trees of Turkey oak (Quercus cerris L.) and Hungarian oak (Q. frainetto Ten.), growing in natural stands in Eastern Balkan Mountains (Bulgaria). During the seasonal drought period (August), assimilation activity, transpiration rate, stomatal conductance and water potential had a seasonal minimum in all the studied tree ages and species. The foliar concentrations of glutathione, ascorbate, α-tocopherol, as well as photosynthetic pigments in oak leaves were significantly affected by season. With the increasing age of the studied trees, we observed a decrease of the physiological activity and an increase of the antioxidants’ accumulation. Both the species were drought tolerant and anisohydric, where Q. frainetto exhibited higher rates of gas exchange than Q. cerris. Moreover, they differed in the extent of increase in the foliar antioxidants and carotenoids.

Effects of an Oxidizing Agent (Hydrogen Peroxide) on the Glutathione System in Epidermal Cells of Allium cepa L. Investigated by Histochemical Staining

The glutathione system in epidermal cells of Allium cepa L. was measured by a quantitative image analysis method, using histochemical staining by monochlorobimane. Blockage of thiol groups with N-ethylmaleimide decreased fluorescence to a small rest fluorescence of maximum 5%. Pre-treatment with dithiothreitol increased fluorescence yield in all cells compared to the monochlorobimane treatment alone. These results correspond to the blockage or the reduction of the total pool of glutathione in the cells. After treatment with N-ethylmaleimide and subsequent incubation with dithiothreitol followed by labelling with bimane a low fluorescence yield was observed which correspond to the proportion of GSSG. Specimens that were incubated in H2O2 prior to the treatments described above exhibited a decrease in total glutathione and in reduced glutathione and an increase in the proportion of GSSG compared to the control.