Effect of SO₂ and O₃ on Production of Antioxidants in Conifers

Abstract

Production of antioxidants was investigated in needles of fir (Abies alba Mill.) and spruce (Picea abies (L.) Karst) after exposure to low concentrations of So2, 03, and a combination of both pollutants. Glutathione reacted most sensitively to pollutants followed by vitamin E and vitamin C. In spruce needles, the overall increase of antioxidants after exposure to air pollutants was lower than in needles of fir. SO2 was more potent than 03. Maximum increase of antioxidants was found in needles after exposure of trees to SO2 + 03.Oxidation of both proteins and lipids is among the major phytotoxic consequences of 03 and SO2 action (1, I1, 13). Oxidative degradation of lipids can be easily detected by decomposition products, such as ethane and malonaldehyde (17). Although ethane is a sensitive indicator, a significant increase in gas production is generally associated with visual injury of plants (4). This limits the specific use of ethane as an early indicator of oxidative stress in plants. Antioxidants, such as the vitamins C and E or glutathione, determine the extent of oxidative degradation of cell components (4,17,18 RESULTS AND DISCUSSIONIn spruce, we found a 3-fold higher glutathione level in the filtered air-treated control needles of the youngest shoot than in control needles of fir (Fig. 1). After long-term exposure to different air pollutants, needles neither had visual injury nor elevated lipid oxidation, measured as ethane production. Treatment of fir and spruce with SO2 gave a higher increase of antioxidants in needles than treatment with 03 or charcoal-filtered air. Further, exposure to the pollutants alone significantly increased (P < 0.01) the glutathione content in fir needles compared to filtered air-treated needles. A combination of both gases gave maximum response and significantly enhanced (P < 0.01) the level of vitamin E and glutathione in needles of both fir and spruce compared to the antioxidant levels in needles either to 03 alone or to filtered air. Needles of fir had a 1.9-fold and 3-fold higher content ofvitamin E and glutathione, respectively, after exposure to S02 + 03 than needles exposed to filtered air. In comparison, needles of spruce had only a 1.3-fold higher content of both antioxidants after treatment with S02 + 03 than needles treated with filtered air.The increase of antioxidant levels above the filtered air-treated control was higher in 2-year-old spruce needles, exposed to air pollutants for 2 years, than in the youngest needles, exposed to pollutants for one vegetation period (Fig. 2). In general, the level ofantioxidants above the control was higher after treatment with SO2 or S02 + 03 than after treatment with 03 alone. Increase of glutathione was the most sensitive reaction to air pollutant treatment. No significant increase (P > 0.05) was found for vitamin C after exposure of 1-year-old needles to different pollutants. However, in 2-year-old needles the amount of all antioxidants tested was significantly higher (P < 0.05) after exposure to S02 + 03 than to 03...

Seasonal changes in antioxidants in red spruce as affected by ozone

“…Glutathione levels and especially the accumulation of GSSG, are believed to be sensitive indicators for oxidative stress Mehlhorn et al, 1986;Smith, 1985). Our results are consistent with the hypothesis that the seedlings experienced increased oxidative processes due to the presence of ozone.…”

“…Whereas our results are consistent with the findings in previous year's needles, the ascorbate content of current year's needles showed a steady increase over the sampling period. Mehlhorn et al (1986) reported increased levels of a-tocopherol in spruce and fir after a 2-year fumigation with ozone or sulphur dioxide in needles sampled in October. Our data for the 7-month period show that a-tocopherol undergoes seasonal changes opposite to those found for glutathione and ascorbate, where the a-tocopherol content increases from spring on, reaches a maximum in summer, and decreases in autumn in both age classes.…”

Response of Photosynthesis and Cellular Antioxidants to Ozone in Populus Leaves

“…If the glutathione and superoxide dismutase do provide an adaptive function by scavenging free radicals, as has been suggested (29), one would expect that the plants at 21 h after ozone fumigation, with their elevated glutathione and superoxide dismutase, would be less susceptible to another ozone exposure. This raises the intriguing possibility that plants can be acclimated to ozone exposure and perhaps much of the contradictory field evidence gathered may be the result of data gathered from acclimated and nonacclimated plants.…”

“…To our knowledge, there have been no published reports of the initial effects of ozone on the scavenging system of plants. Antioxidant increases have indeed been shown to occur in plants (21) after prolonged ozone exposure but no information is available on the pattern of antioxidant accumulation. In this report we document the initial effects of ozone on some aspects of the antioxidant scavenging system of plants.…”

Changes in antioxidant levels and activities of related enzymes in rice leaves exposed to ozone

“…For example, Mehlhorn et al (1986) reported that the contents of ascorbate, glutathione, and oL-tocopherol increased in needles of conifers after long-term exposure to 0.037 • 10 -6 m s m -s of Os and 0.004 • 10 -6 to 0.012 • 10 -6 m s m -a of SO2. Tanaka and Sugahara (1980) showed that poplar (Poplus euramericana L.) trees which had been exposed to a relatively low level of SO2 (0.10x 10 .6 m s m-a), were more resistant to subsequent treatment with 2• 10 .6 m s m -s SO2.…”