Metabolic Basis for Injury to Plants from Combinations of O 3 and SO 2

128

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...

Section: Resultssupporting

confidence: 51%

Effect of SO₂ and O₃ on Production of Antioxidants in Conifers

Mehlhorn¹,

Seufert²,

Schmidt³

et al. 1986

128

“…Fluxes of03, S02, and H20 vapor were measured using a whole-plant gas exchange chamber (8, 15). Environmental conditions were controlled in the chamber at approximately 300 Mmol m-2 s-' PPFD 21°C air temperature and 1 6°C dew point temperature to provide 70% RH and 370 ul L' C02, using procedures described earlier (9).Air dewpoint was maintained by manipulating the amount of water vapor in the incoming air stream. Water vapor was initially removed from the air stream with a Drierite (Hammond Anhydrous) filter, and then added at a controlled rate by passing the air through a bubbler system.…”

mentioning

confidence: 99%

Joint Action of O₃ and SO₂ in Modifying Plant Gas Exchange

Olszyk¹,

Tingey²

1986

Self Cite

The joint action of 03 and S02 stress on plants was investigated by determining the quantitative relationship between air pollutant fluxes and effects on stomatal conductance. Gas exchange measurements of 03, S02, and H20 vapor were made for Pisum sativum L. (garden pea). Plants were grown under controlled environments, and 03, S02, and H20 vapor fluxes were evaluated with a whole-plant gas exchange chamber using the mass-balance approach. A crucial question in interpreting the nature ofthe joint action response between 03 and SO2 stresses is the relationship between the amount of pollutant dose and the magnitude ofthe response. Previous studies have described effects on the basis of pollutant concentrations in the ambient air surrounding the plant (1, 2, 4, 7, 1 1). None of the studies considered the actual absorbed dose of both pollutants to the leaves. Yet pollutant dose is a key factor in using toxicological models that test for an interaction (6, 1 1). These models indicate that a true synergistic effect occurs only if the response from the dose of both gases is greater than the response anticipated from additive effects of the individual gas doses. To date, interaction studies have not been designed to test this toxicological model, even though the results could yield information on the physiological mechanism for joint action of combinations of pollutants (1 1 This study was designed to characterize the important physiological events correlated with exposure to combinations of 03 plus SO2, by determining the relationship between integrated pollutant dose and stomatal conductance.MATERIALS AND METHODS Plant Culture. Peas (Pisum sativum L. cv Alsweet) were grown and exposed using published procedures detailed previously (8,10). Peas had exhibited consistent synergistic injury and stomatal conductance responses in experiments to evaluate the joint action of 03 and SO2 in plants (7, 11). Plants were grown from seed in an artificial medium (Promix BX2),3 and watered with North Carolina State University nutrient solution. They were cultured in controlled environment growth chambers with light/ dark air temperature of approximately 20 ± 1C, PPFD4 of 301 ± 18 ,mol m-2 s-' for 16 h/24 h photoperiod, and light/dark RH of 76/90. Gas exchange was measured when peas had six fully expanded leaves at 19 to 21 d after seeding. Pea leaf area (2-surface) averaged 0.033 ± 0.001 (SE) Mi2.Gas Exchange System. Fluxes of03, S02, and H20 vapor were measured using a whole-plant gas exchange chamber (8, 15). Environmental conditions were controlled in the chamber at approximately 300 Mmol m-2 s-' PPFD 21°C air temperature and 1 6°C dew point temperature to provide 70% RH and 370 ul L' C02, using procedures described earlier (9).Air dewpoint was maintained by manipulating the amount of water vapor in the incoming air stream. Water vapor was initially removed from the air stream with a Drierite (Hammond Anhydrous) filter, and then added at a controlled rate by passing the air through a bubbler system. Dewpoint was measured u...

“…Plants 21 d old were exposed in small exposure chambers housed in growth chambers (23). Environmental conditions were the same as the preexposure plant growth conditions.…”

Section: Ozone Exposurementioning

confidence: 99%

“…Peas (Pisum sativum L. cv Alsweet) and beans (Phaseolus vulgaris L. cv Blue lake 290) were grown from untreated seeds in an artificial medium (Promix BX3) and watered with a complete nutrient solution as described previously (23 for 16 h/d as previously described (23).…”

Section: Plant Culturementioning

confidence: 99%

See 1 more Smart Citation

Increased 8-Hydroxyguanine Content of Chloroplast DNA from Ozone-Treated Plants

Floyd¹,

West²,

Hogsett³

et al. 1989

Self Cite

The mechanism of ozone-mediated plant injury is not known but has been postulated to involve oxygen free radicals. Hydroxyl free radicals react with DNA causing formation of many products, one of which is 8-hydroxyguanine. By using high performance liquid chromatography with electrochemical detection, the 8-hydroxy-2'-deoxyguanosine (8-OHdG) content of a DNA enzymatic digest can be sensitively quantitated. Beans (Phaseolus vulgaris L.) and peas (Pisum sativum L.) were treated with an ozone regime that caused acute injury. Chloroplast DNA was obtained from plants harvested either immediately after ozone treatment or 24 hours later. Ozone-exposed plants in general had nearly two-fold higher levels of 8-OHdG as compared to control plants. In (7,9,10). Hydroxyl free radicals react with DNA to yield numerous products; one is guanine, which becomes hydroxylated at the 8-carbon position (10, 16). Following hydroxyl free radical reaction with DNA and its digestion to the nucleoside, 8-OHdG2 (7, 10, 16) can then be directly quantitated by LCED. The detection sensitivity with LCED is 20 fmol (7). With DNA as an indicator of hydroxyl free radical occurrence and LCED methodology, it was possible to ascertain that oxidative damage to DNA had occurred in a living system subjected to oxidative stress (7). Kasai