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Articles

Metabolic Basis for Injury to Plants from Combinations of O₃ and SO₂¹

Studies with Modifiers of Pollutant Toxicity

Statewide Air Pollution Research Center, University of California, Riverside, Riverside, California 92521, United States Environmenal Protection Agency, 200 S.W. 35th Street, Corvallis, Oregon 97333

Pisum sativum L. cv Alsweet (garden pea) and Lycopersicon esculentum Mill. flacca (mutant tomato) were chosen to evaluate the metabolic basis for plant injury from combinations of O₃ + SO₂. The plants were exposed under conditions reported to specifically alter O₃ or SO₂ toxicity; light versus dark exposures, and treatment with the fungal metabolite fusicoccin (FC), the O₃ injury inhibitor N-[2-(2-oxo-1-imidazolidiny) ethyl]-N'-phenylurea (EDU), and the SO₂ injury stimulator diethyldithiocarbamate (DDTC). Plants were grown in controlled environment chambers and exposed to combinations of O₃ (0.05-0.2 microliters per liter) and SO₂ (0.1-0.3 microliters per liter) for 2 hours. Peas treated with FC had the same or greater injury (quantified by visual rating) with O₃ + SO₂ exposures compared to plants not treated with FC. For plants with open stomata in the dark as well as light, i.e. FC-treated peas and tomatoes, there was no change or an increase in foliar necrosis with O₃ + SO₂ exposures in the dark versus light. Peas treated with EDU had an almost complete absence of O₃ injury, no change in SO₂ injury, and moderate decreases in injury from combinations of O₃ + SO₂ compared to plants not treated with EDU. Tomatoes treated with DDTC showed the same or less injury compared to plants not treated with DDTC and exposed to O₃ or SO₂. The plant responses to the experimental treatments and O₃ + SO₂ resembled O₃ responses more than SO₂ responses. The evidence for O₃-like responses are: no change or increase in injury in the light versus dark, and EDU-induced decreases in injury. Evidences for SO₂-like responses are: incomplete protection from injury with EDU, and no change or increased injury to FC-treated versus untreated plants. Thus, a metabolic mechanism affected by both pollutants may be associated with the combination injury, e.g. effects the plasma membrane.