Fusicoccin and Air Pollutant Injury to Plants : Evidence for Enhancement of SO(2) but Not O(3) Injury

Garden peas (Pisum sativum L. cv Alsweet) and a tomato mutant (Lycopersicon esculentum Mill. var flacca) were sprayed with fusicoccin, a fungal toxin affecting membrane transport properties, before exposure to SO₂ or O₃. Tomatoes treated with 10 micromolar fusicoccin and exposed to SO₂ (0.6 microliter per liter for 2 hours) exhibited twice as much foliar necrosis as untreated plants exposed to SO₂. Peas treated with fusicoccin and exposed to SO₂ (0.7 to 1.0 microliter per liter for 2 hours) exhibited 2 to 6 times more injury than untreated plants exposed to SO₂. Peas treated with fusicoccin and exposed to O₃ had less injury than untreated plants exposed to O₃ (0.1 to 0.3 microliter per liter for 2 hours). Several lines of evidence suggested that the fusicoccin enhancement of SO₂ injury is not the result of increased gas exchange, i.e. the tomato mutant has permanently open stomata under all conditions, and in peas fusicoccin had no effect on SO₂ or H₂O flux in plants exposed to 0.12 microliter per liter SO₂. However, a 21% greater leaf conductance in fusicoccin treated versus untreated plants indicated the possibility of some differences in gas exchange for peas exposed to 1.0 microliter per liter SO₂.