Fusicoccin and Air Pollutant Injury to Plants

Abstract

Garden peas (Pisum satiram L. cv Alsweet) and a tomato mutant (Lyceperuicon ncuewkatwm Mill. varflacca) were sprayed with fusicoccin, a fungal toxin affecting membrane transport properties, before exposure to S02 or 03. Tomatoes treated with 10 micromolar fusicoccin and exposed to S02 (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 03 had less injury than untreated plants exposed to 03(0.1 to 03 microliter per liter for 2 hours). Several lines of evidence suggested that the fusicocNA n en ment of S02 injury is not the result of increased gas exchange, iUe. the tomato mutant has permanently open stomata under all conditions, and in peas fusicoccin had no effect on 52 or H20 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 S02.The phytotoxicity of SO2 and 03 is determined by pollutant uptake, detoxification, and metabolism at cellular perturbation sites (17, 18). The cellular metabolism of the pollutants is especially important since gas-phase conductance alone cannot fully explain plant response to either SO2 or 03 (5, 15, 17, 18). Sulfite and bisulfite are the likely SO2 metabolites transported into cells since the gas is rapidly hydrated following dissolution into water on cellular surfaces (12). The mechanism and importance of sulfite transport into cells in relation to injury has not been directly investigated; however, Bressan et al. (1) suggested that intraspecific variability in SO2 sensitivity in cucumber resulted from differences in the uptake and transport of SO2 and sulfite across the plasma membrane. Ozone is less water soluble than SO2 but may be transported into cells as 03 (10) or as free oxyradicals which can be produced when 03 dissolves in water at high pH (5).The fungal toxin FC2 is widely used in studying membrane transport processes. Marre (9) suggested that FC activated a plasma membrane system which uses ATP for HI extrusion with an accompanying hyperpolarization of the transmembrane elec-

Metabolic Basis for Injury to Plants from Combinations of O3 and SO2

“…Several lines of evidence support the involvement of sulfite in toxicity; (a) the greater toxicity of SO2 in the dark than light (17), which was associated with accumulation of sulfite (16); (b) the correlation between the rate of sulfite oxidation and intraspecific differences in S02 injury (15); and (c) the greater toxicity of SO2 in plants treated with FC (18), which may increase plasma membrane permeability to SO2 metabolites (14). Evidence for the role of free radicals in toxicity is based on (a) the increased SO2 injury in plants treated with DDTC2, an inhibitor of SOD, an enzyme that decomposes free radicals (23), and (b) reports that chemicals that scavenge free radicals reduce SO2 or bisulfite-induced Chl destruction and leaf injury (20,21).…”