Photoreduction of Sulfur Dioxide by Spinach Leaves and Isolated Spinach Chloroplasts

Abstract

Sulfur dioxide is a major atmospheric contaminant and phytotoxicant resulting from the combustion of sulfur-containing fossil fuels. The phyto-toxic behavior of the gas has received considerable attention (6,8,18). Foliar absorption studies have revealed that SO2 is extensively absorbed by leaves when stomates are open (3,6), suggesting that vegetation may act as an important "sink" for atmospheric pollutants (7).Cormis (5) demonstrated that plants exposed to SO2 released measurable quantities of H2S into the surrounding atmosphere. The phenomenon was shown to result from a photoreductive process since no H2S was detected during fumigations with SO2 in darkness. The present investigation examines certain aspects of the foliar absorption of SO2, its cytoplasmic distribution, and a possible mechanism allowing formation of hydrogen sulfide. MATERIALS AND METHODSChamber Fumigations. Six-to eight-week-old spinach plants (Spinacea oleracea L.), grown in a controlled-environment cabinet, were exposed to 35 02 in a glass fumigation chamber (17). The chamber consisted of an 18-liter bell jar, the basal flange of which was clamped to form an airtight seal with an inert-surfaced supporting platform. A squirrel-cage fan blade located within the chamber was used to circulate air within-the closed system.Baffles situated in order to direct the air flow pattern also served as a supporting platform for a single pot of plants.All procedures were performed within the confines of a laboratory hood. Sulfur dioxide containing 35SO2 was generated from the reaction of H235S04 (International Chemical and Nuclear Corp., Irving, Calif.) with thin copper "turnings." The pressure generated by externally applied heat and the reaction carried the evolved gas and confined air through an impinger containing concentrated H2SO4 to remove water vapor and then into a 30-liter Mylar gas bag (Calibrated Instruments Co., Ardsley, N.Y.) contained in a second bell jar. When the SO2 generation was completed, this supply system was isolated by turning a threeway valve attached to the inlet of the Mylar gas bag which served as a gas reservoir. A measured quantity of laboratory air was then added to the bag to dilute the gaseous mixture to the desired SO2 concentration for introduction into the chamber. Withdrawal of a measured volume of the radioactive gas mixture was accomplished by a 50-ml gastight syringe attached to the gas line leading from the reservoir to the fumigation chamber. Measured aliquots could either be expelled into the fumigation chamber, or collected in midget impingers containing 0.03 N H2O2 solutions for analysis (10).Illumination during the fumigations was provided by a bank of five 150-w reflector flood lamps yielding a light intensity of 1200 ft-c at the position of the leaves within the chamber. Plants were illuminated in position for 20 min before lowering the bell jar over them in preparation for exposure to labeled SO2. The chamber temperature during fumigations was 29 + 2 C.Immediately after clamping the chamber in place, a me...

Emission of Hydrogen Sulfide from Sulfur Dioxide-Fumigated Pine Trees

“…Green plants can take up and reduce sulfate (SO4'2-) and sulfite (HSO:3-, S032-) and some, if not all, plants can volatilize the sulfur product H2S from the leaves (11,14,15). H2S emission from leaves was first discovered by de Cormis (3,4) after fumigation of plants with injurious levels of SO2.…”

“…Pine trees in the field and in laboratory experiments continue to emit H2S several hours after the termination of prolonged SO2 fumigation. The maximum emission rates observed from pine trees in the field and in laboratory experiments, 14 and 20 nanomoles per milligram chlorophyll per hour respectively, are about the activity expected for the sulfur assimilation pathway in the chloroplasts.Green plants can take up and reduce sulfate (SO4'2-) and sulfite (HSO:3-, S032-) and some, if not all, plants can volatilize the sulfur product H2S from the leaves (11,14,15). H2S emission from leaves was first discovered by de Cormis (3,4) after fumigation of plants with injurious levels of SO2.…”

Growth Response in Spinach to Sequential and Simultaneous Exposure to NO2 and SO2

“…Plant response to an air pollutant is governed by the pollutant uptake rate into the plant and by subsequent internal metabolic processes (10). The internal detoxification mechanisms of sulfite and nitrite reduction are light-dependent (8,12) and when pollutant uptake occurs in the dark, either as a result of pollutant influence (4) or speciesspecific differences (9) in stomatal opening, the possibility then exists for the internal levels of sulfite/bisulfite and nitrite to increase sufficiently to damage the chloroplast membrane (11).…”

Plant and Leaf Resistance to Gaseous Air Pollution Stress

“…Garsed and Read (1974) report a rapid translocation within 1 h of radioactive sulphur from fumigated leaves to other plant organs in Glycine max Men. As concerns the specific derivatives of SO2 which cause leaf strain, several are implicated including sulphite, bisulphite, sulphate, hydrogen sulphide, increased acidity and hydrated sulphur dioxide (Ziegler, 1975;Silvius, Ingle and Baer, 1975;Silvius et al, 1976;Hocking and Hocking, 1977). Which elicits particular physiological or morphological strain following SO2 exposure is not fully resolved.…”