Sulfur dioxide inhibition of photosynthesis in isolated spinach chloroplasts

Carbon fixation efficiency of plants influenced by sulfur dioxide

In the land ecosystem, the forest can absorb the carbon dioxide (CO2) in the atmosphere and turn the CO2 into organic carbon to store it in the plant body. About 2×10(11) tons of CO2 changes through photosynthesis into organic matter by plant annually. In this research, ten kinds of woody plants were selected for assessing the carbon fixation ability influenced by sulfur dioxide (SO2). The tested trees were put into a fumigation chamber for 210 days in a 40-ppb SO2 environment. The results of this study showed that there was no clear symptom of tested trees under a 40-ppb SO2 environment. The tested trees could tolerate this polluted environment, but it will impact their CO2 absorption ability. The carbon fixation ability will reduce as the polluted period lengthens. The carbon fixation potential of tested trees ranged from 2.1 to 15.5 g·CO2/m2·d with an average of 7.7 g·CO2/m2·d. The changes in CO2 absorption volume for Messerschmidia argentea were more stable during the fumigation period with a variation of 102%. Among the tested trees, Diospyros morrisiana had the best carbon fixation potential of 9.19 g·CO2/m2·d and M. argentea had the least with 2.54 g·CO2/m2·d.

Sulfite inhibition of photochemical activity of intact pea leaves

Sulfite treatment of pea leaf disks in light caused a significant decrease in the relative quantum yield of photosynthetic oxygen evolution and energy storage (ES) as measured by photoacoustic (PA) spectroscopy. The inhibition was concentration dependent and was less in darkness than in light, indicating light-dependent inhibitory site(s) on the photosynthetic electron transport chain. Further, in darksulfite-treated leaves, the energy storage was more affected than the relative quantum yield of oxygen evolution, suggesting that photophosphorylation and/or cyclic electron transport around PS I are sites of sulfite action in darkness. The Rfd values, the ratio of fluorescence decrease (fd) to the steady-state fluorescence (fs), decreased significantly in leaves treated with sulfite in light but were not affected in dark-treated ones, confirming the photoacoustic observations. Similarly, the ratio of variable fluorescence (Fv) to maximum fluorescence (Fm), a measure of PS II photochemical efficiency, was affected by sulfite treatment in light and not changed by treatment in darkness. An attempt was made to explain the mechanism of sulfite action on photosynthetic electron transport in light and in darkness.

Sulfur dioxide inhibits the sucrose carrier of the plant plasma membrane

Plasma membrane vesicles were prepared by phase partition from a microsomal fraction of broad bean (Vicia faba L.) leaf. In order to study the effects of sodium sulfite on active uptake of sucrose, the vesicles were artificially energized by a transmembrane pH gradient (delta pH) and/or a transmembrane electrical gradient (delta psi). At 1 mM, sulfite strongly inhibited sucrose uptake but did not affect the two components of the proton motive force, delta pH (measured by dimethyloxazolidine dione) and delta psi (measured by tetraphenylphosphonium). Moreover, sulfite did not inhibit the proton-pumping ATPase of the plasma membrane vesicles. These data demonstrate that sulfite may inhibit transport of photoassimilates in plant by a direct inhibition of the sucrose carrier of the plasma membrane.

SO(2) Effect on Photosynthetic Activities of Intact Sugar Maple Leaves as Detected by Photoacoustic Spectroscopy

Short-term (4 hours) effect of different concentrations of SO(2) fumigation on in vivo photochemical activities of sugar maple (Acer saccharum Marsh.) leaves was investigated using photoacoustic spectroscopy. The relative quantum yield of O(2) evolution (ratio of O(2) signal to the photothermal signal) and photochemical energy storage are increased by 0.05 microliter per liter of SO(2). This increase is more pronounced in 5 to 7 year old saplings than in 3 month old seedlings. Both oxygen-relative quantum yield and energy storage of seedlings are inhibited by increased concentrations of SO(2) and the inhibition is concentration dependent. The inhibition is greater in seedlings than in saplings at 2 microliters per liter of SO(2), indicating the more susceptible nature of seedlings. The present study indicates a concentration dependent differential effect of SO(2) on photochemical activities of sugar maple leaves.

Effect of sulfur dioxide and sulfite on photochemical energy storage of isolated chloroplasts--a photoacoustic study

Photoacoustic spectroscopy was used to study the effect of sulfite and SO(2) on isolated corn mesophyll chloroplasts by monitoring the photochemical energy storage. Sulfite incubation of isolated chloroplasts, either in light or in darkness, caused a decrease in photochemical energy storage. The more pronounced decrease in light indicates a light-dependent sulfite inhibitory site(s) in chloroplasts. Also diphenylcarbazide caused a partial recovery of energy storage in sulfite treated chloroplasts indicating a possible site of damage at the water oxidizing system. Although the chloroplast membranes were found to be insensitive to high concentrations of SO(2) for relatively short exposure periods (10 min) in light, exposure of chloroplasts to 28.5 ng cm(-3) SO(2) for 10 min caused a decrease in energy storage. An attempt was made to explain the mechanism of action of sulfite and SO(2) in chloroplasts.

Inhibition of Photosystem II Precedes Thylakoid Membrane Lipid Peroxidation in Bisulfite-Treated Leaves of Phaseolus vulgaris

Exposure of leaves to SO(2) or bisulfite is known to induce peroxidation of thylakoid lipids and to inhibit photosynthetic electron transport. In the present study, we have examined the temporal relationship between bisulfite-induced thylakoid lipid peroxidation and inhibition of electron transport in an attempt to clarify the primary mechanism of SO(2) phytotoxicity. Primary leaves of bean (Phaseolus vulgaris L. cv Kinghorn) were floated on a solution of NaHSO(3), and the effects of this treatment on photosynthetic electron transport were determined in vivo by measurements of chlorophyll a fluorescence induction and in vitro by biochemical measurements of the light reactions using isolated thylakoids. Lipid peroxidation in treated leaves was followed by monitoring ethane emission from leaf segments and by measuring changes in fatty acid composition and lipid fluidity in isolated thylakoids. A 1 hour treatment with bisulfite inhibited photosystem II (PSII) activity by 70% without modifying Photosystem I, and this inhibitory effect was not light-dependent. By contrast, lipid peroxidation was not detectable until after the inhibition of PSII and was strongly light dependent. This temporal separation of events together with the differential effect of light suggests that bisulfite-induced inhibition of PSII is not a secondary effect of lipid peroxidation and that bisulfite acts directly on one or more components of PSII.

Toxicity of root-applied sulphite in Zea mays

Zea mays was grown in nutrient solution with different concentrations of sulphite and sulphate (0, 5, and 10 mM) at pH 5 or 7, with or without aeration, for five days. Sulphite injured the plants, especially at low pH. Lack of aeration increased the sulphite injury of the plants at the high pH. in the aerated solutions, sulphite concentrations approached zero after five hours, while the unaerated solutions still contained sulphite after four days. Very little sulphite was found in the plants. The results indicate that the toxicity to the plants of the different chemical species of the sulphite in the solution decreases in the following order: SO2 (aq) > HSO3 (-) > SO3 (2-).

Artificial inhibitory effects of sulfite on photosystem II activity measured by oxygen evolution in chloroplasts

In this report we demonstrate sulfite interaction with oxygen and PSII electron acceptors (ferricyanide and para-benzoquinone) during measurement of oxygen evolution in chloroplasts. Redox potentials of oxygen, ferricyanide and para-benzoquinone allow them to compete for sulfite. Without taking this into account, sulfite inhibition of oxygen evolution can be overestimated, since sulfite consumes oxygen and reduces ferricyanide or para-benzoquinone during the measurement. In order to correctly measure the rate of oxygen evolution in chloroplasts, it is necessary to avoid presence of sulfite during the measurement. After overcoming the artifact, mentioned above, we confirm the sulfite inhibition of oxygen evolution in chloroplasts but at a lesser extent than earlier reported. This, however, is a pretreatment effect.

Effects of Arsenite, Sulfite, and Sulfate on Photosynthetic Carbon Metabolism in Isolated Pea (Pisum sativum L., cv Little Marvel) Chloroplasts

Photosynthetic CO(2)-fixation in isolated pea (Pisum sativum L., cv Little Marvel) chloroplasts during induction is markedly inhibited by 0.4 millimolar sulfite. Sulfate at the same concentration has almost no effect. The (14)CO(2)-fixation pattern indicates that the primary effect of sulfite is inhibition of the reaction catalyzed by ribulose bisphosphate carboxylase and a stimulation of export of intermediates out of the chloroplasts. Inhibition of light modulation of stromal enzyme activity does not appear to account for the toxicity of SO(2) in this Pisum variety. Arsenite at 0.2 millimolar concentrations inhibits light activation and inhibits photosynthetic CO(2) fixation. The (14)CO(2)-fixation pattern indicates that the primary effect of arsenite is inhibition of light activation of reductive pentose phosphate pathway enzyme activity.

The role of photophosphorylation in SO2 and SO 3 (2-) inhibition of photosynthesis in isolated chloroplasts

Sulphur dioxide inhibits noncyclic photophosphorylation in isolated envelope-free chloroplasts. This inhibition was shown to be reversible and competitive with phosphate, with an inhibitor constant of Ki=0.8mM. The same inhibition characteristics were observed when phosphoglycerate (PGA)- or ribulose-1,5-bisphosphate (RuBP)-dependent oxygen evolution was examined in a reconstituted chloroplast system in the presence of SO 3 (2-) . Using an ATP-regenerating system (phosphocreatine-creatine kinase), it was demonstrated that the inhibition of PGA-dependent oxygen evolution is solely the result of inhibited photophosphorylation. It is concluded that at low SO2 and SO 3 (2-) concentrations the inhibition of photophosphorylation is responsible for the inhibition of photosynthetic oxygen evolution.

THE EFFECTS OF BISULPHITE AND SULPHATE UPON PHOTOSYNTHESIS IN SPHAGNUM

The effect of various concentrations of HSO₃ ^- and SO₄ ^2- on photosynthetic oxygen evolution in Sphagnum spp. was studied. Almost instantaneous reductions induced by HSO₃ ^- , the magnitude of which increased with concentration, were not reversed by additions of HCO₃ ^- . SO₃ ^2- had no effect on oxygen evolution. The effect of HSO₃ ^- was markedly pH-dependent, being much greater at lower pH. ¹⁴ CO₂ uptake was less sensitive to HSO₃ ^- than O₂ evolution; low HSO₃ ^- concentrations enhanced ¹⁴ CO₂ fixation but never increased O₂ evolution. ¹⁴ CO₂ fixation in the dark was also inhibited by 0·1 mM HSO₃ ^- but enhanced by lower concentrations. The results are discussed in relation to known mechanisms of sulphite toxicity and to effects of sulphite upon growth of Sphagnum spp.

Photoreduction of sulfur dioxide by spinach leaves and isolated spinach chloroplasts

Labeled sulfur dioxide was found to be extensively absorbed by spinach (Spinacea oleracea L.) leaves. Labeled sulfides detected in leaf blades following fumigations with sulfur dioxide in light indicated that photoreduction of sulfur dioxide had occurred. Measurable proportions of this labeled sulfur was localized within the chloroplast fraction. Suspensions of isolated chloroplasts supplied with labeled sulfur dioxide contained labeled sulfides following a 30-minute illumination period in water-cooled reaction vessels. With reference to recent studies of the chloroplast sulfur reduction pathway, probable points of entry for sulfur dioxide and the subsequent release of hydrogen sulfide are discussed.