Interaction between sublethal pollution by sulphur dioxide and drought stress. The effect on photosynthetic capacity

Five-year-old Picea abies L. plants were grown in growth cabinets in the presence (3.1 μmol m⁻³) or absence of SO₂. After 5 weeks, the photosynthetic capacity of mature needles produced in the year was the same in both conditions. Trees were then submitted in situ to drought stress by withholding water. The decline of leaf photosynthetic capacity was greatest in the presence of SO₂. Chlorophyll decreased only when trees were submitted to dehydration in the presence of SO₂; however, this al-one could not account for the large decline in photosynthetic capacity observed under that condition. Needle water content was the lowest during dehydration in the presence of SO₂. It is concluded that the critical factor in the interaction between pollution by SO₂ and drought stress is the greater dehydration of the tissue found in stressed plants grown in the presence of SO₂. The large decline in photosynthetic capacity under such conditions might be due to this greater dehydration.     

THE COMBINED EFFECTS OF LOW TEMPERATURE AND SO2+NO2 POLLUTION ON THE NEW SEASON'S GROWTH AND WATER RELATIONS OF PICEA SITCHENSIS

Picea sitchensis (Bong.) Carr. seedlings were exposed to SO₂, NO₂ and SO₂+ NO₂ during dormancy in controlled environments, and were taken to night temperatures of 4, 0, −5, −10 and −15 °C in a freezer. Conditions in the freezer were carefully monitored during the low–temperature treatments. In two experiments, different photoenvironments and temperature regimes were imposed prior to the cold treatments, and different effects were observed. In the first, only limited frost hardiness was achieved and night temperatures of −15 °C were lethal. Temperatures of −5 and − 10 °C led to poor survival of lateral buds, particularly in plants exposed to 45 ppb SO₂. The poor bud break in plants exposed to SO₂ and to − 5 °C resulted in a loss of the effectiveness of this temperature as a chill requirement. Pressure-volume analysis showed that the shoots of plants exposed to NO₂ had greater elasticity (lower elastic moduli, e), so that loss of turgor occurred at lower relative water contents. In contrast, a hardening period (2 weeks in night/day temperatures of 3/10 °C and 8 h days at 50 μmol m⁻² s⁻¹ PAR) gave decreased elasticity and lower solute potentials of spruce shoots. In the second experiment, exposure to 30 ppb SO₂ and SO₂+ NO₂ led to slight, but consistent, increases in frost injury to the needles of plants frozen to − 5 and − 10 °C. The results suggest that the main interaction of low temperatures and winter pollutants may be on bud survival rather than on needle damage, but that effects are subtle, only occurring with certain combinations of pollutant dose and cold treatment.     

Ion uptake in Pinus banksiana treated with sodium chloride and sodium sulphate

Within its wide range across Canada, jack pine is exposed to salinity from both natural and anthropogenic sources. To compare the effects of Cl and SO₄ on salt injury, sand and solution-culture grown jack pine ( Pinus banksiana Lamb.) seedlings were treated with nutrient solutions containing 60 or 120 m M NaCl, 60 m M Na₂SO₄, or a mixture of 60 m M NaCl and 30 m M Na₂SO₄. After 5 weeks of salt treatments, concentrations of Cl, K, Na, and SO₄ were determined in roots, stem and needles of the current and previous years growth, and in necrotic needles. To determine the role of water uptake in the absorption and translocation of salts in plants, total transpiration was measured as the loss of water from a sealed system and related to total plant uptake of Cl, Na, and SO₄. Sodium uptake and root-to-shoot transport rates were greater in treatments containing Cl. A delay in root-to-shoot transport of both Na and Cl indicates retention of these ions in the roots. Electrolyte leakage of needles was more closely related to treatment Cl concentrations than treatment Na concentrations. The transport of Na ions to the shoot was related to the presence of Cl, but was not related to transpiration rate.     

Effect of SO2, on the activity of adenosine 5'-phosphosulfate sulfotransferase from spruce trees (Picea abies) in fumigation chambers and under field conditions

The effect of SO₂ on adenosine 5'-phosphosulfate sulfotransferase activity and various other parameters of needles from spruce ( Picea abies L.) was studied using potted grafts in outdoor fumigation chambers and trees growing near a factory. In summer and autumn fumigation of grafted spruce, SO₂, decreased the extractable activity of adenosine 5'-phosphosulfate sulfotransferase to 12–50% of the controls, and reduced the amount of ³⁵S from sulphate incorporated into protein by excised branches to a comparable degree. SO₂ treatment in January and February inhibited the increase in adenosine 5'phosphosulfate sulfotransferase activity measured in the controls during this time. ATP-sulfurylase activity was less affected by SO₂. fumigation. In trees growing near a factory with high SO₂. emission, the activity of adenosine 5'-phosphosulfate sulfotransferase was about 35% of that of trees from a control area. The low enzyme activity was correlated with a high content of sulfate and compounds containing thiol groups.     

Effects of atmospheric SO2 on Azolla and Anabaena symbiosis

The water fern Azolla pinnata R. Br. was fumigated for 1 week with either 25, 50 or 100 nl 1⁻¹ SO₂. The symbiosis of Azolla with Anabaena azollae (spp.) was severely damaged by atmospheric SO₂ even at concentrations as low as 25 nl 1⁻¹, with significant reductions in growth, reduction of C₂H₂, NH₃ assimilation, protein synthesis, and heterocyst development. These disturbances appear to be mainly responsible for the extreme sensitivity of this fern to atmospheric SO₂. Changes in violaxanthin/antheraxanthin and epoxy-lutein/lutein ratios also indicate that free radical products are induced by atmospheric SO₂. These results suggest that the Azolla-Anabaena symbiotic system is a very responsive and reliable lower plant model to study the detailed effects of total sulphur deposition upon the balances between various important plant metabolic processes.     

Diagnostic parameters for selecting against novel spruce (Picea abies) decline: IV. Response of photosynthesis and transpiration to SO2+NO2 exposures

The dose- and time-response effects of 3 days of 6 h day-time sequential exposures to NO₂, SO₂ and SO₂+NO₂ of 0.45–1.81 μl l⁻¹ (ppm) SO₂ and 1.50–7.65 μl l⁻¹ NO₂ on photosynthesis, transpiration and dark respiration were examined for nine Carpatho-Ukrainian half-sib families and a population from the GFR ('Westerhof') of Norway spruce [ Piecea abies (L.) Karst.], all in their 5th growing season.
SO₂+NO₂ inhibited photosynthesis and transpiration and stimulated dark respiration more than SO₂ alone. SO₂ and SO₂+NO₂ at the lowest concentrations inhibited night transpiration, but increased it at the highest concentration, the strongest effects being obtained with combined exposures. Photosynthesis of the different half-sib families was affected significantly differently by SO₂+NO₂ exposures. NO₂ alone had no effects.
Sensitivity to transpiration decline correlated negatively with branch density. Height of trees correlated postitively with decline sensitivity in the seed orchard. The distribution of photosynthesis and transpiration sensitivities over all tested half-sib families correlated negatively with the distribution of decline sensitivity of their parents in a rural Danish seed orchard. The relative photosynthesis and transpiration sensitivities may thus serve as diagnostic parameters for selecting against novel spruce decline.     

Electrophoretic analysis of protein systems of Ctenopharyngodon idella (Val.), Hypophthalmichthys nobilis (Rich.) and their F1 triploid hybrid

Electrophoretic analysis was performed on eight protein systems (lactate dehydrogenase, liver esterases, superoxide dismutase, haemoglobin, isocitrate dehydrogenase, glucose-6-phosphate dehydrogenase, 6-phosphogIuconate dehydrogenase, transferrin) in Ctenopharyngodon idella, Hypophthalmichthys nobilis , and their F₁ triploid hybrid. The data demonstrated codominant Mendelian inheritance at individual loci for each protein system. Transferrin and superoxide dismutase were the only proteins found to be polymorphic in either parental species. Both parental alleles were present and functional at each enzyme locus examined in the F₁ triploid hybrid.     

Plant responses to H2S and SO2 fumigation. II. Differences in metabolism of H2S and SO2 in spinach

Fumigation of spinach (Spinacia oleracea L. cvs Estivato and Monosa) with H₂S or SO, for 1 to 6 days resulted in accumulation of sulfhydryl (SH) compounds in the shoots of both H₂S- and SO₂-exposed plants. The sulfate concentration in shoots of SO₂-exposed plants increased linearly with time. SH accumulation showed saturation kinetics as a function of time as well as H₂S concentration, ascribed to the internal H₂S concentration in the plant and the availability of substrates for glutathione synthesis, respectively. SH compounds accumulated more at lower exposure temperatures, whereas sulfate accumulation was more pronounced at higher temperatures. These results are discussed in relation to the possible foliar uptake of H₂S and SO₂, the temperature dependence of uptake and the water solubility of these gases. The possibility of SO₂-induced H₂S emission rather than sulfate accumulation as a source for SH accumulation is also discussed. Cessation of fumigation resulted in a decrease in SH compounds and sulfate content that could be accounted for by sulfur metabolism and growth, respectively.     

Mycorrhiza formation and elevated CO2 both increase the capacity for sucrose synthesis in source leaves of spruce and aspen

The effects of mycorrhiza formation in combination with elevated CO₂ concentrations on carbon metabolism of Norway spruce ( Picea abies ) seedlings and aspen ( Populus tremula × Populus tremuloides ) plantlets were analysed. Plants were inoculated for 6 wk with the ectomycorrhizal fungi Amanita muscaria and Paxillus involutus (aspen only) in an axenic Petri-dish culture at 350 and 700 μl l⁻¹ CO₂ partial pressure. After mycorrhiza formation, a stimulation of net assimilation rate was accompanied by decreased activities of sucrose synthase, an increased activation state of sucrose-phosphate synthase, decreased fructose-2,6-bisphosphate and starch, and slightly elevated glucose-6-phosphate contents in source leaves of both host species, independent of CO₂ concentration. Exposure to elevated CO₂ generally resulted in higher net assimilation rates, increased starch as well as decreased fructose-2,6-bisphosphate (aspen only) content in source leaves of both mycorrhizal and nonmycorrhizal plants. Our data indicate only slightly improved carbon utilization by mycorrhizal plants at elevated CO₂. They demonstrate however, that both factors which modulate the sink-source properties of plants increase the capacity for sucrose synthesis in source leaves mainly by allosteric enzyme regulation.     

Physiological effects of sulphur dioxide. 1. The effect of SO2 on photosynthesis and stomatal regulation of Vicia faba L.

Abstract. The effect of short-term SO₂ fumigation on photosynthesis and transpiration of Vicia faba L. was measured at different irradiances and SO₂ concentrations. At high irradiances photosynthetic rates were reduced when leaves were exposed to SO₂ and the magnitude of the reduction was linearly related to the rate of SO₂ uptake through the stomata. Photosynthetic rates stabilized within 2 h after the start of fumigation.
The effect of SO₂ on photosynthesis was measured at different CO₂ concentrations to analyse the contribution of stomatal and non-stomatal factors to photosynthetic inhibition. Mesophyll resistance to CO₂ diffusion increased as a result of SO₂ exposure and caused a rapid reduction in photosynthesis after the start of fumigation. Stomatal resistance was not affected directly by SO₂ fumigation, but indirectly as a result of a feedback loop between net photosynthesis and internal CO₂ concentration.
Analysis of gas-exchange measurements in biochemical terms indicated that photosynthetic inhibition during SO₂ exposure can be explained by a stronger reduction in the affinity of RBP carboxylase/oxygenase for CO₂ than for O₂.     

SO2 and assimilatory sulfate reduction in beech leaves

The effect of SO₂ on the extractable activity of ATP sulfurylase (EC 2.7.7.4.). adenosine 5'-phosphosulfate sulfotransferase, ribulosebisphosphate carboxylase, chlorophyll, protein, sulfate, and amino acids was examined in leaves of potted grafts of beech ( Fagus sylvatica L.) treated in outdoor fumigation chambers. Addition of 0.025 and 0.075 μl SO₂ 1⁻¹ to unfiltered ambient air caused a decrease in the extractable activity of adenosine 5'-phosphosulfate sulfotransferase to about 20 to 30% of the controls. Neither the extractable activity of ATP sulfurylase and ribulosebisphosphate carboxylase nor the content in chlorophyll, total amino acids and protein were significantly affected by SO₂, but there was an increase in the sulfate content. Leaves treated with 0.075 μl SO₂ 1⁻¹ contained more alanine and cysteine and less serine than the controls. After transfer of the SO2-treated beech trees to control chambers there was an increase in adenosine 5'-phosphosulfate sulfotransferase activity, but no significant decrease in SO₂₋⁴-sulfur.     

Long-term effects of low levels of SO2 on bean plants (Phaseolus vulgaris). II. Immission-response effects on biomass production: quantity and quality

Bean plants ( Phaseolus vulgaris L. cv. Processer) were grown in water culture with separate air supply to roots for four to five weeks at five levels of SO₂ ranging from 10 μg m⁻³ to 950 μg m⁻³. At harvest the plant material was divided into six fractions: root, stem, fruit and leaves of three age groups.
Plants were mainly affected at and above approx. 250 μg m⁻³ SO₂. Fresh weight was reduced in mature and old leaves, and roots and fruit. Dry weight was also reduced in mature and old leaves, and roots and stem. A reduction was found in chlorophyll a and chlorophyll b in mature and old leaves, and also starch was reduced in the leaves. Sulfur content of leaves and fruit increased with exposure time and concentration, while Br, Ca, Cl, K, Mn, P and Zn increased at the highest SO₂ level only. Total (but not specific) peroxidase activity increased in all aerial fractions, i.e. soluble protein increased just like peroxidase activity. Seventeen studied amino acids all increased on the average by 38% in mature bean pods.
The observed effects may be parts of a reaction for survival and propagation of the plant, as fruit quality was not affected, indeed, it sometimes improved slightly. The latter observation is of commercial interest.     

Influence of air pollutants and nutrient deficiency on D-1 protein content and photosynthesis in young spruce trees

Long-term fumigation with different mixtures of air pollutants, such as O₃, NO₂ and SO₂, in combination with potassium deficiency in 4-year-old spruce trees shows clearly that the photosynthetic apparatus reacts very sensitively to environmental stress. Even when no change in photosynthetic oxygen evolution of the leaves was measurable, the content of D-1 protein in the reaction center of photosystem II already increased significantly at low stress conditions. With increasing concentrations of pollutants, the content of D-1 protein decreased considerably. This pattern was observed with all combinations of gases, although they differed in effectiveness. The most potent effect on the content of D-1 protein was found with a combined fumigation of SO₂ plus NO₂. Obviously, the ratio between synthesis and degradation of the D-1 protein is influenced by stress factors. However, the content of D-1 protein was not strongly correlated with photosynthetic oxygen evolution in whole needles nor with electron transport rate in isolated thylakoids. Under controlled potassium deficiency, effects similar to those observed upon ozone fumigation developed. The results suggest unspecific stress answers for the D-1 content and the photosynthetic reactions rather than specific responses.     

Effects of SO2 on photosynthesis and ribulose bisphosphate carboxylase in pine tree seedlings

Fumigations of 4–7 week old seelings of Pinus silvestris , with ca 400 μg SO₂ m^-3 for 4–5 days resulted in a decrease both in net photosynthetic rate and in the levels of ribulose bisphosphate carboxylase activity of the primary needles. The effect on net photosynthesis was reversible. No visible damages were observed on the needles. Lower concentrations, ca 200 μg SO₂ m^-3, for ca 6 days inhibited net photosynthesis reversibly. The effect on net photosynthesis was not the result of stomata closure or of increased respiration. A dose-response relation for the inhibition of net photosynthesis and ribulose bisphosphate carboxylase is suggested. A similar relation was observed for the chlorophyll content of the needles. The reversible inhibition of photosynthesis was evident only at high quantum flux density, and the quantum yield of photosynthesis at rate limiting quantum flux was not affected. This was also suggested from an experiment with Scots pine in the field.     

Air pollution in the past recorded in width and stable carbon isotope composition of annual growth rings of Douglas-fir

Abstract. Tree-ring indices (TRIs) of annual growth rings in stems of Douglas-fir ( Pseudotsuga menziesii ) growing near a copper smelter showed reduced growth during two multi-year time periods in the past. These periods coincided with World Wars I and II, which are known to represent periods of particularly high SO₂ emissions from the smelter. Reduced growth was correlated with less negative stable carbon isotope composition (δ¹³C) in cellulose purified from wood formed in such years. Based on current models for ¹³C/¹²C in plants, these results indicate that exposure to air pollution resulted in reduced concentration of CO₂ in the intercellular air spaces of the needles. This is consistent with the hypothesis that stomatal closure resulted in impaired photosynthesis and reduced growth during past episodes of high air pollution. The pollution-related change in δ¹³C was superimposed on a change with time in δ¹³C, independent of growth, by - 1.4 per mil from 1902 to 1984.     

Long-term effects of low levels of SO2 on bean plants (Phaseolus vulgaris). I. Immission-response pattern of net photosynthesis and transpiration during life-long, continuous measurements

The immission-response effect of five low levels of sulfur dioxide on net photosynthesis and transpiration was studied during continuous measurements in near-complete life cycles of whole bean plants ( Phaseolus vulgaris L. cv. Processer) grown in a controlled environment. Sixteen plants were grown in individual water cultures in each of five 100 1 glass assimilation chambers with a new type of exposure system with separate root aeration. SO₂ immission ranged from 10 μg m⁻³ to 950 μg m⁻³ during 12-h day-time exposure periods, five days a week, while a low, natural background of NO_x was accepted.
The SO₂-induced photosynthetic reductions were in the short term, but in particular on the long-term level very closely related with stomatal conductance (significance level better than 0.0005). However, a causal coherence was not inferred. Physiological inhibitions were composed of: (1) A reversible component (night and week-end recovery) and (2) an irreversible component (related to reduced green leaf area). The pattern of leaf growth was studied, with the conclusion that SO₂ reduced leaf area by promoting senescence, rather than by interfering with leaf emergence and development.     

Effects of sulphur dioxide on leaf photosynthesis: the role of temperature and humidity

The effect of temperature and humidity on SO₂–induced photosynthetic depression was determined in gas exchange experiments with leaves of Vicia faba , L. Stomatal behaviour was sensitive to humidity resulting in higher uptake rates of SO₂ and stronger reductions of photosynthesis at low VPD (vapour pressure deficit). After a fumigation period of 2 h, when the photosynthetic rate had stabilized, photosynthesis of leaves exposed to SO₂ at 8°C was reduced much more than at 18°C at the same rate of SO₂ uptake. Data analysis with a mechanistic model revealed that this effect was due to the slower rate of S(IV) oxidation at lower temperatures, resulting in higher accumulation of S(IV) and thus stronger reduction of photosynthesis. These results were confirmed by experimental analyses of the S(IV) concentration in leaves following fumigation, which showed that more S(IV) accumulated in leaves exposed at a lower temperature. This may explain the high sensitivity of plants exposed to SO₂ under winter conditions, when both VPD and temperature are low.     

Effect of oxygen concentration on intracellular pH, glucose-6-phosphate and NTP content in rice (Oryza sativa) and wheat (Triticum aestivum) root tips: in vivo 31P-NMR study

Hypoxic pretreatment is known to induce anoxia tolerance in plant species sensitive to oxygen deprivation. However, we still do not have detailed information on changes in cytoplasmic and vacuolar pH (pH_cyt and pH_vac) in plants under low-oxygen availability (hypoxia) and under anoxia. To investigate this, we have studied the influence of hypoxia and anoxia on pH_cyt and pH_vac, glucose-6-phosphate (Glc-6-P) and nucleotide triphosphate (NTP) contents in rice ( Oryza sativa L.) root tips in comparison with those of wheat ( Triticum aestivum L.) with in vivo ³¹P-nuclear magnetic resonance. Both cereals responded to hypoxia similarly, by rapid cytoplasmic acidification (from pH 7.6–7.7 to 7.1), which was followed by slow partial recovery (0.3 units after 6 h). Anoxia led to a dramatic pH_cyt drop in tissues of both species (from pH 7.6–7.7 to less than 7.0) and partial recovery took place in rice only. In wheat, the acidification continued to pH 6.8 after 6 h of exposure. In both plants, NTP content followed the dynamics of pH_cyt. There was a strong correlation between NTP content and cytoplasmic H⁺ activity ([H⁺]_cyt= 10^−pHcyt) for both hypoxic and anoxic conditions. Glc-6-P content increased in rice under anoxia and hypoxia. In wheat, Glc-6-P was not detectable under anoxia but increased under hypoxia. In this study, rice root tips were shown to behave as anoxia tolerant tissues. Our results suggest that the initial cytoplasmic acidification and subsequent pH_cyt are differently regulated in anoxia tolerant and intolerant plants and depend on the external oxygen concentration.     

Effects of SO2 fumigations on photosynthetic CO2 gas exchange, chlorophyll a fluorescence emission and antioxidant enzymes in the lichens Evernia prunastri and Ramalina farinacea

The effects of elevated gaseous SO₂ concentrations in the lichens Evernia prunastri (L.) Ach. and Ramalina farinacea (L.) Ach. were investigated by means of gas exchange, modulated chlorophyll fluorescence analysis and antioxidant enzyme assays. The response to SO₂ of the studied species differed markedly. Net photosynthetic rates were more adversely affected in E. prunastri than in R. farinacea . In addition, processes dependent on thylakoid membrane integrity such as PSII-mediated electron flow and nonphotochemical quenching were reduced to a greater extent by exposure to SO₂ in E. prunastri . Moreover, the ability to reoxidize the quinone pool was lower in this species. Finally, the activity of chloroplastidic and cytoplasmic antioxidant enzymes was decreased in E. prunastri in response to fumigations but increased in R. farinacea . The results suggest that the ability to process and deal with the SO₂ once it has been absorbed must play a role in determining the sensitivity of these lichen species to this air pollutant.     

The Toxicity of Sulphur Dioxide towards Certain Lactic Acid Bacteria from Fermented Apple Juice

This paper describes a method for testing the effect of various concentrations of SO₂ on lactic acid bacteria from ciders. The media and methods were devised to minimize loss of SO₂ due to oxidation or binding with carbonyl compounds. Exposure of laboratory or freshly isolated strains to various concentrations of free SO₂ at pH 4·0 did not readily kill them even at high concentrations of free SO₂ ( c. 150 p/m or 0·97 p/m molecular SO₂) yet they were suppressed at low concentrations ( c. 5 p/m or 0·032 p/m molecular SO₂). Reducing the pH to 3·4 reaffirmed how much more effective SO₂ is against lactic acid bacteria at lower pH levels because more is present as molecular SO₂. As a result of this the idea of quoting SO₂ values as p/m molecular SO₂ is advocated. Addition of hydrogen peroxide or acetaldehyde to a test system containing 142 p/m free SO₂ showed that they had a similar effect in nullifying its antimicrobial properties and allowing the test bacteria to grow. There was no indication that acetaldehyde bisulphite was toxic to the test bacteria.