Effect of high and low sulfate concentrations on adenosine 5'-phosphosulfate sulfotransferase activity from Lemna minor

The effect of Na₂SO₄ concentrations from 0 to 17.6 m M in the nutrient solution of Lemna minor L. strain 6580 on adenosine 5'-phosphosulfate sulfotransferase activity was examined. Routinely, the plants were cultivated on 0.88 mA SO₄²⁻. The enzyme activity was increased by 50 to 100% after transfer to 0 or 0.0088 m M SO₄²⁻. Transfer back to 0.88 m M rapidly decreased the enzyme activity to the initial level. Cultivation on 17.6 mM Na₂SO₄ redueed extractable adenosine 5'-phosphosulfate sulfotransferase by 50%. The original level was rapidly re-established on 0,88 m M . In control experiments, a decrease in adenosine 5'-phosphosulfate sulfotransferase activity was also induced by K₂ SO₄, whereas NaCl caused a small increase. This indicates that the observed effects are dependent on the sulfate ion. ATP-sulfurylase activity measured for comparison was only significantly affected by the omission of sulfate, which induced a 20% increase, indicating that this enzyme activity from Lemna minor is less suseeptible to changes in medium sulfate than adenosine 5'-phosphosulfate sulfotransferase. A close relationship between adenosine 5'-phosphosulfate sulfotransferase activity and the content of asparagine, glutamine, non-protein thiols and sulfate in the tissue was detected, indicating a positive control mechanism induced by amides and a negative mechanism induced by thiols and sulfate.     

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.     

The effect of open-air fumigation with SO2 and O3 on carbohydrate metabolism in Scots pine (Pinus sylvestris) and Norway spruce (Picea abies)

The carbohydrate metabolism of the needles of Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) has been examined in trees that were exposed to SO₂, and O₃, in an open-air fumigation experiment located in the Liphook forest in southern England. Two-year-old seedlings were planted in 1985 in seven experimental plots. Five plots received fumigation treatments of SO₂, O₃ or a combination of these gases to give a 2 × 3 factorial design with one additional ambient plot Fumigation with SO₂, occurred from May 1987 to December 1990 and O₃, fumigation occurred from March to December 1988, May to December 1989 and February to December 1990. Five samples of needles for investigation of carbohydrate metabolism were taken between February and July 1989. The concentrations of soluble carbohydrates (including sucrose and hexoses) were greatly reduced in the needles taken from Scots pine growing in the treated plots, and were also reduced, but to a lesser extent, in the needles taken from Norway spruce. Little variation in the concentration of starch in the needles of either species was detected. The activities of the two final enzymes of sucrose synthesis, sucrose phosphate synthase and sucrose 6-phos-phate phosphatase, were greatly reduced in the needles of Scots pine and were also reduced, but to a lesser extent, in the needles of Norway spruce in the fumigated plots. These reductions could be correlated with decreases in rates of photosynthetic CO₂ assimilation determined by independent groups of researchers working on the Liphook site.     

Plant responses to H2S and SO2 fumigation. I. Effects on growth, transpiration and sulfur content of spinach

Exposure of spinach (Spinacia oleracea L. cv. Monosa) to 0.25 μl l_?1 H₂S reduced the relative growth rate by 26, 47 and 60% at 15, 18 and 25°C, respectively. Shoot to root ratio decreased in plants fumigated at 18 and 25°C. Growth of spinach was not affected by a 2-week exposure to 0.10 or 0.25 μl l_?1 SO₂. Both H₂S and SO₂ fumigation increased the content of sulfhydryl compounds and sulfate. A 2-week exposure to 0.25 μl l_?1 H₂S resulted in an increase in sulfhydryl and sulfate content of 250 to 450% and 63 to 248% in the shoots, respectively, depending on growth temperature. Exposure to 0.15 and 0.30 μl l_?1 H₂S at 20°C for 2 weeks resulted in a 46% increase in sulfate content of the shoots at 0.30 μl l_?1 and no detectable increase at 0.15 μl l_?1 H₂S; the sulfate content of the roots increased by 195 and 145% at 0.15 and 0.30 μl l_?1 H₂S, respectively. Fumigation with 0.25 μl l_?1 SO₂ at 20°C for 2 weeks resulted in an increase in sulfhydryl content and sulfate content in the shoots of 285% and 300 to 1100%. H₂S fumigation during the 12 h light period or only during the dark period resulted in identical growth reduction and accumulation of sulfhydryl compounds; they were about 50 and 67% of those observed in continuously exposed plants. H₂S- and SO₂-exposed plants showed an increased transpiration rate, which was mainly caused by an increased dark-period transpiration. No effect of H₂S and SO₂ on the water uptake of the plants and the osmotic potential of the leaves was detected. Plants fumigated with 0.25 μl l_?1 H₂S for 2 weeks were smaller and differed morphologically from the control plants by slightly more abaxially curved leaf margins. Cross sections of the leaves showed smaller cells at the margins and smaller and fewer air spaces. The increased transpiration in the H₂S-exposed plants is discussed in relation to the observed morphological changes.     

Photosynthetic performance, chloroplast pigments and mineral content of Norway spruce (Picea abies (L.) Karst.) exposed to SO2 and O3 in an open-air fumigation experiment

Photosynthetic performance, mineral content and chloroplast pigments were investigated in August-September 1988 and 1989 in Norway spruce trees (Picea abies (L.) Karst.) exposed to SO₂, and O₃ in an open-air fumigation facility at Liphook, England. The data do not suggest a treatment effect on the mineral content of the needles in terms of nutrient leaching from the foliage. In addition, there were no direct SO₂ and/or O₃ effects on the content and/or composition of the chloroplast pigments. However, the long-term application of SO₂ resulted in a depression of net photosynthesis under light saturation and ambient CO₂ (A ₃₄₀) which was probably caused by a treatment-related depression of the carboxylation efficiency (CE). In 1989, the supposed treatment effects were apparently masked by an insufficient N-supply and probably also by low water availability during summer. However, fumigation appeared to accelerate an N-deficiency-related decrease of CE, stomatal closure and the age-dependent development of the chlorophyll content of the needles. In 1989, an observed depression of the photosynthetic capacity (A₂₅₀₀) was in part accompanied by a decrease in light use efficiency (α), suggesting an enhanced photosensitivity resulting from the impact of several possible interacting stresses (drought, N deficiency and fumigation). The results support the general conclusion that long-term low-level SO₂ dosage adversely affects the photosynthetic performance of the needle, whether directly or indirectly, and may also interact with other environmental stresses. The findings of our investigations are discussed with regard to the hypothesis of forest decline in the mountain regions of the Fichtelgebirge (north-eastern Bavaria, Germany).     

NO2‐induced nitrate reductase activity in needles of Norway spruce (Picea abies) under laboratory and field conditions

The induction of activity of the enzyme nitrate reductase (NR, EC 1.6.6.1, 1.6.6.2) in needles of Norway spruce ( Picea abies [L.] Karst.) by nitrogen dioxide (NO₂) was studied under laboratory and field conditions. In fumigation chambers an increase in nitrate reductase activity (NRA) was detected 4 h after the start of the NO₂ treatment. During the first 2 days with 100 µg NO₂ m⁻³, NRA reached a constant level and did not change during the following 4 days. At the same level of NO₂, NRA was lower in needles from trees grown on NPK‐fertilized soil than on non‐fertilized soil. After the transfer of spruce trees from fertilized soil to NPK‐rich nutrient solution, NRA was transiently increased. This effect was assigned to root injuries causing nitrate transport to the shoot and subsequent induction of NRA. Neither trees on fertilized soil nor trees transferred to NPK‐poor nutrient solution had increased NRA unless NO₂ was provided. The NO₂ gradient in the vicinity of a highway was used to test the long‐term effect of elevated levels of NO₂ on needle NRA of potted and field‐grown spruce trees. Compared with less polluted sites, permanently increased NRAs were detected when NO₂ concentrations were above 20 µg m⁻³. Controls of field measurements some 10 years after the introduction of catalytic converters in cars showed no significant change neither in NO₂ levels nor in the decreasing NRA of spruce needles with the distance from the highway.     

Mycorrhiza formation on Norway spruce (Picea abies) roots affects the pathway of anaplerotic CO2 fixation

Activities of carboxylation enzymes were analyzed in the mycelium of the mycorrhizal fungus Amanita muscaria (L. ex Fr.) Hooker, in non-mycorrhizal short roots of Norway spruce ( Picea abies [L.] Karst.) and in myconhizas of these two partners. While pyruvale carboxylase (PC, EC 6.4.1.1) and phosphoenolpyruvate carboxykinase activities (PEPCK.EC 4.1.1.49) could be detected in the mycelium of A. muscaria , phosphoenolpyruvate carboxyknase (PEPC, EC 4.1.1.31) was only active in root tissue. In A. muscaria , PC activity was generally low (around 10 nmol mg^−tprotein min⁻) but PEPCK activity was above 250 nmol mg⁻¹ protein min⁻¹. Mycorrhizal development on short roots decreased PEPC activity by more than 75%, although dilution by the fungal biomass in mycorrhizas was only 35%. This reduction in activity was paralleled by a decreased content of PEPC protein. By means of micro-analytical methods it was shown that PEPC activity was lowest in the central zones of the mycorrhizas, Whereas PEPC activity was highest in the corresponding central sections in non-mycorrhizal short roots. ¹⁴CO₂ labelling, on the other hand, revealed that in vivo CO₂ fixation was higher in mycorrhizas compared to non-mycorrhizal short roots. It is concluded that fungal carboxylases (probably PEPCK) are important for anaplerotic CO₂ fixation during nitrogen assimilation in mycorrhizas of Norway spruce.     

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.     

Growth of coniferous trees exposed to SO2 and O3 using an open-air fumigation system

Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies (L.) Karst.) and Sitka spruce (Picea sitchensis Bong. Carr.) were planted as 2-year-old seedlings in an open-air fumigation facility at Liphook in southern England in March 1985. The soil was a humoferric podzol of pH 4. SO₂ fumigation began in May 1987 and continued until December 1990. Long-term mean SO₂ concentrations were 4,13 and 22 nmol mo^?1. Three plots, one at each SO₂ level, were also exposed to O₃ at an average of 1–3.times the ambient level. O₃ fumigation ran from March to December 1988, May to December 1989 and February to December 1990. Each species reacted differently to treatment. Scots pine showed no growth response to either pollutant, although other work on the site demonstrated a number of deleterious effects of SO₂ on this species, including increased leaf loss and foliar injury. Stem basal diameter growth of Norway spruce was depressed in SO₂-treated plots. In contrast, extension growth of shoots of Sitka spruce increased in SO₂-treated plots, in apparent response to codeposition of NH₃-N. However, diameter growth of Sitka spruce main stems did not increase. No effects of O₃ on growth were recorded for any species.     

Physiological effects of a long term exposure to low concentrations of NH3, NO2 and SO2 on Douglas fir (Pseudotsuga menziesii)

The above-ground parts of two years old seedlings of Douglas fir (Pseudotsuga menziesii) were exposed to filtered air, NH₃, NO₂₊, SO₂ (66, 96 and 95 μg m^?3, respectively), to a mixture of NO₂+NH₃ (55 + 82 μg m^?3) or SO₂+NO₂ (128 + 129 μg m^?3), for 8 months in fumigation chambers. Both chlorophyll fluorescence and gas exchange measurements were carried out on shoots which had sprouted at the beginning of the exposure period. The chlorophyll fluorescence measurements were performed after 3 and 5 months of exposure (average shoot age 70 and 140 days, respectively). Light response curves of electron transport rate (J) were determined, in which J was deduced from chlorophyll fluorescence. In addition, light response curves of net CO₂ assimilation were determined after 5 months of exposure. After 3 months of exposure (average shoot age 70 days) all exposure treatments showed a lower maximum electron transport rate (J_max) as compared to the control shoots (filtered air). A large reduction (45%) was observed for shoots exposed to SO₂+NO₂. During the exposure period between 3 and 5 months (average shoot age 70 and 140 days, respectively) a decrease of J_max was observed for all treatments. J_max had further declined some time after termination of the exposure, when average shoot age was 310 days. Shoots exposed to SO₂ and SO₂+NO₂ also showed a reduction in maximum net CO₂ assimilation (P_max) as compared to the control shoots. However, shoots exposed to NO₂ showed no reduction and even a higher P_max was observed for shoots exposed to NH₃ or NO₂+NH₃. Needles of these treatments also showed a higher chlorophyll content which might explain the contradictory results obtained for these treatments: the increased amount of photosynthetic units counteracts the reduction in J_max and consequently no reduction in P_max is measured. Shoots exposed to SO₂ and SO₂+NO₂ also showed a reduction in maximum stomatal conductance (g_s). However, the stomatal opening was larger than could be expected on basis of their (maximum) CO₂ assimilation rate. Consequently, water use efficiency of these shoots was lower than that of the control shoots. Also shoots exposed to NO₂ had a lower water use efficiency due to a significantly higher maximum g_s. Shoots exposed to NH₃ showed a high transpiration rate in the dark, indicating imperfect stomatal closure.     

Diagnostic parameters for selecting against novel spruce (Picea abies) decline: I. Tree morphology and photosynthesis response to acute SO2 exposures

The dose- and time-response effects of single 4-h day-exposures to 0.50, 0.79, 1.28, 1.58, 2.38 or 3.35 μl l^?1 (ppm) SO₂ followed by single 3-h night-exposures of 0.60, 0.87, 1.54, 1.91, 2.91 or 3.98 μl l^?1 SO₂ on photosynthesis, transpiration and dark respiration were examined for nine East European (Carpatho-Ukrainian, ‘Rachovo’) half-sib families and for two populations, one from the FRG (‘Westerhof’) and one from the GDR (‘Schmiedefeld’) of Norway spruce [Picea abies (L.) Karst.], all in their 4th growing season. Even the lowest SO₂ concentration reduced photosynthesis and transpiration within 1 h. Photosynthesis of the different spruce types was affected significantly differently, the most sensitive spruce being suppressed 2.5 times more than the most tolerant spruce. ‘Westerhof’ was more resistant to SO₂ than the average ‘Rachovo’ half-sibs. Neither transpiration (stomatal reaction), which was affected alike by all SO₂ concentrations, nor SO₂ uptake, explained adequately the effects on photosynthesis. Night transpiration, but not dark respiratin, was stimulated by night SO₂ preceded by day SO₂ exposure. The gradient of different SO₂ sensitivities among young trees from the half-sib families demonstrated a significant negative correlation with the gradient of different sensitivities to novel decline symptoms of their parents growing in a rural seed orchard in Denmark, and with the gradients of four morphology parameters, (height, branching, branch density and the number of Lammas shoots) of the young trees, which in turn demonstrated a positive correlation with decline sensitivity in the seed orchard. The relative photosynthesis sensitivity and the morphology of half-sibs may serve as diagnostic parameters for laboratory selection of the most resistent trees to novel spruce decline in the field. There was a positive correlation between SO₂ induced scorching of Lammas shoots and the inhibition of photosynthesis, but not between the severity of SO₂ scorching and symptoms of novel spruce decline. The two visible types of symptoms looked very different.     

Effects of elevated CO2, elevated O3 and potassium deficiency on Norway spruce [Picea abies (L) Karst.]: seasonal changes in photosynthesis and non-structural carbohydrate content

Two clones of 5-year-old Norway spruce [Picea abies (L.) Karst.] were exposed to two atmospheric concentrations of CO2 (350 and 750 μmol mol^?1) and O₃ (20 and 75nmolmol^?1) in a phytotron at the GSF-Forschung-szentrum (Munich) over the course of a single season (April to October). The phytotron was programmed to recreate an artificial climate similar to that at a high elevation site in the Inner Bavarian Forest, and trees were grown in large containers of forest soil fertilized to achieve contrasting levels of potassium nutrition, designated well-fertilized or K-deficient. Measurements of the rate of net CO₂ assimilation were made on individual needle year age classes over the course of the season, chlorophyll fluorescence kinetics were recorded after approximately 23 weeks, and seasonal changes in non-structural carbohydrate composition of the current year's foliage were monitored. Ozone was found to have contrasting effects on the rate of net CO₂ assimilation in different needle age classes. After c. 5 months of fumigation, elevated O₃ increased (by 33%) the rate of photosynthesis in the current year's needles. However, O3 depressed (by 30%) the photo-synthetic rate of the previous year's needles throughout the period of exposure. Chlorophyll fluorescence measurements indicated that changes in photosystem II electron transport played no significant role in the effects of O₃ on photosynthesis. The reasons for the contrasting effects of O₃ on needles of different ages are discussed in the light of other recent findings. Although O₃ enhanced the rate at which CO₂ was fixed in the current year's foliage, this was not reflected in increases in the non-structural carbohydrate content of the needles. The transfer of ambient CO₂-grown trees to a CO₂-enriched atmosphere resulted in marked stimulation in the photosynthetic rate of current and previous year's foliage. However, following expansion of the current year's growth, the photosynthetic rate of the previous year's foliage declined. The extent of photosynthetic adjustment in response to prolonged exposure to elevated CO₂ depended upon the clone, providing evidence of intraspecific variation in the long-term response of photosynthesis to elevated CO₂. The increase in photosynthesis induced by CO₂ enrichment was associated with increased foliar concentrations of glucose, fructose and starch (but no change in sucrose) in the new growth. CO₂ enrichment significantly enhanced the photosynthetic rate of K-deficient needles, but there was a strong CO₂soil interaction in the current year's needles, indicating that the long-term response of trees to a high CO₂ environment may depend on soil fertility. Although the rate of photosynthesis and non-structural carbohydrate content of the new needles were increased in O₃-treated plants grown at higher levels of CO₂, there was no evidence that elevated CO₂ provided additional protection against O₃ damage. Simultaneous exposure to elevated O₃ modified the effects of elevated CO₂ on needle photosynthesis and non-structural carbohydrate content, emphasizing the need to take into account not only soil nutrient status but also the impact of concurrent increases in photochemical oxidant pollution in any serious consideration of the effects of climate change on plant production.     

Metabolism of tritiated gibberellin A1 in seedlings of Norway spruce, Picea abies

Five-week-old seedlings of Norway spruce, Picea abies (L.) Karst., metabolized 1,2-/³H/-gibberellin A₁ into a single major compound chromatographically similar to gibberellin A₈. The conversion rate exceeded 10% within the 24-h incubation period.