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).     

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.     

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.     

Isotopic heterogeneity of water in transpiring leaves: identification of the component that controls the δ18O of atmospheric O2 and CO2

Two direct but independent approaches were developed to identify the average δ¹⁸O value of the water fraction in the chloroplasts of transpiring leaves. In the first approach, we used the δ¹⁸O value of CO₂ in isotopic equilibrium with leaf water to reconstruct the δ¹⁸O value of water in the chloroplasts. This method was based on the idea that the enzyme carbonic anhydrase facilitates isotopic equilibrium between CO₂ and H₂O predominantly in the chloroplasts, at a rate that is several orders of magnitude faster than the non-catalysed exchange in other leaf water fractions. In the second approach, we measured the δ¹⁸O value of O₂ from photosynthetic water oxidation in the chloroplasts of intact leaves. Since O₂ is produced from chloroplast water irreversibly and without discrimination, the δ¹⁸O value of the O₂ should be identical to that of chloroplast water. In intact, transpiring leaves of sunflower (Helianthus annuus cv. giant mammoth) under the experimental conditions used, the average δ¹⁸O value of chloroplasts water was displaced by 3—10 % (depending on relative humidity and atmospheric composition) below the value predicted by the conventional Craig & Gordon model. Furthermore, this δ¹⁸O value was always lower than the δ¹⁸O value that was measured for bulk leaf water. Our results have implications for a variety of environmental studies since it is the δ¹⁸O value of water in the chloroplasts that is the relevant quantity in considering terrestrial plants influence on the δ¹⁸O values of atmospheric CO₂ and O₂, as well as in influencing the δ¹⁸O of plant organic matter.     

Opioid-Induced Increase in [Ca2+]i in ND8-47 Neuroblastoma × Dorsal Root Ganglion Hybrid Cells Is Mediated Through G Protein-Coupled δ-Opioid Receptors and Desensitized by Chronic Exposure to Opioid

Abstract: δ-Receptor agonists induce a concentration-dependent increase in intracellular calcium concentration ([Ca²⁺]_i) in ND8-47 cells by activating dihydropyridine-sensitive Ca²⁺ channels. The role of G proteins in transducing the opioid effect has been studied. Pretreatment of cells with pertussis toxin (100 ng/ml, 24 h) almost completely blocked [d -Ser²,Leu⁵]enkephalin-Thr (DSLET)-induced increase in [Ca²⁺]_i. Cholera toxin (10 nM, 24 h) had no effect on DSLET-induced response. Pretreatment of the cells with 1 µM DSLET for 1 h resulted in a 30% inhibition of DSLET-induced increase in [Ca²⁺]_i and a 78% inhibition after exposure for 24 h. After 1 h of exposure to DSLET, there was a decrease in agonist affinity with no significant changes in receptor density. Cells exposed to 1 µM DSLET for 24 h demonstrate a nearly 90% decrease in [³H]diprenorphine binding, with a decrease in affinity for agonist at the remaining binding sites. G protein subunits α_i2, α_i3, α_s, and α_q were detected in ND8-47 cell membranes by western blot; α_o and α_i1 were not present. Chronic DSLET treatment had no significant effect on the quantity of each of the α-subunits. These results suggest that the DSLET-induced increase in [Ca²⁺]_i is mediated through pertussis toxin-sensitive G proteins (probably G_i2 or G_i3) and the attenuation of this response in chronically treated cells is associated with a relatively rapid reduction in receptor affinity to DSLET and a slow reduction in receptor density.