Superoxide Dismutase Activity in Needles of Norwegian Spruce Trees (Picea abies L.)

The activity of superoxide dismutase was investigated in needles of spruce trees. To obtain maximum activity, needles were homogenized in the presence of Triton X-100 and polyvinylpyrrolidone. Superoxide dismutase activity was measured in dialyzed extracts with a modified epinephrine assay (HP Misra, I Fridovich [1972] J Biol Chem 247: 3170-3175) at pH 10.2. The extracts contained 70 to 120 units of superoxide dismutase per milligram protein. One unit of superoxide dismutase was completely inhibited in the presence of 20 micromolar NaCN. On native polyacrylamide gels three electromorphs were visualized after staining for activity. All three species were sensitive to CN⁻ and H₂O₂ and were therefore assumed to be Cu/Zn-superoxide dismutases. Superoxide dismutase activity was dependent on the age of the needles and declined by approximately 25% within 3 to 4 years.     

Role of o-acetylserine in hydrogen sulfide emission from pumpkin leaves in response to sulfate

In the presence of excess sulfate, cysteine synthesis in pumpkin (Cucurbita pepo) leaves is not limited by sulfate reduction, but by the availability of O-acetylserine. Feeding of O-acetylserine or its metabolic precursors S-acetyl-coenzyme-A and coenzyme A to leaf discs enhanced the incorportion of [³⁵S]sulfate into reduced sulfur compounds, mainly into cysteine, at the cost of lowered H₂S emission; the uptake and reduction of sulfate is not affected by these treatments. β-Fluoropyruvate, an inhibitor of the generation of S-acetyl-coenzyme A via pyruvate dehydrogenase, stimulated H₂S emission in response to sulfate. This stimulation is overcompensated by addition of O-acetylserine, S-acetyl-coenzyme A, or coenzyme A. These results indicate that, in the presence of high amounts of sulfate, excess sulfur is reduced and emitted as H₂S into the atmosphere. The H₂S emitted seems to be produced by liberation from a precursor of cysteine rather than by cysteine desulfhydration.     

Developmental changes in the potential for h(2)s emission in cucurbit plants

Based on results obtained with leaf discs exposed to sulfate, leaves on cucurbit plants (Cucurbita pepo L. cv Small Sugar Pumpkin and Cucumis sativus cv Chipper) 1 to 2.5 weeks old have a low potential for H₂S emission (less than 10 picomoles per min per cm² leaf area) in response to sulfate, whereas discs from most of the leaves on plants 3 to 4 weeks old emit H₂S at a higher rate (50 to 150 picomoles per min per cm² leaf area). This difference is determined by the age of the plant, and is independent of the leaves' age or developmental stage. In response to l-cysteine, however, discs from leaves on cucurbit plants 1 to 2.5 weeks old emit H₂S at higher rates (15 to 50 picomoles per min per cm² leaf area) than in response to sulfate. Furthermore, the potential for H₂S emission in response to l-cysteine decreases with increasing age of the individual leaf. Thus, most of the potential for H₂S emission in response to l-cysteine is developed during germination and the early growth of cucurbit plants, but most of the potential for H₂S emission in response to sulfate arises later in the development of the plants.     

Emission of volatile sulfur compounds from spruce trees

Spruce (Picea Abies L.) trees from the same clone were supplied with different, but low, amounts of plant available sulfate in the soil (9.7-18.1 milligrams per 100 grams of soil). Branches attached to the trees were enclosed in a dynamic gas exchange cuvette and analyzed for the emission of volatile sulfur compounds. Independent of the sulfate supply in the soil, H₂S was the predominant reduced sulfur compound continuously emitted from the branches with high rates during the day and low rates in the night. In the light, as well as in the dark, the rates of H₂S emission increased exponentially with increasing water vapor flux from the needles. Approximately 1 nanomole of H₂S was found to be emitted per mole of water. When stomata were closed completely, only minute emission of H₂S was observed. Apparently, H₂S emission from the needles is highly dependent on stromatal aperture, and permeation through the cuticle is negligible. In several experiments, small amounts of dimethylsulfide and carbonylsulfide were also detected in a portion of the samples. However, SO₂ was the only sulfur compound consistently emitted from branches of spruce trees in addition to H₂S. Emission of SO₂ mainly proceeded via an outburst starting before the beginning of the light period. The total amount of SO₂ emitted from the needles during this outburst was correlated with the plant available sulfate in the soil. The diurnal changes in sulfur metabolism that may result in an outburst of SO₂ are discussed.     

Storage and remobilisation of sulphur in beech trees (Fagus sylvatica)

Three-year-old beech trees were fed ³⁵S-sulphate in August 1993 via a flap in a mature leaf of an upper branch. Harvest of beech trees was performed 24 h after feeding ³⁵S-sulphate, before leaf senescence, after leaf abscission, in early winter (January 1994). in late winter (March 1994). before bud break and after bud break. Twenty-four h after feeding ³⁵S-sulphate, 0.7 ± 0.5% of the ³⁵S-radioactivity taken up was exported out of the fed leaf. When trees were analysed 2 months later, i.e., before leaf senescence, this value had increased to 22 ± 7%. The exported ³⁵S-radioactivity was located in the branch containing the fed leaf (2.8 ± 13%). in basipetal parts of the trunk (41 ± 77%) and in the main rool (21 ± 6%). Leaves and apical parts of the trunk were no sink organs for the exported sulphur. Along the tree axis the main proportion of the radiolabel was located in the wood, predominantly in the acid soluble fraction. In the bark the greater portion of the radiolabel was found in the acid insoluble fraction. In both tissues the bulk of the ³⁵S of the soluble fraction was sulphate together with small amounts of glutathione. This pattern did not change until bud break. After bud break, basipetal parts of the trunk lost part of its ³⁵S-radioactivity. Of the ³⁵S-radioactivity which had been exported out of the fed leaf during the previous autumn, 16 ± 2% remained in the trunk, whereas 47 ± 7% of the ³⁵S was found in branches, mainly in the newly developed leaves. The present results show that sulphur, mainly in the form of sulphate, is stored along the tree axis in both bark and wood of beech trees and is re-mobilised during leaf development in spring.     

Exchange of NO and NO2 between wheat canopy monoliths and the atmosphere

The fluxes of NO and NO₂ between wheat canopy monoliths and the atmosphere were investigated with the dynamic chamber technique. For this purpose monoliths were dug out at different plant growth stages from a field site, transported to the institute, and placed in an environmental growth chamber. The wheat canopy monoliths were exposed over a period of four days to the average ratios of atmospheric NO₂ and NO measured at the field site, i.e. NO₂ concentration of about 18 mL L^-1 plus NO concentration lower than 0.5 nL L^-1. Under these conditions NO emission into the atmosphere and NO₂ deposition into canopy monoliths was observed. Both fluxes showed diurnal variation with maximum rates during the light and minimum rates during darkness. NO₂ fluxes correlated with soil temperature as well as with light intensity. NO fluxes correlated with soil temperature but not with light intensity. From the investigation performed the diurnal variation of the NO and NO₂ compensation points, the maximum rates of NO and NO₂ emission, and the total resistances of NO and NO₂ fluxes were calculated. Under the assumption that the measured data are representative for the whole vegetation period, annual fluxes of NO and NO₂ were estimated. Annual NO emission into the atmosphere amounted to 87 mg N m^-2 y^-1 (0.87 kg ha^-1 y^-1), annual NO₂ deposition into canopy monoliths amounted to 1273 mg N m^-2 y^-1 (12.73 kg ha^-1 y^-1). Apparently, the uptake of atmospheric nitrogen by the wheat field from NO₂ deposition is about 15 times higher than the loss of nitrogen from NO emission. It can therefore be assumed that even in rural areas wheat fields are a considerable sink for atmospheric nitrogen. The annual sink strength estimated in the present study is ca. 12 kg N ha^-1 y^-1. The possible origin of the NO emitted and the fate of atmospheric NO₂ taken up by the wheat canopy monoliths are discussed.Preliminary results of this paper were presented at the Joint Workshop COST 611/Working Party 3 and EUROTRAC in Delft, The Netherlands (Ludwig et al., 1991).     

Net Uptake of Sulfate and its Transport to the Shoot in Spinach Plants Fumigated with H2S or SO2: Does Atmospheric Sulfur Affect the “Inter-Organ” Regulation of Sulfur Nutrition?*

Spinach plants (Spinacea oleracea L. cv. Estivato) were grown on nutrient solutions under deficient, normal and excess sulfate supply. In both young and mature plants net uptake of sulfate and its transport to the shoot increased with increasing sulfate supply, but both processes proceeded at a higher rate in young as compared to mature plants. The relative sulfate transport, i.e. the relative amount of the sulfate taken up that is transported to the shoot, decreased with increasing sulfate supply. Apparently, net uptake of sulfate is not strictly controlled by the sulfur demand of the shoot, but xylem loading appears to counteract excess transport of sulfate to the shoot. Fumigation with H₂S or SO₂ reduced net uptake of sulfate by the roots in sulfur-deficient plants and absolute as well as relative sulfate transport to the shoot independent of the three sulfate levels supplied to the plant. At the same time thiol contents of the shoot and the root were enhanced by fumigation with H₂S and SO₂. These findings are consistent with the idea that thiols produced in the leaves can mediate demand-driven control of sulfate uptake by the roots and its transport to the shoot.     

Purification and Properties of Manganese Superoxide Dismutase from Norway Spruce (Picea abies L. Karst)

A manganese-containing superoxide dismutase (SOD; EC 1.15.1.1 [EC] )was purified to electrophoretic homogeneity from seeds of Norwayspruce (Picea abies L.). The apparent molecular mass of thepurified enzyme was 86 kDa, as determined by gel filtration.The subunit molecular mass, estimated by SDS-polyacrylamidegel electrophoresis, was 22 kDa both in the presence and inthe absence of 2-mercaptoethanol. Thus, the native enzyme isa homotetramer with subunits that were not linked by disulfidebonds. The isoelectric point of this Mn-SOD was 5.5. The specificactivity of the Mn-SOD was strongly pH-dependent and was 400units per nmol SOD at pH 7.8 and 30 units per nmol SOD at pH10.4. The first 25 amino acid residues in the amino terminalregion of spruce Mn-SOD exhibited a high degree of sequencehomology to those of Mn-SODs from other organisms. In Mn-deficientneedles the activity of Mn-SOD was only half of that in non-deficientneedles, whereas the activity of CuZn-SOD was doubled. (Received May 20, 1994; Accepted October 31, 1994)     

Interactions of NH4+ and L-glutamate with NO3- transport processes of non-mycorrhizal Fagus sylvatica roots

The processes of NO₃^– uptake and transport and the effectsof NH₄⁺ or L-glutamate on these processes were investigatedwith excised non-mycorrhizal beech (Fagus sylvatica L.) roots.NO₃^– net uptake followed uniphasic Michaelis-Menten kineticsin a concentration range of 10µM to 1 mM with an apparentK_m of 9.2 µM and a V_max of 366 nmol g^–1 FW h^–1.NH₄⁺, when present in excess to NO₃^–, or 10 mM L-glutamateinhibited the net uptake of NO₃^– Apparently, part of NO₃^–taken up was loaded into the xylem. Relative xylem loading ofNO₃^– ranged from 3.21.6 to 6.45.1% of NO₃^– netuptake. It was not affected by treatment with NH₄⁺ or L-glutamate.¹⁶N/¹³N double labelling experiments showed that NO₃^–efflux from roots increased with increasing influx of NO₃^–and, therefore, declined if influx was reduced by NH₄⁺ or L-glutamateexposure. From these results it is concluded that NO₃^–net uptake by non-mycorrhizal beech roots is reduced by NH₄⁺or L-glutamate at the level of influx and not at the level ofefflux. Key words: Nitrate transport, net uptake, influx, efflux, ammonium, Fagus, Fagaceae     

Interactive regulation of root exudation and rhizosphere denitrification by plant metabolite content and soil properties

Plant and Soil - Cyperaceae are common on nutrient-poor soils, including in western Japan. We examined the ability of the native Cyperaceae from western Japan to form dauciform roots and assessed...