Estimating the uptake of traffic-derived NO2 from 15N abundance in Norway spruce needles

The 15N ratio of nitrogen oxides (NOx) emitted from vehicles, measured in the air adjacent to a highway in the Swiss Middle Land, was very high [δ15N(NO2) = +5.7‰]. This high 15N abundance was used to estimate long-term NO2 dry deposition into a forest ecosystem by measuring δ15N in the needles and the soil of potted and autochthonous spruce trees [Picea abies (L.) Karst] exposed to NO2 in a transect orthogonal to the highway. δ15N in the current-year needles of potted trees was 2.0‰ higher than that of the control after 4 months of exposure close to the highway, suggesting a 25% contribution to the N-nutrition of these needles. Needle fall into the pots was prevented by grids placed above the soil, while the continuous decomposition of needle litter below the autochthonous trees over previous years has increased δ15N values in the soil, resulting in parallel gradients of δ15N in soil and needles with distance from the highway. Estimates of NO2 uptake into needles obtained from the δ15N data were significantly correlated with the inputs calculated with a shoot gas exchange model based on a parameterisation widely used in deposition modelling. Therefore, we provide an indication of estimated N inputs to forest ecosystems via dry deposition of NO2 at the receptor level under field conditions

Effect of glucose on assimilatory sulphate reduction in Arabidopsis thaliana roots

With the aim of analysing the relative importance of sugar supply and nitrogen nutrition for the regulation of sulphate assimilation, the regulation of adenosine 5′‐phosphosulphate reductase (APR), a key enzyme of sulphate reduction in plants, was studied. Glucose feeding experiments with Arabidopsis thaliana cultivated with and without a nitrogen source were performed. After a 38 h dark period, APR mRNA, protein, and enzymatic activity levels decreased dramatically in roots. The addition of 0.5% (w/v) glucose to the culture medium resulted in an increase of APR levels in roots (mRNA, protein and activity), comparable to those of plants kept under normal light conditions. Treatment of roots with d‐sorbitol or d‐mannitol did not increase APR activity, indicating that osmotic stress was not involved in APR regulation. The addition of O‐acetyl‐l‐serine (OAS) also quickly and transiently increased APR levels (mRNA, protein, and activity). Feeding plants with a combination of glucose and OAS resulted in a more than additive induction of APR activity. Contrary to nitrate reductase, APR was also increased by glucose in N‐deficient plants, indicating that this effect was independent of nitrate assimilation. [35S]‐sulphate feeding experiments showed that the addition of glucose to dark‐treated roots resulted in an increased incorporation of [35S] into thiols and proteins, which corresponded to the increased levels of APR activity. Under N‐deficient conditions, glucose also increased thiol labelling, but did not increase the incorporation of label into proteins. These results demonstrate that (i) exogenously supplied glucose can replace the function of photoassimilates in roots; (ii) APR is subject to co‐ordinated metabolic control by carbon metabolism; (iii) positive sugar signalling overrides negative signalling from nitrate assimilation in APR regulation. Furthermore, signals originating from nitrogen and carbon metabolism regulate APR synergisticall

Incorporation of atmospheric 15NO2-nitrogen into free amino acids by Norway spruce Picea abies (L.) Karst.

During spring and autumn 1991, potted 6-yearold spruce trees (Picea abies (L.) Karst.) were fumigated with 60 nl1–1 15NO2 for 4 days under controlled conditions in constant light. Current and previous flush needles, the bark and the fine roots were analysed for total 15N content and incorporation of 15N into the -amino nitrogen of free amino acids. In addition, in vitro nitrate reductase activity and stomatal conductance of the needles were measured. Nitrate reductase activity was significantly higher in the needles of fumigated trees compared to control trees exposed to filtered air. With an average of 9.1% 15N, free glutamate was the pool with the most label. Taking into account the time-course of the labelling of this pool, this figure can be taken as an estimate of the minimum contribution of NO2 to the N nutrition of the needles. 15N-labelled amino acids were also detected in the bark and the roots, indicating export from the needles

Regulation of Adenosine 5′-Phosphosulfate Sulfotransferase in Higher Plants

APSSTAse catalyses the transfer of the sulfonylgroup of APS to a carrier (car-SH) to form car-S-SO 3 - . The carrier seems to be reduced glutathione in Chlorella (Tsang and Schiff, 1978). Using mutants blocked for sulfate reduction, APSSTase has been shown to be an enzyme of assimilatory sulfate reduction in Chlorella (Schmidt et al., 1974). The regulatory properties of the enzyme presented in this paper, together with enzymatic analysis (Schmidt, 1976), indicate that it is also involved in assimilatory sulfate reduction of higher plants. APSSTase has been detected in more than 50 families of higher plants (Schmidt, 1975a) and has been partially purified from spinach (Schmidt, 1976)

Changes in ATP sulfurylase and adenosine 5'-phosphosulfate sulfotransferase activity during autumnal senescence of beech leaves

The decrease in extractable activity of ribuloscbisphosphate carboxylase (EC 4.1.1.39), ATP sulfurylase (EC 2.7.7.4) and adenosine 5′-phosphosulfate sulfotransferase and the content in chlorophyll and protein was compared in leaves of cloned beech trees (Fagus sylvatica L.) during autumnal senescence. Leaves excised at the same time but containing different amounts of chlorophyll gave extracts with correspondingly varying amounts of ribulosebisphosphate carboxylase activity. Leaves which had almost completely lost this enzyme activity contained still appreciable ATP sulfurylase and adenosine 5′-phosphosulfate sulfotransferase activity and soluble protein. For all components determined, there was a period lasting until mid or end of October during which there was no or only a small decrease. They were then all lost rapidly from the leaves. The specific activity of ribulosebisphosphate carboxylase decreased during this phase of rapid loss, whereas it remained essentially constant for ATP sulfurylase and adenosine 5′-phosphosulfate sulfotransferase. During this period, the mean half life of ribulosebisphosphate carboxylase was shorter than the one of ATP sulfurylase and of adenosine 5′-phosphosulfate sulfotransferase. These experiments clearly show that ribulosebisphosphate carboxylase was preferentially lost from beech leaves during autumnal senescence as compared to ATP sulfurylase and adenosine 5′-phosphosulfate sulfotransferase

Regulatory Interactions Between Sulfate and Nitrate Assimilation

Sulfate and nitrate, which contain sulfur and nitrogen in their most highly oxidized form, are the dominant species available to many plants for covering their needs for these elements (Schiff 1983; Cram 1990; Oaks 1992). Assimilatory sulfate and nitrate reduction are therefore necessary for the synthesis of amino acids including sulfur containing amino acids like cysteine and methionine, in which both sulfur and nitrogen are present in reduced form. The dominant portion of the amino acids is used for protein synthesis. Therefore, the S/N ratio in plants is usually about 1/20 (Dijkshoorn & van Wijk 1967) reflecting the proportion of these elements in proteins. Only in species where sulfur is accumulated in the form of sulfate or of secondary plant products is the ratio significantly higher (Cram 1990; Ernst 1990). Plants appear to possess mechanisms to coordinate assimilatory sulfate and nitrate reduction so that the appropriate proportions of both sulfur containing and other amino acids are available for protein synthesis. This review focuses on these reciprocal regulatory mechanisms at the level of assimilation, hut the regulation of the uptake of NO3- and SO2 may be at least as important for coordinating both assimilatory pathways (Saccomani & Ferrari 1989; Cram 1990; Clarkson et al., this volume). Assimilatory nitrate (Solomonson & Barber 1990; Oaks 1992) and sulfate (Brunold 1990; Giovanelli 1990; Schmidt 1992) reduction have been reviewed very recently. Therefore, only aspects of both pathways are discussed here which form the basis for reviewing regulatory interactions between them

Localization of O-acetyl-L-serine sulfhydrylase in Spinacia oleracea L.

Roots and hypocotyls of 11 day-old spinach seedlings with fully developed cotyledons contained 30–35% of the total O-acetyl-L-serine sulfhydrylase (OASSase) extractable from the plants. After centrifugation of homogenates from roots on sucrose density gradients, OASSase activity was present in the fractions containing the proplastids. In leaf extract two forms of OASSase could be detected by polyacrylamide disc gel electrophoresis. The form with the lower electrophoretic mobility in 0.1 M Tris-glycine at pH 8.4 could be attributed to the chloroplasts. The chloroplast enzyme was less stable than the extrachloroplastic form if stored without dithioerythritol (DTE)

Effect of Cadmium and/or Removal of Kernels or Shoots on the Levels of Cysteine, y-Glutamyl-cysteine, Glutathione, and TCA-soluble Thiols in Maize Seedlings

Six day old maize seedlings (Zea mays L.) were exposed as intact plants (A), after the removal of kernels (B) or shoots (C) or after the removal of kernels and transfer into the dark (D) to 0 or 50 micromolar cadmium for 2 days. The roots were analyzed for fresh weight, total TCA-soluble thiols (including phytochelatins), glutathione, and its precursor compounds cysteine and gamma-glutamyl-cysteine. With all treatments, cadmium caused an increase in the contents of cysteine, gamma-glutamyl-cysteine and total TCA-soluble thiols and a decrease in glutathione content. Our data indicate that the roots are at least in part autonomous to provide the thiols required for phytochelatin synthesis