SUMMARYWhen spruce {Picea abies L., Karst.) branches were exposed to 5-2-1 8-7 nl NO., T' the flux to the shoots increased linearly with increasing NO^ concentrations. At NO^ concentrations below 2-6 nl T' uptake of NO, by the shoots was not observed. The measured flux of NO2 to the shoots was found to be lower than the NO2 flux predicted from the shoot conductance to diffusion of H2O. These results are consistent with the existence of internal resistances for NO2 influx, e.g. production and emission of NO, by the leaves. However, emission of NOj was not observed. When the NOj flux to the shoots was plotted versus transpiration rate, a linear increase was found with an y-axis intercept. The intercept may be interpreted as the NOj flux to the cuticle and the bark; its value increased with increasing atmospheric NOj concentrations.The flux of NO2 to the shoots showed diurnal variation with high levels in the light and low levels during darkness. NO, flux to the branches was dependent on light intensity. This dependency can largely be explained by light dependent changes in shoot conductance. Daytime light intensity determined also the night-time shoot conductance and, hence, the NOj flux to the branches during the night. The ratio of NO, flux to transpiration rate was higher in the dark than in the light. Whether this observation can be explained by a light dependency of internal resistances remains to be elucidated.The absorption of NO,, by the shoots enhanced the in vitro NR activity of the needles, while NiR and GS activities were not increased signiflcantly. One day after exposure to NO, concentrations of 60 nl 1 \ nitrate reductase (NR) activity was three times higher than that of untreated controls. However, after three days of NOj exposure the NR activity declined to the level of untreated controls. Apparently, the increased in vitro NR activity upon NO2 fumigation is a transient phenomenon in spruce needles. The regulatory events that may modulate NR activity of the needles, when exposed to atmospheric NO,^, are discussed.

SUMMARYThe dynamic chamber technique was applied to investigate NO., influx into Picea abies (L.) Karsten branches, and its effects on net photosynthesis and transpiration, as well as its dependency on irradiance, temperature and relative humidity. The study aimed to quantify effects of climate on atmospheric NO2 fluxes to spruce. Experiments were performed with 3-to 4-yr-old branches of 8-to 9-yr-oId potted trees under controlled environmental conditions. With ambient NO., concentrations increasing from 3*5 to 50 nl T^ a linear increase in the NO2 influx of up to c. 6-8 //mol m"^ s""^ was observed. From this increase a compensation point of 1-64 nl 1~NO.2 was calculated by linear regression analysis. In the range of the NO, concentrations studied, net photosynthesis of spruce was not affected. The responsiveness of the stomata to changes in irradiance and relative humidity was reduced at 45 nl 1"^ NO2 compared with 25 nl 1"^ NOg. With increasing irradiance up to 1000/imol m~" s^^ PAR, increasing NOj flux to spruce branches was observed, which was attributed to a light-dependent increase in stomatal aperture. Variation of the temperature between 14 and 35 °C did not affect the NOg fiux, in light or in darkness. Higher temperatures, up to 45 °C, resulted in an increase in NOg influx in the light; in darkness, changes in NO.^ flux were not observed under these conditions. An increase in relative humidity from 5 to 60 % in the light caused an increase in NOj influx, whereas in darkness NOg influx was not affected by changes in relative humidity. The increase in NOj flux in response to r.h. observed in the light could not be explained by changes in stomatal aperture. A solution of NO, in ultra-thin water films covering the needle surface might explain this phenomenon.

Heterotrophic nitrification by Alcaligenesfaecalis DSM 30030 was not restricted to media containing organic forms of nitrogen. In both peptone-meat extract and defined media with ammonium and citrate as the sole nitrogen and carbon sources, respectively, N02 , N03 , NO, and N20 were produced under aerobic growth conditions. Heterotrophic nitrification was not attributable to old or dying cell populations. Production of N02-, N03-, NO, and N20 was detectable shortly after cultures started growth and proceeded exponentially during the logarithmic growth phase. N02and N03production rates were higher for cultures inoculated in media with pH values below 7 than for those in media at alkaline pH. Neither assimilatory nor dissimilatory nitrate or nitrite reductase activities were detectable in aerobic cultures.

In heterotrophic tobacco cells (Nicotiana tabacum L. cv. Samsun) inhibition of sulfate transport by reduced glutathione (GSH) is a reversible process. When GSH was removed from the culture medium subsequent to a 10‐h treatment with 1 mM GSH, sulfate transport began to recover after a lag period of ca 4 h and reached the transport rates of controls without GSH within another 3–4 h. Recovery was prevented when inhibitors of protein synthesis, i.e. cycloheximide or puromycin, were added to the medium upon removal of GSH, even if low concentrations (cycloheximide 1 μM; puromycin 250 μM) were applied. At these low concentrations the rate of synthesis of sulfate transport entities was maintained at the rate of degradation in the absence of GSH. The post‐transcriptional polyadenylation inhibitor cordycepin and the transcription inhibitor α‐amanitin only slightly reduced recovery of sulfate transport from inhibition by GSH. Apparently, protein synthesis is required for this recovery, suggesting that inhibition of synthesis of sulfate carrier entities is the mechanism of action of GSH on sulfate transport in heterotrophic tobacco cells. An initial rate of net increase in sulfate transport during recovery from inhibition of GSH of 3.6±0.2 U h−1 was calculated [1 U=1 nmol sulfate (g DW)−1 min−1]. This rate of increase is small compared with the rate of decrease in sulfate transport at maximum inhibition by cycloheximide (110±3 U h−1). However, with increasing time of exposure without GSH, the net increase in sulfate transport was enhanced to a maximum rate of 96±3 U h−1, measured 5–7 h after GSH had been removed from the media. Apparently, the rate of synthesis of sulfate transport entities in heterotrophic tobacco cells is about twice its rate of degradation.

1989. Recovery of sulfate transport into heterotrophic tobacco cells from inhibition by reduced glutathione. -Physiol. Plant, In heterotrophic tobacco cells {Nicotiana tabacum L. cv. Samsun) inhibition of sulfate transport by reduced glutathione (GSH) is a reversible process. When GSH was removed from the culture medium subsequent to a 10-h treatment with 1 mM GSH, sulfate transport began to recover after a lag period of ca 4 h and reached the transport rates of controls without GSH within another 3-4 h. Recovery was prevented when inhibitors of protein synthesis, i,e, cycloheximide or puromycin, were added to the medium upon removal of GSH, even if low concentrations (cycloheximide 1 \xM\ puromycin 250 \iM) were applied. At these low concentrations the rate of synthesis of sulfate transport entities was maintained at the rate of degradation in the absence of GSH. The post-transcriptional polyadenylation inhibitor cordycepin and the transcription inhibitor a-amanitin only slightly reduced recovery of sulfate transport from inhibition by GSH. Apparently, protein synthesis is required for this recovery, suggesting that inhibition of synthesis of sulfate carrier entities is the mechanism of action of GSH on sulfate transport in heterotrophic tobacco cells. An initial rate of net increase in sulfate transport during recovery from inhibition of GSH of3.6±0,2Uh ' wascalculated[l U = 1 nmol sulfate (g DW)'min '], This rate of increase is small compared with the rate of decrease in sulfate transport at maximum inhibition by cycloheximide (110 ±3 U h"'). However, with increasing time of exposure without GSH, the net increase in sulfate transport was enhanced to a maximum rate of 96 ± 3 U h~', measured 5-7 h after GSH had been removed from the media. Apparently, the rate of synthesis of sulfate transport entities in heterotrophic tobacco cells is about twice its rate of degradation.