Ozone effects on nitrogen incorporation and superoxide dismutase activity in spruce seedlings (Picea abies L.).

The influence of low concentrations of ozone (100 ppb) on nitrogen incorporation and the specific activity of superoxide dismutase (SOD) in 3-yr-old cloned spruce seedlings was studied under controlled conditions (potted plants in fumigation chambers). For the determination of nitrogen uptake, 15 N tracer experiments were performed using emission spectrometric isotope analysis. Superoxide dismutase (SOD) activity was determined by inhibition of formazan formation. Low doses of ozone led to a significant increase in both NO3 -N uptake from the soil and in specific SOD activity. The results show that stable isotope 15 N tracer technique analysis is a suitable tool for the investigation of potential impacts of air pollutants on the nitrogen metabolism of plants.

Sulphite-induced changes of sulphur metabolism in the lichen alga Trebouxia sp.

Solutions of sodium sulphite have been used to simulate the effect of gaseous sulphur dioxide on the lichen alga Trebouxia sp. The uptake and the metabolism of inorganic and organic [35 S]compounds such as sulphate, sulphite, and cysteine were investigated in cells of Trebouxia under conditions of sulphite preincubation (sulphite-stressed cells: 3 d pretreatment with 50 mmol m-3 and 5 mol m-3 solutions of sodium sulphite). Metabolism was similar, regardless of whether the Trebouxia was provided with [35 S]sulphate or -sulphite. In sulphite-stressed cells, uptake and incorporation into ethanol-soluble compounds, especially cysteine and methionine, was significantly decreased. In Trebouxia exogenous [35 S]cysteine is metabolized only at a very low rate.

[Differences in proline metabolism of a peptide alkaloid producing and a nonproducing strain of Claviceps purpurea]. / Unterschiede im Prolinstoffwechsel eines Peptidalkaloide-produzierenden und eines nichtproduzierenden Stammes von Claviceps purpurea.

Two strains (pepty 695 and pur 221) of Claviceps purpurea have been used to study the dependence of proline turnover on incubation time (1, 3, 6, and 12 hours) under different culture conditions (synthetic saccharose-citrate medium NL 720 and complex wort medium M 107) by means of tracer technique. In the saprophytically ergotoxine producing strain pepty 695 the proline is utilized in the protein and alkaloid biosyntheses. On the other hand, under non-producing conditions (M 10) the radioactivity of proline-14C is incorporated into many fractions and finally into CO2. In submerged culture (NL 720) the Claviceps strain pur 221 which does not produce ergolines uses proline only to a small extent in the protein biosynthesis, while most of this amino acid is not metabolized. The extent of uptake of proline is not correlated with the alkaloid synthesis. For comparison the turnover of L-glutamate-14C and D,L-ornithine-1-14C by strain pepty 695 cultivated in the NL 720 medium has been studied.

Regulation of 6-hydroxy-2,4,5-triaminopyrimidine synthesis by riboflavin and iron in riboflavin-deficient mutants of Pichia guilliermondii yeast.

The effect of riboflavin and iron on 6-hydroxy-2,4,5-triaminopyrimidine synthesis rate was investigated in the cultures of the yeast Pichia guilliermondii (rib2 mutants) with the blocked second reaction to flavinogenesis. It was shown that riboflavin inhibited the 6-hydroxy-2,4,5-triaminopyrimidine synthesis rate in iron-rich and iron-deficient cells of mutants with low riboflavin requirements. Cycloheximide did not prevent the stimulation of 6-hydroxy-2,4,5-triaminopyrimidine synthesis caused by riboflavin starvation. 7-methyl-8-trifluoromethyl-10-(1'-D-ribityl)isoalloxazine strongly inhibited the 6-hydroxy-2,4,5-triaminopyrimidine synthesis, while 7-methyl-8-trifluoro-methyl-10-(beta-hydroxyethyl)izoalloxazine and galactoflavin exerted only a slight effect on this process. The 6-hydroxy-2,4,5-triaminopyrimidine synthesis rate in iron-deficient cells was significantly higher than in iron-rich cells. The 2,2'-dipyridyl treatment of iron-rich cells caused the stimulation of 6-hydroxy-2,4,5-triaminopyrimidine synthesis and cycloheximide abolished this effect. The results suggest that the activity of the first enzyme of flavinogenesis (guanylic cyclohydrolase) is under the control of feedback inhibition by flavins and the biosynthesis of this enzyme is regulated by iron.