PubMed Health⌕ Search

Biomedical subjects

C Brunold

Publications and source records attributed to C Brunold.

29 records · Page 2Linked to original sources
PubMed1990

Regulation of Assimilatory Sulfate Reduction by Herbicide Safeners in Zea mays L.

Effects of the herbicide safeners N,N-diallyl-2,2-dichloroacetamide and 4-dichloroacetyl-3,4-dihydro-3-methyl-2H-1,4-benzooxazin (CGA 154281) on the contents in cysteine and glutathione, on the assimilation of (35)SO(4) (2-), and on the enzymes of assimilatory sulfate reduction were analyzed in roots and primary leaves of maize (Zea mays) seedlings. Both safeners induced an increase in cysteine and glutathione. In labeling experiments using (35)SO(4) (2-), roots of plants cultivated in the presence of safeners contained an increased level of radioactivity in glutathione and cysteine as compared with controls. A significant increase in uptake of sulfate was only detected in the presence of CGA 154281. One millimolar N,N-diallyl-2,2-dichloroacetamide applied to the roots for 6 days increased the activity of adenosine 5'-phosphosulfate sulfotransferase about 20- and threefold in the roots and leaves, respectively, compared with controls. CGA 154281 at 10 micromolar caused a sevenfold increase of this enzyme activity in the roots, but did not affect it significantly in the leaves. A significant increase in ATP-sulfurylase (EC 2.7.7.4) activity was only detected in the roots cultivated in the presence of 10 micromolar CGA 154281. Both safeners had no effect on the activity of sulfite reductase (EC 1.8.7.1) and O-acetyl-l-serine sulfhydrylase (EC 4.2.99.8). The herbicide metolachlor alone or combined with the safeners induced levels of adenosine 5'-phosphosulfate sulfotransferase, which were higher than those of the appropriate controls. Taken together these results show that the herbicide safeners increased both the level of adenosine 5'-phosphosulfate sulfotransferase activity and of the thiols cysteine and glutathione. This indicates that these safeners may be involved in eliminating the previously proposed regulatory mechanism, in which increased concentrations of thiols regulate assimilatory sulfate reduction by decreasing the activities of the enzymes involved.

Journal Article↗
PubMed1988

Regulation of Assimilatory Sulfate Reduction by Cadmium in Zea mays L.

Plants cultivated with Cd can produce large amounts of phytochelatins. Since these compounds contain much cysteine, these plants should have an increased rate of assimilatory sulfate reduction, the biosynthetic pathway leading to cysteine. To test this prediction, the effect of Cd on growth, sulfate assimilation in vivo and extractable activity of two enzymes of sulfate reduction, ATP-sulfurylase (EC 2.7.7.4) and adenosine 5'-phosphosulfate sulfotransferase were measured in maize (Zea mays L.) seedlings. For comparison, nitrate reductase activity was determined. In 9-day-old cultures, the increase in fresh and dry weight was significantly inhibited by 50 micromolar and more Cd in the roots and by 100 and 200 micromolar in the shoots. Seedlings cultivated with 50 micromolar Cd for 5 days incorporated more label from (35)SO(4) (2-) into higher molecular weight compounds than did controls, indicating that the predicted increase in the rate of assimilatory sulfate reduction took place. Consistent with this finding, an increased level of the extractable activity of both ATP-sulfurylase and adenosine 5'-phosphosulfate sulfotransferase was measured in the roots of these plants at 50 micromolar Cd and at higher concentrations. This effect was reversible after removal of Cd from the nutrient solution. In the leaves, a significant positive effect of Cd was detected at 5 micromolar for ATP-sulfurylase and at 5 and 20 micromolar for adenosine 5'-phosphosulfate sulfotransferase. At higher Cd concentrations, both enzyme activities were at levels below the control. Nitrate reductase (EC 1.6.6.1) activity decreased at 50 micromolar or more Cd in the roots and was similarly affected as ATP-sulfurylase activity in the primary leaves.

Journal Article↗
PubMed1984

Intercellular Localization of Assimilatory Sulfate Reduction in Leaves of Zea mays and Triticum aestivum.

The intercellular distribution of assimilatory sulfate reduction enzymes between mesophyll and bundle sheath cells was analyzed in maize (Zea mays L.) and wheat (Triticum aestivum L.) leaves. In maize, a C(4) plant, 96 to 100% of adenosine 5'-phosphosulfate sulfotransferase and 92 to 100% of ATP sulfurylase activity (EC 2.7.7.4) was detected in the bundle sheath cells. Sulfite reductase (EC 1.8.7.1) and O-acetyl-l-serine sulfhydrylase (EC 4.2.99.8) were found in both bundle sheath and mesophyll cell types. In wheat, a C(3) species, ATP sulfurylase and adenosine 5'-phosphosulfate sulfotransferase were found at equivalent activities in both mesophyll and bundle sheath cells. Leaves of etiolated maize plants contained appreciable ATP sulfurylase activity but only trace adenosine 5'-phosphosulfate sulfotransferase activity. Both enzyme activities increased in the bundle sheath cells during greening but remained at negligible levels in mesophyll cells. In leaves of maize grown without addition of a sulfur source for 12 d, the specific activity of adenosine 5'-phosphosulfate sulfotransferase and ATP sulfurylase in the bundle sheath cells was higher than in the controls. In the mesophyll cells, however, both enzyme activities remained undetectable. The intercellular distribution of enzymes would indicate that the first two steps of sulfur assimilation are restricted to the bundle sheath cells of C(4) plants, and this restriction is independent of ontogeny and the sulfur nutritional status of the plants.

Journal Article↗
PubMed1984

Regulation of Sulfate Assimilation by Nitrogen Nutrition in the Duckweed Lemna minor L.

The effect of nitrate and ammonium on the extractable activity of two enzymes of assimilatory sulfate reduction, ATP sulfurylase (EC 2.7.7.4) and adenosine 5'-phosphosulfate sulfotransferase (APSSTase), was examined in Lemna minor L. cultivated under steady state conditions. Nitrate reductase (EC 1.6.6.1) was measured for comparison. Low nitrate concentrations (0.2 and 0.04 millimolar) caused a decrease in the specific activity of all three enzymes measured. Twenty-four hours after transfer to medium without a nitrogen source, the specific activity of APSSTase and nitrate reductase was at less than 30% of the original level, whereas ATP sulfurylase was still at about 80%. NH(4) (+) added to the nutrient solution caused a 50 to 100% increase in the specific activity of APSSTase within 24 hours, followed by a slow decrease. After 72 hours with NH(4) (+), the specific activity was still 25% higher than originally. During the same period, the extractable protein increased by 30% on a fresh weight basis, and total protein by 55 to 60%. Nitrate reductase activity decreased to less than 5%. After omission of NH(4) (+) from the nutrient solution extractable APSSTase activity rapidly decreased to the level of cultures with NO(3) (-) as a nitrogen source. Using [(35)S]SO(4) (2-) as a sulfur source, an increased incorporation of label into the protein fraction could be detected when NH(4) (+) was added to the nutrient solution. This indicated that more sulfate was assimilated and used for protein synthesis. The higher extractable activity of APSSTase with NH(4) (+) may be a regulatory mechanism involved in the formation of sufficient sulfur amino acids during a period of increased protein synthesis.

Journal Article↗
PubMed1983

Measurement of ferredoxin-dependent sulfite reductase activity in crude extracts from leaves using O-acetyl-L-serine sulfhydrylase in a coupled assay system to measure the sulfide formed.

Ferredoxin-dependent sulfite reductase (EC 1.8.7.1) catalyses the reduction of sulfite to sulfide, using reduced ferredoxin as an electron donor. An assay system was developed for measuring this enzyme activity in crude extracts and broken chloroplast preparations from leaves. The assay consists of a coupled system in which the sulfide formed is used for cysteine synthesis by added O-acetyl-L-serine sulfhydrylase (EC 4.2.99.8). Cysteine thus formed is determined with ninhydrin under conditions where O-acetylserine does not react and serves as a measure for ferredoxin-dependent sulfite reductase activity. Cysteine synthesized in the assay can be determined from 10 to 200 nmol. One assay per minute can be performed.

Cysteine↗
PubMed1982

Regulation of Sulfate Assimilation in Plants : XIII. Assimilatory Sulfate Reduction during Ontogenesis of Primary Leaves of Phaseolus vulgaris L.

The correlation between the extractable activities of three key enzymes of assimilatory sulfate reduction and the in vivo incorporation of (35)SO(4) (2-) into amino acids, proteins, and sulfolipids was investigated from greening to senescence in primary leaves of beans (Phaseolus vulgaris L.). The total extractable activity of ATP sulfurylase (EC 2.7.7.4) and of adenosine 5'-phosphosulfate sulfotransferase reached a maximum in the leaves of approximately 7- and 11-day-old seedlings, respectively. During senescence, there was a decrease in both enzyme activities. After approximately 17 days, no appreciable activities remained. In contrast, total O-acetyl-l-serine sulfhydrylase (EC 4.3.99.8) activity decreased to only approximately 50% of the maximal value during the same period. The in vivo incorporation of (35)SO(4) (2-) into amino acid and protein fractions showed a time-course similar to that of the total extractable adenosine 5'-phosphosulfate sulfotransferase activity. Both cysteine and sulfate markedly decreased during senescence. The total extractable activity of ribulosebisphosphate carboxylase (EC 4.1.1.39) was maximal in the primary leaves of 13-day-old seedlings, and approximately 40% of this value was still detectable after 17 days. Taken together with results from the literature, these results show that assimilatory sulfate reduction in primary leaves of P. vulgaris L. stops before CO(2) and nitrate assimilation.

Journal Article↗
PubMed1978

Regulation of Sulfate Assimilation in Plants: 7. Cysteine Inactivation of Adenosine 5'-Phosphosulfate Sulfotransferase in Lemna minor L.

When 0.5 mm cysteine is added to cultures of Lemna minor L. growing with sulfate as the sole sulfur source, there is a rapid 80% loss of extractable adenosine 5'-phosphosulfate sulfotransferase. This loss is accompanied by an inhibition of sulfate uptake; however, lack of sulfate is not responsible for the decreasing adenosine 5'-phosphosulfate sulfotransferase activity.Cultivation with cysteine causes an increase in the cyst(e)ine pool of L. minor. This fact taken together with the observed inactivation of adenosine 5'-phosphosulfate sulfotransferase in crude extracts by cysteine suggests that the cysteine pool is involved in the in vivo regulation of the enzyme.The activity of adenosine 5'-phosphosulfate sulfotransferase is restored within 24 hours after transfer to a culture medium without cysteine. This restoration is partially blocked by 6-methyl purine and actinomycin D and completely by cycloheximide.Cycloheximide added to cultures of L. minor L. causes a loss of extractable APSTase comparable to the one obtained with cysteine. This loss may be in part due to cysteine, since cycloheximide causes a pronounced increase in the cysteine pool of L. minor.

Journal Article↗
PubMed1976

Subcellular localization of O-acetylserine sulfhydrylase in spinach leaves.

A combination of differential centrifugation and isopycnic sucrose density gradient centrifugation of extracts from spinach leaves (Spinacia oleracea L.) shows that about 20% of the O-Acetylserine sulfhydrylase are associated with chloroplasts. No appreciable amounts of O-Acetylserine sulfhydrylase band with mitochondrial and peroxisomal marker enzymes.

Chlorophyll↗
PubMed1976

Studies of sulfate utilization of algae: 15. Enzymes of assimilatory sulfate reduction in euglena and their cellular localization.

Crude extracts of wild-type Euglena grown in the light (WTL) or in the dark (WTD) and a mutant lacking detectable plastid DNA (W(3)BUL) contain adenosine 5'-phosphosulfate (APS) sulfotransferase. Isotope dilution experiments indicate that adenosine 3'-phosphate 5'-phosphosulfate (PAPS) sulfotransferase is absent.Thiosulfonate reductase, requiring addition of NADH or NADPH but not ferredoxin, and O-acetyl-l-serine sulfhydrylase, the two other enzymes of the bound intermediate pathway of assimilatory sulfate reduction, are also present. Increasing levels of all three enzymes were found in WTL, WTD, and W(3)BUL during logarithmic growth but the various activities were similar at comparable stages of growth in all three types of cell.These results show that the three enzymes are not coded in the chloroplast DNA and are not restricted to Euglena cells having fully developed chloroplasts. Consistent with this, they do not increase during light-induced chloroplast development in resting cells and are found to be enriched in the mitochondrial fraction. Further resolution of this fraction on sucrose gradients shows that the APS sulfotransferase is associated with both the microbody (glyoxysomal) and mitochondrial fractions while the thiosulfonate reductase and O-acetyl-l-serine sulfhydrylase are associated only with the mitochondria. Thus the three known enzymes of the bound pathway of assimilatory sulfate reduction are present in Euglena mitochondria.Although the activity of the entire bound pathway (APS to cysteine) is low in extracts, addition of dithiothreitol which releases free sulfite from the product of the APS sulfotransferase reaction, causes an increase in reduction activity indicating that a sulfite reductase is also present. It remains to be shown which reducing system is the significant one in vivo in Euglena.

Journal Article↗