1,721,073 research outputs found
Regulatory Interactions Between Sulfate and Nitrate Assimilation
No full textSulfate 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
Effects of Heavy Metals on Assimilatory Sulfate Reduction in Pea Roots
No full textThe high content of cysteine in the heavy metal sequestring phytochelatins (ɣ-Glu-Cys)n Gly (n =2-11) led to the prediction that plants cultivated with heavy metals should contain increased levels of the enzymes involved in cysteine formation. Indeed, root sections of pea seedlings grown with Cd2+ contained adenosine 5'-phosphosulfate sulfotransferase activity that was up to almost 20 fold higher than in controls. There was a parallel increase in glutathione synthetase, indicating that glutathione (ɣ-Glu-Cys-Gly) is involved in phytochelatin synthesis
Buthionine Sulfoximine (BSO) Reduces Chilling Tolerance of a Chilling Tolerant Maize Genotype
No full textA new approach was applied to find evidence for the hypothesis that glutathione (GSH) protects plants against low temperature damage. In this approach the GSH content was decreased and cold tolerance of plants was determined. Buthionine sulfoximine (BSO), a substance which selectively inhibits GSH synthesis, was used to decrease GSH. It was found, that GSH and gamma-glutamylcysteine were decreased by BSO exposure, that cold injury correlated to the concentration of BSO and that injury was visible only after recovery and not after chilling
Effect of Hydrogen Peroxide Induced Oxidative Stress in Maize Roots
No full textHydrogen peroxide could be involved in many processes in plants: like cold or light induced oxidative stress, cell wall formation, pathogen attack and programmed cell death. Nothing is known about the sulfur assimilation and thiol content in plant roots with increased hydrogen peroxide levels. Therefore we induced oxidative stress in our model system by treatment of roots of hydroponically grown maize plants with hydrogen peroxide
Serine acetyltransferase: A bottleneck for cysteine and glutathione syntheses?
No full textThe cysE gene encoding serine acetyltransferase from Escherichia coli, has been introduced into the genome of potato plants to investigate the role of SAT activity in plastids towards
cysteine synthesis. Transgenic lines with up to 20-fold higher SAT activity exhibited significantly higher levels of cysteine and glutathione. Expression of cysteine synthase
isoforms was unchanged while a marginal effect on activity has been observed. Physiological relevance for cysteine formation is discussed
Localization of adenosine 5′-phosphosulfate sulfotransferase in spinach leaves
Full text linkRoots of spinach (Spinacia oleracea L.) seedlings contained only a very low activity of adenosine 5′-phosphosulfate sulfotransferase compared to the cotyledons. Adenosine 5′-phosphosulfate sulfotransferase activity increased about tenfold in cotyledons during greening. Preparation of organelle fractions from spinach leaves by a combination of differential and isopycnic density gradient centrifugation showed that adenosine 5′-phosphosulfate sulfotransferase banded with NADP-glyceraldehyde-3-phosphate dehydrogenase, a marker enzyme for intact chloroplasts. In the fractions of peroxisomes, mitochondria and broken chloroplasts virtually no adenosine 5′-phosphosulfate sulfotransferase activity was measured. Comparison with the chloroplast enzyme NADP-glyceraldehyde-3-phosphate dehydrogenase indicates that in spinach, adenosine 5′-phosphosulfate sulfotransferase is localized almost exclusively in the chloroplasts
Intracellular localization of serine acetyltransferase in spinach leaves
Full text linkIntact chloroplasts isolated from spinach leaves by a combination of differential and Percoll density gradient centrifugation and free of mitochondrial and peroxisomal contamination contained about 35% of the total leaf serine acetyltransferase (EC 2.3.1.30) activity. No appreciable activity of the enzyme could be detected in the gradient fractions containing broken chloroplasts, mitochondria, and peroxisomes. L-cysteine added to the incubation mixture at 1 mM almost completely inhibited serine acetyltransferase activity, both of leaf and chloroplast extracts. D-cysteine was much less inhibitory. L-cystine up to 5 mM and O-acetyl-L-serine up to 10 mM had no effect on the enzyme activity. When measured at pH 8.4, the enzyme extracted from the leaves had a K m for L-serine of 2.4, the enzyme from the chloroplasts a K m of 2.8 mM
Localization of enzymes of assimilatory sulfate reduction in pea roots
Full text linkThe localization of enzymes of assimilatory sulfate reduction was examined in roots of 5-d-old pea (Pisum sativum L.) seedlings. During an 8-h period, roots of intact plants incorporated more label from 35SO 4 2- in the nutrient solution into the amino-acid and protein fractions than shoots. Excised roots and roots of intact plants assimilated comparable amounts of radioactivity from 35SO 4 2- into the amino-acid and protein fractions during a 1-h period, demonstrating that roots of pea seedlings at this stage of development were not completely dependent on the shoots for reduced sulfur compounds. Indeed, these roots contained activities of ATP-sulfurylase (EC 2.7.7.4), adenosine 5′-phosphosulfate sulfotransferase, sulfite reductase (EC 1.8.7.1) and O-acetyl-l-serine sulfhydrylase (EC 4.2.99.8) at levels of 50, 30, 120 and 100%, respectively, of that in shoots. Most of the extractable activity of adenosine 5′-phosphosulfate sulfotransferase was detected in the first centimeter of the root tip. Using sucrose density gradients for organelle separation from this part of the root showed that almost 40% of the activity of ATP-sulfurylase, adenosine 5′-phosphosulfate sulfotransferase and sulfite reductase banded with the marker enzyme for proplastids, whereas only approximately 7% of O-acetyl-l-serine sulfhydrylase activity was detected in these fractions. Because their distributions on the gradients were very similar to that of nitrite reductase, a proplastid enzyme, it is concluded that ATP-sulfurylase, adenosine 5′-phosphosulfate sulfotransferase and sulfite reductase are also exclusively or almost exclusively localized in the proplastids of pea roots. O-Acetyl-l-serine sulfhydrylase is predominantly present in the cytoplasm
- …
