Interaction of Sulfate Assimilation with Carbon and Nitrogen Metabolism in Lemna minor  

Abstract

Cysteine synthesis from sulfide and O-acetyl-l-serine (OAS) is a reaction interconnecting sulfate, nitrogen, and carbon assimilation. Using Lemna minor, we analyzed the effects of omission of CO 2 from the atmosphere and simultaneous application of alternative carbon sources on adenosine 5Ј-phosphosulfate reductase (APR) and nitrate reductase (NR), the key enzymes of sulfate and nitrate assimilation, respectively. Incubation in air without CO 2 led to severe decrease in APR and NR activities and mRNA levels, but ribulose-1,5-bisphosphate carboxylase/oxygenase was not considerably affected. Simultaneous addition of sucrose (Suc) prevented the reduction in enzyme activities, but not in mRNA levels. OAS, a known regulator of sulfate assimilation, could also attenuate the effect of missing CO 2 on APR, but did not affect NR. When the plants were subjected to normal air after a 24-h pretreatment in air without CO 2 , APR and NR activities and mRNA levels recovered within the next 24 h. The addition of Suc and glucose in air without CO 2 also recovered both enzyme activities, with OAS again influenced only APR. 35 SO 4 2Ϫ feeding showed that treatment in air without CO 2 severely inhibited sulfate uptake and the flux through sulfate assimilation. After a resupply of normal air or the addition of Suc, incorporation of 35 S into proteins and glutathione greatly increased. OAS treatment resulted in high labeling of cysteine; the incorporation of 35 S in proteins and glutathione was much less increased compared with treatment with normal air or Suc. These results corroborate the tight interconnection of sulfate, nitrate, and carbon assimilation.Plants, yeast, and most prokaryotes cover their demand for reduced sulfur, which is essential for function of proteins, oligopeptides, and many coenzymes, by reduction of inorganic sulfate. In the pathway of sulfate assimilation of plants, sulfate is first activated by ATP sulfurylase to adenosine 5Ј-phosphosulfate, which is reduced to sulfite by adenosine 5Ј-phosphosulfate reductase (APR) in a glutathionedependent reaction. Sulfite is further reduced to sulfide by a ferredoxin-dependent sulfite reductase and sulfide incorporated into the amino acid skeleton of O-acetyl-l-Ser (OAS) by OAS (thiol) lyase, forming Cys (Brunold, 1990;Leustek et al., 2000). Cys can further be metabolized to Met or directly incorporated into proteins or glutathione, a tripeptide with important functions as storage and transport form of reduced sulfur, in oxidative stress defense, regulation of sulfur assimilation, etc. (Noctor et al., 1998). Thus, Cys synthesis from OAS and sulfide is a central point of cellular metabolism as this reaction interconnects sulfate, nitrate, and carbon assimilation.Several studies have established regulatory interactions between sulfate and nitrate assimilation in plants (Brunold, 1993;Takahashi and Saito, 1996;Kim et al., 1999;Koprivova et al., 2000). The two assimilatory pathways are well coordinated so that deficiency for one element represses the other pathway. The act...

Effect of nitrogen and sulphur nutrition on yield parameters and protein composition in soybean [Glycine max (L.) Merrill].

“…Soybean plants grown under varying levels of sodium and potassium salts influenced seed storage protein subunit composition (Kaviani et al, 2011). Sulphur as well as N are important nutrients required by crops for protein structure, vitamins and other structural components and also improve plant growth and yield (Marshner, 2005;Kopriva et al, 2002). Nitrogen and S assimilation is well coordinated and deficiencies of one of the nutrient reduce the assimilation of other nutrient (Kopriva and Rennenberg, 2004;Siddiqui et al, 2008).…”

A Two-step Process Controls the Formation of the Bienzyme Cysteine Synthase Complex

“…One example is represented by the transient formation of the cysteine synthase complex (CS) 3 (Scheme 1), involving the specific interaction between the enzymes catalyzing cysteine biosynthesis (Scheme 1), serine acetyltransferase (SAT), the product of cysE, and the pyridoxal 5Ј-phosphate (PLP)-dependent enzyme, O-acetylserine sulfhydrylase-A (OASS-A), the product of cysK. These reactions are at the branch point of the sulfur, carbon, and nitrogen assimilation pathways (Scheme 1) (18) and therefore need to be strictly regulated. In Escherichia coli OASS-A also interacts with ATP sulfurylase (19) and in Bacillus subtilis with the repressor CymR (14).…”

Interaction of sulfate assimilation with nitrate assimilation as a function of nutrient status and enzymatic co-regulation inbrassica juncea roots

“…Furthermore, in Paul's Scarlet Rose cell cultures, AR activity is enhanced by NH4 § and diminished by Cys-feeding, although that cysteine-induced decrease is less pronounced in the presence of NH4 § (Hailer et al, 1986). Even though all of the above results support this regulatory hypothesis, it has not been well studied how assimilatory sulfate and nitrate reduction are coordinated at the molecular level (Brunold and Rennenberg, 1997;Koprivia et al, 2002). In addition, it has been suggested that SiR and NiR may be the coordinating enzymes between sulfate and nitrate assimilation because each contains siroheme as a cofactor (Sakakibara et al, 1996;Hell, 1997).…”