SULFUR

Disentangling the complexity and diversity of crosstalk between sulfur and other mineral nutrients in cultivated plants

A complete understanding of ionome homeostasis requires a thorough investigation of the dynamics of the nutrient networks in plants. This review focuses on the complexity of interactions occurring between S and other nutrients, and these are addressed at the level of the whole plant, the individual tissues, and the cellular compartments. With regards to macronutrients, S deficiency mainly acts by reducing plant growth, which in turn restricts the root uptake of, for example, N, K, and Mg. Conversely, deficiencies in N, K, or Mg reduce uptake of S. TOR (target of rapamycin) protein kinase, whose involvement in the co-regulation of C/N and S metabolism has recently been unravelled, provides a clue to understanding the links between S and plant growth. In legumes, the original crosstalk between N and S can be found at the level of nodules, which show high requirements for S, and hence specifically express a number of sulfate transporters. With regards to micronutrients, except for Fe, their uptake can be increased under S deficiency through various mechanisms. One of these results from the broad specificity of root sulfate transporters that are up-regulated during S deficiency, which can also take up some molybdate and selenate. A second mechanism is linked to the large accumulation of sulfate in the leaf vacuoles, with its reduced osmotic contribution under S deficiency being compensated for by an increase in Cl uptake and accumulation. A third group of broader mechanisms that can explain at least some of the interactions between S and micronutrients concerns metabolic networks where several nutrients are essential, such as the synthesis of the Mo co-factor needed by some essential enzymes, which requires S, Fe, Zn and Cu for its synthesis, and the synthesis and regulation of Fe-S clusters. Finally, we briefly review recent developments in the modelling of S responses in crops (allocation amongst plant parts and distribution of mineral versus organic forms) in order to provide perspectives on prediction-based approaches that take into account the interactions with other minerals such as N.

G. Courbet, K. Gallardo, G. Vigani, S. Brunel-Muguet, J. Trouverie, C. Salon, and A. Ourry,Disentangling the complexity and diversity of crosstalk between sulfur and other mineral nutrients in cultivated plants, Journal of experimental botany, 2019, 70, 4183-4196.

               

 

               

 

               

 

SULFUR

Homeostatic impact of sulfite and hydrogen sulfide on cysteine catabolism

Cysteine is one of the two key sulfur-containing amino acids with important functions in redox homeostasis, protein functionality and metabolism. Cysteine is taken up by mammals via their diet and can also be derived from methionine via the transsulfuration pathway. The cellular concentration of cysteine is kept within a narrow range by controlling its synthesis and degradation. There are two pathways for the catabolism of cysteine leading to sulfate, taurine and thiosulfate as terminal products. The oxidative pathway produces taurine and sulfate, while the H2S pathway involves different enzymatic reactions leading to the formation and clearance of H2S, an important signalling molecule in mammals, resulting in thiosulfate and sulfate. Sulfite is a common intermediate in both catabolic pathways. Sulfite is considered as cytotoxic and produces neurotoxic S-sulfonates. As a result, a deficiency in the terminal steps of cysteine or H2S catabolism leads to severe forms of encephalopathy with the accumulation of sulfite and H2S in the body. This review links the homeostatic regulation of both cysteine catabolic pathways to sulfite and H2S. Linked Articles This article is part of a themed section on Chemical Biology of Reactive Sulfur Species. To view the other articles in this section visit

J. B. Kohl, A. T. Mellis, and G. Schwarz,Homeostatic impact of sulfite and hydrogen sulfide on cysteine catabolism, British journal of pharmacology, 2019, 176, 554-570.

Effect of molybdenum on sulfur metabolism

Enzyme inhibition by molybdate

Both arsenate and sulfate reduction were inhibited by molybdate. Arsenate-reducing bacterium, strain OREX-4, grew on lactate, with either arsenate or sulfate serving as the electron acceptor.

Newman, D.K., Kennedy, E.K., Coates, J.D., Ahmann, D., Ellis, D.J., Lovley, D.R., Morel, F.M.M., Dissimilatory arsenate and sulfate reduction in Desulfotomaculum auripigmentum sp. nov. Archives Of Microbiology, 1997, 168, 380-388.

Reduction of dimethylsulfoxide was not inhibited by molybdate. In Desulfovibrio desulfuricans strain PA2805, DMSO reduction occurred simultaneously-with sulfate reduction and was not effectively inhibited by molybdate, a specific inhibitor of sulfate reduction.

Jonkers, H.M., Vandermaarel, M.J.E.C., Vangemerden, H., Hansen, T.A., Dimethylsulfoxide Reduction By Marine Sulfate-Reducing Bacteria, Fems Microbiology Letters, 1996, 136, 283-287.
Townsend G.T., Ramanand K., Suflita J.M., Reductive dehalogenation and mineralization of 3-chlorobenzoate in the presence of sulfate by microorganisms from a methanogenic aquifer, Applied And Environmental Microbiology, 1997, 63, 2785-2791.

Polycyclic aromatic hydrocarbons, naphthalene and phenanthrene, were oxidized to carbon dioxide under sulfate-reducing conditions. Hydrocarbon oxidation was sulfate dependent. Molybdate, a specific inhibitor of sulfate reduction, inhibited hexadecane oxidation.

Coates, J.D., Woodward, J., Allen, J., Philp, P., Lovley, D.R., Anaerobic degradation of polycyclic aromatic hydrocarbons and alkanes in petroleum-contaminated marine harbor sediments, Applied And Environmental Microbiology,1997, 63, 3589-3593.

In anaerobic treatment of wastewater molybdate inhibited both sulfidogenesis and benzoate degradation. Molybdate inhibition increased progressively with concentration. Biogranules lost 50% of their methanogenic activity when treating waste water containing 48 mg/l of molybdate. In continuous experiments the molybdate toxicity had a threshold level. Below 0.5-0.8 mM molybdate bacterial activities were unaffected. The molybdate toxicity was not permanent. Biogranules were able gradually to regain their bioactivities once molybdate was removed from the waste water.

Liu, Y., Fang, H.H.P., Effects of molybdate on sulfate reduction and benzoate degradation, Journal Of Environmental Engineering-Asce, 1997, 123, 949-953.
Liu, S.M., Kuo, C.L., Anaerobic biotransformation of pyridine in estuarine sediments. Chemosphere, 1997, 35, 2255-2268.

Molybdate through inhibition of sulfate-reducing bacteria inhibits mercury methylation. Group VI anions, MO42-, added to sediment slurries inhibited mercury methylation: tellurate (> 50 nM )> selenate ((> 270 nM )> molybdate (100 mu M)> tungstate (700 mu M). The inhibition of mercury methylation is due to the inhibition of sulfate-reducing bacteria, which are responsible for Hg methylation. In the concentration ranges encountered in most natural aquatic environments, the inhibition of MeHg production by Group VI anions is unlikely.

Barkay, T. 1995, Methylmercury Oxidative-Degradation Potentials In Contaminated And Pristine Sediments Of The Carson River, Nevada, Applied And Environmental Microbiology, 61, 2745-2753.
Chen Y., Bonzongo J.C.J., Lyons W.B., Miller G.C., Inhibition of mercury methylation in anoxic freshwater sediment by Group VI anions, Environmental Toxicology And Chemistry, 1997, 16, 1568-1574 0730-7268.
Oremland, R.S., Miller, L.G., Dowdle, P., Connell, T., Barkay, T. 1995, Methylmercury Oxidative-Degradation Potentials In Contaminated And Pristine Sediments Of The Carson River, Nevada, Applied And Environmental Microbiology, 61, 2745-2753.

The iron oxidising bacterium T. ferrooxidans AP19-3, representative of Mo sensitive strains, could not grow on a Fe2+-medium with 1.0 mM of sodium molybdate. Mo(V), formed by reduction of Mo(VI) by Fe(II), rather than Mo(VI), is the actual inhibitor for the iron oxidation enzyme system, especially for cytochrome c oxidase. Molybdenum(V) binds to the plasma membrane and inhibits iron oxidase; as a result, growth of the bacterium is stopped [Yong et al.,1997].

Yong N.K., Oshima M., Blake R.C., Sugio T., Isolation and some properties of an iron-oxidizing bacterium Thiobacillus ferrooxidans resistant to molybdenum ion, Bioscience Biotechnology And Biochemistry, 1997, 61, 1523-1526.

Molybdate inhibited biotransformation of pyridine in sediments from the Tsengwen River

Liu, S.M., Kuo, C.L. Anaerobic biotransformation of pyridine in estuarine sediments. Chemosphere, 1997, 35, 2255-2268.

Molybdenum enters bacteria by the active transport systems for phosphate and sulfate. Mo(V) binds erythrocytic membrane proteins (Lener and Bibr 1984)and is not mutagenic like Mo(VI). Molybdate causes irreversible cleavage of ATP to AMP by bakers yeast ATP-sulfurylase. Molybdate inhibits the activities of certain enzymes including alkaline phosphatase and NADP+ -2’ nucleotidase (Wetterhahn-Jennette 1981).

Lener, J., and Bibr, B., Effects of molybdenum on the organism, J. Hygene, Epidemiol., Microbiol., Immunol., 1984, 28, 409-19.
Wetterhahn-Jennette, K., The role of metals in carcinogenesis, Environ. Health Perspect.,1981, 40, 233-52.

Phosphatase inhibition by molybdate

Common bean (Phaseolus vulgaris) seedlings accumulate ureides derived from purines after germination. The first step in the conversion of purines to ureides is the removal of the 5'-phosphate group by a phosphatase that has not yes been established.

Two main phosphatase activities were detected in the embryonic axes of common bean using inosine monophosphate as substrate in an in-gel assay. Both activities differed in their sensitivity to the common phosphatase inhibitor molybdate, with the molybdate-resistant as the first enzyme induced after radicalprotrusion.

The molybdate-resistant phosphatase is the first enzyme which shows resistance to molybdate. 

Cabello-Diaz, J.M., Quiles, F.A., Lambert, R., Pineda, M., Piedras, P., Plant physiology and biochemistry, 2012, 53, 54-60. Identification of a novel phosphatase with high affinity for nucleotides monophosphate from common bean (Phaseolus vulgaris).

Molybdate inhibition of phosphatase
Characterization of an acid phosphatase responsible for hydrolysis of pyridoxal 5'-phosphate in tobacco plants

Pyridoxal 5'-phosphate (PLP), the active form of vitamin B(6), is an important cofactor for many enzymatic reactions. PLP is also a very reactive molecule, and the hydrolysis of PLP is crucial for controlling intracellular PLP concentrations. However, little is known about the enzymatic hydrolysis of PLP in plants. In this study, a novel acid phosphatase was purified from tobacco leaves and characterized by using PLP as a substrate. This phosphatase was purified 180-fold with a yield of 28% by ammonium sulfate precipitation and chromatography on DEAE-Sepharose FF, Sephadex G-100 and SP Sephadex C-25. Our data revealed that the purified enzyme was a dimer with a molecular mass of approximately 50kDa. The purified phosphatase had maximum catalytic activity at pH 5.5, and displayed optimal activity at 50°C. The enzyme required divalent metal ion for activity, and Mg(2+), among a few tested cations, was the most effective for catalysis under saturating substrate concentrations. The activity of the purified phosphatase was inhibited by molybdate, fluoride and EDTA, but was not inhibited by levamisole and tartrate. The phosphatase hydrolyzed a broad range of substrates at different rates, and the hydrolysis of PLP was competitively inhibited by ATP, pNPP, and by the reaction products, PL and inorganic phosphate. The phosphatase had a Km of 0.24mM and a Vmax of 2.76mumol/min/mg with PLP. When pyridoxamine 5'-phosphate or pyridoxine 5'-phosphate was tested as a substrate, the phosphatase activity was reduced by 50%. Our study suggests that the enzyme is a nonspecific acid phosphatase responsible for hydrolysis of all three phosphorylated B(6) vitamers in tobacco plants.

Huang, Shuohao, Zhang, Jianyun, Ma, Yaping, Wei, Shu, and Huang, Longquan, Characterization of an acid phosphatase responsible for hydrolysis of pyridoxal 5'-phosphate in tobacco plants, Plant physiology and biochemistry: PPB/Societe francaise de physiologie vegetale, 2012, 57, 114-119.

Enzyme inhibition by molybdate

Fraqueza, G., Carvalho, L., Marques, P., Ohlin, C., Casey, W., and Aureliano, M., Functional and structural interactions of Nb, V, Mo and W oxometalates with the sarcoplasmic reticulum Ca2+ -ATPase reveal new insights into inhibition processes: a combination of NMR, Raman, AA and EPR spectroscopie with kinetic studies, Febs Journal, 2012, 279, 439.