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Biosynthesis of Sulfur-Containing Small Biomolecules in Plants

Sulfur is an essential element required for plant growth. It can be found as a thiol group of proteins or non-protein molecules, and as various sulfur-containing small biomolecules, including iron-sulfur (Fe/S) clusters, molybdenum cofactor (Moco), and sulfur-modified nucleotides. Thiol-mediated redox regulation has been well investigated, whereas biosynthesis pathways of the sulfur-containing small biomolecules have not yet been clearly described. In order to understand overall sulfur transfer processes in plant cells, it is important to elucidate the relationships among various sulfur delivery pathways as well as to investigate their interactions. In this review, we summarize the information from recent studies on the biosynthesis pathways of several sulfur-containing small biomolecules and the proteins participating in these processes. In addition, we show characteristic features of gene expression in Arabidopsis at the early stage of sulfate depletion from the medium, and we provide insights into sulfur transfer processes in plant cells.

Y. Nakai, and A. Maruyama-Nakashita,Biosynthesis of Sulfur-Containing Small Biomolecules in Plants, International journal of molecular sciences, 2020, 21. 3470.

The influence of MoO3-NPs on agro-morphological criteria, genomic stability of DNA, biochemical assay, and production of common dry bean (Phaseolus vulgaris L.)

Molybdenum is considered one of the most important micronutrients applied as a foliar fertilizer for common dry bean. In this study, molybdenum oxide nanoparticles (MoO3-NPs) were applied in different concentrations (0, 10, 20, 30 and 40 ppm) over two sequent seasons, 2018 and 2019, to investigate their effect on the plant morphological criteria, yield, and the genomic stability of DNA. The results showed that the application of 40 ppm MoO3-NPs as a foliar fertilizer showed preferable values of plant morphological criteria, such as the number of leaves and branches per plant, as well as the fresh and dry weight with regard to the common bean plant. In addition, the seed yield increased by 82.4% and 84.1% with 40 ppm, while the shoot residue increased by 32.2% and 32.1% with 20 ppm of MoO3-NPs during two seasons, 2018 and 2019, respectively. Furthermore, the common bean treated with 20 and 40 ppm MoO3-NPs had positive unique bands with ISSR primer 848 at 1400 bp (Rf 0.519) and with primer ISSR2M at 200 bp (Rf 0.729), respectively. In addition, SDS-PAGE reveald some proteins in seedlings which were absent in the flowering stage at 154, 102, 64, 37 and 34 KDa, which may be due to differences in plant proteins required for metabolic processes in each stage. In conclusion, the application of 40 ppm MoO3-NPs was more effective on the productivity of the common bean plants.

S. A. Osman, D. M. Salama, M. E. Abd El-Aziz, E. A. Shaaban, and M. S. Abd Elwahed,The influence of MoO3-NPs on agro-morphological criteria, genomic stability of DNA, biochemical assay, and production of common dry bean (Phaseolus vulgaris L.), Plant Physiology and Biochemistry, 2020, 151, 77-87.

Molybdenum in plants and soils

Molybdenum is essential to plant growth as a component of the enzymes nitrate reductase and nitrogenase. Legumes need more molybdenum than other crops, such as grass or corn, because the symbiotic bacteria living in the root nodules of legumes require molybdenum for the fixation of atmospheric nitrogen. If insufficient molybdenum is available nodulation will be retarded and the amount of nitrogen fixed by the plant will be limited. If other factors are not limiting the amount of molybdenum will determine the amount of nitrogen fixed by the plant. Increasingly vigorous plant growth, higher protein contents and greater buildup of nitrogen in the plant and soil accompany nodulation and symbiotic microbial activity.

Albrigo, L. G., Szafranck, R. C.and Childers, N. F., The Role of Molybdenum in Plants and Soils, Climax Molybdenum Co., Supplemental volume, 1966.
Childers, N. F. and Borys, M. W., The Role of Molybdenum in Plants and Soils, Climax Molybdenum Co., 1962.
Ivanova, N. N., Agrochimica, 1972 (Publ. 1973), 17, 96.
Sequi, P., Agrochimica , 1972 (Publ. 1973), 17 , 119.

Response of chickpea (cicer arietinum) to molybdenum in moderately-alkaline soil

A pot experiment was conducted at ICAR-Indian Institute of Pulses Research, Kanpur during 2010-12 to assess the response of chickpea crop to molybdenum (Mo) in moderately-alkaline Inceptisol (pH 8.0-8.1). Soil application of Mo at 1 kg/ha increased the grain yield by 7.8-11.9% (P<0.05). However, the Mo seed treatment (4 g/kg seed) had a marginal and mostly non-significant effect on growth and yield attributes of chickpea. The higher aboveground dry matter (10.0-19.3%), root weight (11.6-12.5%), nodule weight (7.1-12.1%), and pod number per plant (11.8-22.0%) were observed with soil application of Mo over control treatment. Notably, a negative interaction (P<0.05) between phosphorus and Mo was noticed for aboveground growth of chickpea. Thus, Mo was observed as a limiting nutrient for chickpea in moderately-alkaline soil and application of Mo at 1 kg/ha to soil may be recommended to harvest the potential productivity of chickpea.

M. S. Venkatesh, K. K. Hazra, P. K. Ghosh, S. S. Singh, S. K. Chaturvedi, and N. P. Singh, Response of chickpea (cicer arietinum) to molybdenum in moderately-alkaline soil, Indian Journal of Agricultural Sciences, 2020, 90, 58-63.

Chemometric optimization of the methodology for determination of molybdenum in soils and plants by square wave adsorptive stripping voltammetry

The method is based on the adsorptive accumulation of complex molybdenum(VI) with 8-hydroxyquinoline, using voltammetric square wave cathodic stripping voltammetry. The composition and concentration of the supporting electrolyte. frequency (Hz), amplitude (mV) and deposition time (s), were optimized by factorial design in relation to current reduction of molybdenum(VI). The optimum methodology provided the following values for the process variables: scan increase (0.5 mV), pulse amplitude (127 mV), frequency (96 Hz). adsorption time (80 s) and drop size (0.60 mm 2 ), the concentration of KNO3 (2.0 mol L-1), acetate buffer (0.5 mol L-1) and 8-hydroxyquinoline (0.01 mol L-1). The results obtained after optimization showed a linear response in the range from 1.0 to 6.0 mg L-1 and limits of detection and quantification, respectively equal to 0.02 and 0.08 mg L-1. The molybdenum contained in the samples were determined using the optimized methodology, with values consistent with the values determined by atomic emission spectrometry with inductively coupled plasma (ICP-AES).

J. R. de Carvalho, E. L. Reis, C. Reis, O. I. C. Damasceno, A. A. Neves, and A. A. Matias, Chemometric optimization of the methodology for determination of molybdenum in soils and plants by square wave adsorptive stripping voltammetry, Journal of the Brazilian Chemical Society, 2020, 31, 716-723.

Nitrogen fixation

The mechanism of nitrogen fixation in enzymes and in model systems in vitro has been extensively investigated.

Burris, R. H. and Roberts, G. P., Ann. Rev. Nutrition, 1993, 13, 317.
Sellman, D., Agnew. Chem. Int. Ed., 1993, 105, 64.

The microorganisms which fix molecular nitrogen fall into two classes: (a) the symbiotic microorganisms which fix nitrogen in association with plants, e.g., Rhizobium; (b) asymbiotic microorganisms which are free-living and include Azotobacter vinelandii and Clostridium Pasteurianum . From cell-free extracts of C. Pasteurianum, two metalloproteins have been obtained. The hydrogen donating system, azoferredoxin, which contains iron and sulfide and the nitrogen activating system, molybdoferredoxin, which contains molybdenum, iron, and sulfide. The structure of the active centre has been shown by X-ray crystallography to be a Fe-Mo-S cluster.

Chen, J., Christiansen, J., Campbasso, N., Bolin, J. T., Tittsworth, B. C., Hales, B. J., Rehr, J. J. and Cramer, S. P., Angew. Chem. Int. Edn. ,1993, 32,1592.
Kim, J., Woo, D. and Rees, D. C., Biochemistry ,1993, 32,7104.
Rudolf, M. and Kroneck, P. M. H., The nitrogen cycle: Its biology, Biogeochemical Cycles of Elements, 2005, 43, 75-103.

Nitrate reduction

In plants and some animals the first stage in the reduction of nitrate is to nitrite. The reduction is catalysed by nitrate reductase, a flavoprotein enzyme which has molybdenum as the only metal requirement. Molybdenum acts as an electron acceptor from reduced FAD in the enzyme. The molybdenum cofactor is an oxomolybdenum sulfur species with a pterin ligand [Berks et al., 1995; Campbell, 1996; Collison et al., 1996].

Berks, B. C., Ferguson, S. J., Moir, J. W. B. and Richardson, D. J., Biochim. Biophys. Acta - Bioenergetics, 1995, 1232, 97.
Campbell, W. H., Plant Physiology, 1996, 111, 355.
Collison, D., Garner, C. D. and Joule, J. A., Chem. Soc. Rev., 1996, 25, 25.

Concentrations in normal herbage may range from 0.1 to 1.5 ppm on a dry matter basis, see Natural occurrence of molybdenum: molybdenum in plants. The molybdenum may be present as soluble ammonium molybdate, insoluble molybdenum trioxide, calcium molybdate and molybdenum disulfide. In areas of high industrial activity herbage values of up to 231 ppm have been found. The differential in the molybdenum concentration of soils due to pH could result in differing levels due to the consumption of herbage grown in soils of regional type.

Gardner, A. W. and Hall-Patch, P. K., J. Nutr. , 1962, 84 , 31.

Some soils may require supplemental molybdenum. These include soils low in organic matter, severely eroded or heavily weathered soils, soils low in total molybdenum, sandy soils, soils high in iron, and acid soils (pH <6.3). Molybdenum is not readily absorbed by plants from acid soils and liming or addition of molybdenum is required to increase the molybdenum concentration in pasture. Some plants exhibit visual symptoms of molybdenum deficiency, e.g., the classic whiptail in cauliflower and yellow spot in citrus, but often visual symptoms of molybdenum deficiency are not present or appear as symptoms of nitrogen deficiency. A typical supplemental molybdenum addition for legumes is approximately 0.25 kg molybdenum per acre. Molybdenum can be applied in fertilisers, by seed treatment or foliar sprays.

Some pastures have exceptionally high concentrations of molybdenum (generally associated with alkaline soils) and may give rise to symptoms of molybdenum toxicity in sheep and cattle. Guideline values of up to 50 mg/kg dry weight have been fixed for molybdenum concentrations in agricultural soils [Hornick et al., 1977]. A higher incidence of uratic diathesis was reported from a locality in Armenia where the soil was found to contain 77 mg/kg of molybdenum and 39 mg/kg of copper. The total daily intake of molybdenum and copper in the adults of this area were estimated to be 10 times that of an adult in a control area [Kovalskij et al., 1961; ILO Geneva, 1980].

Hornick, S. B., Baker, D. E. and Guss, S. B., Molybdenum in the Environment , 1977, 2, Marcel Dekker, New York.
Kovalskij, V. V., Jarovaja, G. A. and Smavonjan, D. M., Z. Obsc. Biol., 1961, XII, 179.
ILO, Occupational Exposure Limits, 2nd (revised) Ed., Occupational Safety and Health Series, 1980, 37, ILO Geneva.

A clay loam topsoil that tends to form surface crusts was mixed with unweathered fly ash from a western Canada coal burning power plant in mixtures ranging from 0 to 100% fly ash (v/v). Fly ash increased plant Mo concentrations to alter Cu/Mo such that it could be a concern for ruminant diets.

Sale, L.Y., Naeth, M.A., Chanasyk, D.S., Plant And Environment Interactions - Growth-Response Of Barley On Unweathered Fly Ash-Amended Soil, Journal Of Environmental Quality, 1996, 25, 684-691.

Simultaneous determination of Mo and Ni in wine and soil amendments by HR-CS GF AAS

The use of high-resolution continuum-source graphite furnace atomic absorption spectrometry (HR-CS GF AAS), equipped with a linear charge-coupled device (CCD) array detector, makes simultaneous determination of more than one element possible. In this work, HR-CS GF AAS was used for the simultaneous determination of Mo (313.259 nm) and Ni (313.410 nm), for which two analytical methods were developed: direct solid sample analysis for soil amendments and direct sample injection for wine samples. For both these methods, a pyrolysis temperature of 1200 degrees C and an atomization temperature of 2650 degrees C were used. Aqueous standard solutions were used for calibration. The linear correlation coefficient was higher than 0.997 for the two analytes. Detection limits of 0.05 and 0.8 mu g L-1 for wine samples and 0.04 and 0.60 mg kg(-1) for soil amendments were found for Mo and Ni, respectively. To investigate the accuracy of the developed method, digested and undigested wine samples were evaluated with spike recovery values between 94% and 106%. For solid samples, three CRM were evaluated, and the values found for Mo were not significantly different from the certified ones; however, those for Ni were always too high. It was found that this was due to a direct line overlap of the Ni line with the Fe line. This effect was overcome by determining Fe using the unresolved analytical line doublet at 312.565/ 312.568 nm and subtracting this value from the total concentration (Ni + Fe) determined at 313.410 nm. Note that this interference was not observed in wine samples because of their low Fe concentration

Boschetti, W., Borges, A. R., Duarte, A. T., Dessuy, M. B., Vale, M. G. R., de Andrade, J. B., and Welz, B., Simultaneous determination of Mo and Ni in wine and soil amendments by HR-CS GF AAS, Analytical Methods, 2014, 6, 4247-4256.

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