The Effect of Sulfur Nutrition on Plant Glucosinolate Content: Physiology and Molecular Mechanisms

Abstract

Glucosinolates are sulfur-rich plant metabolites of the order Brassicales that function in the defense of plants against pests and pathogens. They are also important in human society as flavor components, cancer-prevention agents, and crop biofumigants. Since glucosinolates may represent up to 30 % of the total sulfur content of plant organs, their accumulation should depend intimately on the sulfur status of the entire plant. Here we review the literature on how sulfur supply affects glucosinolate content. In field and greenhouse experiments involving soil, hydroponic and tissue culture media, sulfur fertilisation usually led to an increase in glucosinolate content ranging from 25 % to more than 50-fold, depending on the plant species, amount of sulfur applied, and type of treatment. The effect was greater on glucosinolates derived from the sulfur amino acid, methionine, than on glucosinolates derived from tryptophan. These changes are regulated not by simple mass action effects, but by extensive changes in gene transcription. In sulfur-deficient plants, there is a general down-regulation of glucosinolate biosynthetic genes which accompanies an up-regulation of genes controlling sulfur uptake and assimilation. Glucosinolates may be considered a potential source of sulfur for other metabolic processes under low-sulfur conditions, since increased breakdown of glucosinolates has been reported under sulfur deficiency. However, the pathway for sulfur mobilisation from glucosinolates has not been determined. The breakdown of indolic glucosinolates to form auxin in roots under sulfur-deficient conditions may help stimulate root formation for sulfur uptake.

Evaluating strategies to improve glucosinolate concentration and root yield of field-grown horseradish in a Mediterranean environment: preliminary results

“…In sprouts, GLS concentration remained almost constant over time and similarly to the roots they benefited from the fertilisation. It has been reported that sulphur fertilisation allowed an increase in GLS concentration in most cases, even by over 10 times, suggesting that there are substantial opportunities to manipulate the GLS concentration in plants to enhance their organoleptic and health properties, or their value as biofumigants (Falk et al, 2007). On wasabi, whose flavour, as for horseradish comes from the liberation of the allyl-isothiocyanate (AITC) by the hydrolysis of precursor SIN, Sultana et al (2002) found that fertilisation with ammonium sulphate produced the highest-quality rhizomes with an increase by 72% in AITC yield, while nitrogen fertiliser alone reduced the AITC yield by up to 15%, showing the importance of sulphur in improving the AITC concentration.…”

Optimisation of enzymatic production of sulforaphane in broccoli sprouts and their total antioxidant activity at different growth and storage days

“…Sulforaphane is a sulfur-containing isothiocyanates that is hydrolyzed from glucosinolates by myrosinase. Sulforaphane production decreased with seed growth because of degradation of glucosinolates to support the formation of other sulfur-containing compounds, particularly under lowsulfur conditions (Falk et al 2007). Much of the reduction in concentration may be simply a result of plant expansion, which diluted the compounds and decreased their content per weight unit (Doughty et al 1991).…”

Variation of glucosinolates concentration and root growth of horseradish as affected by nitrogen and sulphur supply

“…In roots a wide range of GLS concentration (from 1.7 up to 296 μmol/g DW) depending on genotype is reported by several authors (Li and Kushad 2004, Agneta et al 2013, Wedelsbäck Bladh 2014. Besides genotype, sulfur fertilization led to enhanced glucosinolate content in a number of Brassica species, and increases of over 10-fold were reported (Falk et al 2007). On wasabi, whose flavor as for horseradish comes from the liberation of the allyl-isothiocyanate (AITC) by the hydrolysis of precursor SIN, Sultana et al (2002) found that fertilization with ammonium sulphate produced the highest-quality rhizomes with an increase of 72% in AITC yield, while N alone reduced it by up to 15%.…”

“…Among agronomic practices, the fertilization has been largely studied in numerous Brassicaceae crops to maximize benefits for production and GLS content. Several studies highlighted that S led to increases of GLS in most cases (Falk et al 2007) while N level, form and application timing exhibited diverse responses. Referring to horseradish, the influence of N and S on GLS content was mostly studied in embryoids, suspension cells and calli, and plantlets grown in vitro; in the latter, Alnsour et al (2012) found that GLS concentrations could be modulated 20-fold by varying the sulphate concentration in the medium.…”