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Sulfur is an essential element for growth and physiological functioning of plants, however, its content strongly varies between plant species and it ranges from 0.1 to 6 % of the plants' dry weight. Sulfate taken up by the roots is the major sulfur source for growth, though it has to be reduced to sulfide before it is further metabolized. Root plastids contain all sulfate reduction enzymes, however, the reduction of sulfate to sulfide and its subsequent incorporation into cysteine takes predominantly place in the shoot in the chloroplast. Cysteine is the precursor or reduced sulfur donor of most other organic sulfur compounds in plants. The predominant proportion of the organic sulfur is present in the protein fraction (up to 70 % of total sulfur), as cysteine and methionine residues. Cysteine and methionine are highly significant in the structure, conformation and function of proteins. Plants contain a large variety of other organic sulfur compounds, as thiols (glutathione), sulfolipids and secondary sulfur compounds (alliins, glucosinolates, phytochelatins), which play an important role in physiology and protection against environmental stress and pests. Sulfur compounds are also of great importance for food quality and for the production of phyto-pharmaceutics. Sulfur deficiency will result in the loss of plant production, fitness and resistance to environmental stress and pests.