Sulfur for Plants: Active Metabolism
Sulfur (S)
For the plant – active metabolism.
In the plant organism sulfur participates in nitrogen and carbohydrate metabolism, in respiration, and in fat synthesis. The main amount of it in plants is found in proteins (sulfur is a component of the amino acids cysteine, cystine, and methionine) and other organic compounds – enzymes, vitamins, mustard and garlic oils.
Plants obtain sulfur from the soil in the form of soluble sulfates, and putrefactive bacteria convert sulfur from proteins into hydrogen sulfide H2S (hence the unpleasant smell of decay). However, most hydrogen sulfide is formed during the reduction of sulfates by sulfate-reducing bacteria. This H2S is oxidized by phototrophic bacteria in the absence of molecular oxygen to sulfur and sulfates, while in the presence of O2 it is oxidized to sulfates by aerobic sulfur bacteria.
In many bacteria, sulfur is temporarily stored in the form of granules. Its amount depends on the content of hydrogen sulfide: in its deficiency, sulfur is oxidized to sulfuric acid:
In many bacteria, sulfur is temporarily stored in the form of granules. Its amount depends on the content of hydrogen sulfide: in its deficiency, sulfur is oxidized to sulfuric acid:
2H2S + O2 → 2H2O + 2S + energy
2S + 3O2 + 2H2O → 2H2SO4 + energy
2S + 3O2 + 2H2O → 2H2SO4 + energy
In water bodies where the water contains hydrogen sulfide, colorless sulfur bacteria Beggiatoa and Thiothrix live, which do not require organic food. For chemosynthesis, they use hydrogen sulfide: as a result of reactions between H2S, CO2, and O2, carbohydrates and elemental sulfur are formed.
Most of the sulfur is not assimilated by plants but helps them absorb phosphorus.
The sulfur content in plants averages 0.05% (by weight).
Sulfur deficiency first manifests on older leaves. Then its signs appear on younger leaves, changing their color to light green and then yellow, as sulfur deficiency reduces the intensity of photosynthesis. In sulfur deficiency, small leaves with a light yellowish tint form on elongated stems, growth and development of plants worsen, and maturity is delayed.
Excessive amounts of sulfur can cause premature leaf drop.
Indicator plants for increased sulfur content in the soil are species of the genus Astragalus L., Fabaceae.
Medicinal plants containing sulfur:
• field horsetail Equisetum arvense L., Equisetaceae (herb);
• plants of the cabbage family Brassicaceae Burnett, legume family Fabaceae Lindl., and celery family Apiaceae Lindl.
• field horsetail Equisetum arvense L., Equisetaceae (herb);
• plants of the cabbage family Brassicaceae Burnett, legume family Fabaceae Lindl., and celery family Apiaceae Lindl.