Sulfur-containing Compounds in Lemna perpusilla 6746 Grown at a Range of Sulfate Concentrations

Lemna perpusilla 6746, grown photoautotrophically at a series of sulfate concentrations ranging from 0.32 to 1,000 μm, was labeled to radioisotopic equilibrium with ³⁵SO₄²⁻. Sulfur-containing compounds were isolated and purified from the colonies. Radioactivity in each compound was a measure of the amount of that compound present in the tissue. The following compounds were identified and quantitated: inorganic sulfate, glutathione, homocyst(e)ine, cyst(e)ine, methionine, S-methylmethionine sulfonium, S-adenosylmethionine, S-adenosylhomocysteine, cystathionine, chloroformsoluble (presumed to be sulfolipid), protein cyst(e)ine, and protein methionine. γ-Glutamylcyst(e)ine, erythro- and threo-thiothreonine, and S-methylcysteine were not detected. No volatile ³⁵S compounds were formed during plant growth at 1,000 μm sulfate, nor were significant amounts of ³⁵S compounds excreted into the medium.