Hydrogen Sulfide Emission by Cultured Tobacco Cells

Abstract

Cultured tobacco cells emit a volatile, sulfur-containing compound into the headspace of suspensions which was identified by odor, Pb-acetate precipitation, and gas chromatography on two different columns to be hydrogen sulfide. Emission of hydrogen sulfide was observed when heterotrophic tobacco cells were transfered from media with sulfate to media with glutathione as sole sulfur source; however, emission proceeded for the first 12–16 h after transfer, only. The amount of hydrogen sulfide emitted into the headspace of the suspensions, though more than 6 orders of magnitude smaller than the GSH concentration in the medium, was proportional to the concentration of this sulfur source up to 1.73 mM, but did not increase further at higher GSH concentrations. At the highest, 0.8 nmol hydrogen sulfide were measured in the headspace per 30 ml suspension under these conditions. Photoheterotrophic tobacco cells did not emit hydrogen sulfide when transfered from sulfate-containing to GSH-containing media, most likely because GSH was not taken up very intensively by the cells so that sulfur starvation occurred. However, green tobacco cells emit hydrogen sulfide in amounts up to 7 nmol per 30 ml suspension when transfered from media with sulfate to media with L-cysteine as sulfur source. Under sulfur starvation, photoheterotrophic as well as heterotrophic tobacco cells did not emit hydrogen sulfide. When sulfate or GSH was added after a period of sulfur starvation up to 1 nmol hydrogen sulfide were found per 30 ml suspension within the first 4 hours of culture on the new sulfur source. Growth of the cells was not resumed until 24 h after addition of sulfur to the medium. From these experiments it is concluded that hydrogen sulfide is emitted by tobacco cells when their sulfur metabolism has to be adjusted to a new sulfur source. A period of sulfur starvation before feeding of the new sulfur source also seems to make such an adjustment necessary. Hydrogen sulfide may be emitted under these conditions to prevent the accumulation of dangerous amounts of sulfur inside the cells, when a sulfur source is taken up in amounts exceeding its metabolism.