Synthesis and emision of hydrogen sulfide by higher plants.

Hydrogen sulfide is emitted by higher plants in response to the uptake of sulfate, sulfur dioxide, L- and D-cysteine. For each of these sulfur sources a different pathway of synthesis of hydrogen sulfide has been established. Apparently, these pathways are part of an intracellular sulfur cycle that may operate to maintain the cysteine concentration in plant cells at the observed low level when sulfur is present in excess. Hydrogen sulfide emission by higher plants is not a laboratory artefact but is also observed in the field. Though a proper quantification of the volatile sulfur emitted on a global scale can not be obtained from the data presently available, hydrogen sulfide emission by higher plants seems to be a significant contribution to the biogeochemical cycle of sulfur.