Factors affecting production of COS and CS2 in Leucaena and Mimosa species

Carbon disulfide (CS2) and carbonyl sulfide (COS) are colorless, foul-smelling, volatile sulfur compounds with biocidal properties. Some plants produce CS2 or COS or both. When used as an intercrop or forecrop, these plants may have agronomic potential in protecting other plants. Most of the factors which affect production of these plant-generated organic sulfides are unknown. We determined the effects of sulfate concentration, plant age, nitrogen fixation, drought stress, root injury (through cutting), and undisturbed growth on COS production in Leucaena retusa or Leucaena leucocephala and the effect of some of these factors on CS2 production in Mimosa pudica. In addition, we determined if organic sulfides were produced in all Leucaena species. When L. retusa and M. pudica seedlings were grown in a plant nutrient medium with different sulfate concentrations (50 to 450 mg S L(-1)), COS or CS2 from crushed roots generally increased with increasing sulfate concentration. COS production was highest (less than or equal to 74 ng mg(-1) dry root) for young L. retusa seedlings and declined to low amounts (<5 ng mg(-1) dry root) for older seedlings. Nitrogen fixation reduced the amounts of COS or CS2 produced in L. leucocephala and M. pudica. Under conditions of undisturbed growth, root cutting, or drought stress, no COS production was detected in 4- to 8-weeks-old L. retusa plants. COS or CS2 or both was obtained from crushed roots or shoots of all 13 known Leucaena species.