Ethylene and Ethane Production from Sulfur Dioxide-injured Plants.

After alfalfa (Medicago sativa) seedlings were exposed to approximately 0.7 microliter per liter SO(2) for 8 hours, elevated ethylene and ethane production was observed. Ethylene production peaked about 6 hours and returned to control levels by about 24 hours following the fumigation, while ethane production peaked about 36 hours and was still above control levels 48 hours after the fumigation. Light had an opposite effect upon the production of the two gases: ethane production rates were higher from plants held in light, whereas ethylene production rates were higher from those held in the dark. Peak ethylene and ethane production rates from SO(2)-treated plants were about 10 and 4 to 5 times greater, respectively, than those of the control plants. Ethylene appeared to be formed primarily from stressed yet viable leaves and ethane from visibly damaged leaves. The different time courses and light requirements for ethylene and ethane production suggest that these two gases were formed via different mechanisms. Light appears to have a dual role. It enhances SO(2)-induced cellular damage and plays a role for repairs.