Ethylene and Ethane Production from Sulfur Dioxide-injured Plants

Abstract

After alfalfa (Medicago sativa) seedlings were exposed to approximately 0.7 microliter per liter SO2 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 SOs-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 S02-induced cellular damage and plays a role for repairs.Ethylene is produced from plants under normal conditions in relatively low amounts, but when plants are perturbed or injured, elevated ethylene production rates usually occur (1, 23). Stressinduced ethylene production has been reported to occur in plants exposed to air pollutants, such as ozone (5, 21) and SO2 (3,4). Stress ethylene from ozone-injured plants reached a maximum within 2 to 4 hr, and returned to control levels by 24 hr after exposure to ozone (5, 21). Bressan et al. (3, 4) exposed leaf tissues of cucurbits to bisulfite solution or SO2 gas and found that ethylene production greatly increased in slightly injured leaves, but declined in severely injured leaves. Both ethylene and ethane can be produced from freeze-injured tissue (8). We have recently reported that both of these gases were produced in a chemical system consisting of linolenic acid hydroperoxide and bisulfite (15). In the present study we examined ethylene and ethane production from intact alfalfa plants exposed to SO2.MATERIALS at the exit chamber port immediately before and at 1 and 5 hr after the plants were placed in the chambers, were 1.5, 0.5 and 0.6 ,ul/l, respectively. Gas samples were collected in 2-liter Erlenmeyer flasks and S02 concentration was measured by the West-Gaeke method as modified by Scaringelli et al (18). The temperature and light intensity during the fumigation were the same as that at which the plants were grown.To determine the ethylene and ethane production rates, each pot of plants was enclosed periodically in a 1-liter glass chamber for 4 hr over a period both before and after the S02 fumigation.A 3-ml gas sample was withdrawn from each chamber at the beginning and end of each 4-hr period, and the gas concentrations were measured by gas chromatography employing an alumina column and a flame ionization detector. Between each 4-hr period the chambers were left open for 30 min and then reclosed for the...

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