Volatile Hydrocarbon Production by Stressed Plants

Red pine (Pinus resinosa Ait.) and paper birch (Betulapapyrafera Marsh.) seedlings exposed to sulfur dioxide produced acetaldehyde and ethanol, and exhibited increased production of ethylene and ethane. Gas chromatographic measurement of head space gas from incubation tubes containing leaves or seedlings was a simple method of simultaneously measuring all four compounds. Increased ethylene production had two phases, a moderate increase from the gnnng of the stress period and a large increase just prior to appearance of leaf lesions. Ethane production in SO2-stressed plants did not increase until lesions appeared. Acetaldehyde and ethanol production began within 6 hours at 03 microliter per liter SO2 and 24 hours at 0.1 microliter per liter SO2 and continued throughout a 6-day fumigation. Production of acetaldehyde and ethanol continued when plants were removed to clean air for up to 2 days. A higher concentration of SO2 (0.5 microliter per liter) induced acetaldehyde and ethanol production within 2 hours of the start of fumigation of birch and pine seedlings. A number of other stresses, including water deficit, freezing, and ozone exposure induced production of acetaldehyde and ethanol. Production of these compounds was not due to hypoxia, as the 02 partial pressure in the incubation vessels did not decline. Increasing the 02 partial pressure to 300 miimeters Hg did not affect production of these compounds. Production of ethylene, acetaldehyde, and ethanol declined when more than 80% of the leaf area became necrotic, while ethane production was linearly related to the percentage of necrosis. A number of woody and herbaceous plant species produced acetaldehyde and ethanol in response to freezing stress, while others did not. Measurement of these four compounds simultaneously in the gas phase may be a valuable method for monitoring plant stress, particularly air pollution stress. Production of ethylene by plants increases as a result of environmental stress or wounding (16, 17), and measurement of stress ethylene can be a useful indicator of the onset of stress and/or the degree of stress which a plant is experiencing (14, 16). For example, ethylene evolution by ozone-stressed plants was well correlated with the ozone dose in a large number of plant species (14). There are difficulties with the use of stress ethylene as a diagnostic tool, however. Ethylene is produced by unstressed plants, and the amount varies with age of the tissue and with environmental conditions (16). When stress results in death of cells, ethylene evolution declines. Therefore, the correlation between stress and ethylene evolution may be poor (5). Plants under stress also produce ethane, and unlike ethylene, the amount produced by unstressed plants is normally quite low. Elstner and Konze (5) found that ethane evolution by freezing' Supported by the College of Agricultural and Life Sciences, University of Wisconsin, Madison. stressed plants was linearly correlated with the amount of leaf necrosis. Other studies indicated that ethane production is a common response to wounding (8, 10), and simultaneous measurement of stress ethylene and ethane may be of considerable use in evaluating plant stress. Ethane evolution is the result of free-radical-mediated peroxidation ofmembrane linolenic acids and apparently occurs because free-radical scavenging mechanisms are overcome when cells are decompartmented (6, 7, 10). Bressan et al. (2) and Peiser and Yang (12) reported that ethane is evolved from S02-stressed plants. The proposed mechanism is that Chl-initiated oxidation of bisulfite by a free-radical mediated process results in co-oxidation of linolenate (12). We investigated the production of ethylene and ethane by woody plants exposed to SO2 in order to determine whether (a) measurement of ethylene and ethane can be a useful method for objectively evaluating environmental stress; and (b) whether ethane production is the result of a specific S02-driven process, as suggested by Peiser and Yang (12), or the result of necrosis and decompartmentation of cells. During gas-chromatographic measurement of ethylene and ethane production by woody plants, we found that ethanol and acetaldehyde were produced by stressed plants in addition to ethylene and ethane. Ethanol and acetaldehyde production is usually associated with anaerobic processes such as occur in flooded plants. Under aerobic conditions, little or none ofthese glycolytic metabolites is normally produced (4). Ethanol and acetaldehyde are also produced by some fruits, such as strawberries, and by deteriorating seeds (11, 15). In all of these cases, reduced 02 availability or reduced 02 transport is thought to inhibit TCA electron transport leading ultimately to formation of acetaldehyde and ethanol (4). Our experiments show that ethanol production by plants under stress does not require restricted 02 availability. In the present study, we examined production of ethylene, ethane, acetaldehyde, and ethanol by woody plants exposed to S02 and water stress. Further experiments examined the production of these compounds as a result of several kinds of stress and wounding in a variety of woody and herbaceous plants. MATERIALS AND METHODS Plant Material. Woody plants were grown from commercially available seed in a greenhouse with supplemental lighting to give a 16-h photoperiod. Paper birch (Betula papyrifera Marsh.) and red pine (Pinus resinosa Ait.) seeds were germinated in 3:2:1 peat: Perlite:vermiculite, and seedlings were transplanted 2 to 4 weeks after germination into the same soil mix in 10-cm pots. Seeds of other woody plants were germinated in peat moss and transplanted into 3:2 loam:sand in 30-cm pots. Plants were watered daily and fertilized weekly with Hyponex. Herbaceous plants were grown in various soil mixes in the greenhouse under continuous lighting. SO2 Stress. Plants were transferred to fumigation chambers of the University of Wisconsin Biotron the night before fumigation.