ISOPRENE INCREASES THERMOTOLERANCE OF ISOPRENE-EMITTING SPECIES

Isoprene-emitting plants lose a large portion of their assimilated C a s isoprene. Because isoprene synthesis can be regulated, it has been a ssumed that isoprene benefits the plant. Since the rate of isoprene em ission from leaves is highly responsive to temperature, we hypothesize d that isoprene benefits plants by increasing their thermotolerance. W e used three methods to measure isoprene-induced thermotolerance in le aves. Each technique assayed thermotolerance under conditions that sup pressed endogenous isoprene synthesis. When measured by chlorophyll fl uorescence, thermotolerance of kudzu (Pueraria lobata [Willd.] Ohwi.) leaves increased as much as 4 degrees C in very low light. With higher light, isoprene increased thermotolerance of kudzu leaves by as much as 10 degrees C. When measured as the temperature at which photosynthe sis declined to zero, thermotolerance increased with added isoprene by 2.5 degrees C. All three measures of thermotolerance were dose depend ent. Both fluorescence techniques also showed isoprene-induced thermot olerance in white oak (Quercus alba L.). Thermotolerance was not obser ved in bean (Phaseolus vulgaris var Linden), a species that does not e mit isoprene. None of the experiments was designed to determine the me chanism of thermotolerance, but we theorize that isoprene functions by enhancing hydrophobic interactions in membranes.