Effects of source of plant material and temperature on the production of smoke extracts that promote germination of light-sensitive lettuce seeds

Smoke is now widely recognized as a germination cue for fire-dependent and non-fire-dependent plant species. Although the identity of the stimulant(s) and its mode of action remain unknown, it needs to be established whether burning or heating of all plant materials generate the active compound(s). In view of the variation in fire intensity in the wild it must also be established at what temperatures the active compound(s) is produced. Heating dry Themeda triandra leaves at a range of temperatures showed that the active component(s) is produced between 160 and 200 degrees C. At higher temperatures activity is lost, apparently due to volatilization of the stimulatory compounds. Aqueous smoke extracts prepared from a range of plants, and extracts prepared by heating agar and cellulose, contained compounds that stimulated the germination of light-sensitive lettuce seeds. Chromatographic evidence obtained by thin-layer chromatography and high-performance liquid chromatography suggest that the same active compound(s) is produced from T. triandra leaves, agar and cellulose used in this study.