Does smoke substitute for red light in the germination of light-sensitive lettuce seeds by affecting gibberellin metabolism?

Plant-derived smoke extracts are known to stimulate seed germination In a number of species, but the active compound(s) and mechanism remain unknown. The key to understanding the process underlying the induction of germination lies in the characterisation of the relationship between temporal patterns of physiological and developmental changes. Germination time-course studies revealed that the onset of germination in smoke-treated Grand Rapids lettuce seeds was delayed compared to seeds treated with red light or gibberellic acid. Both red light and smoke-induced germination can be reversed by far-red light, but the escape time is shorter for smoke-treated seeds. Paclobutrazol and AMO 1618, inhibitors of gibberellin biosynthesis, decreased the germination of smoke-treated seeds significantly at concentrations of 0.1 and 1mM, but did not substantially diminish germination of red light-treated seeds. Levels of endogenous gibberellins, estimated using the dwarf rice microdrop assay, were significantly higher in red light-treated seeds than in controls, and peaked after 100% germination was obtained. In contrast, the level of gibberellins in smoke-treated seeds remained low initially, but rose concurrent with the start of germination. The peak level of gibberellins in smoke-treated seeds was markedly higher than In red light-treated seeds. Gibberellin synthesis Is thus considered to be a likely component of the mechanism underlying smoke-induced germination.