Effects of Xanthium Leaf Extracts on Lettuce Seed Germination

Abstract

Seed germination in lettuce var. Grand Rapids, and floral induction in Xanthium are phytochrome-mediated processes. The pigment conversion which triggers these two rather diverse developmental events appears to be essentially the same. The present work was conducted to test the possibility that secondary metabolic steps following the initial triggering phase might also be shared by these two morphological processes. Aqueous extracts were made from leaves of vegetative Xanthium, plants, as well as from those having received one or five floral inductive photoperiods. These extracts were applied to lettuce seeds to test for their possible promotive or inhibitory effects on germination. No promotive effect on germination could be demonstrated. Extracts from vegetative Xanthium plants had a marked inhibiting effect on germination of lettuce seeds. This inhibitory effect could be substantially reduced if the Xanthium plants were given floralinductive treatments prior to extraction. Thus, as Xanthium leaves progress from noninductive to inductive photoperiods, there appears to be a decrease in content of a gerination- inhibiting substance, which parallels the generally accepted time period of flowering stimulus build-up.