Promotion of cocklebur seed germination by allyl, sulfur and cyanogenic compounds

Abstract

The effects of allyl, sulfur and cyanogenic compounds on the germination of upper cocklebur (Xanthium pennsylvanicum Wallr.) seeds were examined. Mercaptoethanol and methylmercaptan as well as KCN, substrates for β-cyanoalanine synthase (CAS), and H2S and thiocyanate, the products of the CAS catalyzing reaction, were effective in promoting germination, suggesting the involvement of CAS in germination. Most of allyl compounds, especially allylthiourea, as well as ethylene which activated CAS [Hasegawa et al. (1994) Physiol. Plant. 91: 141], promoted the germination in an abnormal type which occurred by the predominant growth of cotyledons as did C2H4 [Katoh and Esashi (1975) Plant Cell Physiol. 16: 687]. However, they failed to activate CAS unlike ethylene, and to liberate free ethylene daring an incubation period. It was thus possible that an C2H4-like double bond within allyl compounds can act to promote seed germination.