Involvement of cyanogens in the promotion of germination of cocklebur seeds in response to various nitrogenous compounds, inhibitors of respiratory and ethylene

Nitrogenous inhibitors of respiration, namely, KCN, NaN₃ and NH₂OH, which promote the germination of cocklebur (Xanthium pennsylvaniicum Wallr.) seeds, enhanced the accumulation of cyanogenic compounds. Urea and cyanamide, which were ineffective, did not. Part of the exogenously applied KCN was converted to cyanogenic glycosides and lipids, but these compounds were only produced at low levels in NaN₃-treated seeds. Exposure to NH₂OH caused a slight accumulation of both types of cyanogenic compounds. Thiourea, effective in stimulating germination, did not increase the cyanogenic compounds, which suggests that the mechanism of its effect on germination is different from that of other nitrogenous compounds. Thiocyanate had a slightly promotive effect and caused minor increases in the levels of cyanogenic compounds. Ethylene increased the metabolic utilization of the accumulated cyanogens in response to KCN or NaN₃. The response to ethylene of seeds in secondary dormancy was restored only after pre-treatment with KCN or NaN₃. The response occurred once the level of cyanogens had increased. By contrast, enhancement of the effects of KCN and NaN₃ on germination by propyl gallate or benzohydroxamate, inhibitors of CN-resistant respiration, was accompanied by the increased accumulation of cyanogens within the seeds that had been exposed to KCN or NaN₃ in combination with the other types of respiratory inhibitors. Thus, it is suggested that endogenous cyanogens might be involved in the germination of cocklebur seeds.