Effects of ethylene and some other environmental factors on different stages of germination in red root pigweed (Amaranthus retroflexusL.) seeds*

Abstract.Ethylene was found to promote two distinct processes during germination of redroot pigweed (Amarantus retroflexusL.) seeds: embryo expansion that splits the seed coat (incomplete germination), and radicle penetration through the more elastic endosperm (complete germination). The two events can be separated in time by subjecting seeds to low water potential or low CO2levels, which arrest germination of some seeds at the incomplete stage. Ethylene applications to incompletely germinated seeds promote complete germination, with a response threshold near 0.02 cm3m−3and saturation near 0.5 cm3m−3. Higher ethylene concentrations (0.5 to 50 cm3m−3) given during the first day of seed imbibition also increase the percentage of seeds which initiate embryo expansion and split the seed coat. Light and elevated CO2also promote radicle penetration of the endosperm in seeds incubated under water stress. The results support the view that the germination pause at the incomplete stage is an adaptation to environmental stresses that can be overcome with exogenous ethylene or certain other stimuli.