Hormonal and environmental regulation of seed germination in flixweed (Descurainia sophia)

Flixweed is one of the most abundant weeds in North America and China, and causes a reduction in crop yields. Dormancy of flixweed seeds is deep at maturity and is maintained in soil for several months. To identify regulators of seed dormancy and germination of flixweed, the effect of environmental and hormonal signals were examined using dormant and non-dormant seeds. The level of dormancy was decreased during after-ripening and stratification, but long imbibition (over 5 days) at 4 degrees C in the dark resulted in the introduction of secondary dormancy. The strict requirement of duration of cold treatment for the break of dormancy may play a role in the seasonal regulation of germination. The germination of non-dormant flixweed seeds was critically regulated by red (R) and far-red (FR) light in a photoreversible manner. Sodium nitroprusside, a donor of nitric oxide (NO), promoted germination of half-dormant seeds, suggesting that NO reduced the level of seed dormancy. As has been shown in other related species, light elevated sensitivity to GA(4) in dark-imbibied flixweed seeds, but cold treatment did not affect GA(4)-sensitivity unlike in Arabidopsis. Taken together, our results indicate that seed germination in flixweed and its close relative Arabidopsis is controlled by similar as well as distinct mechanisms in response to various endogenous and environmental signals.