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

Abstract

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°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.

Dormancy of Nicotiana benthamiana seeds can be broken by different compounds

“…The process is quick (few weeks), mainly in case of room temperature (Fig. 1A), compare to species such as Descurainia sophia (one year) (Li et al 2005). Our result suggests that after-ripening could be common among Nicotiana species because it was observed in case of many tobacco (Nicotiana tabaccum) cultivars where it is also fast (Leubner-Metzger & Meins 2000).…”

“…2). SNP is a photolabile molecule which releases NO so it is used as a NO donor (Giba et al 1998;Beligni & Lamattina 2000;Kopyra & Gwózd 2003;Bethke et al 2004a;Li et al 2005). This donor is often employed because of its low price and stability during storage ).…”

“…However, SNP produces cyanide (Boullerne et al 1999;Libourel et al 2006) which can influence the experimental system. It was shown that SNP promotes germination of wide range of species such as Lactuca sativa L. (Giba et al 1998), Lupinus luteus (Beligni & Lamattina 2000), Paulownia tomentosa (Kopyra & Gwózd 2003), Arabidopsis thaliana (Bethke et al 2004a), Descurania sophia (Li et al 2005) and Panicum virgatum (Sarath et al 2006) in NO dependent manner. Recently has been shown on Arabidopsis seeds that cyanide, not NO, is responsible for enhancing germination .…”

“…Although it is well known that GAs are essential hormones that promote seed germination (Koornneef & van der Veen 1980;Finkelstein et al 2008) not all known GAs are bioactive forms (Crozier et al 2000) and do not have the same influence in different species on dormancy breakage (Crozier et al 2000;Li et al 2005).…”

“…However, unlike gibberellins brassinosteroids and ethylene cannot break photodormancy (Leubner-Metzger 2001). However, seed germination is not observed in a presence of inhibitors of ent-kaurene oxidase -uniconazole or paclobutrazol (Nambara et al 1991;Li et al 2005) due to inhibition of GA synthesis. The enzyme ent-kaurene oxidase catalyzes the three step oxidation of ent-kaurene to ent-kaurenoic acid in the GA biosynthesis pathway and when paclobutrazol is applied it binds to an iron atom in the ent-kaurene oxidase and so blocks GA synthesis (Swan et al 2005).…”