Dormancy, seed

Lefebvre, V., H. North et al. (2006). Functional analysis of Arabidopsis NCED6 and NCED9 genes indicates that ABA synthesized in the endosperm is involved in the induction of seed dormancy. Plant J. 45(3) 309-319. 

DEBEAUJON, I LEON-KLOOSTERZIEL, K.M., KOORNNEEF, M., Influence of the testa on seed dormancy, germination, and longevity in Arabidopsis, Plant Physiol., 2000,122,403-413. 

Solarization effects on weed population was hypothesized to be due to different mechanisms, such as changes in cell metabolism and ultrastructure (Singla et al. 1997), microbial parasitism on seeds weakened by sublethal temperatures, seed dormancy interruption by raising temperatures, and foliar scorching of weeds under the plastic mulch (Egley 1990 Katan and DeVay 1991). Moreover, imbalance of 02 and C02 or release of acetaldehyde, ethylene, and other volatile toxic compounds were also reported as accounting for weed death (Rubin and Benjamin 1984 Gamliel et al. 2000). 

A chemical stimulant, a root exudate, is required to break seed dormancy of a parasitic weed and initiate seed germination. Upon receiving a signal for germination, a radicle emerges from the seed coat. However, an additional chemical signal is needed for the radicle to penetrate host roots and form a haustorium. Therefore several plants can serve as catch crops or trap crops for the reduction of the parasitic weed seed bank in infested soil. 

A developing embryo produces ABA, which incepts and maintains mature seed dormancy. Germination begins with the uptake of water by imbibition of the dry seed and is followed by embryo expansion. Usually, it is considered complete when the radicle is through all the covering layers. There is still controversy whether... 

Many seeds become dormant as a means of survival and are able to germinate after many years in the soil. Factors that influence seed germination and seed dormancy include temperature, moisture, oxygen, light, inhibitors (e.g., allelopathic effects), hardness or impermeability of seed coats, mechanically resistant seed coats, immature embryos, and after-ripening requirements (e.g., cool temperatures for several months). Weed seeds may survive and germinate due to several of these characteristics (Pareja et al, 1985). 

Cuphea. Cuphea plants furnish seeds with oils that may be rich in Cg, Cjo, C12, or Ci4 acids. They generally contain >30% of oil and are expected to produce a commercial crop in the period 2005-2010. Problems of seed dormancy and seed shattering have already been solved. As markets for lauric oils already exist, there should be no difficulty in substituting cuphea oUs. More recently, it has been reported that cuphea will be used as a commercial source of lauric acid from 2003 onward (30, 102, 103). Pandey et al. (104) have described the oil (17-29%) from Cupea procumbens containing 89-95% of decanoic acid. See also Section 9.2. 

Koomneef et al., 2002 published a review article on seed dormancy and germination. Higher plants have complex adaptive traits of seed dormancy and germination. These two genes influence by large number of genes and environmental factors. 

Li, C., P. Ni, M. Francki, A. Hunter, Y. Zhang, D. Schibeci, H. Li, etal. 2004. Genes controlling seed dormancy and pre-harvest sprouting in a rice-wheat-barley comparison. Fund Integr Genomics 4 84—93. 

The concentration of ABA increases in late embryo development shortly before the onset of desiccation and seed dormancy [42,81], ABA inhibits precocious germination of immature embryos in culture [70]. Genetic studies have shown that ABA is involved in dormancy and ABA deficient and ABA-insensitive mutants have been isolated [44]. Reciprocal crosses of wild type and ABA-deficient aba mutants of Arabidopsis showed that there are two different pools of ABA in Arabidopsis seeds. The embryonic ABA is... 

Harvest losses of safflower can be one to live times the recommended seeding rate. Safflower seeds have some short-term sprouting resistance but no seed dormancy, which limits persistence in the soil seed bank. This oilseed is attractive to seed predators, including small mammals and birds (personal observation), which may reduce seed density but may facilitate transport of seed from the field. The distance and amount of seed transported by animals have not been quantified, and the fate of transported seed is unknown. Volunteer populations are restricted to the first follow year in conventional fields. Although they can be controlled by conventional herbicides in subsequent crops, there is the potential for survivors to flower, set viable seed, and contribute to both PMGF and SMGF. 

Gulden, R.H., Shirtliffe, S.J., and Thomas, A.G. 2003b. Secondary seed dormancy prolongs persistence of volunteer canola in western Canada. Weed Sci. 51(6) 904—913. 

Gibberellins stimulate cell division and elongation, break seed dormancy, and speed up germination. If the seeds of some species are difficult to germinate you can soak them in a gibberellin solution to get them started. 

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