Hormonal Regulation of Dormancy in Developing Sorghum Seeds

Abstract

YPreharvest sprouting is one of the main problems encountered in sorghum (Sorghum bicolor [L.] Moench.) production, particularly when seed maturation takes place under damp conditions. Although it is known that genetic variability for sprouting resistance exists, the underlying physiological mechanisms are poorly understood. Sprouting resistance in sorghum is related to the maintenance of a sufficient dormancy level during development (Steinbach et al., 1995). Indeed, although isolated embryos from both susceptible and resistant varieties can germinate equally well in water from early stages of development (i.e. 15 DAP or earlier), the germination capacity of intact developing caryopses from resistant varieties is much less than that observed for susceptible genotypes. This coat-imposed dormancy is the barrier preventing untimely germination.The acquisition of dormancy has been shown in severa1 species to be related to ABA action during seed development. In most seeds the ABA level increases steadily dur-'

Dormancy in cereals (not too much, not so little): about the mechanisms behind this trait

“…Although it became clear from these and many other experiments that manipulating ABA has an impact on dormancy, differences in endogenous ABA content in cereal varieties do not usually appear to be linked to the observed differences in dormancy (Walker-Simmons, 1987;Steinbach et al, 1997). Instead, responsiveness of isolated embryos to exogenous ABA is highly correlated with dormancy expressed in the intact grains from several species, such as wheat (Walker-Simmons, 1987;Morris et al, 1989;Gerjets et al, 2010), barley (Wang et al, 1995;Benech-Arnold et al, 1999Leymarie et al, 2008;Barrero et al, 2009), oat (Corbineau et al, 1991, sorghum (Steinbach et al, 1995) and rice (Gianinetti and Vernieri, 2007).…”

“…For example, maize kernels are viviparous if the ABA signal is reduced or abolished (as in vp5 and vp1 mutants, which are ABA deficient and ABA insensitive, respectively, or with the application of fluridone, an ABA biosynthesis inhibitor) . Spraying young sorghum panicles with fluridone reduced ABA content in the grains and anticipated dormancy release, making a sprouting-resistant line behave as a sprouting-susceptible one (Steinbach et al, 1997). Several rice mutants exhibit vivipary and photooxidation in the light.…”

“…Several studies have focused on the evolution of embryonic ABA content during grain development in wheat, sorghum and barley (Walker-Simmons, 1987;Steinbach et al, 1997;Benech-Arnold et al, 1999), expecting to find less ABA in genotypes displaying an anticipated release from dormancy. However, ABA peaked at around physiological maturity and declined thereafter, and the ABA content of developing grains did not correlate with a particular time of exit from dormancy.…”

Nitrate reductase in detached embryos may serve as a marker of the preharvest tolerance of wheat seeds

“…In wheat, barley, and sorghum cultivars that are susceptible to pre-harvest sprouting, there is a relative sensitivity of the embryo to ABA as compared to resistant cultivars, generally in the absence of any substantial differences in ABA content, or a higher ABA content in the susceptible cultivars [5,6]. Interestingly, the expression pattern of the sorghum VP1 gene is different in two cultivars genotypes exhibiting differential resistance to preharvest sprouting at physiological maturity.…”

“…More specifically, in the embryos of the susceptible cultivar, transcripts encoding VP1 peak at a relatively early stage of grain development (20 days after pollination), whereas the peak in the resistant cultivar occurs at much later developmental stages, when seed maturation is almost complete [5]. Tanner showed that PHS in corn was linked with deficiency of molybdenum [6]. Premature germination in maize was eliminated by Mo applications to the soil or the leaves.…”