Seed Development and Germination

Plant Signaling & Behavior

2009

165

104

The seed is an important organ of higher plants regarding plant survival and species dispersion. The transition between seed dormancy and germination represents a critical stage in the plant life cycle and it is an important ecological and commercial trait. A dynamic balance of synthesis and catabolism of two antagonistic hormones, abscisic acid (ABA) and giberellins (GAs), controls the equilibrium between seed dormancy and germination. Embryonic ABA plays a central role in induction and maintenance of seed dormancy, and also inhibits the transition from embryonic to germination growth. Therefore, the ABA metabolism must be highly regulated at both temporal and spatial levels during phase of dessication tolerance. On the other hand, the ABA levels do not depend exclusively on the seeds because sometimes it becomes a strong sink and imports it from the roots and rhizosphere through the xylem and/or phloem. All theses events are discussed in depth here. Likewise, the role of some recently characterized genes belonging to seeds of woody species and related to ABA signaling, are also included. Finally, although four possible ABA receptors have been reported, not much is known about how they mediate ABA signalling transduction. However, new publications seem to shown that almost all these receptors lack several properties to consider them as such.

Section: Aba Is Not the Only Signal In Establishment And Dormancy Releasementioning

confidence: 99%

Seed dormancy and ABA signaling

Rodríguez-Gacio

Matilla-Vázquez

Plant Signaling & Behavior

2009

165

104

“…The seed, which is the dispersal unit in angiosperms and ensures the survival and perpetuation of the mother plant, is formed by zygotic embryogenesis. This complex process, regulated by hormones and a developmental programme ( Yamaguchi and Nambara, 2006 , and references therein), is divided into two extensive phases called morphogenesis and maturation. During seed maturation, the cell cycle ceases, molecular dependence on the mother plant disappears, water content diminishes, storage products are synthesized, abscisic acid (ABA) accumulates, and primary dormancy is established (reviewed in Hilhorst and Toorop, 1997 ; Raz et al , 2001 ; Finkelstein et al , 2002 ; Kermode, 2005 ; Weber et al , 2005 ; Finch-Savage and Leubner-Metzger, 2006 ; Holdsworth et al , 2008 ).…”

Section: Introductionmentioning

confidence: 99%

“…Many plant hormones have been shown to be involved in germination ( Kucera et al , 2005 ). Among these, GAs have long been known as stimulators and ABA as an inhibitor ( Finkelstein et al , 2002 , 2008; Yamaguchi and Kamiya, 2002 ; Yamaguchi and Nambara, 2006 ). However, the role of ethylene (ET) seem less obvious than that of ABA and GAs, since the intervention of ET during the maintenance of seed dormancy and during the transition from dormancy to germination involves a complex network with many steps still to be clarified (Vandenbussche and Van der Straeten, 2007).…”

Section: Introductionmentioning

confidence: 99%

After-ripening alters the gene expression pattern of oxidases involved in the ethylene and gibberellin pathways during early imbibition of Sisymbrium officinale L. seeds

Iglesias‐Fernández

Journal of Experimental Botany

2009

After-ripening (AR) in Sisymbrium officinale seeds altered SoACS7, SoACO2, SoGA20ox2, SoGA3ox2, and SoGA2ox6 gene expression. Except for SoGA20ox2 expression, which sharply diminished, the expression of the other genes rose during development, particularly that of SoACS7. In contrast, only the SoACO2 and SoGA2ox6 transcripts increased with seed desiccation; the others decreased. AR increased the SoGA3ox2 transcript in dry seed, but dramatically decreased the SoACS7 transcript. At the onset of imbibition, AR inhibited SoACS7 and SoACO2 expression and stimulated that of SoGA20ox2, SoGA3ox2, and SoGA2ox6, demonstrating that the participation of ethylene (ET) and gibberellins (GAs) differs in after-ripened and non-after-ripened seeds. The inhibition of SoACO2 expression in the presence of GA4+7, paclobutrazol (PB), inhibitors of ET synthesis and signalling (IESS), and notably ET+GA4+7 indicated ET–GA cross-talk in non-after-ripened seeds. A positive effect of AR in reversing this inhibition was found. The idea of ET–GA cross-talk is also supported by the effect of ET on SoGA3ox2 expression, notably induced by the AR process. In contrast, SoGA20ox2 expression did not appear to be susceptible to AR. SoGA2ox6 expression, poorly known in seeds, suggests that AR prompted an up-regulation under all treatments studied, whereas in non-after-ripened seeds expression was down-regulated. On the other hand, the β-mannanase (MAN) activity dramatically increased in dry after-ripened seed, being significantly boosted by ET. The absence of MAN inhibition by IESS suggests that although ET seems to be one of the factors controlling MAN, its presence did not appear to be essential. GA4+7 only increased MAN in seeds wich were after-ripened. Here, it is proposed that ET and GAs participate actively in establishing the AR process.

“…In contrast with ABA, GAs levels are initially very low in dry seeds and rise upon seed imbibition (Yamaguchi and Nambara ). The Arabidopsis genome contains RGL1 and RGL2, with RGL2 being a regulator of seed germination in response to GAs (Lee et al , ).…”

Section: Discussionmentioning

confidence: 99%

Nitrate‐induced early transcriptional changes during imbibition in non‐after‐ripened Sisymbrium officinale seeds

Carrillo-Barral

Iglesias‐Fernández

et al. 2012

Physiologia Plantarum

We have here demonstrated for the first time that nitrate not only accelerates testa rupture of non- AR seeds but also modifies expression pattern of the cell-wall remodeling proteins (mannanases; SoMAN6 and SoMAN7) and key genes belonging to metabolism and signaling of ABA (SoNCED6, SoNCED9, SoCYP707A2 and SoABI5) and GAs (SoGA3ox, SoGA20ox, SoGA2ox and SoRGL2). These results were obtained during Sisymbrium officinale seed imbibition in the absence of endosperm rupture. Exogenous ABA induced a notable inhibition of testa rupture in both absence and presence of nitrate being this effect sharply reversed by GA(4+7). However, nitrate was capable to provoke testa rupture in absence of ABA synthesis. The expression of SoMAN6 and SoMAN7 were positively altered by nitrate. Although ABA synthesis seems apparent at the start of non-AR seed imbibition, taken together the results of SoNCED6, SoNCED9 and SoCYP707A2 expression seem to suggest that nitrate leads to a strong net ABA decrease. Likewise, nitrate positively affected the SoABI5 expression when the SoNCED9 expression was also stimulated. By contrast, at the early and final of imbibition, nitrate clearly inhibited the SoABI5 expression. The expression of SoGA2ox6 and SoGA3ox2 are strongly inhibited by nitrate whereas of SoGA20ox6 was stimulated. On the other hand, SoRGL2 transcript level decreased in the presence of nitrate. Taken together, the results presented here suggest that the nitrate signaling is already operative during the non-AR S. officinale seeds imbibition. The nitrate, in cross-talk with the AR network likely increases the favorable molecular conditions that trigger germination.