Seed dormancy and ABA signaling

Abstract

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.

ArabidopsisPaired Amphipathic Helix Proteins SNL1 and SNL2 Redundantly Regulate Primary Seed Dormancy via Abscisic Acid–Ethylene Antagonism Mediated by Histone Deacetylation

“…Altered expression of genes regulating ABA levels or sensitivity leads to changed seed dormancy levels (Rodríguez-Gacio et al, 2009). Induction of NCED6 during imbibition increases ABA levels and is sufficient to prevent seed germination (Martínez-Andújar et al, 2011).…”

Regulation of abscisic acid metabolism in relation to the dormancy and germination of cereal grains

“…Thus, the direct indicator of the depth of dormancy is not always the level of ABA in the grains before imbibition, but rather the varied capacity of grains to catabolize and synthesize ABA upon imbibition [26]. It is assumed that the decrease in ABA content observed during grain imbibition results from intensified catabolism of this phytohormone, as it was accompanied by an increase in phaseic acid (PA) content, an oxidative catabolite of ABA [10,13]. On the other hand, studies using norflurazon, which disturbs the synthesis of ABA, due to inhibition of carotenoid synthesis, revealed that de novo ABA synthesis is responsible, in some extent, for maintaining the dormancy of imbibed grains of deep dormant rice cultivar.…”

“…Dormancy release is accompanied by a decrease in embryo ABA content and/or a decrease in the sensitivity of embryos to ABA in parallel with a simultaneous increase in gibberellin levels. However, gibberellins are increasingly considered to promote germination after dormancy release, rather than to participate in breaking seed dormancy [6,[9][10][11][12][13].…”

Dissecting the role of Arabidopsis thaliana AMIDASE 1 in auxin biosynthesis

“…SA, GA, ET or Brassinosteroids) until the environmental conditions comply with the requirements that most probably facilitate successful germination (Finkelstein, Gampala, and Rock 2002;Rodríguez--Gacio, Matilla--Vázquez, and Matilla 2009). Taking the severe ami1--2/rty1 embryo phenotype into account, the overexpression of genes related with ABA in the ami1--2 genetic background can likely be taken as a further confirmation for an involvement of AMI1 in embryo development and seed maturation in Arabidopsis, respectively.…”