Abstract
The dormancy and germination of seeds are determined by the balance between the embryo growth potential and the binding force imposed by the seed coat. The germination of different seeds is not synchronized, and the stimulus required to promote germination varies greatly. Before germination, the seeds need to undergo water absorption, reactivate metabolic activities and redifferentiate embryonic tissues to mobilize nutrients stored in seeds and initiate meristematic activities. The transition from dry seeds to seedlings is highly sensitive to different environmental conditions, especially light, temperature and water. This response to environmental signals is regulated by one or more hormones. Various plant hormones regulate seed germination through highly complex interactions. Among them, the role of GA (gibberellin) and ABA (Abscisic acid) in regulating seed germination is particularly critical. This article reviewed the mechanisms by which GA and ABA control seed dormancy at the molecular level, and discussed the way they interact with other hormones. Finally, the development direction of plant hormone research on seed germination is prospected.
Highlights
The dormancy and germination of seeds are determined by the balance between the embryo growth potential and the binding force imposed by the seed coat
NCED is mainly involved in the synthesis of ABA, and ABA8'OH is a key enzyme in ABA catabolism, which is encoded by CYP707A (Millar et al, 2006)
ABA can be synthesized both in dormant seeds and non-dormant seeds, ABA catabolism is stronger in non-dormant seeds, and dormant seeds are more conducive to ABA synthesis, that is, dormancy induces changes in ABA metabolism (Millar et al, 2006)
Summary
ABA plays an important role in maintaining seed dormancy and regulating seed germination. It controls seed germination by controlling the germination of the radicle and inhibiting the loosening and expansion of the cell wall (Gimeno-Gilles et al, 2009). NCED (9-cis-epoxycarotenoid dioxygenase) and ABA8'OH (ABA 8'-hydroxylase) are the key enzymes in ABA metabolism. NCED is mainly involved in the synthesis of ABA, and ABA8'OH is a key enzyme in ABA catabolism, which is encoded by CYP707A (Millar et al, 2006). Overexpression of NCED delayed the germination of seeds, Arabidopsis cyp707a2 mutant seeds increased the ABA level and delayed germination (Zheng et al, 2015). Atper mutants were shown to inhibit seed dormancy and the deletion of CYP707A gene can reduce the dormancy inhibition of atper seeds (Chen et al, 2019)
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