Abstract
Primary seed dormancy is the phenomenon whereby seeds newly shed by the mother plant are unable to germinate under otherwise favorable conditions for germination. Primary dormancy is released during dry seed storage (after-ripening), and the seeds acquire the capacity to germinate upon imbibition under favorable conditions, i.e., they become non-dormant. Primary dormancy can also be released from the seed by various treatments, for example, by cold imbibition (stratification). Non-dormant seeds can temporarily block their germination if exposed to unfavorable conditions upon seed imbibition until favorable conditions are available. Nevertheless, prolonged unfavorable conditions will re-induce dormancy, i.e., germination will be blocked upon exposure to favorable conditions. This phenomenon is referred to as secondary dormancy. Relative to primary dormancy, the mechanisms underlying secondary dormancy remain understudied in Arabidopsis thaliana and largely unknown. This is partly due to the experimental difficulty in observing secondary dormancy in the laboratory and the absence of established experimental protocols. Here, an overview is provided of the current knowledge on secondary dormancy focusing on A. thaliana, and a working model describing secondary dormancy is proposed, focusing on the interaction of primary and secondary dormancy.
Highlights
Seeds comprise an important phase in the life cycle of seed plants, as they are the generation of the plant and can be widely dispersed
Secondary dormancy induction occurs in nature when seeds cannot germinate due to the environmental conditions, e.g., when a seed becomes buried in the soil
It is expected that the immediate environmental conditions, rather than those experienced by the mother plant, dominate to determine secondary dormancy levels
Summary
Seeds comprise an important phase in the life cycle of seed plants, as they are the generation of the plant and can be widely dispersed. The timing of seed germination determines in which environment the seedling will grow and defines whether seedling establishment will be successful. Seed dormancy functions to time the moment of germination in the right (seasonal) environment. There are different types of dormancy including physical dormancy, morphological dormancy, physiological dormancy, and combinational dormancy [1,4,5,6]. In certain types of physical dormancy, seeds have a hard, impermeable seed coat which has to be weakened first (e.g., by acids found in the digestive tract of an animal) before water can be taken up and germination can initiate. Plants 2020, 9, 749 different types of dormancy can occur, e.g., morphophysiological dormancy. In this perspective, the focus will be on Arabidopsis thaliana which displays physiological dormancy [7]. A brief overview of secondary dormancy research in A. thaliana is provided, a working model is proposed, and a perspective on future research is given
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