Abstract
Dormancy is an innate constraint on germination that occurs across all life forms. In this study, we investigated the seed dormancy release and germination characters of Taxus yunnanensis by exploring the seed morphology, permeability, germination inhibitors, endogenous hormones, and embryo germination in vitro during wet sand storage. Our results showed that seeds and embryos grew to a critical size to germination and permeability increased with the extension of storage. Seed coat and kernel methanol extracts reduced Brassica campestris seed vigor index. The in vitro embryo germination rate increased by 12.20% after storage for 30–360 d, whereas seed germination occurred after 450 d. Gibberellic acid and zeatin riboside contents were relatively stable, whereas abscisic acid (ABA) content decreased; indole acetic acid (IAA) content and the IAA/ABA ratio showed increasing trends. These results indicate that ABA is the key inhibitor of germination in Taxus. The chemical(s) in seed coat and kernel cause the inhibition of seed germination. Taken together, Taxus seeds have morphophysiological dormancy, in which the embryos can continue to grow and hormone imbalance inhibits further development and germination. Further, seed dormancy is active even during the middle of storage and shows “double peaks” during the entire dormancy process.
Highlights
Seed dormancy and germination are distinct physiological processes, and the transition from dormancy to germination is a critical developmental step in the life cycle of plants but is important for agricultural production[1]
The seed coat plays a critical role in the control of dormancy in many species[6] and has been shown to regulate permeability to water, oxygen, or germination inhibitors that leach from the seed[7,8,9]
Seeds of most Taxus species are protected in many areas and many studies have been conducted on their cytobiology[27], seed dispersal[28], and spatial patterns[29], little is known regarding the dynamic characteristics of seed dormancy and germination in T. yunnanensis
Summary
Seed dormancy and germination are distinct physiological processes, and the transition from dormancy to germination is a critical developmental step in the life cycle of plants but is important for agricultural production[1]. Phytohormones play key roles as signaling molecules for communication between the three seed compartments (embryo, endosperm and seed coat) to coordinate appropriate seed formation[10] They can act as important signals influencing seed development processes such as maturation, dormancy, and germination[11]. Plant endogenous hormones have important physiological effects on the process of seed formation, and the major ones are indole acetic acid (IAA), gibberellic acid (GA), zeatin riboside (ZR), and abscisic acid (ABA)[12] These endogenous hormones play a critical role in plant growth, cell division, and elongation. Taxus seeds are usually placed on a sand bed blended with wet sand for storage over one year to germinate[19,20] During this release of dormancy, the window of environmental conditions at which the seed can germinate is slowly opening[16]. A better understanding of its reproductive physiology might provide valuable information concerning the propagation of these hard-to-germinate species and facilitate complementary seed dispersal, enhancing population regeneration and expansion
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