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Wait, rest, pause : dormancy in nature
\"Plenty of plants and animals tough out the harshest conditions by becoming dormant. Explore the science behidn the many different ways plants and animals wait, rest, and pause.\"--Dust jacket.
Book
The great diversity in kinds of seed dormancy: a revision of the Nikolaeva–Baskin classification system for primary seed dormancy
This review provides a revised and expanded word-formula system of whole-seed primary dormancy classification that integrates the scheme of Nikolaeva with that of Baskin and Baskin. Notable changes include the following. (1) The number of named tiers (layers) in the classification hierarchy is increased from three to seven. (2) Formulae are provided for the known kinds of dormancy. (3) Seven subclasses of class morphological dormancy are designated: ‘dust seeds’ of mycoheterotrophs, holoparasites and autotrophs; diaspores of palms; and seeds with cryptogeal germination are new to the system. (4) Level non-deep physiological dormancy (PD) has been divided into two sublevels, each containing three types, and Type 6 is new to the system. (5) Subclass epicotyl PD with two levels, each with three types, has been added to class PD. (6) Level deep (regular) PD is divided into two types. (7) The simple and complex levels of class morphophysiological dormancy (MPD) have been expanded to 12 subclasses, 24 levels and 16 types. (8) Level non-deep simple epicotyl MPD with four types is added to the system. (9) Level deep simple regular epicotyl MPD is divided into four types. (10) Level deep simple double MPD is divided into two types. (11) Seeds with a water-impermeable seed coat in which the embryo-haustorium grows after germination (Canna) has been added to the class combinational dormancy. The hierarchical division of primary seed dormancy into many distinct categories highlights its great diversity and complexity at the whole-seed level, which can be expressed most accurately by dormancy formulae.
Journal Article
evolution of seed dormancy: environmental cues, evolutionary hubs, and diversification of the seed plants
Seed dormancy, by controlling the timing of germination, can strongly affect plant survival. The kind of seed dormancy, therefore, can influence both population and species‐level processes such as colonization, adaptation, speciation, and extinction. We used a dataset comprising over 14 000 taxa in 318 families across the seed plants to test hypotheses on the evolution of different kinds of seed dormancy and their association with lineage diversification. We found morphophysiological dormancy to be the most likely ancestral state of seed plants, suggesting that physiologically regulated dormancy in response to environmental cues was present at the origin of seed plants. Additionally, we found that physiological dormancy (PD), once disassociated from morphological dormancy, acted as an ‘evolutionary hub’ from which other dormancy classes evolved, and that it was associated with higher rates of lineage diversification via higher speciation rates. The environmental sensitivity provided by dormancy in general, and by PD in particular, appears to be a key trait in the diversification of seed plants.
Journal Article
Seed dormancy cycling and the regulation of dormancy mechanisms to time germination in variable field environments
Many molecular mechanisms that regulate dormancy have been identified individually in controlled laboratory studies. However, little is known about how the seed employs this complex suite of mechanisms during dormancy cycling in the variable environment of the soil seed bank. Nevertheless, this behaviour is essential to ensure germination takes place in a favourable habitat and climate space, and in the correct season for the resulting plant to complete its life cycle. During their time in the soil seed bank, seeds continually adjust their dormancy status by sensing a range of environmental signals. Those related to slow seasonal change (e.g. temperature) are used for temporal sensing to determine the time of year and depth of dormancy. This alters their sensitivity to signals related to their spatial environment (e.g. light, nitrate, and water potential) that indicate that conditions are suitable for germination, and so trigger the termination of dormancy. We review work on the physiological, molecular, and ecological aspects of seed dormancy in Arabidopsis and interpret it in the context of dormancy cycling in the soil seed bank. This approach has provided new insight into the co-ordination of mechanisms and signalling networks, and the multidimensional sensing that regulates dormancy cycling in a variable environment.
Journal Article
Trait analysis reveals DOG1 determines initial depth of seed dormancy, but not changes during dormancy cycling that result in seedling emergence timing
• Seedling emergence timing is crucial in competitive plant communities and so contributes to species fitness. To understand the mechanistic basis of variation in seedling emergence timing, we exploited the contrasting behaviour of two Arabidopsis thaliana ecotypes: Cape Verde Islands (Cvi) and Burren (Bur-0).
• We used RNA-Seq analysis of RNA from exhumed seeds and quantitative trait loci (QTL) analyses on a mapping population from crossing the Cvi and Bur-0 ecotypes.
• We determined genome-wide expression patterns over an annual dormancy cycle in both ecotypes, identifying nine major clusters based on the seasonal timing of gene expression, and variation in behaviour between them. QTL were identified for depth of seed dormancy and seedling emergence timing (SET).
• Both analyses showed a key role for DOG1 in determining depth of dormancy, but did not support a direct role for DOG1 in generating altered seasonal patterns of seedling emergence. The principle QTL determining SET (SET1: dormancy cycling) is physically close on chromosome 5, but is distinct from DOG1. We show that SET1 and two other SET QTLs each contain a candidate gene (AHG1, ANAC060, PDF1 respectively) closely associated with DOG1 and abscisic acid signalling and suggest a model for the control of SET in the field.
Journal Article
A review of the seed biology of Paeonia species (Paeoniaceae), with particular reference to dormancy and germination
The genus Paeonia (Paeoniaceae) includes many popular ornamentals, has colorful flowers and contains several Chinese medicinal species. The germination protocol for seeds of Paeonia species is complex and impedes the breeding of new cultivars and contributes to the rarity and high cost of the plants. Although numerous reports on seed dormancy/germination in peonies are scattered throughout the literature, most of them are in Chinese. The primary aims of this paper are to provide a general overview of the available information on seed dormancy/germination in peonies and to make some suggestions regarding propagation for the peony industry and breeders. Most Paeonia species have epicotyl dormancy. The embryo is differentiated into organs, but it is underdeveloped (small) and must grow inside the seed before the radicle can emerge. Germination of peony seeds requires warm stratification for embryo growth and radicle protrusion followed by cold stratification for epicotyl growth. In addition, the epicotyl is sensitive to cold stratification only after the root has grown to a certain length. GA₃ treatment enhances embryo growth and subsequent germination percentages. Further investigations on the physiology, genetics and proteomics would contribute to a better understanding of seed dormancy in Paeonia.
Journal Article
Auxin controls seed dormancy through stimulation of abscisic acid signaling by inducing ARF-mediated ABI3 activation in Arabidopsis
The transition from dormancy to germination in seeds is a key physiological process during the lifecycle of plants. Abscisic acid (ABA) is the sole plant hormone known to maintain seed dormancy; it acts through a gene expression network involving the transcription factor ABSCISIC ACID INSENSITIVE 3 (ABI3). However, whether other phytohormone pathways function in the maintenance of seed dormancy in response to environmental and internal signals remains an important question. Here, we show that the plant growth hormone auxin, which acts as a versatile trigger in many developmental processes, also plays a critical role in seed dormancy in Arabidopsis . We show that disruptions in auxin signaling in MIR160- overexpressing plants, auxin receptor mutants, or auxin biosynthesis mutants dramatically release seed dormancy, whereas increases in auxin signaling or biosynthesis greatly enhance seed dormancy. Auxin action in seed dormancy requires the ABA signaling pathway (and vice versa), indicating that the roles of auxin and ABA in seed dormancy are interdependent. Furthermore, we show that auxin acts upstream of the major regulator of seed dormancy, ABI3, by recruiting the auxin response factors AUXIN RESPONSE FACTOR 10 and AUXIN RESPONSE FACTOR 16 to control the expression of ABI3 during seed germination. Our study, thus, uncovers a previously unrecognized regulatory factor of seed dormancy and a coordinating network of auxin and ABA signaling in this important process.
Journal Article
The Time Required for Dormancy Release in Arabidopsis Is Determined by DELAY OF GERMINATION1 Protein Levels in Freshly Harvested Seeds
Seed dormancy controls the start of a plant's life cycle by preventing germination of a viable seed in an unfavorable season. Freshly harvested seeds usually show a high level of dormancy, which is gradually released during dry storage (after-ripening). Abscisic acid (ABA) has been identified as an essential factor for the induction of dormancy, whereas gibberellins (GAs) are required for germination. The molecular mechanisms controlling seed dormancy are not well understood. DELAY OF GERMINATION1 (DOG1) was recently identified as a major regulator of dormancy in Arabidopsis thaliana. Here, we show that the DOG1 protein accumulates during seed maturation and remains stable throughout seed storage and imbibition. The levels of DOG1 protein in freshly harvested seeds highly correlate with dormancy. The DOG1 protein becomes modified during after-ripening, and its levels in stored seeds do not correlate with germination potential. Although ABA levels in dog1 mutants are reduced and GA levels enhanced, we show that DOG1 does not regulate dormancy primarily via changes in hormone levels. We propose that DOG1 protein abundance in freshly harvested seeds acts as a timer for seed dormancy release, which functions largely independent from ABA.
Journal Article
miR169 and PmRGL2 synergistically regulate the NF-Y complex to activate dormancy release in Japanese apricot (Prunus mume Sieb. et Zucc.)
Key message
This study is the first to demonstrate that GA
4
-induced dormancy release is associated with the NF-Y complex, which interacts with gibberellin inhibitor RGL2 in Japanese apricot.
Seasonal dormancy is not only vital for the survival in cold winter but also affects flowering of temperate fruit trees and the dormancy release depends on the accumulation of the cold temperatures (Chilling requirement-CR). To understand the mechanism of dormancy release in deciduous fruit crops, we compared miRNA sequencing data during the transition stage from paradormancy to dormancy release in the Japanese apricot and found that the miR169 family showed significant differentially up-regulated expression during dormancy induction and was down-regulated during the dormancy release periods. The 5′ RACE assay and RT-qPCR validated its target gene
NUCLEAR FACTOR-Y subunit A
(
NF-YA
), which exhibited the opposite expression pattern. Further study showed that exogenous GA
4
could inhibit the expression of the gibberellic acid (GA) signal transduction suppressor
PmRGL2
(
RGA-LIKE 2
) and promote the expression of
NF-Y
. Moreover, the interaction between the NF-Y family and GA inhibitor
PmRGL2
was verified by the yeast-two-hybrid (Y2H) system and a bimolecular fluorescence complementarity (BiFC) experiment. These results suggest that synergistic regulation of the NF-Y and PmRGL2 complex leads to the activation of dormancy release induced by GA
4
. These findings will help to elucidate the functional and regulatory roles of miR169 and NF-Y complex in seasonal bud dormancy induced by GA in Japanese apricot and provide new insights for the discovery of dormancy release mechanisms in woody plants.
Journal Article