Dormancy and germination: How does the crop seed decide?

Whether seeds germinate or maintain dormancy is decided upon through very intricate physiological processes. Correct timing of these processes is most important for the plants life cycle. If moist conditions are encountered, a low dormancy level causes pre‐harvest sprouting in various crop species, such as wheat, corn and rice, this decreases crop yield and negatively impacts downstream industrial processing. In contrast, a deep level of seed dormancy prevents normal germination even under favourable conditions, resulting in a low emergence rate during agricultural production. Therefore, an optimal seed dormancy level is valuable for modern mechanised agricultural systems. Over the past several years, numerous studies have demonstrated that diverse endogenous and environmental factors regulate the balance between dormancy and germination, such as light, temperature, water status and bacteria in soil, and phytohormones such as ABA (abscisic acid) and GA (gibberellic acid). In this updated review, we highlight recent advances regarding the molecular mechanisms underlying regulation of seed dormancy and germination processes, including the external environmental and internal hormonal cues, and primarily focusing on the staple crop species. Furthermore, future challenges and research directions for developing a full understanding of crop seed dormancy and germination are also discussed.     

Engineered <Emphasis Type="Italic">In Vitro</Emphasis> Models of Tumor Dormancy and Reactivation

Metastatic recurrence is a major hurdle to overcome for successful control of cancer-associated death. Residual tumor cells in the primary site, or disseminated tumor cells in secondary sites, can lie in a dormant state for long time periods, years to decades, before being reactivated into a proliferative growth state. The microenvironmental signals and biological mechanisms that mediate the fate of disseminated cancer cells with respect to cell death, single cell dormancy, tumor mass dormancy and metastatic growth, as well as the factors that induce reactivation, are discussed in this review. Emphasis is placed on engineered, in vitro, biomaterial-based approaches to model tumor dormancy and subsequent reactivation, with a focus on the roles of extracellular matrix, secondary cell types, biochemical signaling and drug treatment. A brief perspective of molecular targets and treatment approaches for dormant tumors is also presented. Advances in tissue-engineered platforms to induce, model, and monitor tumor dormancy and reactivation may provide much needed insight into the regulation of these processes and serve as drug discovery and testing platforms.     

光信号与激素调控种子休眠和萌发研究进展

休眠是种子植物在长期进化过程中产生的适应性性状, 通过抑制种子在不适宜的环境中萌发进而保证植物能够在逆境中生存。此外, 休眠有助于种子的长距离运输和扩散, 因此休眠对种子延续和物种保存具有重要意义。种子由休眠向萌发的发育转变不仅关系到物种的繁衍, 而且对保证农业生产中作物的产量和品质也具有重要作用。种子的休眠和萌发受到内源激素和外源光信号的共同调控。其中, 外源光信号主要通过调控内源ABA和GA的生物合成及信号转导进而调控种子休眠和萌发。该文系统综述了外源光信号和内源激素调控种子休眠和萌发的作用通路以及两类信号通路之间的交互作用, 旨在为农业生产中利用光和激素调控种子休眠与萌发提供参考。     

光信号与激素调控种子休眠和萌发研究进展

休眠是种子植物在长期进化过程中产生的适应性性状, 通过抑制种子在不适宜的环境中萌发进而保证植物能够在逆境中生存。此外, 休眠有助于种子的长距离运输和扩散, 因此休眠对种子延续和物种保存具有重要意义。种子由休眠向萌发的发育转变不仅关系到物种的繁衍, 而且对保证农业生产中作物的产量和品质也具有重要作用。种子的休眠和萌发受到内源激素和外源光信号的共同调控。其中, 外源光信号主要通过调控内源ABA和GA的生物合成及信号转导进而调控种子休眠和萌发。该文系统综述了外源光信号和内源激素调控种子休眠和萌发的作用通路以及两类信号通路之间的交互作用, 旨在为农业生产中利用光和激素调控种子休眠与萌发提供参考。     

Regulation of potato tuber dormancy and sprouting

Dormancy is the final stage of tuber life serving to preserve tubers as organs of vegetative reproduction under unfavorable growth conditions. Since the duration of potato tuber dormancy and their sprouting time have significant economic importance, much attention is given to the study of the regulation of these processes. This review considers metabolite, genetic, and hormonal aspects of regulation of potato (Solanum tuberosum L.) tuber dormancy and sprouting. Particular attention is paid to the relationship between processes occurring in different parts of the tuber: its storage tissues and buds. The interaction of hormonal and metabolite (carbohydrate) regulation of dormancy and sprouting is discussed.     

脱落酸调控种子休眠和萌发的分子机制

脱落酸(ABA)是调控种子休眠和萌发过程的主要植物激素。种子内源ABA含量和种胚对ABA敏感性共同调控种子休眠和萌发过程, 确保植物种子以休眠状态在逆境中保持其自身繁衍能力, 并在适宜的环境下启动萌发程序。种子ABA合成代谢和ABA信号转导途径涉及许多重要基因家族, 它们通过复杂的调控网络精确地控制着种胚发生、种子成熟、休眠及萌发进程。该文对ABA调控种子休眠和萌发的分子机制最新研究进展进行综述, 并展望了今后的研究方向。     

Antagonistic effects of abscisic acid and gibberellic acid on the breaking of dormancy of Fagus sylvatica seeds

Study of the factors involved in the dormancy of Fagus sylvatica seeds shows that such dormancy is due partly to the seed coats and partly to endogenous factors. Seed coat removal accelerates both the release from dormancy and the effects of the other treatments that abolish it. The dormancy of these seeds is eliminated by cold treatment at 4°C over a period longer than 8 weeks, and exogenous application of abscisic acid (ABA) reverses the effects of low temperature, the seeds remaining in an ungerminated state. Additionally, ABA reduces protein synthesis but slightly increases RNA synthesis, which suggests its involvement in the synthesis of RNAs related to this process. In vitro translation of the RNAs isolated from these seeds shows that ABA delays the disappearance of at least 2 polypeptides (of ca 22 and 24 kDa), which are abundant in dormant seeds and under conditions that prevent the release from dormancy, but which disappear under treatments that abolish it. Exogenous application of gibberellic acid (GA₃) proved to be efficient in breaking the dormancy of these seeds and in substituting for cold treatment as well as in antagonizing the effects of ABA on the synthesis of both DNA and proteins. GA₃ also accelerates the disappearance of the two polypeptides abundant in dormant seeds and in ABA-treated seeds. These findings suggest that both ABA and GA₃ could be involved in the regulation of nucleic acid and protein metabolism during dormancy, acting antagonistically in these processes and, specifically, in the regulation of the synthesis of the two proteins that appear to play a role in the maintenance of dormancy in these seeds.     

MicroRNA在种子发育、休眠与萌发过程中的作用

植物microRNA(miRNA)是一类小分子非编码RNA,对植物的生长发育发挥着重要调控作用。种子发育、休眠与萌发是植物生命进程中的重要阶段。在这一阶段内,种子受各种环境因子及内源激素调控,并且不同植物种子具有不同发育及休眠特性。随着人们对种子发育、休眠及萌发机理的探究,越来越多miRNA被鉴定,它们能够基于植物激素信号传导、抗氧化作用、关键转录因子调控等途径参与种子形态建成、物质代谢及各种胁迫响应。本文主要综述了近年来植物miRNA的形成及调控机理,以及在种子发育、休眠及萌发过程中发挥的调控作用,旨在为今后的研究方向提供参考。     

Seed dormancy and germination: the role of abscisic acid and gibberellins and the importance of hormone mutants

Over the past decades many studies have aimed at elucidating the regulation of seed dormancy and germination. Many hypotheses have been proposed and rejected but the regulatory principle behind changes in dormancy and induction of germination is still a black box. The majority of proposed mechanisms have a role for certain plant hormones in common. Abscisic acid and the gibberellins are the hormones most frequently suggested to control these processes. The development of hormone-deficient mutants made it possible to provide direct evidence for the involvement of hormones in germination and dormancy related processes.In the present paper an attempt is made to assess the role of abscisic acid and gibberellins in the transitions between dormant and non-dormant states and germination. First a conceptual framework is presented in which the different states of dormancy and germination are defined in order to contribute to a solution of the semantic confusion about these terms that has existed since the beginning of seed physiology.It is concluded that abscisic acid plays a pivotal role during the development of primary dormancy and gibberellins are involved in the induction of germination. Changes in sensitivity to these hormones occur during changes in dormancy. Both synthesis of and responsiveness to the hormones are controlled by natural environmental factors such as light, temperature and nitrate.     

DELLA-mediated cotyledon expansion breaks coat-imposed seed dormancy

Seed dormancy is a key adaptive trait in plants responsible for the soil seed bank. The long established hormone-balance theory describes the antagonistic roles of the dormancy promoting plant hormone abscisic acid (ABA), and the germination promoting hormone gibberellin (GA) in dormancy control. Light, temperature, and other dormancy-breaking signals function to modulate the synthesis and perception of these hormones in the seed. However, the way in which these hormones control dormancy in the imbibed seed remains unknown. Here, we show that the DELLA protein regulators of the GA response are required for dormancy and describe a model through which hormone signal integration and dormancy regulation is achieved. We demonstrate that cotyledon expansion precedes radicle emergence during Arabidopsis seed germination and that a striking correlation exists between final seedling cotyledon size and seed dormancy in the DELLA mutants. Furthermore, twelve previously characterized seed-dormancy mutants are also defective in the control of cotyledon size in a manner consistent with their effect on germination potential. We propose that DELLA-mediated, light-, temperature-, and hormone-responsive cotyledon expansion prior to radicle emergence overcomes dormancy imposed by the seed coat and underlies seed-dormancy control in Arabidopsis.     

THE CHEMICAL REGULATION OF THE DORMANCY PHASES OF BUD DEVELOPMENT

literature pertaining to the development and regulation of dormancy in the buds of woody species is reviewed and interpreted as follows. Morphological observations, the effects of environmental factors, and other evidence support the concept that bud dormancy involves a cycle of 3 separate phases of development. Beginning at the developmental pattern of spring, the 3 phases are: (1) dormancy development leading to the dormant state; (2) release from dormancy leading to the non-dormant state; and (3) the initiation of spring burst leading again to spring development. The regulation of dormancy is, therefore, discussed in terms of the regulation of development of the apex within each phase and the regulation of transitions between phases. The principal existing theory of dormancy regulation implies that dormancy consists, in total, of merely the inhibition of spring development, and that regulation involves first the accumulation of an inhibitor then its disappearance. The conceptual basis of this inhibitor theory is argued to be inadequate as is the experimental evidence for the existence of a specific inhibitor and for a correlation between its concentration and dormancy induction or release. There is little direct evidence on the mechanism of the regulation of bud development within any developmental phase. Circumstantial evidence suggests the developmental patterns arise from chemical patterns resulting from the interactions of classes of growth regulator such as auxin, kinin, and gibberellin. Some evidence exists concerning the regulation of the transitions between the phases of dormancy. A substance has recently been detected which may be a hormone regulating the initiation of dormancy development. The production of this substance may be photoperiodically determined. A role for gibberellins in the regulation of dormancy release has been postulated.     

Light effects on cell development and secondary metabolism in Monascus

In nature, light is one of most crucial environmental signals for developmental and physiological processes in various organisms, including filamentous fungi. We have found that both red light and blue light affect development in Monascus, influencing the processes of mycelium and spore formation, and the production of secondary metabolites such as -aminobutyric acid, red pigments, monacolin K and citrinin. Additionally, we observed that the wavelength of light affects these developmental and physiological processes in different ways. These findings suggest that Monascus possesses a system for differential light response and regulation.     

Vertebrate cell death in energy-limited conditions and how to avoid it: what we might learn from mammalian hibernators and other stress-tolerant vertebrates

Dormancy in vertebrates may expose cells to acidosis, hypoxia/anoxia, oxidative damage, and extremes in temperature. All of these insults are known to be pro-apoptotic in typical vertebrate cells, especially mammals. Since dormancy is presumably the result of a need for energy conservation, the inherent energetic demand of replenishing cells that underwent apoptosis seems at odds with this strategy. This review will discuss processes to mitigate apoptosis and how these processes might be regulated in stress-tolerant vertebrates such as mammalian hibernators. As data directly addressing such issues are scarce and often conflicting, an apparently complex regulation of apoptosis seems to be at work. For example, apoptosis is mitigated during dormancy, key signaling events including the activation of caspase-3 may still occur. However, both passive, temperature-induced depression of apoptotic signaling as well as active suppression of apoptosis appear to work in synergy in these systems. In many instances cell death is prevented by simply avoiding the cellular triggers (e.g. leakage of proteins from the mitochondria or increases in intracellular calcium) that initiate apoptotic signaling. In this review we discuss what is known about programmed cell death in these under-studied models and highlight features of their physiology that likely support survival in the face of conditions that would induce cell death in typical vertebrate cells.     

CLINAL VARIATION IN SEED TRAITS INFLUENCING LIFE CYCLE TIMING IN ARABIDOPSIS THALIANA

Early life‐history transitions are crucial determinants of lifetime survival and fecundity. Adaptive evolution in early life‐history traits involves a complex interplay between the developing plant and its current and future environments. We examined the plant's earliest life‐history traits, dissecting an integrated suite of pregermination processes: primary dormancy, thermal induction of secondary dormancy, and seasonal germination response. We examined genetic variation in the three processes, genetic correlations among the processes, and the scaling of germination phenology with the source populations’ climates. A spring annual life history was associated with genetic propensities toward both strong primary dormancy and heat‐induced secondary dormancy, alone or in combination. Lineages with similar proportions of winter and spring annual life history have both weak primary dormancy and weak thermal dormancy induction. A genetic bias to adopt a spring annual strategy, mediated by rapid loss of primary dormancy and high thermal dormancy induction, is associated with a climatic gradient characterized by increasing temperature in summer and rainfall in winter. This study highlights the importance of considering combinations of multiple genetically based traits along a climatic gradient as adaptive strategies differentiating annual plant life‐history strategies. Despite the genetic‐climatic cline, there is polymorphism for life‐history strategies within populations, classically interpreted as bet hedging in an unpredictable world.     

Cytoneme-mediated cell-to-cell signaling during development

Cell-to-cell communication is vital for animal tissues and organs to develop and function as organized units. Throughout development, intercellular communication is crucial for the generation of structural diversity, mainly by the regulation of differentiation and growth. During these processes, several signaling molecules function as messengers between cells and are transported from producing to receptor cells. Thus, a tight spatial and temporal regulation of signaling transport is likely to be critical during morphogenesis. Despite much experimental and theoretical work, the question as to how these signals move between cells remains. Cell-to-cell contact is probably the most precise spatial and temporal mechanism for the transference of signaling molecules from the producing to the receiving cells. However, most of these molecules can also function at a distance between cells that are not juxtaposed. Recent research has shown the way in which cells may achieve direct physical contact and communication through actin-based filopodia. In addition, increasing evidence is revealing the role of such filopodia in regulating spatial patterning during development; in this context, the filopodia are referred to as cytonemes. In this review, we highlight recent work concerning the roles of these filopodia in cell signaling during development. The processes that initiate and regulate the formation, orientation and dynamics of cytonemes are poorly understood but are potentially extremely important areas for our knowledge of intercellular communication.     

Label-free quantitative proteomics analysis of dormant terminal buds of poplar

Induction and break of bud dormancy are important features for perennial plants surviving extreme seasonal variations in climate. However, the molecular mechanism of the dormancy regulation, still remain poorly understood. To better understand the molecular basis of poplar bud dormancy, we used a label-free quantitative proteomics method based on nanoscale ultra performance liquid chromatography-ESI-MS^E for investigation of differential protein expression during dormancy induction, dormancy, and dormancy break in apical buds of poplar (Populus simonii × P. nigra). Among these identified over 300 proteins during poplar bud dormancy, there are 74 significantly altered proteins, most of which involved in carbohydrate metabolism (22 %), redox regulation (19 %), amino acid transport and metabolism (10 %), and stress response (8 %). Thirty-one of these proteins were up-regulated, five were down-regulated during three phase, and thirty-eight were expressed specifically under different conditions. Pathway analysis suggests that there are still the presence of various physiological activities and a particular influence on photosynthesis and energy metabolism during poplar bud dormancy. Differential expression patterns were identified for key enzymes involved in major metabolic pathways such as glycolysis and the pentose phosphate pathway, thus manifesting the interplay of intricate molecular events in energy generation for new protein synthesis in the dormant buds. Furthermore, there are significant changes present in redox regulation and defense response proteins, for instance in peroxidase and ascorbate peroxidase. Overall, this study provides a better understanding of the possible regulation mechanisms during poplar bud dormancy.