Nitric oxide and HCN reduce deep dormancy of apple seeds

Nitric oxide (NO) and cyanide (HCN) are small gaseous molecules that have been intensively studied to explain their role in plant development, metabolism and reaction to stresses. Cyanide and NO are known to be produced endogenously during early phase of seed germination or are present in the environment. Both molecules regulate breakage of seed dormancy and accelerate seed germination. Regulatory role of cyanide in breaking of dormancy seems to be understood to some extend, while the NO mode of action is much less explained. However, some similarities could be suggested. The mechanisms involved in HCN-dependent dormancy breakage in apple embryos are summarized in relation to NO-donor mediated stimulation of germination.     

快速打破结缕草种子休眠方法的比较

用水和30%NaOH对结缕草(Zoysia japonica Steud.)种子进行浸种处理,筛选能快速打破结缕草种子休眠的方法.结果表明:用水浸种6d,8d内发芽率仅为14.70%;用30%NaOH浸种120min,8d内发芽率也仅达28.00%;而用水浸泡2d后再用30%NaOH处理40min,8d内结缕草种子的发芽率达到了82.00%.说明用水和30%NaOH综合处理的方法可以快速有效打破结缕草种子休眠,缩短发芽周期,达到快速出苗的目的.     

结缕草(Zoysia japonica Steud.)种子打破休眠方法的比较

结缕草 (ＺｏｙｓｉａｊａｐｏｎｉｃａＳｔｅｕｄ .)为禾本科多年生草本植物 ,广泛分布于我国东部沿海地区 ,集中分布在我国的辽宁和山东境内 ,在胶东和辽东半岛有大面积的野生种群 ,是我国结缕草种子的主要产地。结缕草具有极其发达的根茎和匍匐茎 ,是适于放牧的优良牧草 ,也是抗逆性强、低矮密集型的优质草坪植物。然而 ,结缕草种子具有深休眠特性 ,在自然条件下发芽率低、发芽速度慢 ,从而给它的开发和利用带来了阻碍。近年来国内外已有一些学者对其深休眠的原因进行了研究。韩建国等认为该种子休眠为综合型休眠 ,颖苞对水分和空气的进…     

Fire‐related cues break seed dormancy of six legumes of tropical eucalypt savannas in north‐eastern Australia

Abstract This paper describes an assessment of the effect of exposure to fire‐related cues (heat shock, smoke and nitrate) and the interactions between the cues on seed dormancy release of tropical savanna legumes in north‐eastern Australia. Ten legume species were tested, comprising both native and exotic species. The ten species responded variously to the treatments. Brief exposure to temperatures between 80 and 100°C was found to break the seed dormancy of the native ephemeral herbs Chamaecrista mimosoides, Crotalaria calycina, Crotalaria montana, Indigofera hirsuta and Tephrosia juncea, as well as the exotic ephemeral herb Crotalaria lanceolata. Exposure to 80°C combined with treatment with a nitrate solution produced an additive effect on the germination of Chamaecrista mimosoides and Crotalaria lanceolata. However, the four species with the heaviest seeds, two exotic ephemeral herbs (Chamaecrista absus and Crotalaria pallida) and two native perennials (Galactia tenuiflora and Glycine tomentella) displayed no significant increase in germination with exposure to fire‐related cues. Exposure to 120°C for 5 min produced seed mortality in all species tested. Two of the largest seeded species, Crotalaria pallida and Galactia tenuiflora, displayed the lowest tolerance to heat shock, with seed mortality after exposure to 100°C for 5 min. These data indicate that fire can promote the germination of some tropical savanna legumes. As a proportion of seeds of each species displayed no innate dormancy, some germination may occur in the absence of fire, especially of exotic species.     

Physiological dormancy in seeds of tropical montane woody species in Hawai`i

Worldwide, there is relatively little information on seed dormancy and germination of tropical montane species. Our aim was to help fill this knowledge gap by conducting seed dormancy/germination studies on woody species from this vegetation zone in Hawai`i. All species had water-permeable seeds with a fully developed embryo. Seeds of 29 species (23 genera) were incubated in light/dark at 15/6, 20/10 and 25/15°C and germination monitored at 2-week intervals for 16–128 weeks. Seeds of Chenopodium oahuense, Dubautia menziesii and Silene lanceolata were non-dormant (ND) and those of 26 other species had physiological dormancy (PD); 10 of the 26 species had conditional PD. The optimum germination temperature regime(s) was (were) 25/15°C, 17 species; 25/10 and 20/10°C, 2; 20/10°C, 6; 20/10 and 15/6°C, 2; and 15/6°C, 2. Worldwide, PD in the woody genera included in our study is more common than ND. In addition to its contribution to the world biogeography of seed dormancy/germination, this study will be useful to conservation biologists who need to germinate seeds of tropical montane species.     

Embryo growth and dormancy in seeds of six Hosta species native to Korea

Although it has been speculated that Hosta seeds have an underdeveloped embryo and morphological (MD) or morphophysiological dormancy (MPD), no detailed studies have been carried out to definitively confirm this suggestion. Our first purpose was to determine if embryos of six Korean species of Hosta (H. capitata, H. clausa, H. jonesii, H. minor, H. venusta and H. yingeri) grew inside the seeds prior to germination (i.e., were underdeveloped) or did not do so (i.e., were fully developed). Our second purpose was to identify the class of dormancy found in these seeds by examining germination during incubation at 15 and/or 25°C. The initial embryo : seed ratio in seeds of the six Hosta species was between 0.78 and 0.85, and embryos elongated by 9.6 to 17.5% prior to germination. Seeds of H. capitata, H. clausa, H. venusta and H. yingeri germinated to ≥65% in light and darkness at 15 and 25°C within 30 days, those of H. minor germinated to ≥80% in light and darkness at 25°C and to 24% in light and 50% in darkness at 15°C, and those of H. jonesii germinated to 100% in light at 25°C. We conclude that embryos in seeds of these six Hosta species are underdeveloped at maturity. Because high percentages of H. capitata, H. clausa, H. venusta and H. yingeri seeds germinated at cold and warm temperatures within 30 days, they have MD. On the other hand, seeds of H. minor germinated to high and low percentages at warm and cold temperatures, respectively. Thus, some seeds have MD and others may have MPD.     

Evidence for physiological seed dormancy cycling in the woody shrub Asterolasia buxifolia and its ecological significance in fire‐prone systems

• Dormancy cycling is a key mechanism that contributes to the maintenance of long‐term persistent soil seed banks, but has not been recorded in long‐lived woody shrub species from fire‐prone environments. Such species rely on seed banks and dormancy break as important processes for post‐fire recruitment and recovery.
• We used germination experiments with smoke treatments on fresh seeds and those buried for 1 year (retrieved in spring) and 1.5 years (retrieved the following late autumn) to investigate whether Asterolasia buxifolia, a shrub from fire‐prone south‐eastern Australia with physiologically dormant seeds, exhibited dormancy cycling.
• All seeds had an obligation for winter seasonal temperatures and smoke to promote germination, even after ageing in the soil. A high proportion of germination was recorded from fresh seeds. but germination after the first retrieval was significantly lower, despite high seed viability. After the second retrieval, germination returned to the initial level. This indicates a pattern of annual dormancy cycling; one of the few observations, to our knowledge, for a perennial species. Additionally, A. buxifolia’s winter temperature and smoke requirements did not change over time, highlighting the potential for seeds to remain conditionally dormant (i.e. restricted to a narrow range of germination conditions) for long periods.
• For physiologically dormant species, such as A. buxifolia, we conclude that dormancy cycling is an important driver of successful regeneration, allowing seed bank persistence, sometimes for decades, during fire‐free periods unsuitable for successful recruitment, while ensuring that a large proportion of seeds are available for recruitment when a fire occurs.

     

Morphophysiological dormancy in seeds of the ANA grade angiosperm Schisandra arisanensis (Schisandraceae)

We determined the kind of seed dormancy in Schisandra arisanensis, an ANA grade ([A]mborellales [N]ymphaeales [A]ustrobaileyales) angiosperm with medicinal value. Seeds have small underdeveloped embryos, and following seed maturity their length increased approximately 360% before radicle emergence. Germination was delayed 6–8 weeks, and the percentage and rate were much higher at 15/6, 20/10 and 25/15°C than at 30/20°C. For seeds incubated at 5/5°C (8 weeks) → 15/6°C (4 weeks) → 20/10°C (8 weeks) → 25/15°C (12 weeks) → 20/10°C (5 weeks), embryos grew at 15/6°C → 20/10°C, and almost all seeds that germinated (89%) did so at 20/10°C → 25/15°C. When seeds were incubated in a complementary temperature sequence, 25/15°C (12 weeks) → 20/10°C (8 weeks) → 15/6°C (4 weeks) → 5/5°C (9 weeks) → 15/6°C (4 weeks), embryos grew at 25/15°C → 20/10°C. Nearly all seeds that germinated (93%) did so at 25/15°C → 20/10°C and at 15/6°C following 9 weeks at 5/5°C. Based on the temperature requirements for embryo growth and seed germination, seeds of this species have non‐deep simple morphophysiological dormancy (C_1bB).     

Factors affecting the induction and release of secondary dormancy in Kalanchoë seeds

Abstract. Several short daily R irradiations are required from the first day of incubation on water to induce germination of Kalanchoë seeds. When the same light treatment is given after a prolonged dark incubation period at 20°C, secondary dormancy prevents germination. Factors controlling the induction and breaking of secondary dormancy have been investigated. The induction of secondary dormancy is very temperature dependent. Locally puncturing the seed coat strongly delays it. Secondary dormancy is not induced in the presence of GA₃ during the first 10 d of dark incubation, although this growth substance cannot induce dark germination. Prolonged or cyclic daily R irradiations can relieve secondary dormancy of seeds kept on water, even after a dark period of 20 d. A 24 h treatment at 4°C restores responsiveness to short R exposures of slightly secondarily dormant seeds. The synergism between GA₃ and Pfr in non-dormant Kalanchoë seeds, leading to high effectiveness of even one short FR irradiation, still occurs in seeds made secondarily dormant before transfer to GA₃, but more R or FR irradiations, in combination with GA₃, are required for the release of secondary dormancy. A combination of red light and 6-benzyl-aminopurine is ineffective in removing dormancy.     

The physiological basis of seed dormancy in Avena fatua. IX. Characterization of two dormancy states

The dormancy-breaking effect of several known germination promoters was studied in 9 genetically pure lines of Avena fatua L. during a period of controlled after-ripening. Changes in the germination response show at least two dormancy states in the caryopses of these lines. The first state is overcome by a short period of after-ripening and is insensitive to nitrate and azide, while the second state is more persistent and is sensitive to nitrate and azide. Both states are sensitive to gibberellic acid (OA,) and ethanol. In the most dormant lines a third ethanol-insensitive dormancy state is present. The duration of both major dormancy states was related to several environmental factors influencing plant growth and seed storage. Duration was increased in caryopses produced from plants matured under low temperatures (15°C) and decreased in caryopses produced from plants matured under high temperatures (25°C). Duration was increased in caryopses after-ripened under low temperatures (4°C) and decreased in caryopses after-ripened under high temperatures (45°C). Dehulling the seeds prior to after-ripening reduced the duration of both major dormancy states. The multiple state dormancy system and its environmentally induced plasticity are discussed with reference to previous explanations of the dormancy mechanism in wild oats.     

Radicle emergence with increased temperatures following summer dispersal in Trillium camschatcense: A species with deep simple double morphophysiological dormancy in seeds

Seeds with deep simple double morphophysiological dormancy (MPD) need cold stratification during the first winter after dispersal for radicle emergence, followed by the summer for root and bud development and finally a second winter for shoot emergence. In a previous study, we demonstrated that Trillium camschatcense seeds have this type of dormancy with radicles emerging from most seeds after the first winter. However, radicles also emerged from a few seeds in autumn during the same year as dispersal. We thought that temperatures after seed dispersal played a role in radicle emergence before the first winter. To confirm our idea, we investigated germination phenology outdoors, relationships between temperatures after seed dispersal and radicle emergence in the first year outdoors, radicle emergence in the first winter under varied temperatures using incubators, and shoot emergence from seeds with an emerged radicle in the first year outdoors. Our phenology study confirmed that T. camschatcense seeds have deep simple double MPD. Over 7 years, 0.2–7.5% of radicles emerged in the first year before winter and these percentages were moderately positively correlated with temperatures, especially minimum temperatures. Increasing August and September temperatures increased radicle emergence in the laboratory. Shoots emerged from seeds with an emerged radicle in the first year after the first winter. With increased autumn temperatures in warmer regions or with global warming, we predict that germination phenology may shift: increased radicle emergence in the first year and shoot emergence following the first (and not second) winter.     

Temperature mediates secondary dormancy in resting cysts of Pyrodinium bahamense (Dinophyceae)

High‐biomass blooms of the toxic dinoflagellate Pyrodinium bahamense occur most summers in Tampa Bay, Florida, USA, posing a recurring threat to ecosystem health. Like many dinoflagellates, P. bahamense forms immobile resting cysts that can be deposited on the seafloor—creating a seed bank that can retain the organism within the ecosystem and initiate future blooms when cysts germinate. In this study, we examined changes in the dormancy status of cysts collected from Tampa Bay and applied lessons from plant ecology to explore dormancy controls. Pyrodinium bahamense cysts incubated immediately after field collection displayed a seasonal pattern in dormancy and germination that matched the pattern of cell abundance in the water column. Newly deposited (surface) cysts and older (buried) cysts exhibited similar germination patterns, suggesting that a common mechanism regulates dormancy expression in new and mature cysts. Extended cool‐ and warm‐temperature conditioning of field‐collected cysts altered the cycle of dormancy compared with that of cysts in nature, with the duration of cool temperature exposure being the best predictor of when cysts emerged from dormancy. Extended warm conditioning, on the other hand, elicited a return to dormancy, or secondary dormancy, in nondormant cysts. These results directly demonstrate environmental induction of secondary dormancy in dinoflagellates—a mechanism common and thoroughly documented in higher plants with seasonal growth cycles. Our findings support the hypothesis that a seasonal cycle in cyst germination drives P. bahamense bloom periodicity in Tampa Bay and point to environmentally induced secondary dormancy as an important regulatory factor of that cycle.     

Characterization of alternating-temperature regimes that remove seed dormancy in seeds of Brachiaria humidicola (Rendle) Schweickerdt

Abstract Seeds of Brachiaria humidicola were subjected, on a thermogradienl plate, to a wide range of alternating-temperature cycles (24 h) and constant temperatures with intermittent exposure to diffuse laboratory light, in the presence and absence of 10 mol m^?3 KNO_V The optimum regime for maximum percentage germination was alternating temperatures of 35°C for 4hd^?1 and 13°C for 20 hd^?1. Almost no germination occurred at any constant temperature. Thermoperiods in which the warmer temperature was applied for the longer part of the 24 h cycle were much less stimulatory; in the presence of KNO₃, however, the germination under such regimes was much improved, although there was little effect on seeds experiencing near-optimum alternating-temperature regimes. This investigation is the first step in identifying which of 10 attributes of alternating temperatures are stimulatory, in order to predict the efficacy of different temperature regimes and to identify the stimulatory characteristics that must ultimately be explained by cellular physiology. The work shows that amplitude, thermoperiod and mean temperature must all be incorporated in a quantitative model.     

Effects of the Neotyphodium endophyte fungus on dormancy and germination rate of Lolium multiflorum seeds

Abstract Neotyphodium frequently occurs as an endophyte in grasses. Evidence shows enhanced fitness of endophyte infected grasses relative to non‐infected ones. Some studies of seed germination show endophyte enhancement of plant fitness in various environments, but inconsistent results indicate that further studies are needed. So far, experiments have failed to separate the confounded effects of population origin and seed management. For this reason, we evaluated the effects of endophyte infection on seed dormancy and germination in Lolium multiflorum using an experimental design controlling these factors. Depending on the year of seed production, endophyte infection modified seed response to light quality, affecting predominantly seed dormancy levels. Nevertheless, the endophyte did not affect base temperature or thermal time of germination. We concluded that endophytes were not a strong influence on germination behaviour. We speculate from our results that the presence of the endophyte changes germination by an indirect effect, in extending growth of the maternal plant during seed development and ripening. The direct effect of hyphae in the seed on seed behaviour was disregarded, because the difference between infected and non‐infected seed varied within the year of seed production. Future experiments should focus on effects of the endophyte on the canopy of parent plants during seed production and ripening, and, hence, on subsequent dormancy and germination of the seeds.     

Molecular mechanisms underlying the entrance in secondary dormancy of Arabidopsis seeds

As seasons change, dormant seeds cycle through dormant states until the environmental conditions are favourable for seedling establishment. Dormancy cycle is widespread in the plant kingdom allowing the seeds to display primary and secondary dormancy. Several reports in the last decade have focused on understanding the molecular mechanisms of primary dormancy, but our knowledge regarding secondary dormancy is limited. Here, we studied secondary dormancy induced in Arabidopsis thaliana by incubating seeds at 25 °C in darkness for 4 d. By physiological, pharmacological, expression and genetics approaches, we demonstrate that (1) the entrance in secondary dormancy involves changes in the content and sensitivity to GA, but the content and sensitivity to ABA do not change, albeit ABA is required; (2) RGL2 promotes the entrance in secondary dormancy through ABI5 action; and (3) multivariate analysis with 18 geographical and environmental parameters of accession collection place suggests that temperature is an important variable influencing the induction of secondary dormancy in nature.     

Seed dormancy and germination in three Crocus ser. Verni species (Iridaceae): implications for evolution of dormancy within the genus

The aim of this work was to examine whether seed ecophysiological traits in three closely related Crocus species were associated with ecological niche differentiation and species divergence. Seeds of the temperate tetraploid cytotype of Crocus neapolitanus, the sub‐Mediterranean C. etruscus and the Mediterranean C. ilvensis were placed either on agar in the laboratory under different periods of simulated seasonal conditions or in nylon mesh bags buried outdoors to examine embryo growth, radicle and shoot emergence. In agreement with the phenology observed outdoors, in the laboratory embryos required a cool temperature (ca. 10 °C) to grow to full size (embryo length:seed length, E:S ratio ca. 0.75) but only after seeds received a warm stratification; radicle emergence then followed immediately (November). Shoot emergence is a temporally separated phase (March) that was promoted by cold stratification in C. neapolitanus while in the other two species this time lag was attributed to a slow continuous developmental process. These species have similar embryo growth and radicle phenology but differ in their degree of epicotyl dormancy, which is related to the length of local winter. Conclusions from laboratory experiments that only consider root emergence could be misleading; evaluating the phenology of both root and shoot emergence should be considered in order to demonstrate ecologically meaningful differences in germination behaviour and to develop effective propagation protocols. Although these taxa resulted from recent speciation processes, the outcomes suggest an early onset of adaptation to local ecological factors and that phylogeny may represent a significant constraint in the evolution and expression of seed traits in Crocus.     

A combined physical and physiological dormancy controls seasonal seedling emergence of Geranium robertianum

Temperate forest herbs with seeds exhibiting both a physical and a physiological dormancy mechanism are rare, and knowledge on the factors regulating germination of these species is fragmentary. The biennial Geranium robertianum L. grows mainly in temperate woodlands, but can also be found in exposed habitats. Seedlings of G. robertianum are known to emerge from spring until autumn, but little is known about the environmental factors regulating germination. In this study, phenology of seedling emergence and of physical dormancy loss was examined for seeds buried at shaded or sunny exposed locations. The role of temperature in regulating dormancy and germination was analysed by incubating seeds in temperature sequences simulating temperatures that seeds experience in nature. The results indicate that most seeds of G. robertianum buried in sunny conditions germinate immediately after physical dormancy loss in summer. Seeds buried in shaded conditions also lose physical dormancy mainly during summer, but remain physiologically dormant and do not germinate until late winter or early spring. Besides physical dormancy, seeds of G. robertianum also initially have a high level of physiological dormancy, which is reduced during dry storage. Physiological dormancy is reduced through chilling in winter, thus enabling the seeds to germinate at low temperatures. We conclude that a complex combination of physical and physiological dormancy ensures that G. robertianum seeds germinate in summer at exposed sites and in early spring at shaded sites.     

Physiological dormancy in seeds of two endemic species of Begonia from Yunnan Province,China: diagnosis and classification

With the purpose of assessing the status of dormancy in seeds of two Begonia species (Begonia lithophila and Begonia guishanensis), freshly matured seeds were given gibberellic acid and moist chilling and allowed to dry after ripening. The seeds were then germinated on media with or without KNO₃ at 15, 20, 25, 30 and 18/25°C. All three treatments significantly increased germination percentages. Examination by X‐ray revealed that seeds of both species have a fully developed embryo and thus have no morphological component of dormancy; seeds readily imbibed water and KNO₃ solution. Therefore, we conclude that seeds of the two Begonia species have non‐deep physiological dormancy. Although KNO₃ significantly increased germination in both species, alternating temperatures did not, suggesting that the most favorable microhabitat for germination is small‐scale disturbances under the forest canopy.