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PubMed1981

Metabolic Changes in Gladiolus Cormels During the Break of Dormancy: The Role of Dark CO(2) Fixation.

Dark CO(2) fixation in Gladiolus X gandavensis Van Houtte cormels increases during the break of dormancy by low-temperature storage or by cytokinins. The in vitro activities of phosphoenolpyruvate carboxylase and phosphoenolpyruvate carboxykinase in preparations from dormant and nondormant cormels were compared with dark fixation rates in vivo. The distribution of (14)C-label in the carboxylation products in dormant, nondormant, water-imbibed, and benzyladenine- and abscisic acid-treated cormels was compared by pulse-chase experiments. Dormant cormels have more label in malate and less in citrate and amino acids. Malate utilization in dormant cormels is slower than in nondormant ones. Citrate and glutamine accumulate in dormant cormels in inactive pools. Benzyladenine induces in dormant cormels changes similar to cold storage. Dark fixation is among the first reactions which are activated during the break of dormancy by both benzyl adenine and cold storage.

Journal Article↗
PubMed1975

Dark CO(2) Fixation in Gladiolus Cormels and Its Regulation during the Break of Dormancy.

The increase in dark CO(2) fixation during cold storage of Gladiolus x gandavensis van Houtte-type grandiflorus cormels is used to monitor changes in their state of dormancy. Dark fixation is also promoted by benzyladenine, which breaks cormel dormancy, and is inhibited by abscisic acid and gibberellin A(3), which inhibit cormel germination. The rate of dark fixation by nondormant cormels is five times higher than that in dormant ones. Dark fixation is not due to microorganisms. It is temperature-dependent and can be measured stoichiometrically in vivo. The apex and base of the cormels accumulate more label than the central part. Dark fixation of both dormant and nondormant cormels is also promoted by imbibition in water. The fate of the labeled assimilates was followed by ion exchange chromatography.

Journal Article↗
PubMed1987

Seed Dormancy in Red Rice : VI. Monocarboxylic Acids: A New Class of pH-Dependent Germination Stimulants.

The weak acid character of many previously identified, but otherwise chemically dissimilar, dormancy-breaking compounds may contribute to their physiological activity. To test this idea, short chain monocarboxylic acids of one to six carbons, for which no previous reports of such activity exist, were incubated with dormant, dehulled red rice (Oryza sativa) seeds. Greater than 90% germination was observed after 24 hours of imbibition with 19 millimolar formic, 53 millimolar acetic, 20 millimolar propionic, 28 millimolar butyric, 20 millimolar valeric, or 16 millimolar caproic acid followed by 7 to 14 days incubation on water at 30 degrees C. Dormancy-breaking activity was pH-dependent. Incubation medium pH values that favored formation of the protonated species resulted in the highest germination percentages. There was no promotive effect of medium pH itself in the range of 3 to 7. In contrast, germination of intact seeds was less than 40% in the presence of 55 millimolar monocarboxylic acids at pH 3, unless seeds were partially dry-afterripened. The pH-dependent activity of these acids was maintained during afterripening of intact seeds. The results are consistent with the idea that the dissociable proton of weak acids is responsible for their dormancy-breaking activity. Many other weak acids may break seed dormancy but have been over-looked due to the rigid pH dependence necessary for activity.

Journal Article↗
PubMed2004

Evidence of a cross-talk regulation of a GA 20-oxidase (FsGA20ox1) by gibberellins and ethylene during the breaking of dormancy in Fagus sylvatica seeds.

Gibberellin 20-oxidase (GA 20-oxidase) is an enzyme that catalyses the last three steps in the synthesis of active GAs and is a potential control point in the regulation of GA biosynthesis. Reverse transcriptase-polymerase chain reaction with degenerated oligonucleotides conserved among GA 20-oxidases was used to isolate a cDNA clone for this enzyme in Fagus sylvatica L. seeds. This clone contains all the features and exhibits homology to GA 20 oxidases from several plant species. Expression of this clone, named FsGA20ox1, as a fusion protein expressed in Escherichia coli confirmed that it was able to metabolize [(14)C]GA(12) to [(14)C]GA(9) and [(14)C]GA(53) to [(14)C]GA(20). Analysis of FsGA20ox1 transcript levels showed similar low expression during stratification at 4 degrees C and in the presence of gibberellic acid or ethephon (compound that releases ethylene in solution), treatments proved to be efficient in breaking the dormancy of beech seeds. However, there was a drastic increase of FsGA20ox1 transcript levels in the presence of paclobutrazol (PCB), a well-known GAs biosynthesis inhibitor, or of 2-aminoxyacetic acid (AOA), an inhibitor of ethylene biosynthesis. Furthermore, the effect of AOA was reversed by the addition of GA(3) and that of PCB by ethephon. This indicates that the gene product is subjected to down-regulation by GA and ethylene, and further suggests a cross-talk gene regulation by these two hormones during the transition from seed dormancy to germination.

Journal Article↗
PubMed2005

Possible role of catalase in post-dormancy bud break in grapevines.

Changes in the activity of catalase (Cat) and in the levels of H2O2 were followed throughout dormancy in buds of grapevines (Vitis vinifera L.). In grapevines grown in the Elqui valley in Chile, a region with warm-winters, the activity of Cat increased during the recess period of buds, reaching a maximum and thereafter decreased to less than one third of its maximal activity. Three isoforms of Cat were detected in extracts of buds by native PAGE analysis, and the extracted activity was inhibited competitively by hydrogen cyanamide (HC), a potent bud-break agent. Furthermore, HC applications to field-grown grapevines in addition to the expected effect on advancing bud break, reduced the Cat activity during bud dormancy. Similar reductions were observed during dormancy in buds of grapevines grown in the Central valley in Chile, a region with temperate winters, suggesting that HC and winter chilling inhibits the activity of the main H2O2 degrading enzyme in grape buds. A transient rise in H2O2 levels preceded the release of buds from endodormancy, moreover, the peak of H2O2 and the onset of bud break occurred earlier in HC treated than in control grapevines, suggesting the participation of H2O2 as a signal molecule in the release of endodormancy in grape buds. The relationship between Cat inhibition, rise in H2O2 levels and initiation of bud break are discussed.

Catalase↗
PubMed1989

Seed Dormancy in Red Rice : VII. Structure-Activity Studies of Germination Stimulants.

Many chemically dissimilar substances break dormancy of seeds, but the relationship between chemical structure and physiological activity is unknown. In this study, the concentrations of organic acids, esters, aldehydes, alcohols, and inorganic weak acids required to elicit 50% germination of initially dormant, dehulled red rice seeds (Oryza sativa) were determined. The activity of most substances was very highly and inversely correlated to lipophilicity as measured by octanol/water partition coefficients; chemicals with the highest partition coefficients required the lowest concentrations to elicit the germination response. Relative efficacy was also dependent upon the functional group; generally, monocarboxylic acids were more effective than aldehydes, esters, hydroxyacids, and alcohols. Relative hydrophobicity plots supported a modulating role of the functional group. Dormancy-breaking activity of methyl formate, formic acid, nitrite, azide, and cyanide was higher than predicted based on lipophilicity and apparently was related to molecular size; compounds with smaller molecular widths were required at lower concentrations to achieve the 50% germination response.

Journal Article↗
PubMed2006

Dormancy and the fire-centric focus: germination of three Leucopogon species (Ericaceae) from South-eastern Australia.

BACKGROUND AND AIMS: Germination studies of species from fire-prone habitats are often focused on the role that fire plays in breaking dormancy. However, for some plant groups in these habitats, such as the genus Leucopogon (Ericaceae), dormancy of fresh seeds is not broken by fire cues. In the field, these same species display a flush of seedling emergence post-fire. Dormancy and germination mechanisms therefore appear complex and mostly unknown. This study aimed to identify these mechanisms by establishing dormancy class and testing the effects of a set of typical germination cues, including those directly related to fire and entirely independent of fire. METHODS: To classify dormancy, we assessed seed permeability and embryo morphology, and conducted germination experiments at seasonal temperatures in incubators. To test the effects of fire cues on germination, factorial combinations of smoke, heat and dark treatments were applied. Ageing treatments, using burial and seasonal incubation, were also tested. Germination phenology was established. KEY RESULTS: Seeds were dormant at release and had underdeveloped embryos. Primary dormancy of the study species was classified as morphophysiological. Seasonal temperature changes overcame primary dormancy and controlled timing of germination. Fire cues did not break primary dormancy, but there was a trend for smoke to enhance germination once this dormancy was overcome. CONCLUSIONS: Despite the fact that fire is a predominant disturbance and that many species display a flush of emergence post-fire, seasonal temperatures broke the primary physiological dormancy of the study species. It is important to distinguish between fire being responsible for breaking dormancy and solely having a role in enhancing levels of post-fire germination for seeds in which dormancy has been overcome by other factors. Biogeographical evidence suggests that morphological and physiological factors, and therefore seasonal temperatures, are likely to be important in controlling the dormancy and patterns of post-fire germination of many species in fire-prone regions.

Australia↗
PubMed2003

Role of an ABI3 homologue in dormancy maintenance of yellow-cedar seeds and in the activation of storage protein and Em gene promoters.

ABI3/VP1 proteins are members of a large group of transcription factors that act as intermediaries in regulating abscisic acid (ABA)-responsive genes during seed development, including those involved in reserve deposition, acquisition of desiccation tolerance and dormancy induction. CnABI3, an ABI3/VP1 gene homologue was recently cloned from yellow cedar, a conifer species that produces seeds that are deeply dormant at maturity. Here, we investigated whether the conifer ABI3/VP1 gene homologue shares characteristics with its angiosperm counterparts. CnABI3 was synthesized exclusively in seeds, with no detectable protein in leaves and roots. Stable expression of the CnABI3 gene in two transgenic tobacco lines previously transformed with chimeric constructs (vicilin and napin 5' regions linked to a beta-glucuronidase (GUS) gene-coding region) showed that the ectopic expression of the CnABI3 protein strongly activated both the vicilin and napin storage protein gene promoters in leaves and other vegetative tissues. GUS activities were up to more than 1000-fold of those in control plants. ABA had a synergistic effect, further enhancing GUS activity levels. When expressed transiently in yellow-cedar embryos, CnABI3 activated the expression of a chimeric Em-GUS gene in the presence of ABA. The role of CnABI3 in dormancy maintenance of yellow-cedar seeds was examined by monitoring the expression of the CnABI3 gene at the mRNA and protein levels before, during and after dormancy termination. CnABI3 protein was present in the megagametophyte and embryo of dormant mature and warm stratified seed, but declined during subsequent moist chilling, a treatment effective in breaking dormancy. In contrast, the protein was preserved (albeit in lower amounts) in seeds subjected to a control treatment (12 weeks in warm, moist conditions) that is ineffective in breaking dormancy. A decline in CnABI3 gene transcripts was also positively correlated with dormancy breakage, but did not occur during moist chilling itself, but rather during subsequent germination, indicating potential control at the post-transcriptional level.

Arabidopsis Proteins↗
PubMed2002

Modelling kiwifruit budbreak as a function of temperature and bud interactions.

This paper presents two models of budbreak on canes of 'Hayward' kiwifruit (Actinidia deliciosa). A conventional 'chill unit' (CU) type model is compared with an alternative 'loss of potential' (LOP) approach, which assumes that the number of buds developing in spring depends on climate and node position-dependent bud-to-bud interactions that vary in duration and intensity. Both models describe how temperature, and application of a dormancy-breaking chemical, determine the overall amount of budbreak for whole canes. However, the LOP model does so by describing patterns of budbreak along canes. To do this, the cumulative influence of distal neighbours is assumed to cause a progressive fall in the capacity for bud development over the autumn-winter period, an influence that gets stronger as temperature rises. The LOP model also assumes that the rate of decline varies along the cane, as a function of some inherent bud property. These two factors mean that buds towards the base of the cane break less often under the suppressive influence of distal neighbours, while low temperature ('chilling') increases budbreak by diminishing the intensity of suppression relative to bud development rate. Under this scenario, dormancy-breaking chemicals (such as hydrogen cyanamide, HC) enhance budbreak by diminishing the duration of suppression. Models were calibrated using daily temperature series and budbreak proportion data from a multi-year regional survey, and were then tested against independent data sets. Both models were run from a fixed start date until the time budbreak was almost complete, or until a standard date. The fitted models described 87 % of variation in amount of budbreak due to site, year, HC and node position effects in the original data set. Results suggest that the correlation between chilling and the amount of budbreak can be interpreted as a population-based phenomenon based on interaction among buds.

Actinidia↗
PubMed2026

From dormancy to germination: Transcriptome analysis reveals the potential involvement of heat shock proteins in gibberellin-induced seed dormancy release in Solanum torvum.

Solanum torvum, a superior vegetable grafting rootstock and medicinal Solanaceae plant, exhibits strong seed dormancy, which limits its commercial cultivation. Among various strategies explored to improve the germination rate of S. torvum, exogenous application of gibberellin (GA) has been shown to be effective. In this study, a GA concentration of 2.5 mM was established as the optimal for breaking dormancy in S. torvum seeds. Transcriptome analysis of dry, water-soaked, GA-soaked, and GA-induced germinated seeds was conducted to investigate the molecular mechanism of GA-mediated dormancy release. During the soaking period, GA application significantly induced transcriptome changes in processes including protein processing, translation, and peptide biosynthesis. Concurrently, GA treatment promoted plant hormone signal transduction, enhanced DNA-binding transcription factor activity, and activated monocarboxylic acid biosynthetic process, all of which facilitated seed water absorption. Furthermore, the differentially expressed genes (DEGs) induced by GA during soaking primarily functioned in signal transduction or activation. While most of these DEGs returned to their pre-treatment expression levels before subsequent recovery, a subset persisted until seed germination. During radicle protrusion, the persistent DEGs were associated with energy metabolism and cell structure establishment. Notably, heat shock protein (HSP) genes showed dynamic expression across all stages (soaking, germination, and radicle penetration). Furthermore, by adjusting germination conditions, temperature was confirmed to be a necessary but not sufficient condition for GA-induced S. torvum seed germination. However, functional validation (e.g., using HSP inhibitors or genetic approaches) is still required to confirm the causal role of HSPs. Collectively, these findings not only clarify the molecular basis of GA-regulated seed dormancy breaking in S. torvum but also provide practical guidance for optimizing its commercial propagation protocols.

Gibberellins↗
PubMed2006

Protein changes between dormant and dormancy-broken seeds of Prunus campanulata Maxim.

Seed dormancy is regulated by complex networks in order to optimize the timing of germination. However, the biochemical basis of the regulation of seed dormancy is still poorly understood. Many temperate timber species, which are of ecological and/or economic interest, are deeply dormant in seeds, such as Prunus campanulata. Freshly harvested seeds require warm plus cold stratification to break dormancy before they can begin to germinate. According to the results of germination, both warm and cold stratifications are the critical influences for breaking seed dormancy. Significant variations in seed proteins were observed by 2-DE before and after the breaking of seed dormancy. Among the 320, 455, and 491 reproducibly detected spots on the cotyledons, embryos, and testae, respectively, 71 dramatic changes in abundances were observed following warm and/or cold stratification. Among these protein spots, dehydrin, prunin 1 precursor, prunin 2 precursor, and prunin 2 were identified by MS and sequence comparison. The implications of protein changes in relation to the breaking of seed dormancy and germination are discussed. This is the first report of a proteomic analysis of dormancy breaking in woody plant seeds.

Amino Acid Sequence↗
PubMed2002

Changes in ABA turnover and sensitivity that accompany dormancy termination of yellow-cedar (Chamaecyparis nootkatensis) seeds.

Yellow-cedar (Chamaecyparis nootkatensis [D. Don] Spach) seeds exhibit prolonged coat-imposed dormancy following their dispersal from the parent plant. Analyses were undertaken using S-(+)-[(3)H] abscisic acid (ABA) to monitor the capacity of embryos to metabolize ABA following their isolation from seeds subjected to various dormancy-breaking and control treatments. Radiolabelled phaseic acid (PA) and dihydrophaseic acid (DPA) were detected in embryos and, to a greater extent in the surrounding media, by 48 h regardless of whether the embryos had been excised from seed previously subjected to only a 3 d soak or to a full dormancy-breaking treatment. Of the two enantiomers of ABA, only the natural S-(+)-ABA effectively inhibited germination of isolated embryos. A metabolism-resistant synthetic ABA analogue S-[8',8',8',9',9',9']-hexadeuteroabscisic acid, S-(+)-d6-ABA, consistently slowed the germination rate of excised embryos to a greater extent than that caused by natural S-(+)-ABA. The deuterium-labelled ring methyl groups of the analogue made it more resistant to oxidation by yellow-cedar embryos and thus rendered the analogue more persistent and possessing greater activity. With increasing time of exposure to moist chilling, yellow-cedar embryos became increasingly insensitive to both ABA and to the analogue. Subjecting seed to chemical treatments (GA(3) in combination with 1-propanol) prior to moist chilling strongly enhanced the germinability of whole seeds. This treatment also had a relatively greater impact on ABA metabolism than did moist chilling alone, as indicated by a greater capacity of S-(+)-d6-ABA to inhibit the germination of embryos as compared to S-(+)-ABA. Moist chilling was most critical for reduced ABA sensitivity of embryos. A change in the embryo's ability to metabolize ABA and reduced embryo sensitivity to ABA are two factors associated with dormancy termination of whole seeds of yellow cedar; a change in only one of these factors is insufficient to elicit high germinability.

1-Propanol↗
PubMed2002

Breakage of Pseudotsuga menziesii seed dormancy by cold treatment as related to changes in seed ABA sensitivity and ABA levels.

The main aims of the present work were to investigate whether a chilling treatment which breaks dormancy of Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) seeds induces changes in the sensitivity of seeds to exogenous ABA or in ABA levels in the embryo and the megagametophyte, and whether these changes are related to the breaking of dormancy. Dormant seeds germinated very slowly within a narrow range of temperatures (20-30 degrees C), the thermal optimum being approximately 25 degrees C. The seeds were also very sensitive to oxygen deprivation. Treatment of dormant seeds at 5 degrees C improved further germination, and resulted in a widening of the temperature range within which germination occurred and in better germination in low oxygen concentrations. In dry dormant seeds the embryo contained about one-third of the ABA in the megagametophyte. ABA content of both organs increased during the first 4 weeks of chilling. It then decreased sharply in the megagametophyte to the level in the embryo after 7-15 weeks of chilling. At 15 degrees C, a temperature at which dormancy was expressed, the ABA level increased in the embryo and the megagametophyte of dormant unchilled seeds whereas it decreased in the organs of chilled seeds. The longer the chilling treatment, the faster the decrease in ABA after the transfer of seeds from 5 degrees C to higher temperatures, and the decrease was faster at 25 than at 15 degrees C. These results suggest that the breaking of dormancy by cold was associated with a lower capacity of ABA biosynthesis and/or a higher ABA catabolism in the seeds subsequently placed at 15 or 25 degrees C. Moreover, the chilling treatment resulted in a progressive decrease in the sensitivity of seeds to exogenous ABA. However, seeds remained more sensitive to ABA at 15 than at 25 degrees C. The possible involvement of ABA synthesis and of responsiveness of seeds to ABA in the breaking of dormancy by cold treatment is discussed.

Journal Article↗
PubMed1980

cis-4-Cyclohexene-1,2-dicarboximide: Inhibitor of phytochrome-promoted seed germination.

cis-4-Cyclohexene-1,2-dicarboximide (CHDC) inhibits the germination of light-requiring seeds in both light and darkness but has no effect upon the germination of non-light-requiring seeds. In lettuce seeds, CHDC inhibits the action of far-red-absorbing form of phytochrome in breaking dormancy. This inhibition can be overcome by benzyladenine and red light together, but not by a combination of red light and gibberellic acid. Gibberellic acid-induced germination of lettuce seeds in darkness is inhibited also by CHDC. Embryos isolated from dark-imbibed lettuce seeds germinate on the inhibitor. CHDC was thought to be an "analogue" of cycloheximide, but it does not inhibit protein synthesis in lettuce seeds. Our results lead us to conclude that CHDC inhibits germination of seeds that require red light to break dormancy and interferes with some aspect of metabolism that is stimulated by far-red-absorbing form of phytochrome.

Journal Article↗
PubMed1986

Seed dormancy in red rice : v. Response to azide, hydroxylamine, and cyanide.

The activity of NaN(3) (0.5 millimolar), hydroxylamine-HCl (10-18 millimolar), and potassium cyanide (1 millimolar) as dormancy-breaking agents of dehulled red rice (Oryza sativa) is pH-dependent such that medium pH values favoring formation of the uncharged chemical species resulted in the highest germination percentages. There was no promotive effect of pH itself in the range of 3 to 10. The minimum contact times for maximum response (>/=90% germination) to NaN(3), KCN, and NH(2)OH-HCl are 8 hours at pH 4, 24 hours at pH 8, and 72 hours at pH 6 or 7, respectively, for exposure commencing at the start of imbibition. Dehulled seeds, imbibed first in water, show only slightly reduced germination when subsequently transferred to solutions of dormancy-breaking chemicals.Intact seeds remain dormant in the presence of NaN(3), KCN, or NH(2)OH-HCl unless partially dry-afterripened. The pH dependence of these chemicals is reduced in intact, afterripening seeds.

Journal Article↗
PubMed1977

The effect of gamma radiation on breaking of dormancy in Phycomyces spores.

Dormant sporangiospores of Phycomyces blakesleeanus were activated by Cs-137 gamma rays. After a dose of about 300 krad, between 80 and 90% of the spores germinated normally. However, further development of the mycelium was inhibited. Even with dry spores a partial activation was obtained. Activation by gamma rays was not accompanied by an increase in trehalase activity.

Cesium Radioisotopes↗
PubMed2006

Plant development: multiple strategies for breaking seed dormancy.

Plant seeds will not germinate when in a dormant state. What then are the factors controlling dormancy? A recent study has uncovered two basic-helix-loop-helix proteins which repress germination and are critical for maintaining dormancy. The combined action of light and cold synergistically alleviates activity of these repressors thus stimulating germination.

Arabidopsis↗