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PubMed1972

Polysome Formation in Light-controlled Dormancy.

Lettuce (Lactuca sativa) seeds var. Grand Rapids could be maintained many weeks in the dark without germination. Following illumination with white light, a gradual increase in polyribosome population up to the time of germination was demonstrated by sucrose gradient centrifugation. Polysomes could not be detected in imbibed seeds maintained continuously in the dark. Thus, polysome formation and therefore the capacity for a high rate of protein synthesis required for germination and growth, is not associated with the process of imbibition, but is dependent upon the seeds having received the dormancy-breaking stimulus of illumination.

Journal Article↗
PubMed1981

Studies in Wild Oat Seed Dormancy: I. THE ROLE OF ETHYLENE IN DORMANCY BREAKAGE AND GERMINATION OF WILD OAT SEEDS (AVENA FATUA L.).

Seed of Avena fatua were shown to exhibit a characteristic loss of dormancy during dry storage at 25 C, whereas similar seed stored at 5 C maintained dormancy. 2-Chloroethylphosphonic acid was shown to increase germination of partly dormant seed imbibed under certain temperature regimes; a similar effect could not be established for fully dormant or fully nondormant seed. Using gas-liquid chromatography, natural ethylene levels were followed during imbibition of fully dormant and nondormant seed. A large peak in production was observed in the period prior to radicle emergence in the case of the nondormant seed. Measurements of ethylene production taken at 15 C, following periods of after-ripening in moist soil at either 5 or 25 C, indicated that endogenous production was unlikely to be a main cause of dormancy breakage in this species. The possibility that endogenous ethylene could play a role in natural dormancy breakage in aged seeds is discussed. The practical possibilities of 2-chloroethylphosphonic acid as a dormancy breaking agent in a field situation are outlined.

Journal Article↗
PubMed2001

Interspecific and intraspecific variation in seed size and germination requirements of Sarracenia (Sarraceniaceae).

Seed size and germination requirements of eight (of nine) Sarracenia species, and 13 populations of S. purpurea were studied. All species except for S. purpurea are restricted to the southeastern United States, whereas S. purpurea ranges across Canada, southward along the eastern United States into Maryland and Virginia (S. purpurea ssp. purpurea), and from New Jersey southward into northern Florida and the coast of the Gulf of Mexico (S. purpurea ssp. venosa). I tested the hypotheses that dormancy-breaking requirements vary predictably among species across a latitudinal gradient. I also sought to determine whether seed size and germination requirements were useful characters for resolving systematic and phylogenetic questions within this genus. Seed size varied significantly among species, but variability in seed size within S. purpurea exceeded the variability in seed size observed across all eight species studied. Seeds of all species are morphophysiologically dormant upon dispersal. Length of required cool, moist pretreatment varied among species, and germination in higher latitude populations is enhanced with longer pretreatment. In contrast, variability in germination requirements of subspecies, varieties, and populations of the geographically wide-ranging S. purpurea was not related clearly to geographic location (latitude or elevation). Germination requirements do not map onto a proposed phylogeny of Sarracenia, but observed differences in germination requirements of S. purpurea ssp. venosa var. burkii relative to other populations of S. purpurea support the recent proposal to elevate this variety to species status.

Journal Article↗
PubMed1981

Effect of various inhibitors of polyamine synthesis on the growth of Helianthus tuberosus.

The growth effect of various inhibitors of polyamine synthesis was studied on explants obtained from Helianthus tuberosus tubers during dormancy and dormancy break and cultured for 20 days on a sterile agarized medium. Explant growth was strongly inhibited by canavanine and canaline, natural non-protein amino acid analogues of arginine and ornithine, respectively, as well as by canavanine in combination with putrescine. Methylglyoxal-bis-guanylhydrazone, an inhibitor of S-adenosylmethionine decarboxylase, did not increase growth inhibition caused by canavanine. Methylglyoxal-bis-guanylhydrazone alone, as well as alpha-methylornithine, 1,3-diaminopropane and 1,3-diaminopropan-2-o1 - which are inhibitors of ornithine decarboxylase - showed no growth inhibition with respect to the control treated with 2,4-dichlorophenoxyacetic acid. 1,3-Diaminopropane caused a paradoxic enhancement of callus growth and a much greater polyamine accumulation than in the control with 2,4-dichlorophenoxyacetic acid alone. During the first cell cycle inactivated tuber slices, 40 microM methylglyoxal-bis-guanylhydrazone inhibited spermidine and spermine synthesis up to 6 h, and their accumulation up to 1 h; RNA synthesis and accumulation and DNA accumulation were reduced at 1 h, and later enhanced. During the same period, 1 mM canavanine inhibited putrescine synthesis in the S and M phases, and spermidine and spermine synthesis only at 24 h; accumulation of putrescine and spermidine was reduced only at 12 h. Canavanine also reduced RNA synthesis throughout the S and M phases, while RNA accumulation was reduced at 18 and 24 h. Two different hypotheses are put forward concerning the induction of new pathways of polyamine synthesis.

Adenosylmethionine Decarboxylase↗
PubMed1975

Breaking of seed dormancy by catalase inhibition.

Germination of some dormant seeds is promoted by solutions of thiourea, sodium nitrite, and hydroxylamine salts. The promotions are accompanied by irreversible inhibition of catalase (EC 1.11.1.6) in extracts from the seeds. The seeds are also promoted in germination by catechol and pyrogallol solutions. These effects are recorded for lettuce (Lactuca sativa L. cv. Grand Rapids) and pigweed (Amaranthus albus L.) seeds. The results indicae that metabolically derived hydrogen peroxide, spared from decomposition by catalase inhibition, oxidizes reduced NADPH required as the oxidant in the pentose pathway of glucose use. The metabolic system for such use of H2O2 involves the enzymes, peroxidase (EC 1.11.1.7) and pyridine nucleotide quinone oxidoreductase (EC 1.6.99.2), which are present in the dormant seed prior to imbibition of water.

Catalase↗
PubMed2005

Nitric oxide reduces seed dormancy in Arabidopsis.

Dormancy is a property of many mature seeds, and experimentation over the past century has identified numerous chemical treatments that will reduce seed dormancy. Nitrogen-containing compounds including nitrate, nitrite, and cyanide break seed dormancy in a range of species. Experiments are described here that were carried out to further our understanding of the mechanism whereby these and other compounds, such as the nitric oxide (NO) donor sodium nitroprusside (SNP), bring about a reduction in seed dormancy of Arabidopsis thaliana. A simple method was devised for applying the products of SNP photolysis through the gas phase. Using this approach it was shown that SNP, as well as potassium ferricyanide (Fe(III)CN) and potassium ferrocyanide (Fe(II)CN), reduced dormancy of Arabidopsis seeds by generating cyanide (CN). The effects of potassium cyanide (KCN) on dormant seeds were tested and it was confirmed that cyanide vapours were sufficient to break Arabidopsis seed dormancy. Nitrate and nitrite also reduced Arabidopsis seed dormancy and resulted in substantial rates of germination. The effects of CN, nitrite, and nitrate on dormancy were prevented by the NO scavenger c-PTIO. It was confirmed that NO plays a role in reducing seed dormancy by using purified NO gas, and a model to explain how nitrogen-containing compounds may break dormancy in Arabidopsis is presented.

Abscisic Acid↗
PubMed1975

Some properties of trehalase from Phycomyces blakesleeanus.

Trehalase (alpha, alpha-trehalase glucohydrolase EC 3.2.1.28) from Phycomyces spores occurs in two different forms which are convertible in vivo: a form with low activity found in dormant spores and an active form after breaking the dormancy. Between the two forms no difference in molecular weight and electrophoretic mobility can be detected. The molecular weight is estimated by gel filtration at about 210 000. The relation between substrate concentration and trehalase activity follows the Michaelis-Menten equation (K-m plus or minus 55 mM) in activated spores whereas in dormant spores trehalase shows a different substrate binding, indicating a negative cooperative effect. They differ further in thermostability and in sensitivity to inhibition by ATP. Other nucleosidephosphates have no inhibiting effect. Heating the spores at different temperatures between 38 and 44 degrees C results in a partial breaking of dormancy of the spore population and a corresponding partial activation of trehalase. This suggests a close connection between breaking dormancy and trehalase activation.

Chromatography, Gel↗
PubMed1982

Relation of polyamine biosynthesis to the initiation of sprouting in potato tubers.

The polyamines putrescine, spermidine, and spermine and their biosynthetic enzymes arginine decarboxylase, ornithine decarboxylase and S-adenosyl-l-methionine decarboxylase are present in all parts of dormant potato (Solanum tuberosum L.) tubers. They are equally distributed among the buds of apical and lateral regions and in nonbud tissues. However, the breaking of dormancy and initiation of sprouting in the apical bud region are accompanied by a rapid increase in ornithine decarboxylase and S-adenosyl-l-methionine decarboxylase activities, as well as by higher levels of putrescine, spermidine, and spermine in the apical buds. In contrast, the polyamine biosynthetic enzyme activities and titer remain practically unchanged in the dormant lateral buds and in the nonbud tissues. The rapid rise in ornithine decarboxylase, but not arginine decarboxylase activity, with initiation of sprouting suggests that ornithine decarboxylase is the rate-limiting enzyme in polyamine biosynthesis. The low level of polyamine synthesis during dormancy and its dramatic increase in buds in the apical region at break of dormancy suggest that polyamine synthesis is linked to sprouting, perhaps causally.

Journal Article↗
PubMed1966

Effect of Growth Regulators on CO(2) Assimilation in Leaves, and its Correlation with the Bud Break Response in Photosynthesis.

Experiments have been done to confirm the previously reported effect of indoleacetic acid (IAA) on the rate of CO(2) assimilation in bean leaves. It was shown that spraying the leaves of a variety of plants caused an increase in the rate of CO(2) assimilation from 30% to 100% during the half-hour to 1 hour period following spraying. The only plant tested which did not show such an effect was corn.The breaking of dormancy of axial buds in the bean plant was correlated with an increase in the rate of CO(2) assimilation in adjacent leaves for a brief period of time. It has been shown that IAA solution sprayed on 1 leaflet of a leaf can cause an increase in the rate of CO(2) assimilation in the other leaflets, and that IAA applied to the cut stem of a leaflet or a developing bud can be transported to adjacent leaves and cause an increase in the CO(2) assimilation rate. The reaction caused by IAA is very similar to that caused by the breaking of dormancy of a bud. This indicates that the bud break response in CO(2) assimilation in leaves is caused by auxin synthesized in a bud as it begins to grow, and exported into adjacent leaves.

Journal Article↗
PubMed2005

The effect of seed source, light during germination, and cold-moist stratification on seed germination in three species of Echinacea for organic production.

Organic production of one of the most popular botanical supplements, Echinacea, continues to expand in the U.S. Echinacea seeds typically show a high degree of dormancy that can be broken by ethephon or gibberelic acid (GA), but these methods are currently disallowed in organic production. In order to determine the efficacy of non-chemical seed treatments, we evaluated the effect of varying seed source and supplying light, with and without cold-moist stratification, on seed germination of the three most important medicinal species of Echinacea, E. angustifolia DC, E. purpurea (L) Moench, and E. pallida (Nutt.) Nutt. Treatments included cold-moist stratification under 24 h light, 24 h dark, and 16/8 h light/dark to break seed dormancy. We found that germination was greater in the E. purpurea and E. pallida seeds from a commercial organic seed source compared to a public germplasm source. When seeds were not cold-moist stratified, 16-24 h light increased germination in E. angustifolia only. Echinacea angustifolia, E. purpurea, and E. pallida seeds that were cold-moist stratified under 16-24 h of light for 4 wk had a significantly greater percentage and rate of germination compared to seeds germinated in the dark. Therefore, cold-moist stratification under light conditions is recommended as a method to break seed dormancy and increase germination rates in organic production of Echinacea.

Journal Article↗
PubMed1997

The expression of an abscisic acid-responsive glycine-rich protein coincides with the level of seed dormancy in Fagus sylvatica.

By differential screening of a cDNA library constructed from poly (A+) RNA of ABA-treated seeds of Fagus sylvatica L., we have isolated an ABA-responsive clone that is present in dormant seeds and under conditions that maintain dormancy, but it tends to disappear under conditions breaking seed dormancy. A search of the sequence data bases showed that the clone codes for a Glycine-Rich Protein and has sequence similarity to RNA-binding proteins. The clone, which exibits the characteristics of lea-genes, is up-regulated by ABA and down-regulated by GA3. Paclobutrazol abolishes the effect of GA3, which is restored upon addition of GA3. The possible relationship of this Glycine-Rich Protein to seed dormancy in F. sylvatica is discussed.

Abscisic Acid↗
PubMed2001

A role for brassinosteroids in germination in Arabidopsis.

This paper presents evidence that plant brassinosteroid (BR) hormones play a role in promoting germination. It has long been recognized that seed dormancy and germination are regulated by the plant hormones abscisic acid (ABA) and gibberellin (GA). These two hormones act antagonistically with each other. ABA induces seed dormancy in maturing embryos and inhibits germination of seeds. GA breaks seed dormancy and promotes germination. Severe mutations in GA biosynthetic genes in Arabidopsis, such as ga1-3, result in a requirement for GA application to germinate. Whereas previous work has shown that BRs play a critical role in controlling cell elongation, cell division, and skotomorphogenesis, no germination phenotypes have been reported in BR mutants. We show that BR rescues the germination phenotype of severe GA biosynthetic mutants and of the GA-insensitive mutant sleepy1. This result shows that BR stimulates germination and raises the possibility that BR is needed for normal germination. If true, we would expect to detect a germination phenotype in BR mutants. We found that BR mutants exhibit a germination phenotype in the presence of ABA. Germination of both the BR biosynthetic mutant det2-1 and the BR-insensitive mutant bri1-1 is more strongly inhibited by ABA than is germination of wild type. Thus, the BR signal is needed to overcome inhibition of germination by ABA. Taken together, these results point to a role for BRs in stimulating germination.

Abscisic Acid↗
PubMed2005

Investigations into seed dormancy in Grevillea linearifolia, G. buxifolia and G. sericea: anatomy and histochemistry of the seed coat.

BACKGROUND AND AIMS: Seeds of east Australian Grevillea species generally recruit post-fire; previous work showed that the seed coat was the controller of dormancy in Grevillea linearifolia. Former studies on seed development in Grevillea have concentrated on embryology, with little information that would allow testing of hypotheses about the breaking of dormancy by fire-related cues. Our aim was to investigate structural and chemical characteristics of the seed coat that may be related to dormancy for three Grevillea species. METHODS: Seeds of Grevillea linearifolia, Grevillea buxifolia and Grevillea sericea were investigated using gross dissection, thin sectioning and histochemical staining. Water movement across the seed coat was tested for by determining the water content of embryos from imbibed and dry seeds of G. sericea. Penetration of intact seeds by Lucifer Yellow was used to test for internal barriers to diffusion of high-molecular-weight compounds. KEY RESULTS: Two integuments were present in the seed coat: an outer testa, with exo-, meso- and endotestal (palisade) layers, and an inner tegmen of unlignified sclerenchyma. A hypostase at the chalazal end was a region of structural difference in the seed coat, and differed slightly among the three species. An internal cuticle was found on each side of the sclerenchyma layer. The embryos of imbibed seeds had a water content six times that of dry seeds. Barriers to diffusion of Lucifer Yellow existed at the exotestal and the endotestal/hypostase layers. CONCLUSIONS: Several potential mechanisms of seed coat dormancy were identified. The embryo appeared to be completely surrounded by outer and inner barriers to diffusion of high-molecular-weight compounds. Phenolic compounds present in the exotesta could interfere with gas exchange. The sclerenchyma layer, together with strengthening in the endotestal and exotestal cells, could act as a mechanical constraint.

Germination↗
PubMed2026

ATX1-COMPASS-like complex participates in the bud dormancy release of tree peony by regulating H3K4me3 modification.

Bud dormancy release in woody plants is crucial for survival, regrowth, flowering, and fruiting. Tree peony (Paeonia suffruticosa), an important ornamental and economic plant, undergoes bud endodormancy in winter, and sufficient chilling duration and exogenous gibberellins (GAs) can effectively break the dormancy. However, the epigenetic regulation mechanism remains poorly understood. Here, immunoblotting revealed that H3K4me3, but not H3K4me1 or H3K4me2, was associated with chilling- and GA3-induced dormancy release. Chromatin immunoprecipitation sequencing (ChIP-seq) combined with RNA-seq results revealed that H3K4me3 enriched near transcription start sites (TSS). H3K4me3 enrichment genes (HEGs) and differentially expressed genes (DEGs) were commonly enriched in KEGG pathways, such as plant hormone signal transduction and MAPK signaling. The expression patterns of these marker genes, such as EARLY BUD-BREAK 3 (PsEBB3), CYCLIND3.1 (PsCYCD3.1), CYCLIND3.3 (PsCYCD3.3), and β-1,3-glucanase 6 (PsBG6), were correlated with their H3K4me3 enrichment and were validated by chromatin immunoprecipitation-quantitative PCR (ChIP-qPCR). Four COMPASS-like component homologs and one histone methyltransferase were screened; among them, PsWDR5a, PsRBL, PsASH2R, and PsATX1 were upregulated by prolonged chilling and GA3 treatments. Yeast two-hybrid (Y2H), yeast three-hybrid (Y3H), luciferase complementation (LCA), and co-immunoprecipitation (Co-IP) analyses revealed that PsRBL interacts with PsWDR5a and PsASH2R as a bridge. PsATX1 was confirmed as an H3K4me3 methyltransferase and interacted with PsWDR5a and PsRBL to form the PsATX1-COMPASS-like complex using Y2H, LCA, and Co-IP assays. Functional analyses showed that PsWDR5a, PsRBL, PsASH2R, and PsATX1 significantly promoted budburst by elevating genomic H3K4me3 levels. Our findings provide insights into the epigenetic regulation of dormancy transitions in woody perennials.

Histones↗
PubMed1973

Effects of Oxygen and Respiratory Inhibitors on Induction and Release of Dormancy in Aerial Tubers of Begonia evansiana.

Effects of O(2) and some respiratory inhibitors on the induction and release of bud dormancy were examined with the aerial tubers of different ages of Begonia evansiana Andr. Oxygen was needed not only for tuber sprouting but also during the chilling process at 2 to 5 C to break tuber dormancy. If the mature tubers were exposed to blue light during the chilling period, their dormancy was strikingly released even by the chilling given under an O(2) concentration as low as 3%. Blue light pretreatment promoted photo-sprouting of immature tubers only when given under lower O(2) concentrations. On the other hand, red light became effective in inducing dormancy in the immature tubers and in prolonging dormancy in the mature tubers as O(2) tension was increased. This was also the case with the induction of dormancy in the immature tubers by exposing them to a lower temperature (17 C) in the dark. The development of dormancy was suppressed by 2,4-dinitrophenol, p-nitrophenol, and sodium azide.

Journal Article↗
PubMed1977

Dormancy and Impotency of Cocklebur Seeds: VII. Inability of Dormant Cotyledons to Form Chlorophyll.

Dormant seeds of cocklebur (Xanthium pennsylvanicum Wallr.) were characterized by the lack of ability to form chlorophyll. Such an inability of cotyledons of the dormant seeds was improved by the application of various factors and reagents which were capable of breaking the dormancy and of increasing cotyledon enlargement. Of these, ethylene, benzyladenine, and high temperature treatments were particularly effective, and, in turn, oxygen enrichment, gibberellic acid, thiourea, carbon doxide, and potassium nitrate were also promotive to the greening of the dormant cotyledons. The effects of benzyladenine, oxygen enrichment, and high temperature were reduced in the presence of absorbents for endogenously evolve carbon dioxide and ethylene. delta-Aminolevulinic acid could not restore their greening ability.

Journal Article↗