Interactions of phytochrome and exogenous gibberellic acid on germination of Lamium amplexicaule L. seeds

Summary In henbit (Lamium amplexicaule L.) seeds, micromolar levels of gibberellic acid (GA₃) introduced at the onset of imbibition markedly stimulated germination. Sensitivity to GA₃ stimulation is rapidly lost if the seeds are pretreated in darkness at 15° for 1 day or more on a water substrate. Loss in responsiveness to GA₃ is hastened by pretreatment in far-red or by dark pretreatment at higher (25°) temperatures and is reduced by pretreatments at 5°. A portion of the lost responsiveness to GA₃ at 15° or higher is attributable to onset of a secondary dormancy, but the results of far-red treatment at 5°, where secondary dormancy is not a factor, clearly indicate that some phytochrome in the far-red absorbing form increased the effectiveness of gibberellic acid action.Abbreviations GA gibberellin - GA₃ gibberellic acid - R red light - FR far-red - P_r red-absorbing form of phytochrome - P_fr far-red-absorbing form of phytochrome Mention of a trade name or proprietary product does not constitute a guarantee or warranty of the product by the U.S. Department of Agriculture and does not imply its approval to the exclusion of other products that may also be suitable     

Effect of Temperature, Oxygen, and Gibberellic Acid on the Development of Photosensitivity in Oldenlandia corymbosa L. Seeds during Their Incubation in Darkness

Two successive phases can be distinguished in the development of the responsiveness to light in Oldenlandia corymbosa L. seeds during their incubation in darkness. During phase I, the responsiveness to light increases with time if there is sufficient O₂, and the higher the temperature, the faster the increase. This phase is stimulated by gibberellic acid. During the following phase (II), seeds remain responsive to light at 10 or 20°C, but lose their responsiveness at higher temperature (≥30°C). This second phase depends on O₂: loss of responsiveness is accelerated at lower O₂ concentration. Phase II is only slightly affected by gibberellic acid. The results are discussed in terms of variation of phytochrome and of a reaction along the transduction chain initiated by phototransformation of this pigment, which is finally expressed in germination.     

Germination characteristics of some plant species from calcareous fens in southern Germany and their implications for the seed bank

Seeds of 25 plant species from calcareous fen hay meadows were exposed to different experimental conditions and their germination was characterised. Constant temperature inhibited germination especially in Cyperaceae . Both gibberellic acid and potassium nitrate failed to terminate dormancy. Increased germination rates were found in dicot species after treatment with gibberellic acid. Temperature fluctuations increased germination of Cyperaceae as well as dicotyledons. Treatment with gibberellic acid removed the chilling requirement in some of the species. Dormancy of small seeds with thin seed coats was broken by the application of gibberellic acid or fluctuating temperature; large thick-coated seeds were unaffected by gibberellic acid. No obligatory darkness requirement was found in any species; three species germinated irrespective of light treatments. All other species achieved higher percentage germination in daylight or in red (670 nm) light. Permanent darkness and far-red light (730 nm) reduced germination drastically. The results indicate that germination characteristics of the species investigated can be related to their seed bank types.     

Secondary dormancy (skotodormancy) in seeds of lettuce (Lactuca sativa cv. Grand Rapids) and its release by light, gibberellic acid and benzyladenine

Lettuce seeds (Lactuca sativa L. cv. Grand Rapids) imbibed in darkness at supra-optimal temperatures (23 ± 1°C) develop a secondary dormancy, termed skotodormancy. The seeds first lose their ability to be promoted to germinate by gibberellic acid, and then lose their ability to be promoted by red light. A combination of red light and gibberellic acid will break skotodormancy for longer than either alone, but red light and benzyladenine together are much more effective. Desiccation of skotodormant seeds does not diminish their dormancy. Embryos dissected from skotodormant seeds will germinate, and are as capable of radicle expansion in the osmoticum polyethylene glycol as are newly-imbibed seeds. Hence skotodormancy is a whole seed dormancy and does not reside within the embryo as an inherent block to germination processes, but as an inability to respond to the stimulation of red light or to hormone.     

The Effects of Gibberellic Acid and Scarification on the Seed Dormancy and Germination in Luzula spicata

Luzula spicata L. seeds are completely dormant at maturity. A germination inhibitor is present at the micropylar end. Normally, the only effective means of eliciting germination is a precise scarification of the micropylar end which inactivates the inhibitor. Exogenous application of gibberellic acid, kinetin, KNO₃, and thiourea have no affect on the dormancy of unscarified seeds. Scarification of the hilar end of the seed does not elicit germination, but when gibberellic acid is applied to the hilar scarified seeds moderate germination results. Presumably, these seeds are dormant due to a deficit of endogenous gibberellin; a condition which can be overcome by the application of gibberellic acid to seeds scarified at a site in itself ineffective in producing germination. Apparently the gibberellic acid serves to initiate amylase activity in the endosperm, overcoming the inhibitor block. Luzula spicata seed dormancy is apparently unique in that a germination inhibitor is operative in conjunction with the commonly recognized gibberellin-amylase mechanism.     

Germination Promotion of Loblolly Pine and Baldcypress Seeds by Stratification and Chemical Treatments

The effects of 4 chemicals on the germination promotion of stratified and unstratified seeds of loblolly pine (Pinus taeda) and baldcypress (Taxodium distichum) were studied. The chemicals used were gibberellic acid, kinetin, potassium nitrate and thiourea, each at 3 different concentrations. Stratification promoted the germination of both seed species. Certain concentrations of gibberellic acid, potassium nitrate and thiourea improved the germination of unstratified loblolly pine and baldcypress seeds while kinetin had no stimulatory effect. All 4 chemicals at specific concentrations promoted the germination of loblolly pine seeds stratified for a short period of time. Considering both speed and completeness of germination, best results were obtained when 21-day stratified seeds were treated with either gibberellic acid (100 mg/1) or kinetin (10 mg/1). In baldcypress, on the other hand, none of these chemicals had any stimulatory effect on the germination of stratified seeds. Germination of both species of seeds was either partially or completely inhibited by the highest concentration of thiourea (30,000 mg/1) used.     

Allelopathy in Heracleum laciniatum: Inhibition of Lettuce Seed Germination and Root Growth

Both dark and red light germination of lettuce seeds (cv. “Maikönig”) as well as their root and hypocotol elongation were inhibited when the seeds were sown in petri dishes together with a few seeds of Heracleum laciniatum Horn. This inhibition was not significantly counteracted by the presence of gibberellic acid (GA₃) or/and 6-benzylaminopurine (BA). However, a large proportion of the lettuce seeds germinated abnormally (only cotyledons emerged) when treated with BA in the presence of Heracleum seeds. GA₃ had alone no significant effect on abnormal germination, but it counteracted the effect of BA to some extent. The inhibitory effect of Heracleum seeds gradually disappeared during a moist incubation period of one to seven days in darkness at 25°C. When lettuce seeds were pre-incubated together with Heracleum seeds for one to five days the remaining, non-germinated lettuce seeds had lost their ability for subsequent germination in darkness in distilled water. This induced dark dormancy was to a great extent broken by red light, but not by GA₃ or/and BA. H. laciniatum seeds inhibited the germination of Salix pentandra seeds and to some extent also the germination of radish but had no effect on the germination of spruce.     

Promoting Effect of Fusicoccin on Seed Germination

The effects of fusicoccin on the germination of dormant, light-requiring or abscisic acid-inhibited seeds has been investigated. (1) Fusicoccin (10^?6M) induces germination in dormant wheat seeds (Triticum durum cv. Cappelli; 1972 crop) and stimulates it in seeds already relieved from dormancy (1971 crop), with an effect similar to that of gibberellic acid. (2) Fusicoccin (1.5 × 10^?6M) is more active than the two phytohormones gibberellic acid and benzyladenine and than white light in stimulating light-requiring lettuce seeds (Lactuca sativa cv. Grand Rapids) to germinate. Germination of radish seeds (Raphanus sativus) is also accelerated by fusicoccin, while benzyladenine and gibberellic acid are less active in this material. (3) Fusicoccin (1.5 × 10^?5M) removes almost completely the inhibitory effect of abscisic acid on germination of radish and lettuce seeds, whereas benzyladenine (10^?4M) and gibberellic acid (3 × 10^?4M) remove the inhibition only partially. The possible relationship between these results and previous information on growth by cell enlargement is discussed in terms of the mechanism of action of fusicoccin as compared with natural hormones.     

Actions of gibberellic Acid and phytochrome on the germination of grand rapids lettuce seeds

Red light and gibberellic acid were about equally effective in promoting germination of Grand Rapids lettuce (Lactuca sativa L.) seeds. With initial far red light treatment more than 80% remained dormant in subsequent dark storage. After 2 days of dark storage, red light effectively promoted germination, while gibberellic acid action was weak. With between 2 and 10 days of dark storage, gibberellic acid had little effect, while promotion by red light decreased slowly and finally disappeared. After 10 days of dark storage, both gibberellic acid and red light were required for germination. The dark storage treatment interferes with phytochrome-independent germination processes and cannot be overcome by added gibberellic acid. However, storage may also decrease the effectiveness of endogenous gibberellins. Phytochrome-dependent germination seems to require only low levels of endogenous gibberellin activity or the addition of gibberellic acid. Gibberellins and red light appear to act on germination by regulation of sequential sites of a branched-looped pathway.     

Seed enhancing treatments: comparative analysis of germination characteristics of 23 key herbaceous species used in European restoration programmes

• The response of seeds from 23 wild plant species to a range of seed enhancing treatments was studied. We tested the hypothesis that sensitivity of the 23 species to these compounds is related to their ecological niche. The three ecological niches considered were open land, open‐pioneer and woodland. Hence, the germination of a species is likely adapted to different light conditions and other environmental signals related to the niche.
• As representatives of environmental signals, the effects of smoke‐related compounds (karrikinolide, KAR₁), nitrate and plant growth regulator (gibberellic acid, GA₃) on germination were studied. Seeds were exposed to these additives in the imbibition medium; all described as germination cues. We also investigated the effect of light regimes and additives on germination parameters, which included final germination, germination rate and uniformity of germination. Seeds were placed to germinate under three light conditions: constant red light, constant darkness and 12 h white light photoperiod.
• We observed inhibition by KAR under light in some species, which may have ecological implications. The results showed that no single treatment increased the germination of all the tested species, rather a wide variation of responsiveness of the different species to the three compounds was found. Additionally, no interaction was found between responsiveness to compounds and ecological niche. However, species in the same ecological niche and dormancy class showed a similar responsiveness to light.
• Species that share a similar environment have similar light requirements for germination, while differences exist among species in their responsiveness to other germination cues.

     

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.     

Gibberellins regulate seed germination in tomato by endosperm weakening: a study with gibberellin-deficient mutants

The germination of seeds of tomato [Lycopersicon esculentum (L.) Mill.] cv. Moneymaker has been compared with that of seeds of the gibberellin-deficient dwarf-mutant line ga-1, induced in the same genetic background. Germination of tomato seeds was absolutely dependent on the presence of either endogenous or exogenous gibberellins (GAs). Gibberellin A₄₊₇ was 1000-fold more active than commercial gibberellic acid in inducing germination of the ga-1 seeds. Red light, a preincubation at 2°C, and ethylene did not stimulate germination of ga-1 seeds in the absence of GA₄₊₇; however, fusicoccin did stimulate germination independently. Removal of the endosperm and testa layers opposite the radicle tip caused germination of ga-1 seeds in water. The seedlings and plants that develop from the detipped ga-1 seeds exhibited the extreme dwarfy phenotype that is normal to this genotype. Measurements of the mechanical resistance of the surrounding layers showed that the major action of GAs was directed to the weakening of the endosperm cells around the radicle tip. In wild-type seeds this weakening occurred in water before radicle protrusion. In ga-1 seeds a similar event was dependent on GA₄₊₇, while fusicoccin also had some activity. Simultaneous incubation of de-embryonated endosperms and isolated axes showed that wild-type embryos contain and endosperm-weakening factor that is absent in ga-1 axes and is probably a GA. Thus, an endogenous GA facilitates germination in tomato seeds by weakening the mechanical restraint of the endosperm cells to permit radicle protrusion.Abbreviations GA(s) gibberellin(s) - GA₃ gibberellic acid     

Effects of Germination-promoting Substances Given in Conjunction with Red Light on the Phytochrome-mediated Germination of Dormant Lettuce Seeds (Lactuca sativa L.)

Ethylene or thiourea can substitute for gibberellic acid but not for red light in breaking the secondary dormancy induced by extended dark storage of fully hydrated lettuce seeds (Lactuca sativa cv. Grand Rapids). After 10 days of storage, ethylene, thiourea, or gibberellic acid applied either separately or in any combination in conjunction with red light induced near maximal germination. When applied separately without red light, none of the substances promoted germination of seeds stored 10 days. Combinations of any two or all three of the substances in the absence of red light induced some germination but no combination was as effective as any single substance given with red light.     

Seed moisture content affects afterripening and smoke responsiveness in three sympatric Australian native species from fire‐prone environments

Germination of freshly collected seeds of three sympatric herbaceous species native to fire‐prone environments in south‐western Australia was significantly improved through the application of novel combinations of dry heat, gibberellic acid, smoke water and dry afterripening. For fresh seeds, combinations of dry heat, gibberellic acid and/or smoke water resulted in >80% germination in Austrostipa elegantissima (Poaceae) and Stylidium affine (Stylidaceae) seeds and >60% germination in Conostylis candicans (Haemodoraceae) seeds, compared with <10% germination of control seeds. For fresh seeds, two broad germination patterns were observed in response to smoke water: nil – low germination for both control and smoke water‐treated seeds (A. elegantissima and S. affine); and a significant smoke response (35%) compared with control seeds (1%) (C. candicans). During afterripening, high germination for A. elegantissima seeds was achieved following 3 months storage of seeds at equilibrium relative humidities of 23–75%, but seeds stored at 5–13% equilibrium relative humidities took 6–36 months to achieve similar levels of germination. Germination of C. candicans seeds also increased after 3 months storage, to >60% at each equilibrium relative humidity and further increases over time were slight. For S. affine seeds >60% germination was achieved only after 36 months storage at 50% equilibrium relative humidity. Seeds from all three species were smoke‐responsive at some point, but the interaction/effects of afterripening on the smoke response varied significantly between species. This study highlights an apparent effect of seed dormancy status on response to smoke and a surprisingly high level of ecological variation in pre‐germination requirements (cues) for these co‐occurring species that may relate to variation(s) in microsite selection forces operating on the soil seed bank of the different species.     

The germination characteristics of <Emphasis Type="Italic">Scrophularia marilandica</Emphasis> L. (Scrophulariaceae) seeds

Investigations on seeds of Scrophularia marilandica L. were undertaken to determine their germination requirements. Seeds were collected from three naturally occurring sites and one greenhouse-grown population in London, Ontario in September and October of 1997. Some were set to germinate immediately after collection; others were stored in or on soil outside and/or under controlled laboratory conditions before testing. Germination was assessed under two light/temperature regimes (35°C 14 h light, 20°C 10 h dark and 25°C 14 h light, 10°C 10 h dark), in continuous darkness, and in the presence of two germination-promoting chemicals (GA₃ and KNO₃). Fresh seeds germinated best at 35/20°C, while stored seeds germinated best at 25/10°C. No differences in percent germination were found among three seed-maturity stages. All chemical treatments, except 0.01 M KNO_3, increased percent germination. Significant differences were found both among and within sites for most chemical treatments, but exposure to 3 × 10⁻⁴ M GA₃ caused almost every seed to germinate. When compared to the control, both the gibberellic acid and the soil-storage treatments contributed to faster germination. Exposure of seeds to naturally prevailing conditions on the soil surface followed by testing under the 25/10°C regime produced the highest percent germination. No seeds germinated in the dark. In summary, seeds of S. marilandica exhibit physiological dormancy, which can be alleviated by exposure to light, after-ripening and/or cold stratification. It is probable that the differences in germination response among sites can be attributed to differences in environmental conditions during seed production. These experiments indicate that the seeds of S. marilandica must be buried shortly after dispersal in order to form a persistent seed bank.     

Synergism between gibberellic acid and low Pfr levels inducing germination of Kalanchoë seeds

Sown on water, seeds of Kalanchoëbiossfetdiana Poelln. cv. Feuerblute are absolutely light-requiring and show full red/far-red reversibility. In seeds, sown on 2 ×10^-3 M gibberellic acid, red/far-red reversibility disappears and both short red and far-red irradiations induce germination. Gibberellic acid alone does not induce germination, but it increases the physiological activity of P_fr to the extent, that the low P_fr level obtained by far-red irradiation becomes very effective. The synergism between gibberellic acid and far-red light appears after a two-day incubation; period. The nature of this lag phase was examined by measuring both germination and uptake of labelled gibberellic acid in intact seeds and seeds with a punctured seed coat. The lag phase was shown to be independent of the uptake kinetics of gibberellic acid and allows development to a specific stage, necessary for germination after phytochrome-phototransformation. The kinetics of the uptake of gibberellic acid by intact seeds and embryos of intact seeds are different. In intact seeds most of the gibberellic acid is retained in the seed coat; only a small fraction actually penetrates to the embryo where it can exert its physiological activity.     

Effect of water stress and gibberellic acid on germination of flax,sesame and onion seeds

The effects of different osmotic stresses (from 0 to –8× 10⁵ Pa) obtained with NaC or polyethylene glycol 6000 solutions on the germination of flax, sesame and onion seeds were investigated. The effect of presoaking with gibberellic acid (GA³) on the germination of the above mentioned seeds was also studied. It was found that the rate of seed germination and the final germination percentages as well as the amount of water absorbed by the seeds were considerably lowered with the rise of osmotic stress levels whatever the stress agent used, more considerable reduction was obtained under polyethylene glycol 6000 than under NaCl. Presoaking with gibberellic acid increased the rate and the final germination percentage of osmotically stressed flax and sesame seeds, while those of stressed onion seeds were slightly retarded.     

Mode of action of gibberellic Acid and light on lettuce seed germination

The seeds of lettuce (Lactuca sativa L. cv. Grand Rapids) germinate in darkness at 25 C when treated by gibberellic acid (GA₃) for 1 hour following 2 hours of imbibition. The time of GA₃ application influences the rate and the final percentage of seeds that germinate. In contrast, red light illumination given at different times affects only the rate and not the final germination percentage. The early process(es) of germination initiated by GA₃ or light treatment can be arrested by subjecting the treated seeds to a nongerminative temperature of 35 C. The results suggest differences in the mode of action of light and GA₃ during germination. They indicate that different kinds of processes are involved in the biochemical control of germination.     

Dormancy in Dioscorea: Gibberellin-Induced Inhibition or Promotion in Seed Germination of D. tokoro and D. tenuipes in Relation to Light Quality

Effects of light and gibberellic acid (GA₃) application on the germination of Dioscorea tokoro Makino and Dioscorea tenuipes Franch. et Savat. were observed. For complete germination, seeds of both species required prechilling in moist condition before incubation at a higher temperature. Red light irradiation during the incubation after the prechilling promoted germination; blue, green, or far red light markedly inhibited the germination of both species.     

SOME FACTORS AFFECTING THE GERMINATION OF SEED OF THE SAGUARO CACTUS (CARNEGIEA GIGANTEA)

Alcorn , Stanley M. (U. S. Dept. of Agric., Tucson, Ariz.), and Edwin B. Kurtz , Jr . Some factors affecting the germination of seed of the saguaro cactus (Carnegiea gigantea). Amer. Jour. Bot. 46(7): 526–529. 1959.—Germination of saguaro cactus seeds is stimulated by red light (approx. 6550 A) or daylight and far-red light (approx. 7350 A) counteracts this effect. About 0.1% germinate in continuous darkness. A single exposure to red light was most effective when the seeds were imbibed 24 hr., but maximum germination resulted from multiple exposures to red light during a 72-hr. imbibition period. The optimum temperature for germination was 25°C.; no germination occurred at 15°C. and only slight germination at 35°C. Imbibition of light-treated seeds in 0.05 to 0.2% KNO₃ increased germination. Germination of seeds in either light or dark was increased by imbibing the seeds in 500 to 1000 p.p.m. gibberellic acid.