Hormonal Regulation of Seed Dormancy in Hazel (Corylus avellana L.) and Beech (Fagus sylvatica L.)

Dormancy in seeds of hazel (Corylus avellana L.) and beech (Fagussylvatica L.) has been studied with special reference to changesin growth-promoting and inhibiting substances during after-ripening.About 12 weeks at low temperature and under moist conditionsis necessary for complete after-ripening. Gibberellic acid,kinetin, and thiourea stimulate germination in dormant seedsbut have no effect on nuts with the pericarp intact. Gibberellin‘D’ is ten times more active than gibberellic acid.Bio-assays, following chromatographic fractionation of seedextracts, have revealed no significant changes in the concentrationsof auxins and inhibitors during after-ripening. Dwarf maize-leafsection assays have revealed low concentrations of gibberellin-likesubstances in purified extracts of chilled, dormant hazel seedbut no gibberellin activity in extracts of dormant seed. Gibberellinsare present in both dormant and germinating beech seeds butthere appear to be differences in the chromatographic patternof activity. The possible role of endogenous gibberellins inthe after-ripening process is discussed.     

Spatial and Developmental Variation in Seed Dormancy Characteristics in the Fire-responsive Species Anigozanthos manglesii(Haemodoraceae) from Western Australia

Anigozanthos manglesii(Haemodoraceae) is a colourful, herbaceousperennial exhibiting intra- and inter-populational variationin germination in response to smoke and heat. This study investigatedthe extent and nature of this variation in A. manglesii populationscollected along a 550 km latitudinal cline from kwongan scrub(30°S) to more mesic jarrah forest habitats (34°S) insouthwestern Australia. Variation in seed germination alonga maturing inflorescence was also investigated. Germinationof this species is known to be prolific following fire, andtwo germination treatments, aerosol smoke and heat, were usedas germination cues. There was a trend of increasing responsivenessof A. manglesii to smoke with increasing latitude along a clinalrange, but there were no differences in germination of seedsalong the cline in response to control or heat treatments. Therewas no significant difference in intra-population seed germinationin response to any treatment. Lastly, a significant and increasingresponse to smoke for seeds from the apex to base of the inflorescencewas detected. This latter trend may be attributed to higherresource allocation and an accelerated after-ripening of basipetalcompared to acropetal seeds. Possible reasons for the clinalvariation are discussed.Copyright 2001 Annals of Botany Company Anigozanthos manglesii, populations, geographical cline, inflorescence level, germination, smoke, heat, fire, seed development     

The Effect of Low Temperature Pre-Sowing Treatment on the Germination Performance and Membrane Integrity of Artificially Aged Tomato Seeds

Loss of seed viability and decrease in germination rate appearto be due to two independent sets of events occurring duringartificial ageing in tomato (Lycopersicon esculentum Mill) seeds.Only the second category of physiological damage is reversible:a low temperature pre-sowing treatment being capable of greatlyreducing the time to fifty percent germination of both unagedand aged seeds, but having no effect on germination capacity.Leakage of ionic solutes from the seeds did not increase followingageing, but there were considerable increases in losses of smallorganic molecules. Low temperature pretreatments did not reducethe rate of loss of either amino acids or reducing sugars fromaged seeds. The implications of the use of artificial ageingin combination with low temperature pre-sowing treatments inthe study of small seed physiology is discussed, as is the valueof solute leakage studies in this kind of seed. Key words: Tomato seeds, Accelerated ageing, Seed treatment, Membranes     

A Model for Germination Rate during Dormancy Loss in Hordeum vulgare

A quantitative model for change in germination rate of barley(Hordeum vulgare L.) during and after loss of primary dormancyis presented. Change in mean germination time on a logarithmicscale is normally distributed within the period of after-ripeningand the standard deviation of this distribution is shown tobe a quantitative function of after-ripening temperature. Therate of change of mean germination time is in inverse proportionto the product of the standard deviation and a parameter whichis characteristic of the seed population. The latter parameteris the rate constant for change in probit cumulative germinationas a negative linear function of the logarithm of mean germinationtime. A model based solely on dormancy loss is combined withan existing model of change in probit viability as a functionof mean germination time to produce a model which predicts thetime to and optimum value of mean germination rate of a populationas it after-ripens. The model provides a quantitative link betweenthe effect of pre-germination and germination environments ontotal and rate of germination of an initially dormant population.Experimental data from dormant barley (cv. Triumph) stored at27, 38, 45, 50 and 60 °C, and germinated at 18 °C wereused to validate the model. The data show that germination ratecontinues to increase after primary dormancy is lost until itreaches an upper limit determined by the intrinsic germinativevigour of the seed lot. Rate of loss of primary dormancy andincrease in germination rate thus appear to be quantitativelylinked as a function of after-ripening temperature and factorswhich may be specific to the mode of induction of dormancy withina seed lot prior to harvest.Copyright 1995, 1999 Academic Press Hordeum vulgare L. barley, germination rate model, dormancy, vigour, after-ripening temperature     

Effects of after-ripening and gibberellic acid on the thermoinduction of seed germination in Solarium melongena

Daily alternating temperatures or a short exposure to low orhigh temperatures were necessary for the germination of eggplantseeds at the initial stage of after-ripening. But requirementsbecame less strict with the progress of after-ripening, andafter 4 to 8 months of afterripening, germination occurred easilyboth at constant (20 and 25) and daily alternating temperatures(30 for 16hrs and then 20 for 8hrs). With further progress in after-ripening, however, daily alternatingtemperatures or a short exposure to low or high temperaturesbecame again indispensable for attaining a high percentage ofgermination. The progress of after-ripening was greatly influencedby the degree of seed ripening, that is, by the period beforethe seeds were sampled from fruits after anthesis (ripening). The effect of GA on the germination of egg plant seeds varieddepending on the concentration of GA, temperature and the degreeof maturity (ripening and after-ripening) of the seeds. (Received March 8, 1968; )     

Patterns of seed after-ripening in Bromus tectorum L

For grass seeds that lose dormancy through after ripening indry storage, the probability of germination following a particularwetting event can be predicted only if the relationship betweenstorage temperature and change in after-ripening status is known.This study examined patterns of seed dormancy loss in Bromustectorum L., quantifying changes in germination percentage,speed, and uniformity through time. Seed collections from threesemi-arid habitats were stored at temperatures from 10–40C. At monthly intervals, subsamples were incubated at 5/15,10/20, 15/25, and 20/30 C. For recently harvested seeds, germinationpercentage, mean germination time, and days between 10% and90% of total germination (D90–D10) ranged from 1–75%,10–24 d, and 10–20 d, respectively. Recently harvestedseeds were generally most dormant, slowest to germinate andleast uniform at high incubation temperatures. In contrast,after ripened seeds for all collections had nearly 100% germination,mean germination times <5 d, and D90–D10 values <5d. Three indices were used to characterize after-ripening ratesfor each seedlot at each incubation temperature. The mean dormancyperiod, the mean rate index, and the mean uniformity index definedthe storage period required for seedlots to become half as dormantas at harvest, to progress half-way to the fastest speed, andto progress half-way to the greatest uniformity, respectively.Seeds required longer storage to germinate uniformly than togerminate completely or quickly, because germination time-coursecurves for incompletely after-ripened seeds were positivelyskewed rather than sigmoidal. Mathematically, the three indiceswere described as negative exponential functions of storagetemperature, which suggests that after-ripening is likely completedin late summer or early autumn regardless of summer conditions. Key words: Seed dormancy, germination timing     

Dormancy in Seeds of Anona crassiflora Mart

The seeds of Anona crassiflora Mart., an important tree of theBrazilian cerrado, have been found to take about 8 months forgermination to commence, and some 35-70 d more to achieve itfully; such seeds must remain in moist ground all this time.A poorly developed embryo, little more than a hyaline mass ofcells, was all that could account for the delayed germination.Inhibition by extracts of seed parts was negligible. In A. crassifloraafter-ripening is related more to morphological changes in theembryo than to chemical changes. As the seed cannot endure evena brief sojourn in dry soil, vegetative reproduction is themeans by which the tree spreads into new areas.     

Action of Respiratory Inhibitors on Seed Germination and Oxygen Uptake in Avena fatua L.

The effects of sodium azide, potassium cyanide (cytochrome oxidaseinhibitors), and salicylhydroxamic acid (SHAM; an alternativerespiration inhibitor) on germination and respiration of Avenafatua L. seeds were studied. Azide and cyanide released seeddormancy at similar concentrations and treatment durations.Cyanide, however, stimulated germination of seeds with littleafter-ripening, whereas azide had no effect under similar conditionsunless the seeds were after-ripened for several months; theduration of after-ripening required for seeds to respond toazide varied with seed batch. There was also a greater lag priorto germination in the case of azide, compared to cyanide treatedseeds. SHAM inhibited the stimulation of germination and respirationby azide, but not by cyanide. Furthermore, respiration induced by azide or cyanide could notbe inhibited by the subsequent application of SHAM. These findingssuggest that the respiration stimulated by azide and cyanideis not alternative (SHAM-sensitive) and, therefore, this respiratorypathway cannot be involved in the stimulation of germinationby cytochrome oxidase inhibitors. While embryos excised fromcontrol, azide or cyanide pretreated seeds had the capacityto perform alternative respiration, the actual contributionof this pathway was negligible. A large proportion of respirationof embryos excised from azide or cyanide pretreated seeds wasresidual, i.e. insensitive to both SHAM and cyanide. Alternative respiration, azide, cyanide, dormancy, salicylhydroxamic acid, wild oats     

Interaction Between Cryopreservation, Rewarming Rate and Seed Humidification on the Germination of Two Spanish Endemic Species

The effects of humidification, storage in liquid nitrogen (1or 30 d) and rewarming rate on seed germination were studiedin two Spanish endemics. Humidification resulted in higher germinationpercentages only in the species with hard covers, especiallyin slowly rewarmed seeds. In an experiment lasting 21 weeks,seeds stored in liquid nitrogen were removed for 10 min eachweek to mimic the withdrawal of samples from a seed bank; thishad no effect on germination.Copyright 1998 Annals of BotanyCompany Centaurea hyssopifolia,Limonium dichotomum, cryopreservation, cypsela, endemics, germination, humidification, seeds.     

Analysis of the role of COMATOSE and peroxisomal beta-oxidation in the determination of germination potential in Arabidopsis

Comparative physiological analysis of mutant Arabidopsis seeds under defined environmental conditions was used to analyse the relative contributions of components of peroxisomal beta-oxidation in the control of seed germination potential. The COMATOSE (CTS) and KAT2 loci were shown to play essential roles in regulating germination and establishment potentials, whereas LACS6 and LACS7 loci only influenced establishment following germination. The viability and desiccation tolerance of three different mutant alleles of CTS were shown to be intermediate between that of dormant and non-dormant wild-type seeds. Analysis of ttg-1 cts-1 double mutant seeds demonstrated that the cts lesion did not influence after-ripening capacity. These data demonstrate the importance of peroxisomal beta-oxidation in the control of germination potential, but suggest that breakdown of stored lipid is not an important prerequisite for germination. A function is suggested for CTS following after-ripening within pathways related to the progression of germination prior to radicle emergence.     

Water Relations of Seed Development and Germination in Muskmelon (Cucumis melo L.): VII. INFLUENCE OF AFTER-RIPENING AND AGEING ON GERMINATION RESPONSES TO TEMPERATURE AND WATER POTENTIAL

The effects of storage conditions on the germination of developingmuskmelon (Cucumis melo L.) seeds were tested to determine whetherafter-ripening is required to obtain maximum seed vigour. Seedswere harvested at 5 d intervals from 35 (immature) to 60 (fullymature) days after anthesis (DAA), washed, dried, and storedat water contents of 3·3 to 19% (dry weight basis) at6, 20, or 30°C for up to one year. Germination was testedin water and in polyethylene glycol 8000 solutions ( –0·2to –1·2 MPa osmotic potential) at 15, 20, 25 or30°C. Germination percentages and rates (inverse of meantimes to radicle emergence) were compared to those of newlyharvested, washed and dried seeds. For 40 and 60 DAA seeds,one year of storage at 20°C and water contents <6·5%significantly increased germination percentages and rates at20°C, but had little effect on germination at 25 and 30°C.Storage reduced the estimated base temperature (T_b) and meanbase water potential (_b) for germination of both 40 and 60 DAAseeds by approximately 5°C and 0·3 MPa, respectively.Immature 35 DAA seeds showed the greatest benefit from storageat 3 to 5% water content and 30°C, as germination percentagesand rates increased at all water potentials (). Storage underthese same conditions had little effect on the germination ofmature seeds in water, but increased germination percentagesand rates at reduced 's. Accelerated ageing for one month at30°C and water contents from 15 to 19° increased germinationrates and percentages of mature seeds at reduced 's, but longerdurations resulted in sharp declines in both parameters. Immatureseeds lost viability within one month under accelerated ageingconditions. An after-ripening period is required at all stagesof muskmelon seed development to expand the temperature andwater potential ranges allowing germination and to achieve maximumgerminability and vigour. Post-harvest dormancy is deepest atthe point of maximum seed dry weight accumulation and declinesthereafter, both in situ within the ripening fruit and duringdry storage. Key words: Muskmelon, Cucumis melo L., seed, development, dormancy, germination, vigour, after-ripening     

The Effects of Priming and Ageing on Resistance to Deterioration of Tomato Seeds

The influence of seed priming and ageing treatments on viabilityand rate of germination of tomato (Lycopersicon esculentum Mill.)seeds was examined under both long-term and controlled-deteriorationstorage conditions. Seeds of a single lot of tomato were eitherprimed or aged to increase or decrease the rate of germination(Argerich and Bradford, 1989). They were then stored at 6% moisturecontent (dry weight basis) at either 4 ?C or 30 ?C for 1 year.Both viability and germination rate were unaffected by eitherstorage temperature in control seeds, or by 4 ?C storage inprimed or aged seeds. At 30 ?C, however, viability and germinationrate of primed and aged seeds was markedly reduced after 6 monthsof storage. The temperature dependence of the germination rateand the spread of germination times within the population wasalso adversely affected by high temperature storage, particularlyfor primed seeds. Under controlled deterioration conditions(13.5% moisture content and 50 ?C), the rate of loss of viabilitywas greater for primed seed than for control or aged seeds.The relationship between seed viability and the mean germinationrate, however, was not influenced by the seed treatments. Thesedata are analysed in relation to current models of seed deteriorationduring storage and seed repair during priming. The results indicatethat enhancement of seed germination rates by priming treatmentssimultaneously lowers the resistance of seeds to deterioration.Primed tomato seeds must, therefore, be considered to be vigorousseeds with a reduced storage life. Key words: Tomato, controlled deterioration, seed germination rate, seed viability     

Characterization of the Germination Responses of Silene dioica (L.) Clairv., Populations from Europe

Germination tests were done on 20 populations of Silene dioicacollected in different parts of Europe. Seeds collected fromwild plants and from their progeny growing at R.B.G. Kew, weretested using both freshly harvested and stored seeds. Responseswere compared from tests done on thermo-gradient bars and inincubators to examine germination and after-ripening processesbetween c. 2-c. 45 °C. The responses of different populations were characterized byidentifying variations due to the proportions of dormant seeds,the maximum and minimum temperatures favouring germination,and the time course of germination at particular temperaturesof freshly shed and stored seed. Germination and after-ripeningresponses of different populations displayed marked qualitativesimilarities, but differences in the degree of their expressionresulted in statistically significant quantitative differenceswhich could sometimes be correlated with features of the geographicaldistribution of the populations. The results are discussed in relation to the occurrence of thisspecies in a well-defined natural habitat in Europe, and itis concluded that they represent a situation in which fundamentallysimilar control patterns underlying the responses of every populationexamined are modulated quantitatively to produce variationsin the number of seeds germinating at particular seasons orremaining dormant within the soil.     

Seed Dormancy and Germination in Cimicifuga nanchuanensis

Seed anatomy, dormancy breakage, the temperature effect to seed germination and seed life-span of Cimicifuga nanchuanensis Hsiao were studied and the endangerment of this plant in association to these biological characteristics was explored. The embryos were at the globular stage at the time of seed shedding in late November. Low temperature and humid conditions or treatment with exogenous GA3 stimulated the development of embryos and sped up the process of seed germination. The optimum temperature of germination was 20 ℃, but the seeds almost lost their viability after 9 months of storage. Nevertheless, in its natural habitation, the seeds could not acquire enough environmental humidity to accomplish their after-ripening during the dry and cold winter from late November to the following March; after then the temperature in the spring (averaged 10.1 ℃ in April and May) was much lower than 20 ℃ or so which is favorable for seed germination. Moreover, the testa could not provide adequate protection for the embryos and the short life-span of the seeds prevents their survival until the next germination. Therefore it seems reasonable to infer that the unfavorable environmental condition during the process of after-ripening until seed maturation is involved in the cause of endangerment of this plant species.     

Germination of Stored Cassava Seed at Constant and Alternating Temperatures

Cassava seed is only capable of germinating over a restrictedrange of constant temperatures. During storage the optimum constanttemperature for germination decreases from about 35 to 30 °Cor possibly less. The rate at which the optimum temperaturechanges during dry storage increases with increase in storagetemperature over the range 0 to 40 °C. Some alternating-temperatureregimes (16 h at the lower temperature; 8 h at the higher temperature)can provide conditions as favourable for germination as theoptimum constant temperatures. Furthermore, it has been shownthat temperature alternation itself is stimulatory because whenthe range of the alternation does not include the optimum constanttemperature value, percentage germination is often higher thancould be obtained at any constant temperature within the range,though this stimulatory response declines during storage. Forthese reasons it is provisionally recommended that cassava seedshould be germinated at 25/35 °C which is as stimulatorya treatment as any which has so far been investigated and hasthe advantage of encompassing the range over which the optimumconstant temperature changes during storage. Manihot esculenta Crantz, cassava, germination, dormancy, seed viability, storage of seeds, after-ripening     

Wheat seed proteins regulated by imbibition independent of dormancy status

Seed dormancy is an important trait in wheat (Trticum aestivum L.) and it can be released by germination-stimulating treatments such as after-ripening. Previously, we identified proteins specifically associated with after-ripening mediated developmental switches of wheat seeds from the state of dormancy to germination. Here, we report seed proteins that exhibited imbibition induced co-regulation in both dormant and after-ripened seeds of wheat, suggesting that the expression of these specific proteins/protein isoforms is not associated with the maintenance or release of seed dormancy in wheat.     

濒危植物巴东木莲种子休眠与萌发特性的研究

巴东木莲(Manglietia patungensis)为我国特有种, 属国家重点保护植物。为找出其生殖环节中的致危因素, 作者对巴东木莲种子休眠与后熟过程中的形态和萌发特性进行了研究。结果表明, 巴东木莲种胚发育不完全可能是种子休眠的主要原因, 在其后熟过程中胚不断分化、发育成熟; 种皮具有较好的透性, 与休眠的关系不大; 种子不同部位均存在萌发抑制物, 胚乳中高含量的萌发抑制物是影响胚萌发的重要因素。内源激素ABA和IAA在巴东木莲种子休眠与萌发过程中起着重要作用, ABA是引起休眠的关键因素, IAA有助于种子的萌发, IAA/ABA相对含量的变化对种子的休眠和萌发产生重要影响。巴东木莲种子的休眠是由种子本身的形态和生理特点引起的综合休眠, 在4℃低温保湿条件下才能完成其形态和生理后熟过程, 而自然条件下, 巴东木莲种子成熟时正值秋季少雨, 很容易失水而不能完成其后熟过程而失去生活力, 这可能是导致该物种自然更新困难的重要原因。     

After-Ripening in Festuca idahoensis Seeds: Adaptive Dormancy and Implications for Restoration

Festuca idahoensis (Idaho fescue) was a common native perennial bunchgrass in the sagebrush steppe of the western United States until the introductions of domestic livestock and alien plants. Restoration of Idaho fescue to degraded sites will likely involve reseeding, and one of the factors affecting reseeding success is germinability of the seeds employed. We investigated effects of after-ripening and storage temperature on germinability of Idaho fescue seeds collected from a central Oregon site. Six months of after-ripening were required before maximum germination was obtained. Storage of dry seeds at either room temperature (20°C) or at cooler, alternating temperatures (5/15°C) did not alter the rate at which dormancy was lost. Storage at the warmer temperature promoted rapid germination in seeds that had broken dormancy. Seed longevity varied greatly from year to year. Seeds produced in a very dry year had poorer germination and shorter longevity than seeds produced during a year with near normal precipitation. Because seed dispersal occurs in late July and early August for Idaho fescue in central Oregon, a six-month after-ripening requirement ensures that the greatest potential germination coincides with the spring period most likely to provide sufficient moisture for seedling establishment.     

Prehydration and Priming Treatments that Advance Germination also Increase the Rate of Deterioration of Lettuce Seeds

The influence of prehydration in water or priming in –1.5 MPa polyethylene glycol 8000 solution for various periods,followed by redrying, on germination rate and longevity of lettuce(Lactuca sativa L.) seeds (achenes) was determined during controlleddeterioration at 10% moisture content (fresh weight basis) and40°C. Short prehydration treatments (up to 1 h) had littleeffect on either germination rate or longevity, but significantlyimproved root growth rates. Increasing durations of prehydrationor priming reduced the mean time to germination by up to 61%relative to untreated seeds, but also reduced mean seed longevityby as much as 84% Prehydration and priming altered the relationshipsbetween germination rate and viability and between normal andabnormal seedlings during ageing. Prehydration in abscisic acidor at a temperature inhibitory to germination did not preventthe reduction in longevity under controlled deterioration conditions.While prehydration or priming treatments effectively acceleratesubsequent germination rates of lettuce seeds, the redried seedsare nonetheless highly susceptible to deterioration in storage. Key words: Lettuce, Lactuca sativa L., seed priming, seed deterioration, germination rate