Biochemical Characteristics Associated with the Development of the Desiccation-sensitive Seeds of Machilus thunbergii Sieb. & Zucc.

Biochemical properties, i.e. endogenous abscisic acid, proline,sugars, respiration, adenosine phosphates and adenylate energycharge, and growth and moisture content were measured duringthe development of seeds of Machilus thunbergii. As dry matteraccumulated in the embryo during development, moisture content,ABA, proline, respiration and sugars all declined. At maturity,the dry mass of the seeds failed to attain a plateau beforethe period of natural seed shedding; the axis and cotyledonsreached moisture contents of 58 and 45%, respectively. Dryingof immature seeds at 73% relative humidity and 25 °C for30 d resulted in a complete loss of viability at all developmentalstages tested with the exception of mature seeds that were ableto tolerate a 5% decrease in moisture content before germinationdeclined. ABA was detected in all embryos tested, with a maximum value16.·16 µg g^-1 d. wt about midway through development.Although the presence of ABA induced no tolerance to desiccationof mature seeds, it did coincide with decreased content of waterin the developing seeds and decreased respiration. Desiccationdamage of M. thunbergii seeds occurred when moisture contentwas still high (45%) and this damage was not related to theabsence of oligosaccharides in the mature seeds. We concludethat developing embryos and mature seeds of M. thunbergii haveproperties common to many recalcitrant seeds, with seeds beingsensitive to desiccation at all stages, having a prominent ABApeak, little proline, lacking oligosaccharides, and specifically,little dormancy and a moderate rate of respiration of matureseeds (0·9 µmol O₂ min^-1 g^-1 f. wt). Adenosinetriphosphate content and energy charge decreased from stagefour to stage eight of seed development, then increased againto 103 nmol g^-1 d. wt and 0·73, respectively, in matureseeds. The moderate energy charge observed in mature seeds indicatesthat continuous metabolism is also a characteristic of recalcitrantseeds.Copyright 1995, 1999 Academic Press Machilus thunbergii, seed development, recalcitrant seed, abscisic acid, energy charge     

Priming and accelerated ageing affect L-isoaspartyl methyltransferase activity in tomato (Lycopersicon esculentum Mill.) seed

Damage and degradation of cellular proteins is observed duringage-induced seed deterioration. L-Isoaspartyl protein methyltransferase(EC 2.1.1.77 [EC] ) is an enzyme hypothesized to play a role in limitingand repairing age-induced damage to proteins. Tomato (Lycopersiconesculentum Mill. ‘New Yorker’) seeds were assayedfor changes in L-isoaspartyl methyl-transferase activity duringaccelerated ageing and after osmotic priming. Accelerated ageingof seeds for 1–4 d at 45C and 100% relative humidityreduced germination from 94% to 71%, increased the mean timeof germination (MTG) from 2.4 to 5.8 d, and was accompaniedby a correlative decrease in L-isoaspartyl methyltransferaseactivity (r²=0.90). Aged and untreated seeds were primed for7 d at 20C in darkness using aerated solutions of 3% KNO₃ orpolyethylene glycol 8000 (PEG) with equivalent osmotic potential(–1.25 MPa). Priming with KNO₃ decreased the MTG, butdid not improve germination percentage for untreated seeds.Priming did not affect L-isoaspartyl methyltransferase activityin untreated seeds, but restored activity in aged seeds primedin KNO₃ to levels near that of untreated seeds. Priming withPEG did not effectively improve the MTG or increase L-isoaspartylmethyltransferase activity. During germination, L-isoaspartylmethyltransferase activity remained constant for 48 h post-imbibitionand then declined, suggesting that the enzyme was developmentallyregulated and inactivated or degraded as radicle emergence occurred. Key words: L-Isoaspartyl methyltransferase, protein repair, seed priming, accelerated ageing, Lycopersicon esculentum     

Normalizing Development of Cultured Triticum aestivum L. Embryos: I. LOW OXYGEN TENSIONS AND EXOGENOUS ABA

Wheat (Triticum aestivum L.) embryos form in dynamically-regulatedovular environments. Our objectives were to improve developmentof cultured immature wheat embryos by simulating, in vitro,abscisic acid (ABA) levels and O₂ tensions as found in wheatovules during zygotic embryogenesis. We characterized from intactwheat kernels embryo respiration, embryo morphology and embryoand endosperm + ABA levels at 13, 19 and 25 d post-anthesis(DPA). Young (13 DPA) embryos were then excised and culturedin vitro, where they were exposed to 0·2 or 2·Ommol m^–3 ±ABA and 2.·1, 2·5 or 7·4mol m^–3 (6, 7 and 21%, respectively) gaseous O₂. At 6and 12 d in culture, + ABA levels, embryo respiration and embryomorphology were characterized by treatment. Thirteen-day-oldembryos from two different plant populations differed by 17-foldin initial ABA content. However, this difference did not affectprecocious germination in vitro, nor did it affect the amountof exogenous ABA required to reduce precocious germination by40%. In this respect, embryos from both populations were equallysensitive to exogenous ABA. Cavity sap O₂ levels (2·1to 2·5 mol m^–3) were much more effective in preventingprecocious germination of cultured embryos than were cavitysap levels of ABA (0·2 to 2·0 mmol m^–3).The combination of physiological levels of both ABA and O₂ largelynormalized DW accumulation and embryo morphology without alteringendogenous + ABA levels. Residual respiration of cultured embryoswas higher than that of embryos grown in situ, and was not influencedby the exogenous O₂ and ABA treatments Key words: Abscisic acid, embryo development, oxygen tensions, respiration, wheat     

Photoperiodically Induced Changes in Seed Growth Rate of Soybean as Related to Endogenous Concentrations of ABA and Sucrose in Seed Tissues

Short-day photoperiods can increase the partitioning of assimilatesto filling seeds of soybean (Glycine max L. Merr.), resultingin higher seed growth rates. The plant growth substance ABAhas been implicated in the regulation of assimilate transferwithin filling soybean seeds. Thus, we hypothesized that anincreased concentration of endogenous ABA in seeds may enhancesucrose accumulation and seed growth rate of soybeans exposedto short-day photoperiods. Plants of cv. Hood 75 were grownin a greenhouse under an 8-h short-day photoperiod (SD) until11 d after anthesis (DAA) of the first flower, when half ofthe plants were transferred to a night-interruption (NI) treatment(3 h of low-intensity light inserted into the middle of thedark period). Plants remaining in SD throughout seed developmenthad seed growth rates 43% higher than that of plants shiftedto NI (7·6 mg seed^–1 d^–1 vs. 5·3 mgseed^–1 d^–1). On a tissue-water basis, the concentrationof ABA in SD seeds increased rapidly from 7.6 µmol l^–1at 11 DAA to 65·2 µmol l^–1 at 18 DAA, butthen declined to 6·6 µmol l^–1 by 39 DAA.In contrast, the concentration of ABA increased more slowlyin NI seeds, reaching only 47·4 µmol l^–1by 18 DAA, peaking at 57·0 µmol l^–1 on 25DAA, and declining to 10·2 µmol l^–1 by 39DAA. The concentration of sucrose in SD embryos peaked at 73·5mmol l^–1 on 25 DAA and remained relatively constant forthe remainder of the seed-filling period. In NI, the concentrationof sucrose reached only 38·3 mmol 1^–1 by 25 DAA,and peaked at 61·5 µmol l^–1 on 32 DAA. Thusin both SD and NI, sucrose accumulated in embryos only afterthe peak in ABA concentration, suggesting that ABA may havestimulated sucrose movement to the seeds. The earlier accumulationof ABA and sucrose in SD suggests that ABA may have increasedassimilate availability during the critical cell-division period,thus regulating cotyledon cell number and subsequent seed growthrate for the remainder of the seed-filling period. Glycine max L. Merr. cv. Hood 75, soybean, assimilate partitioning, abscisic acid, photoperiod, source-sink     

Theoretical Basis of Protocols for Seed Storage III. Optimum Moisture Contents for Pea Seeds Stored at Different Temperatures

In previous work, we demonstrated that there was an optimummoisture level for seed storage at a given temperature (Vertucciand Roos, 1990), and suggested, using thermodynamic considerations,that the optimum moisture content increased as the storage temperaturedecreased (Vertucci and Roos, 1993b). In this paper, we presentdata from a two year study of aging rates in pea (Pisum sativum)seeds supporting the hypothesis that the optimum moisture contentfor storage varies with temperature. Seed viability and vigourwere monitored during storage under dark or lighted conditionsat relative humidities between 1 and 90%, and temperatures between-5 and 65°C. The optimum moisture content varied from 0·015g H₂O g^-1 d.wt at 65°C to 0·101 g H₂O g^-1 d.wt at15°C under dark conditions and from 0·057 at 35°Cto 0·092 g H₂O g^-1 d.wt at -5°C under lighted conditions.Our results suggest that optimum moisture contents cannot beconsidered independently of temperature. This conclusion hasimportant implications for 'ultra-dry' and cryopreservationtechnologies.Copyright 1994, 1999 Academic Press Seed storage, seed aging, seed longevity, water content, temperature, glass, desiccation damage, ultradry, Pisum sativum L., pea, cryopreservation     

Contrasted Effects of CO2 on the Regulation of Dormancy and Germination in Xanthium pennsylvanicum and Setaria faberi Seeds

The effects of CO₂ on dormancy and germination were examinedusing seeds of cocklebur (Xanthium pennsylvanicum Wallr.) andgiant foxtail (Setaria faberi Herrm.). The rate of germinationof the giant foxtail seeds as well as cocklebur was promotedby exogenously applied CO₂ at a concentration of 30 mmol mol^-1regardless of the sowing conditions. However, seeds which failedto germinate in the presence of CO₂, entered a secondary phaseof dormancy under unfavourable germination conditions. If CO₂was applied to seeds under conditions such as water stress imposedwith a 200 mol m^-3 mannitol solution, a hypoxic atmosphere of100 mmol mol^-1 O₂ or a treatment of 0·1 mol m^-3 ABA,development of secondary dormancy was accelerated. These contrastedeffects of CO₂ were observed in ecological studies. Under naturalfield conditions germination of buried giant foxtail seeds respondedpositively to CO₂ during a period of release from primary dormancyfrom Feb. to May, but CO₂ accelerated secondary dormancy commencingin early Jun. In other words, in the presence of CO₂, both theenvironmental conditions and the germination states of the seedsclearly showed secondary dormancy-inducing effects. Thus, itseems that CO₂ has contrasted effects on regulation of dormancyand germination of seeds depending on the germination conditions.Copyright1995, 1999 Academic Press Xanthium pennsylvanicum, cocklebur, Setaria faberi, giant foxtail, CO₂, water stress, hypoxia, ABA, germination, secondary dormancy     

The Role of ABA in the Control of Apple Seed Dormancy Re-appraised by Combined Gas Chromatography-Mass Spectrometry

Measured by GC—MS²—SIR³, endogenous ABA⁴ in embryonicaxes of seeds of Malus pumila L. cv. Golden Delicious decreased8-fold and cotyledon ABA by only 60%, during 10–50 d ofstratification at 5 ?C, after ABA leaching during an initial24 h soaking. During stratification, the percentage germinationof embryos transferred to 17?C showed a significant linear dependenceon log_e of ABA levels in the axes at transfer. Between 50 and70 d, ABA levels increased markedly in axes and testa both ofstratified seeds and seeds allowed to re-dry at 17 ?C afterinitial soaking. The ability of fully stratified axes with elevatedendogenous ABA to germinate indicated that stratification haddecreased their ABA sensitivity. Changes in cotyledon ABA couldnot account for the promotory effect of cotyledons on germinationduring the first 30 d of stratification. Loss of testa inhibitionof germination during stratification was not linked with changesin testa ABA. Stratification markedly increased the sequestrationin the axes of exogenous ABA supplied via the cotyledons. Changesboth in axis ABA levels and sensitivity were thus correlatedwith dormancy release, but subject to modifying control by thecotyledons and testa not involving ABA. Rehydration of driedseeds affected axis ABA later during storage via mechanismsunconnected with dormancy. Key words: ABA, seed dormancy, stratification     

Activation of the Cell Cycle in Tomato (Lycopersicon esculentum Mill.) Seeds during Osmoconditioning as Related to Temperature and Oxygen

Using flow cytometric analyses of the nuclear DNA content, westudied the effects of various conditions of osmopriming onthe activation of the cell cycle in embryo root tips of tomato(Lycopersicon esculentum‘Elko’) seeds. In dry untreatedseeds, 90.7% of the nuclei revealed 2C signals. Priming of seedsin polyethylene glycol-8000 (PEG) improved the germination rateof seeds transferred onto water at 15 °C. This was associatedwith an increase in 4C signals when priming was carried outat -1.0 and -1.5 MPa. Priming at -2.0 MPa enhanced subsequentgermination but had no effect on DNA replication. For temperaturesduring priming up to 25 °C, a positive linear correlationexisted between the efficiency of the treatment, evaluated bythe reciprocal of time to obtain 50% germination at 15 °C,and the frequency of 4C nuclei or the 4C/2C values. Such a correlationdid not exist when priming was performed at higher temperatures.At least 5% oxygen in the atmosphere was required during primingfor the induction of DNA replication and for the enhancementof subsequent germination. In the presence of 5x10^-4M and 10^-3MNaN₃during priming, most of the cells were maintained with 2CDNA levels and the treatment had no stimulatory effect on germination.The results show a positive linear relationship between thefrequency of 4C DNA nuclei or the 4C/2C ratio and the improvingeffect of priming. However, in suboptimal conditions of priming(-2.0 MPa or temperatures higher than 25 °C), the improvementof seed germination was not associated with the onset of DNAreplication.Copyright 1999 Annals of Botany Company Cell cycle, germination, osmopriming, oxygen, temperature, Lycopersicon esculentum, tomato.     

An Analysis of Seed Development in Pisum sativum: VIII. DOES ABSCISIC ACID PREVENT PRECOCIOUS GERMINATION AND CONTROL STORAGE PROTEIN SYNTHESIS?

The influence of abscisic acid (ABA) on the precocious germinationand storage protein production of pea seeds has been examinedusing embryo and pod culture. The precocious germination ofembryos in culture could not be inhibited fully by ABA on apermissive medium (2% sucrose) even at 0.1 mol m^–3. However,increasing the sucrose concentration to 5% caused near completeinhibition when ABA was added to the medium. Embryos of differentweights cultured on a high osmoticum (mannitol-containing medium),equivalent to 10% sucrose, did not show any consistent differencein ABA content. When fluridone was added to a non-permissiveculture medium, no decrease in ABA content of the embryos couldbe observed and no precocious germination was induced. In contrast,fluridone was able to prevent the accumulation of ABA in seedspresent in pods cultured in its presence from an early stageof development. These seeds, however, grew normally and reachedmaturity, did not germinate precociously in vivo, were desiccationtolerant and still produced storage protein message whetheror not ABA was included in the culture medium. It does not appear,therefore, that ABA regulates normal development or storageprotein synthesis in pea embryos. Key words: Abscisic acid, peas, Pisum sativum, seed development     

Restoration of Seed Germination at Supraoptimal Temperatures by Fluridone, an Inhibitor of Abscisic Acid Biosynthesis

Fluridone, an inhibitor of ABA biosynthesis, restored the seedgermination of lettuce (Lactuca sativa L. cv. Grand Rapids)and many other plant species at supra-optimal temperatures.ABA content in lettuce seeds after imbibition quickly decreasedat 23°C, but not at 33°C (a supraoptimal temperature).Fluridone caused a decrease in ABA content at 33°C, whichsuggests that the maintenance of high ABA content could be responsiblefor high-temperature inhibition of germination of lettuce seeds.This probably results from an increase in the rate of ABA biosynthesisat the higher temperature. The present study indicates thatABA plays a decisive role in the regulation of seed germinationat supraoptimal temperatures. ¹ Corresponding author: fax 81-22-717-8834; e-mail yoshi@bios.tohoku.ac.jp     

The Effects of Priming and Ageing on Seed Vigour in Tomato

A comparison was made of the effects of seed priming or ageingtreatments on the performance of tomato (Lycopersicon esculentumMill. cv. UC204C) seeds according to a number of indices ofseed vigour. A single lot of tomato seeds was primed in 120mol m^–3 K2HPO4 + 150 mol m^–3 KNO₃ for 5 d at 20?C, or aged at 13% moisture content (dry weight basis) and 50?C for 6 d. Germination percentage (>98%) was unaffectedby priming and reduced to 85% by ageing. X-ray photographs andlongitudinal sections revealed the formation of free space surroundingthe embryo in dry primed seeds, which was not evident in controlor aged seeds. Priming increased the rate of germination atall temperatures above the base temperature (T_b), while ageingdecreased it. T_b was unaffected by priming and only slightlyincreased by ageing. The variation in individual times to germinationwas approximately doubled in both primed and aged seed comparedto the control, based upon the slopes of probit germinationpercentage versus log thermal time curves. Root growth aftergermination tests and seedling growth in both greenhouse andfield tests were not influenced by either priming or ageing.The conductivity test was found to be unreliable as a vigourtest for tomato seeds. The results identify several indiceswhich can be used to quantify seed vigour in tomato. They alsoillustrate that seed priming can enhance seed performance accordingto some criteria, while having no effect or decreasing qualityaccording to other criteria. Seed vigour can apparently be separatedinto various components which can be independently influencedby seed enhancement treatments. Key words: Tomato, seed germination rate, seed priming, seed vigour     

Amounts of Nuclear DNA and Internal Morphology of Gibberellin- and Abscisic Acid-deficient Tomato (Lycopersicon esculentum Mill.) Seeds During Maturation, Imbibition and Germination

Using X-ray photography and flow cytometry, the internal morphologyand DNA replication activity of wild type (wt), GA- (gib-1 )and ABA-deficient (sit^w ) tomato (Lycopersicon esculentum Mill.cv. Moneymaker) mutant seeds were studied. During seed formation,from 30 to 45 d after pollination (DAP) the endosperm becomessolid and the seed starts to gain desiccation tolerance. Atthis time significant changes occur in the amounts of DNA inradicle tip cells. At 30 DAP, radicle tip cells of the threegenotypes manifest about 60% of 2C, 30% of 4C and 10% of 8Camounts of DNA. Upon maturation (45 DAP onwards), most cellsin the seeds of the three genotypes arrest in the G₁phase ofthe cell-cycle with 2C amounts of DNA. However, a relativelyhigh proportion of cells with 4C amounts of DNA was detectedin the radicle tip cells ofsit^w compared with wild type andgib-1. At the well-matured stage (60 DAP), there were about 2% ofseeds with free space in wild type andgib-1 , and about 13%insit^w . At the over-matured stage (75 DAP), even more seedswith free space were found insit^w , whereas no increase in theproportion of the seeds with free space was detected in theother two genotypes. In -1.0 MPa PEG-6000 with or without 10µM GA₄₊₇, no germination occurred in well-matured wildtype andgib-1 seeds, whether or not they were dried after harvest.However,sit^w seeds were able to germinate both in over-maturefruit and in -1.0 MPa PEG-6000. Priming of dried seeds in -1.0MPa PEG induced a large amount of free space in almost all seedsof the three genotypes, and nuclear DNA synthesis in the radicletip cells of wild type andsit^w seeds. However, PEG priming offresh (non-dried) seeds had no effect on the amount of freespace and 2C/4C DNA ratios in wild type orgib-1 seeds, but didinduce free space in about 20–25% ofsit^w seeds and provoked4C signals insit^w seeds. Removal of the endosperm and testaopposite the radicle tip of seeds resulted in root protrusion,the induction of free space and an increase of 4C DNA signalsin the three genotypes. It is concluded that ABA is crucialfor the efficient arrest of tomato embryo radicle tip cellsin G₁phase upon maturation, whereas GAs play an important rolein re-initiating 4C DNA levels upon germination. Dormancy; flow cytometry; free space; Lycopersicon esculentum ; maturation; priming; seed; tomato     

Relationship between Coleoptile Elongation and Alcoholic Fermentation in Rice Exposed to Anoxia. II. Cultivar Differences

The relationship between coleoptile elongation and survivalvs. alcoholic fermentation of rice under anoxia is examinedusing eight cultivars differing in submergence tolerance. Anoxiawas imposed on either 1 or 4 d aerated seeds either by N₂ flushingsubmerged tissues or by incubating tissues in stagnant deoxygenatedagar at 0·1% w/v; the latter simulated the stagnant conditionsof waterlogged soil. Two cultivars that were most tolerant tosubmergence also had the greatest tolerance to anoxia, whilea submergence intolerant cultivar was also intolerant to anoxia. Coleoptile growth under anoxia was related to rates of ethanolsynthesis (R_E), however differences between growth during anoxiaand survival after anoxia indicated that post-anoxic injurymay also be important in rice seeds exposed to anoxia. The correlationbetween coleoptile growth and R_E measured on a tissue basisusing intact seeds was r² = 0·67 among six varietiesover 0-3 d anoxia. This correlation improved to about r² = 0·85using R_E of (embryos plus coleoptiles) over 0-3 d, or coleoptilesat 3 d after anoxia. Coleoptile growth of individual seeds wasusually poorly correlated to R_E in these cultivars at 2-3 dafter anoxia. When coleoptiles of similar lengths were obtainedfrom different cultivars using 4 d aerated seeds, there weredifferences in R_E and coleoptile growth which were related tocoleoptile growth during 3 or 5 d anoxia, either on a tissue(r² = 0·85) or a fresh weight basis (r² = 0·70-0·97respectively). Results are discussed in relation to factorswhich may limit ethanol synthesis in rice exposed to anoxiaand the importance of growth to the survival of seeds and matureplants during submergence in the natural environment.Copyright1994, 1999 Academic Press Anoxia, ethanol, alcoholic fermentation, Oryza sativa L., rice, submergence     

Light Actions in the Germination of Cocklebur Seeds: IV. DISAPPEARANCE OF RED LIGHT-REQUIREMENT FOR THE GERMINATION OF UPPER SEEDS SUBJECT TO ANOXIA, CHILLING, CYANIDE OR AZIDEPRETREATMENT

Esashi, Y., Fuwa, Nn Kojima, K. and Hase, S. 1986. Light actionsin the germination of cocklebur seeds. IV. Disappearance ofred light-requirement for the germination of upper seeds subjectto anoxia, chilling, cyanide or azide pretreatmenL—J.exp. Bot. 37: 1652–1662. The effects on the germination of positively photoblastic uppercocklebur (X anthium pennsylvanicum Wallr.) seeds by pretreatingwith anoxia, chilling, cyanide or azide, which stimulates theirdark germination, were examined in relation to light actions.Prior to experiments, seeds were pre-soaked at 23 °C inthe dark for 1 or 2 weeks to remove the pre-existing Pfr. Whenthe prctreatment conditions were suboptimal for germinationinduction, the stimulating effects of the pretreatments on germinationduring a subsequent dark period at 23 °C were manifest onlywhen seeds were irradiated with red light before or after thepretreatment Red light promotion was reversed by blue or far-redlight treatment. However, both prc-chilling for 6 d at 8 °Cand prctreatment with 1· 5 mol m ^{– 3} NaN³ for 2d could induce full germination without red light exposure.On the other hand, both pre-exposure to anoxia for 8 d and pretreatmentwith 30 mol m^–3 KCN could induce the dark germinationonly when germination occurred at 33 °C which is known toaugment the ratio of an alternative respiration flux to a cytochromeone. Moreover, the dark germination in response to these inductionswere strongly inhibited by the inhibitors of alternative respiration,propyl gallate and benzohydroxamic acid, applied during a subsequentdark period. It was thus suggested that Pfr has some relationto the operation of two respiration systems of cocklebur seeds,but it is not indispensable to germination of this positivelyphotoblastic seed. Key words: Anoxia, azide, blue light, chilling cyanide, dark germination, far-red light, red light, seed germination, X anthium pennsylvanicum     

Effect of Matric-Priming Duration and Priming Water Potential on Germination of Four Grasses

In this study, a matric-potential control system was used todetermine the effect of matric-priming duration and primingwater potential on the germination response of Bouteloua curtipendula(Michx.) Torr., Cenchrus ciliaris L., Eragrostis lehmannianaNees, and Panicum coloratum L. Seeds were primed at water potentialsof –1·5 to –7·7 MPa for up to 14 d.Optimum germination generally occurred in treatments primedat high water potential for the shortest period. Germinationof seeds primed at lower water potential and for longer periodsexhibited a negative germination response relative to the control.Seeds were not redried after the priming treatment. Seed-wateruptake measurements suggest that a reduction in the lag timeof imbibition accounted for at least some germination-rate enhancementin the positive-priming treatments Key words: Germination, matric-priming, imbibition     

Effects of Temperature and dl-Strigol on Seed Conditioning and Germination of Witchweed (Striga asiatica)

Seed conditioning and germination in witchweed (Striga asiatica(L.) Kuntze) were temperature-dependent. With higher conditioningtemperatures, shorter conditioning time was required for germinationwith terminal dl-strigol (strigol) treatment at 30 °C. Maximumgermination (80–100%) was obtained by conditioning inwater at 20, 25, 30 and 35 °C for 14, 7, 5 and 3 d, respectively,and terminally treating with 10^–6 M strigol at 30 °C.Seeds conditioned in 10^–8 M strigol instead of water germinatedmuch less with the same terminal strigol treatment. Generally,conditioning was slower when seeds were conditioned in strigolrather than water. The reduction in germination rate by pretreatmentin strigol or pretreatment at low temperatures could be overcomeby increasing the terminal strigol concentration in the germinationtest. Conditioned seeds did not germinate at 10 and 15 °Cwith a terminal 10^–6 M strigol treatment but yielded closeto maximum germination at 25, 30 and 35 °C with the sameterminal strigol treatment. To obtain maximum germination, boththe minimum conditioning temperature and the minimum germinationtemperature for conditioned seeds were 20 °C. Factors suchas conditioning time, and strigol concentration and temperatureduring conditioning and/or germination determine whether seedsremain in the conditioning phase or shift to a germination phase. dl-Strigol, germination stimulation, parasitic plants, seed conditioning, seed germination, Striga asiatica, temperature, weed control     

An Analysis of Seed Development in Pisum sativum: VI. ABSCISIC ACID ACCUMULATION

The abscisic acid (ABA) content of wrinkled (rr) pea seed tissueshas been quantified during development using multiple-ion-monitoringcombined gas chromatography-mass spectrometry and a deuteratedinternal standard. The level of ABA in the embryo generallyincreased with increasing cotyledon fresh weight while thatin the testa showed a distinct maximum at the time of maximumendosperm volume and the slowing in the growth of the testa.Pods contained relatively little ABA on a fresh weight basis.The total seed ABA content showed a biphasic distribution, thefirst maximum following the maximum growth rate of the testaand the second that of the embryo. The biphasic distributionof ABA in the pea seed was confirmed using a second pea genotype,near-isogenic to the first except for the r locus, and by theanalysis of individual seeds using a radioimmunoassay for ABA.The first maximum was composed mainly of a testa component andthe second mainly of an embryo component. When plants were grownin different environments, wrinkled seeds were found to containslightly more ABA than round (RR) but this was only significantlate in development. Immature seeds were capable of metabolizing17'-deoxy ABA to ABA, as determined by incorporation of either³H or ²H, and the metabolite was present mainly in the testa.The production of ABA in pea seeds is discussed in relationto the development of the different seed tissues. Key words: Abscisic acid, peas, seed development     

Alternating Temperatures and Rate of Seed Germination in Lentil

The effect of alternating temperatures on the times taken byseeds of lentil (Lens culinaris Medikus) to germinate was investigatedusing a two-way temperature-gradient plate. Between 5 and 25°C,warmer temperatures increased the rate of germination. Variationamong the individual seeds in the times required for germinationat different constant temperatures within this range were describedwell by a log-normal distribution of thermal times, accumulatedabove a base temperature of 1·5°C. Even with amplitudesas great as 20°C, no effect of alternation per se on thethermal time required for germination was detected—whetherthe cool temperature was applied for 8 or 16 h d^-1. Similarly,in alternating temperature regimes where the minimum temperatureof the diurnal cycle was between 0°C and the base temperature,the thermal times required for germination (where no thermaltime accrued during the periods when temperature was below T_b)were in close agreement with those values provided by the modeldetermined at warmer constant temperatures. However, where theminimum temperature applied was < 0°C the germinationof all but the earliest germinators was delayed beyond modelpredictions, and more so where the sub-zero minimum temperaturewas applied for 16 rather than 8 h d^-1. The results, therefore,contradict the view that alternation in temperature per se reducesthe thermal time required for seed germination. Rather, rateof germination responds instantaneously to current temperature,but prolonged exposure to sub-zero temperatures can result indamage sufficient to delay germination when seeds are returnedto regimes warmer than the base temperature.Copyright 1994,1999 Academic Press Lens culinaris Medikus, lentil, seed germination, alternating temperatures, thermal time, temperature-gradient plate     

The Use of Abscisic Acid to Synchronize Carrot Seed Germination Prior to Fluid Drilling

Abscisic acid (ABA) was used as a reversible block to the progressof carrot seed germination in a practical seed treatment. Pre-treatingseeds with 10^–4M ABA solution at 15 °C for 12 d gave93% germination of viable seeds on subsequent transfer to waterbefore radicle lengths became too long for fluid drilling. Thiscompared with only 31 % without pre-treatment ABA pretreatment significantly increased the synchrony of carrotseed germination and did not affect final percentage germinationor early seedling growth rates. Seedling emergence from ABA-treatedgerminating seeds was earlier and more uniform than from untreatedgerminating seeds and seedlings from both these treatments emergedbefore those from ungerminated seeds Daucus carota L., carrot, germination, seed treatment, fluid drilling, abscisic acid, radicle extension     

The Influence of Pre and Post-storage Hydration Treatments on Chromosomal Aberrations, Seedling Abnormalities, and Viability of Lettuce Seeds

A 2 h soaking treatment in distilled water, or in aqueous solutionsof cysteine, potassium iodide, or sodium thiosulphate, had nosignificant effect (P > 0.25) on the subsequent longevityof lettuce seeds (Lactuca sativa L.) in two different storageenvironments. Neither did these treatments influence relationsbetween loss in germination and the frequency of chromosomalaberrations observed during first mitoses after storage. Incontrast partial hydration of lettuce seeds after storage byexposure to moist air (humidification) or to an osmoticum (priming)reversed some of the damage which resulted from ageing. Mostof the benefits occurred during the first 3 d of humidificationduring which seed moisture content rose to 34 per cent, or duringthe first 7 d of priming when seed moisture content increasedto 44 per cent. Both post-storage hydration treatments reducedthe frequency of chromosomal aberrations, increased the rateof root growth, and decreased the frequency of morphologicallyabnormal seedlings. Either treatment could be of practical use,but it is suggested that humidification is more convenient.Consideration should be given to adopting a humidification treatmentas standard practice following long-term seed storage for geneticconservation. Lactuca sativa, lettuce, seed storage, seed viability, chemical pre-treatment, seed longevity, seed humidification (conditioning), seed priming, chromosome repair, seedling abnormalities