The Effects of Priming and Accelerated Ageing upon the Nucleic Acid Content of Leek Seeds and their Embryos

Using seed priming and accelerated ageing techniques, a singlelot of leek (Allium porrum) seeds was manipulated to producefour lots of seeds with different germination performance. Changesin content of the major nucleic acid species in whole seedsand embryos of two of these lots (primed and unprimed), weredetermined over the early stages of germination. The major effectof priming was an increased level of RNA species in the seedsand embryos, and this difference was maintained during germination.Comparison of nucleic acid levels in the dry seeds of thesetwo lots and two others (aged and aged then primed) indicatedthat there was no correlation with germination performance.Similar comparisons of the nucleic acid levels in the embryosof seeds imbibed for 1 d showed only a limited correlation betweenrRNA levels and germination performance. Analysis of these datasuggests that accelerated ageing has an adverse effect uponendosperm cells, which results in the degradation of their nucleicacids during priming. Furthermore, the viability of these agedseeds also falls during priming. The data also indicate thatratios of rRNA to DNA correlate with germination performanceof the four lots of seeds studied. It is proposed that sucha relationship is indicative of the efficiency of a primingtreatment, and may be useful in comparisons of naturally varyingseed lots. Key words: Leek, seed, germination, priming, nucleic acids     

Changes in RNA and Protein Metabolism Associated with Alterations in the Germination Efficiency of Sunflower Seeds

Precise knowledge of seed quality after harvest and during storageis of particular importance for seed producers. We analyseddifferent sunflower seed lots (Helianthus annuusL.) characterizedby extremes of germination ability. We used RNA analysis tostudy possible changes in gene expression in seeds unable togerminate. Total RNA content was very small in dry seeds showinga low germination ability. Capacity for total RNA synthesisat the onset of imbibition was also reduced in these seeds.In addition, correlations were found between these parametersand germination ability at 19 °C. We demonstrated a highcorrelation between the amount of total RNA in the dry seed,the capacity of RNA synthesis at the onset of imbibition andthe seed moisture content at the time of the harvest. The abilityof dry seed mRNAs to be translatedin vitrowas also reduced andseven polypeptides, from stored mRNAs, were characteristic ofthe cotyledons from high germinability seeds. Germination canthus be affected at several levels including membrane, enzymaticand nucleic acid deteriorations. Gene expression; germination ability; Helianthus annuusL.; marker; protein; RNA; seed; sunflower     

A Comparison of Changes in the Germination Responses and Phospholipid Composition of Naturally and Artificially Aged Tomato Seeds

The changes in germinability and phospholipid content of naturallyand artificially aged tomato seeds, variety Kingley Cross, werecompared. Subsequent low temperature pre-sowing treatment (LTPST)was unable to prevent decreases in the germination capacityof aged samples, but significantly improved germination rates.However, in contrast to previous studies on artificial ageingusing the variety Moneymaker, losses of total phospholipid werenot always well correlated with decreased germinability. Totalphospholipid levels in naturally aged seeds were largely unaffectedby pre-sowing treatment, but the proportion of phosphatidylcholinewas greatly increased. These results strongly suggest that lossesof phospholipid are coincidental rather than causative eventsin the loss of seed viability during ageing, and that the patternof changes depends on the type of ageing experienced by theseeds. Controlled deterioration, seed ageing, tomato seeds, seed treatment, phospholipids     

Studies on the Changes in the Major Nucleic Acid Components of Tomato Seeds (Lycopersicon esculentum Mill.) Resulting from Osmotic Presowing Treatment

Extensive accumulation of nucleic acid may be one of the factorsinvolved in the acceleration of tomato seed germination by osmoticpresowing treatment. The experiments reported here were designedto characterize the changes in the major nucleic acids duringosmotic pretreatment and subsequent germination. Polyacrylamidegel electrophoresis showed that ribosomal RNA comprised themajor part of this net synthesis, but it was more difficultto ascertain whether or not there was a proportional increasein sRNA, as part of the latter peak may comprise comigratingfragments of degraded rRNA. The mass ratio of 25S: 18S rRNAsextracted from dry seeds was near unity, while during normalgermination and during pretreatment this ratio increased toabout 1?9:I, close to the theoretical ratio assuming 25S and18S rRNAs occur in equimolar proportions. This leads to thespeculation that replacement of old ribosomes may occur duringearly germination and pretreatment, although this would notaccount for all the synthetic activity observed during the latterprocess. Use of the diphenylamine colour reaction showed that no increasein DNA results from pretreatment and that the onset of the firstS-phase during subsequent germination of pretreated seeds wascommensurate with the advancement of the time to 50% germination.     

Changes in Nucleic Acid Fractions of Seed Components of Red Pine (Pinus resinosa Ait.) during Germination

Changes in nucleic acid fractions of Pinus resinosa during seed germination were studied. At various stages of seed germination, embryos and megagametophytes were surgically separated and nucleic acids were extracted separately by a phenol-method. Total nucleic acids were fractionated on single-layer methylated albumin kieselguhr (MAK) columns. Total nucleic acids in embryos increased significantly 2 days after seeds were moistened, whereas, in megagametophytes, total nucleic acids stayed almost at a constant level until they degenerated at the time of shedding. In embryos, ribosomal RNAs (rRNA) increased 2 days after seeds were sown, whereas soluble RNA (sRNA) increased at 3 days. By comparison, nucleic acid fractions of megagametophytes did not show any quantitative changes during germination, except that rRNA fractions decreased shortly before shedding of seed coats. In dormant embryos the proportion of DNA was high and the proportions of sRNA and rRNA were low, whereas in megagametophytes at dormancy the proportions were completely reversed. As seed germination progressed, proportions of nucleic acid fractions in embryos changed significantly. In megagametophytes, although proportions of individual fractions remained almost constant throughout the experimental period, incorporation of ³²P into sRNA and rRNA of megagametophytes indicated turnover of these fractions.     

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     

Natural Ageing: Poly(A) Polymerase in Germinating Embryos of Triticum durum Wheat

The viability of seeds is associated with ageing and storageconditions. A loss of viability is accompanied by slow germination,reduced growth, and a decline in protein and poly(A)⁺RNA synthesis.This paper reports on the activity of poly(A) polymerase indry and germinating embryos of Triticum durum Desf. cv. Cappellicaryopses of different ages and viability. The enzyme was presentas a single form during ageing and germination. The poly(A)polymerase was active at decreasing levels in all aged dry embryos,in parallel with loss of viability. Its activity strongly increasedduring the germination only in viable embryos. The observedincrease was due to de novo synthesis of the enzyme. Poly(A)polymerase synthesis was low during germination of less viableembryos and absent in older ones. Reduced poly(A) polymeraseactivity in dry or germinated wheat embryos may cause a shorteningof poly(A) chains in vitro and a decline in poly(A)⁺RNA synthesis.Copyright1995, 1999 Academic Press Triticum durum Desf. cv. Cappelli, wheat, embryo, natural ageing, poly(A) polymerase     

Tomato Seed Germination. Osmotic Pretreatment and Far Red Inhibition

At 25 °C germination of tomato (Lycopersicon lycopersicum)seeds is inhibited by continuous and intermittent far red illumination.It is also inhibited by a single 30 min far red irradiationgiven 8 h from the start of imbibition. The incubation of seedsin a mannitol solution inhibitory for germination has no effecton the final germination percentage after seeds are subsequentlytransferred to water. A 30 min far red irradiation at the timeof transfer results in partial inhibition of germination. Thisinhibition can be released by the continuation of osmotic incubationfor several days before the transfer to water. At the end ofa 7 d dark period of osmotic incubation, inhibition of subsequentgermination in water can be realized only by continuous farred illumination. Seeds osmotically pretreated for 7 d and afterwardsdried-back show a mean time to 50% germination significantlylower than that of untreated seeds. Moreover, besides singleand intermittent, even continuous far red light has no inhibitoryeffect on the germination of these seeds. It is concluded that,in addition to the already known germination advantages, osmoticpresowing treatment also induces the ability of seeds to germinateunder unfavourable light conditi.     

Inter-nucleosomal DNA fragmentation and loss of RNA integrity during seed ageing

The germination of viable seeds is the basis for new plant growth and development. Seeds lose viability during storage, but the biochemical mechanisms of seed death are not fully understood. This study aimed to investigate degradation patterns of nucleic acids during seed ageing and subsequent water uptake. Seeds of Pisum sativum L. were artificially aged at 50°C and 12% seed water content (WC). Nucleic acids degradation was studied during ageing and during imbibition of four seed lots with differential viability from highly viable to dead. As seeds lost viability during ageing, DNA was gradually degraded into internucleosomal fragments, resulting in ‘DNA laddering’, in conjunction with disintegration of 18S and 28S rRNA bands. During imbibition, non-aged controls had high levels of DNA and RNA integrity through to radicle protrusion. In an aged seed lot with 85% total germination (TG) DNA fragmentation decreased upon imbibition probably due to nucleosome degradation, while rRNA integrity did not improve. In an aged seed lot with 44% TG, neither DNA nor rRNA integrity improved upon imbibition. Dead seeds showed DNA degradation as laddering throughout imbibition along with extensive degradation of rRNA. We present a model in which interlinked programmed and non-programmed events contribute to seed ageing, and suggest that protection of nucleic acids during ageing is key to seed longevity.     

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     

Studies on the Germination of the Seeds of Striga hermonthica: III. On the Nature of Pretreatment and after-ripening

An attempt has been made to elucidate some of the changes whichtake place in seeds of Striga hermonthica (immature, ripe andoverripe), (a) during moisture-treatment at three temperatures(15°C., 22°C., and 32°C.), and (b) during after-ripeningin dry storage. Observations on the drift of respiration of immature seed throughoutpretreatment at 15°C. show that an inverse relationshipexists between germination and respirational activity. Thissuggests that germination depends on the accumulation of somemetabolite during pretreatment. It would seem that this metabolitemay also be used as a substrate for respiration during pretreatment. After-ripening of the immature seeds has been shown to changethe nature of the seeds in some way so that their peak respirationon exposure to moisture is at first progressively reduced. Thisreduction has been ascribed to the presence of some barriercapable of restricting gaseous diffusion. The data presented, togetherwith those of the previous paperof this series, suggest that the specific metabolite requiredfor germination might be proteinaceous. Certain other data appearto rule out the suggestion that germination capacity is conditionedby the sugar content of the seeds. Reasons are given which supportthe view that one of the main effects of the stimulating solutionon the seed is to increase the permeability of the seeds togaseous diffusion.     

Changes in Levels and Integrity of Ribosomal RNA During Seed Maturation and Germination in Carrot (Daucus carota L.)

Thompson, S., Bryant, J. A. and Brocklehurst, P. A. 1987. Changesin levels and integrity of ribosomal RNA during seed maturationand germination in carrot (Daucus carota L.).—J. exp.Bot. 38: 1343–1350. Amounts and integrity (percentage of complete un-nicked molecules)of ribosomal RNA (rRNA) during germination in carrot seed lotsof differing vigour and viability were examined using aqueousand formamide gel electrophoresis. In unaged seed, amounts ofrRNA per seed in dry seed are not related to maturity, vigouror viability. However, rRNA in immature seed is more vulnerableto damage by ageing than rRNA in mature seed; thus, amountsof rRNA per seed in aged seed are indicators of vigour and viability.On imbibition of aged or unaged seed, more rRNA fragmentationoccurs in immature seed than in mature seed, and the time atwhich the effects of synthesis outweigh the effects of degradationis earlier during germination in mature than in immature seed. Key words: rRNA, seed maturation, seed germination, Daucus carota L.     

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     

RNA Metabolism During Breakage of Seed Dormancy by Low Temperature Treatment of Fruits of Acer plataanoides(Norway Maple)

Stratification of Acer platanoides fruits at 4 °C led toan accumulation of RNA in the embryo axis and to breakage ofseed dormancy. The accumulated RNA was mainly rRNA. Storageof fruits at 17 °C led neither to an accumulation of RNAnor to breakage of dormancy. The proportion of embryo axis mRNA,as measured by poly(A) content, decreased during both fruitstorage and stratification, although levels of poly(A) wereconsistently lower in embryo axes from stored seeds. Isolatedembryos from both stored and stratified fruits were capableof incorporating [³H]uridine into embryo axis RNA. When assayedat 17–20 °C, however, this incorporation was significantlylower in embryos of stored fruits. The distribution of radioactivitybetween the different RNA species was similar in both storedand statified seeds. Acer platanoides, Norway Maple, dormancy, fruit, seed, ribonucleic acid, stratification, nucleic acid metabolism     

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 evaluation of the potential of low temperature pre-sowing treatments of tomato seeds as a means of improving germination performance

Low temperature pre-sowing treatment of tomato seeds substantially enhanced germination rates and was much more effective at improving uniformity of germination than equivalent osmotic treatments. Although radicle emergence was inhibited by the low temperature, imbibition studies showed that seeds were maintained at lag-phase moisture contents during treatment and some aspects of germinative metabolism began. No evidence was found for improved seedling growth rates per se as a result of pretreatment: in fact, initial axis growth may be temporarily reduced, probably as a consequence of depletion of reserves during the treatment period.     

Effects of Priming and Endosperm Integrity on Seed Germination Rates of Tomato Genotypes: I. GERMINATION AT SUBOPTIMAL TEMPERATURE

The bases of differences in germination rates (GR_g = inverseof time to germination [t_g] of percentage g) among three cold/salt-toleranttomato (Lycopersicon esculentum Mill.) accessions (PI 341988,PI 120256, and PI 174263) and one cold/salt-sensitive tomatocultivar (T5) were investigated. The effects of seed priming(6 d imbibition in aerated –1.2 MPa polyethylene glycolsolution at 20 ?C followed by redrying) and of removing theendosperm/testa cap covering the radicle on the temperaturesensitivity of GR_g, and the interaction of these treatmentswith genotypes, were also examined. GR_g decreased linearly withdecreasing temperature for all genotypes and seed treatments.The minimum or base temperatures for germination (T_b) variedby 1 ?C among the tomato lines, so genotypic differences inGR_g were due to differing thermal time requirements for germination.The mean thermal time requirement for germination of T5 seeds was 22% and 19% greater than that of PI 341988 andPI 120256 seeds, respectively, but only 9% greater than thatof PI 174263 seeds. Seed priming did not lower Tb of any genotype,but significantly reduced by 24, 49, 41, and 49% in T5, PI 341988, PI 120256, and PI 174263, respectively,indicating that priming increased the rate at which the seedsprogressed towards germination when T>T_b, but did not lowerthe minimum temperature at which germination could occur. Primingincreased the GR_g of T5 seeds to equal or exceed those of control(non-primed) seeds of the cold/salt-tolerant genotypes at anyT>T_b, but the PI lines exhibited an even greater responseto priming. Times to germination within each seed lot were normallydistributed on a logarithmic scale. Priming increased the variancein tg within a seed lot when compared to control seeds. However,the variation in thermal time for germination between the 10thand 90th percentiles of the seed population (_T(10–90))was relatively unaffected by priming due to the reduction in in primed seeds. Removing the endosperm cap and testa opposite the radicle tip decreased almost 6-fold and and reduced T_b by 5 ?C in T5 and PI 341988,implicating processes in the endosperm/testa as the limitingfactors in germination at suboptimal temperatures. Key words: Lycopersicon esculentum Mill., tomato, genetic variation, seed priming, thermal time, germination rate     

Effects of Kinetin and Salinity on Germination of Tomato, Barley and Cotton Seeds

The effects of kinetin and the interaction between kinetin andsalinity on seed germination of three plant species namely Lycopersiconesculentum, Hordeum vulgare and Gossypium hirsutum were studiedKinetin was applied exogenously to the seeds in order to determinewhether this growth-promoting hormone would promote germinationand to see if osmotically-induced dormancy caused by NaCl couldbe alleviated The results indicate that kinetin is capable ofbreaking dormancy in these species and there is a significantinteraction with salinity in tomato and cotton Kinetin, germination, salinity, water stress, salt stress, Lycopersicon esculentum Mill, tomato, Hordeum vulgare L, barley, Gossypium hirsutum L, cotton     

Proteolytic Activities in x Haynaldoticum sardoum Seeds of Different Ages

Carboxypeptidase, aminopeptidase and proteinase activities weremeasured in endosperms from dry and germinating x Haynaldoticumsardoum naturally aged seeds. Carboxypeptidase activity, presentin dry seeds, decreased slightly during germination and remainednearly unchanged during the storage period. Aminopeptidase activityincreased during germination in younger seeds, but decreasedin non-viable seeds. Proteinase activity was absent in dry seeds,increased during germination in younger seeds and disappearedin the older ones. Proteinase activity was not recovered in old endosperms followingtransplantation of young embryos, and was recovered only toa very small extent in young endosperms following transplantationof old embryos. Young endosperms onto which young embryos hadbeen transplanted gave maximum recovery of enzyme activity,although this was lower than in young intact seeds. These results suggest that the reduced or delayed availabilityof nutrients to the embryo axis is not the only factor causingthe failure of seeds to germinate, the ageing process beinga progressive phenomenon affecting both embryo and endosperm. x Haynaldoticum sardoum, Denti de cani, seed ageing, proteolytic activities, embryo-transplantation     

Nucleic Acid Chemistry of the Ilyanassa Embryo

A morphological study of Ilyanassa embryogenesis was made fromsections of several stages and the nucleic acid content wasmeasured throughout the course of development. The kineticsof uptake and incorporation of radioactive precursors into RNAwas determined. The RNAs synthesized at different stages ofembryogenesis were fractionated by methylated albumin kieselguhrchromatography, and the polyadenylation of RNA during developmentwas measured. From these studies it was concluded that the Ilyanassa embryo,beginning with the 4-cell stage, synthesizes dRNA, rRNA, 4SRNA, and 5S RNA throughout all stages of development. The extensivesynthesis of dRNA and the higher proportion of RNAs polyadenylatedby the pregastrula embryo was considered to be of particularsignificance. The localization of nucleic acids and nucleic acid precursorsin the polar lobe and the effect of removing the polar lobeon nucleic synthesis was reviewed. Recent work on the ultrastructure of the Ilyanassa egg was reviewedin relation to the problem of ooplasmic segregation. The discoveryof a new cytoplasmic organelle in the Ilyanassa oocyte was reviewed.