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     

A Comparison of the Quantitative Effects of Seed Moisture Content and Temperature on the Accumulation of Chromosome Damage and Loss of Seed Viability in Lettuce

The rate of accumulation of cells containing chromosome aberrationsin lettuce (Lactuca sativa L.) seeds is a positive functionof temperature and moisture content. It may be described byan equation similar to that for loss of seed viability. Therelative effect of temperature on the rates of loss of viabilityand accumulation of chromosome aberrations is the same. In contrast,the relative effect of moisture on the rate of loss of viabilityis greater than that for the rate of accumulation of aberrations.Hence considerably more chromosome damage accumulates beforedeath in drier lettuce seeds. Lactuca sativa, lettuce, seed storage, seed viability, seed longevity, chromosomal aberrations temperature, moisture content     

Survival and Vigour of Lettuce (Lactuca sativa L.) and Sunflower (Helianthus annuus L.) Seeds Stored at Low and Very-low Moisture Contents

Seeds of lettuce (Lactuca sativa L.) and sunflower (Helianthusannuus L.) were stored hermetically at 35 °C with 11 differentmoisture contents between 1·3 and 6·9%, and between1·3 and 7·1% of fresh mass, respectively. Germinationand vigour (mean germination time, root length, seedling dryweight) were determined after storage for 0, 8, or 16 weeks(sunflower) or 0, 8, 16, or 48 weeks (lettuce) in these environmentsfollowed by various humidification treatments (to avoid imbibitioninjury). The range of seed storage moisture contents over whichdeterioration was minimized depended upon the criterion of deteriorationused, and varied somewhat between species. Comparison of theseranges for seeds stored for the longest durations showed thatfor some criteria seed performance was poorer (P < 0·05)at both the lowest and highest moisture contents investigatedthan at certain of the intermediate storage moisture contents(e.g, most rapid germination occurred in sunflower followingstorage at 2·2-4·7% moisture content), whereasfor other criteria all the drier storage moisture contents weresuperior to the more moist (e,g. greatest seedling growth occurredin sunflower following storage at 1·3-5·1% moisturecontent). But none of these results suggested that lettuce andsunflower seeds stored hermetically at 2·5-3·0%or 2·2-2·5% moisture content, respectively, wereless vigorous than at any other moisture content tested. Inboth species, these storage moisture contents are in equilibriumwith about 8-10% relative humidity (r.h.) at 20 °C, whichis similar to and indeed marginally less than the 10-13% r.h.recommended following earlier studies on the longevity of seedsin hermetic storage at much warmer temperatures. Thus, theseresults show no evidence that the optimum seed moisture contentfor storage increases with decrease in temperature, at leastover the range 35-65 °C, as has been suggested elsewhere.We conclude that the international recommendation for the long-termseed storage for genetic conservation at 5 ± 1% moisturecontent should not be revised upwardly, and that in situationswhere refrigeration cannot be provided storage at even lowermoisture contents is worthy of further investigation for thoseseeds in which desiccation at 20 °C to equilibrium at 10%r.h. results in moisture contents well below 5%.Copyright 1995,1999 Academic Press Helianthus annuus L., sunflower, Lactuca sativa L., lettuce, desiccation, seed storage, seed vigour     

Germination and Dormancy in Immature and Fresh-mature Lettuce Seeds

The effects of red light, far-red light, Gibberellin A₃, andethephon were studied on the germination of lettuce seeds cv.Grand Rapids harvested at different stages of development. Seeds did not become capable of germination until 8 days afteranthesis. Red light promoted seed germination from the age of8–9 days following anthesis up to the newly mature stage.Ten or 11 days following anthesis, a large percentage of seedsbecame capable of germination in the dark and therefore couldbe considered not dormant. They were affected by far-red light,but less so than the mature seeds. The effect of light on the germination of developing seeds appearedto be similar to the known light effect on mature lettuce seedgermination. Gibberellin A₃ and ethephon had no effect on immatureand fresh seed germination. Lactuca sativa L., Lettuce, germination, dormancy, red light, far-red light, gibberellin A₃, ethephon     

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     

Promotive effects of organic solvents and kinetin on dark germination of lettuce seeds

Significant promotion in dark germination was observed when Grand Rapids lettuce (Lactuca sativa L.) seeds were soaked in acetone or dichloromethane, vacuum-dried, and imbibed at 25 C. Permeation of kinetin via these organic solvents further enhanced the dark germination. Those seeds that were affected by acetone and acetone-kinetin treatments and germinated in the dark escaped red-far red photocontrol of germination. Although abscisic acid was not detected in the organic solvent leachates, they did contain other inhibitory substances affecting lettuce seedling growth. In the light, acetone and acetone-kinetin treatments also enhanced the rate of germination and the increased germination by acetone-kinetin treatment was correlated with increased polyribosome formation. The possible mechanisms involved in promotion of lettuce seed germination by organic solvents and kinetin are discussed.     

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     

Effects of 35 C heat treatments on photosensitive grand rapids lettuce seed germination

Grand Rapids lettuce (Lactuca sativa L.) seeds were given 35 C heat treatments to increase photodormancy in a subsequent 20 C dark period. Short heat treatments (1-5 hours) induced a significant germination percentage increase of from 16% to over 50% depending on seed lot. With longer heat treatments dark germination percentage was gradually reduced to zero. If given at the end of 35 C, far red or red followed by far red further increased the amount of dark germination.     

Loss of Viability in Lettuce Seeds and the Accumulation of Chromosome Damage under Different Storage Conditions

Loss of seed viability in lettuce (Lactuca sativa L.) duringstorage is associated with an increase in the frequency of cellsin the surviving seeds showing chromosome damage during firstmitoses. The relation is linear when probit of the frequencyof aberrant cells is plotted as a function of probit percentagenormal germination. The slope of the relation, however, variesaccording to moisture content so that the proportion of aberrantcells for any given loss of germination increases with decreasein moisture content over the range 13.0–5.5 per cent.At 3.3 per cent moisture content, however, the proportion ofaberrations was no greater than at 5.5 per cent moisture content;and at 18.1 per cent moisture content the proportion was noless than at 13.0 per cent moisture content. Despite these differences,the increase in chromosomal aberrations per unit time for agiven temperature was always less the lower the moisture content.Diplontic selection markedly reduced the frequency of chromosomalaberrations and eliminated the differences in these frequenciesbetween the different storage treatments. But even after fiveweeks' growth, root tips from aged seed still contained abouttwice as many aberrant cells as compared with similar root tipsderived from the original seed stock. Studies on the frequencyof recessive mutations indicated that excessive amounts of heritablemutations were not present in the progenies of aged seed, evenwhen stored at moisture contents as low as 5.5 per cent. Allthis and other evidence reinforces the view that orthodox seedsfor genetic conservation should be stored at not more than about5 per cent moisture content, and that even lower moisture contentsare worth considering. The results also emphasise the need formaintaining a high regeneration standard, i.e. the percentageto which seed viability is allowed to fall during storage beforethe seed stock is regenerated. Lactuca sativa, lettuce, seed storage, seed viability, chromosomal aberrations, phenotypic mutations     

The Effect of Sodium Hypochlorite on Germination of Lettuce Seed at High Temperature

Investigations into the effects of treatment with sodium hypochloritesolution on high-temperature germination of lettuce seed aredescribed. A 2 h treatment in a solution with 10% availablechlorine enabled up to c. 70% of seeds to germinate at 35 °C,without impairing germination and normal seedling developmentat 20 °C. A 10 min rinse in 0.01 N HCI following such treatmentenhanced its effect and treated seeds retained their abilityto germinate at high temperature for at least 18 months. Seedlingdevelopment at 20 °C following treatment was influencedby treatment temperature and batch of hypochlorite solution.Emergence from compost in a cycling (30/15 °C) temperatureregime was improved in three out of five cultivars tested, andthere were indications that hypochlorite treatment enabled oneof the other cultivars to escape induced thermodormancy. Key words: Lactuca sativa L., Sodium hypochlorite, Thermo-inhibition     

Effects of Temperature of Mother-plant Environment on Yield and Germination of Seeds of Lettuce (Lactuca sativa)

Experiments on the production of two separate crops of lettuceseeds, each in three different temperature environments, andsubsequent tests on the seed are described. Low production temperatures(20 °C day, 10 °C night) gave a low yield of large seeds,and high temperatures (30 °C, 20 °C) gave a higher yieldof much smaller seed; the highest yield came from medium temperatures(25 °C, 15 °C), which gave medium-sized seed. After-ripening,manifested as an increase in percentage germination at hightemperatures with increase in seed age, occurred in seed fromall three production environments of the first crop, thoughthere were differences in degree, and in that from the two higherproduction temperatures, but not the lowest, of the second crop.Measurements of the forces required to penetrate the layerssurrounding the embryo showed an inverse relationship with temperatureof the production environment for pericarps but not for endosperms,and a gradual reduction during storage for pericarps but notendosperms. Measurements of germination potential showed thatembryos from seeds produced in cool conditions were less ableto cope with high temperatures than those from warner conditions.These results are discussed in relation to the control of germinationin lettuce. Lettuce, Lactuca sativa (L.), seed production, germination, seed coverings, germination potential     

Seed Viability Constants for Lettuce

Seeds of two lettuce cultivars (Lactuca sativa L., cv. Meikoninginand cv. Grand Rapids) were hermetically stored with constantmoisture contents ranging between 3.6 and 17.9 per cent (freshweight basis) at constant temperatures ranging between 5 and75 °C. The decline with time in percentage germination andpercentage normal seedlings was determined for each storagetreatment. The data were fitted to an equation which containsthe constants: K₁, the probit of the initial percentage germinationor normal seedlings; K_E, a species constant; C_W, the constantof a logarithmic moisture term; C_H, the constant of a lineartemperature term and C_Q, the constant of a quadratic temperatureterm. Regression analysis of data from storage periods up to5.5 years at temperatures of 5–75 °C and seed moisturecontents of 3.6–13.6 per cent yielded the following values:K_E= 8.218, C_W=4.797±0.163, C_H=0.0489±0.0050 andC_Q=0.000365±0.000056. Although this equation consistentlyprovided a better fit, simplified equations, assuming eithera log-linear relationship between seed longevity and temperature,or a log-linear relationship between seed longevity and bothmoisture content and temperature, accounted for more than 94per cent of the variation at the restricted temperature rangeof 5–40 °C. Longevity of the same seed lots at sub-zero temperatures (–5,–10 and –20 °C) was studied in separate tests.Freezing damage, resulting in abnormal seedlings in the germinationtest, occurred at –20 °C when the moisture contentof the seeds exceeded 12 per cent. No decline in percentagenormal seedlings was observed after a storage period of 18 monthsor longer at –20 °C, provided the seed moisture contentdid not exceed 9.5 per cent. For seeds stored at –5 and–10 °C with 9.6–12.5 per cent moisture content,the observed rate of decline of percentage normal seedlingswas adequately predicted by the viability equation, using theabove values for the constants. This suggests that for low moisturecontents the viability equation can be applied to estimate longevityat sub-zero temperatures. Lettuce, Lactuca sativa (L.), seed longevity, seed storage, viability constants, storage conditions     

Water Relations of Seed Development and Germination in Muskmelon (Cucumis melo L.): VI. INFLUENCE OF PRIMING ON GERMINATION RESPONSES TO TEMPERATURE AND WATER POTENTIAL DURING SEED DEVELOPMENT

Seed priming (imbibition in water or osmotic solutions followedby redrying) generally accelerates germination rates upon subsequentre-imbibition, but the response to priming treatments can varyboth within and among seed lots. Seed maturity could influenceresponsiveness to priming, perhaps explaining variable primingeffects among developmentally heterogeneous seed lots. In thecurrent study, muskmelon (Cucumis melo L.) seeds at two stagesof development, maturing (40 d after anthesis (DAA)) and fullymature (60 DAA), were primed in 0?3 M KNO₃ for 48 h at 30 ?C,dried, and imbibed in polyethylene glycol 8000 solutions of0 to –1?2 MPa at 15, 20, 25, and 30 ?C. Germination sensitivitiesto temperature and water potential () were quantified as indicatorsof the influence of seed maturity and priming on seed vigour.Germination percentages of 40 and 60 DAA control seeds weresimilar in water at 30 ?C, but the mean germination rate (inverseof time to germination) of 40 DAA seeds was 50% less than thatof 60 DAA seeds. Germination percentages and rates of both 40and 60 DAA seeds decreased at temperatures below 25 ?C. Reductionsin also delayed and inhibited germination, with the 40 DAAseeds being more sensitive to low than the 60 DAA seeds. Primingsignificantly improved the performance of 40 DAA seeds at lowtemperatures and reduced , but had less effect on 60 DAA seeds.Priming lowered both the minimum temperature (T_b) and the minimum (_b) at which germination occurred. Overall, priming of 40 DAAseeds improved their germination performance under stress conditionsto equal or exceed that of control 60 DAA seeds, while 60 DAAseeds exhibited only modest improvements due to priming. Asthe osmotic environment inside mature fruits approximates thatof a priming solution, muskmelon seeds may be ‘primed’in situ during the late stage of development after maximum dryweight accumulation. Key words: Cucumis melo L., seed priming, germination, vigour, development, temperature     

Temperature and Seed Storage Longevity

Seed survival data for eight diverse species, namely the cerealbarley (Hordeum vulgare L.), the grain legumes chickpea (Cicerarietinum L.), cowpea [Vigna unguiculata (L.) Walp.] and soyabean [Glycine max (L.) Merr.], the timber trees elm (Ulmus carpinifoliaGleditsch.), mahogany (Swietenia humilis Zucc.), and terb (Terminaliabrassii Exell.), and the leaf vegetable lettuce (Lactuca sativaL.) were compared over a wide range of storage environments(temperatures from –13 °C to 90 °C, seed moisturecontents from 1.8 to 25% f. wt) using a viability equation developedpreviously. In accordance with that equation, the effect oftemperature on seed longevity was dependent upon the temperaturerange. The temperature coefficients of the viability equationdid not differ significantly (P > 0.05) among the eight speciesdespite their contrasting taxonomy. Thus the quantitative relationbetween seed longevity and temperature does not vary among diversespecies. The same conclusion was obtained for the coefficientsof a proposed alternative model of the relation between seedlongevity and temperature. The implications of the two temperaturemodels in the viability equation for extrapolations to low andvery low temperatures are discussed. Seed storage, seed longevity, seed moisture, temperature, viability equation, genetic resources conservation, Cicer arietinum L., Glycine max (L.) Merr., Hordeum vulgare L., Lactuca sativa L., Swietenia humilis Zucc., Terminalia brassii Exell., Ulmus carpinifolia Gleditsch., Vigna unguiculata (L.) Walp     

Investigations on the Control of Lettuce Seed Germination at High Temperatures

The activity of sodium hypochlorite solution in relieving thermo-inhibitionof germination of lettuce seed is shown to be due to its chlorinecontent. Results of experiments in which the pericarp, and pericarpand endosperm were removed, together with direct measurementsof penetration forces, suggest that the relief of thermo-inhibitionresults from weakening of the pericarp by the hypochlorite.Differences between the cultivars ‘Cobham Green’and ‘Grand Rapids’ in the contributions made bypericarp and endosperm to germination control at 35 °C aredemonstrated. Key words: Lactuca sativa L, Chlorine, Thermo-inhibition     

Respiration of Grand Rapids lettuce (Lactuca sativa L.) seeds in relation to chemical and photocontrol of germination

A 10-min irradiation with red light (R) of ‘Grand Rapids’lettuce (Lactuca sativa L.) seeds increased respiratory rates(QO₂ and QCO₂) over those of far red (FR)-irradiated seeds within2 to 3 hr. Differences in respiration between R- and FR-irradiatedseeds became more pronounced with time. The respiration, indarkness at 25?C, of seeds air dried after germination promotingimpregnation treatments with 1.0 mM GA₃+0.5 mM kinetin in acetonewas stimulated slightly by the 6th hour after planting and markedlyby the 12th and 24th hour. Results with seeds in GA₃+kinetindissolved in water were similar. ABA, which inhibits germinationand seedling growth, prevented stimulation in respiration oflight-induced seeds. ABA also repressed respiration when usedwith GA₃+kinetin. The germination and growth retardant, isopropylN-(3-chlorophenyl) carbamate (CIPC), did not affect the respirationof either R- or FR-treated seeds. A comparison of the effectsof chemical and light treatments on respiration indicate thatchemical and photocontrol mechanisms are not identical. (Received May 17, 1976; )     

Interaction of Moisture Stress and Three Phenolic Compounds on Lettuce Seed Germination

No interactions between water stress and three phenolic acids(p-coumaric, caffeic and ferulic acids) on lettuce (Lactucasativa L. var. Grand Rapids) seed germination were found. Probitanalysis indicated that mechanisms of action of water stressand the phenolic inhibitors were similar. The relative effectivenessof the compounds was p-coumaric > ferulic > caffeic. Nointeraction was found between p-coumaric and ferulic acid, whereasantagonism was found between caffeic acid and each of the othertwo phenolic acids. Lactuca sativa L., lettuce, germination, phenolic compounds, moisture stress, allelopathy, seed     

Characterization of the Germination Responses to Temperature of Lettuce (Lactuca sativa L.) Achenes

Germination tests were done on 23 cultivars of lettuce (Lactucasativa L.) comprising a variety of different morphological formsselected for cultivation at various seasons. Significant differences at the upper limit of temperature tolerancewere found between different cultivars: maximum temperaturesfor 50 per cent germination ranged from 23 to 32 °C, andsusceptibility to the induction of secondary dormancy by hightemperatures varied widely from one cultivar to another. Nocorrelations were established between germination responsesand heading type, achene colour or growing season The germination responses of all cultivars at temperatures fromjust above 0 to 20 °C were closely similar and results froma large number of experiments were used to produce a standardgermination reference curve foti culvars of L. sativa. Departfuresrom this curve were found to arise predominantly from variationsin seed quality or test conditions rather than from the genotypeof the cultivar. Detailed comparisons of germination at all possible combinationsof alternate and constant day/night temperatures are presentedfor two cultivars. One with relatively high tolerance to high-temperatureinducedinhibition, the other with low tolerance. The results are discussed in relation to the original distributionof the species as a wild plant and its history of cultivationby man. Lactuca sativa L., Lettuce, achene germination, temperature response     

A water relations analysis of seed germination rates

Seed germination culminates in the initiation of embryo growth and the resumption of water uptake after imbibition. Previous applications of cell growth models to describe seed germination have focused on the inhibition of radicle growth rates at reduced water potential (Ψ). An alternative approach is presented, based upon the timing of radicle emergence, to characterize the relationship of seed germination rates to Ψ. Using only three parameters, a `hydrotime constant' and the mean and standard deviation in minimum or base Ψ among seeds in the population, germination time courses can be predicted at any Ψ, or normalized to a common time scale equal to that of seeds germinating in water. The rate of germination of lettuce (Lactuca sativa L. cv Empire) seeds, either intact or with the endosperm envelope cut, increased linearly with embryo turgor. The endosperm presented little physical resistance to radicle growth at the time of radicle emergence, but its presence markedly delayed germination. The length of the lag period after imbibition before radicle emergence is related to the time required for weakening of the endosperm, and not to the generation of additional turgor in the embryo. The rate of endosperm weakening is sensitive to Ψ or turgor.